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Optics 5

This weblog post is the fifth of a series of nine, about optics and optical equipment. This post is about safety glasses/ goggles and other equipment to protect the eyes.

Bluewear Raptor safety glasses are a personal favourite for eye protection inside a workshop.

Our household has numerous personal protective equipment (PPE) items available for people to use. Almost all items have been sold as Bluewear, a clothing and accessory brand of Jula, a company that was started at Skara, near Goteborg in south-west Sweden in 1979. Bluewear is a wordplay on the Swedish Blåkläder = blue clothes, a company that was started at Svenljunga, also near Goteborg, in 1959. It has developed a major American presence, today. We often compare safety equipment with the brands offered by Biltema and Clas Ohlsen, as well as Coop. Their house brand products are similar, and typically cost about 50% of the price charged for 3M and Caterpillar equipment. The main criteria for selecting protective equipment are: 1) that it meets appropriate safety standards, and 2) that it is comfortable to wear. The international brands typically emphasize (read: market) a specific specification. Often this is lower than that provided by the house brands.

Protective eyewear (PPEE) conform to EN 166, the European standard. At Cliff Cottage, almost every PPE item is different, because together they constitute a collection. In much the same way that other people may collect stamps, I like to collect PPEs that are diverse and designed to counter a variety of risks. In terms of eyewear these include splatter, impact and light filtration, including UV light. Currently, none are designed to withstand molten metal. In many situations, eyes need protection from foreign objects, such as dust particles, caustic fluids and metal swarf shavings. Eye protection should be worn even if there is no immediate risk.

PPEEs tends to be split into four categories: safety glasses, goggles, visors/face shields and sunglasses. Currently, there is no welding equipment in our workshop, but should this situation change, a fifth category of eyewear would also be needed.

Separate tests are undertaken to ensure suitability against: droplets or splashes of liquids, large dust particles, gases and fine dust particle, short circuit electric arcs, molten metals and hot solids, surface damage by fine particles, fogging, enhanced infrared reflectance, have replacement oculars. Not all products pass all of the tests. Not all products offer the same level of protection, even if they meet the standard, generally.

One also wants protective items to fit and be comfortable. Here, individuals may find one item fits better than another. For me, the house brands are suitable, and I see no need to buy international brands. Confession: I own three pairs of socks labeled with a yellow CAT name. They were bought because they were cheaper than everything else. When I wear them, sometimes people comment. I then feign an appreciation of felines. It is a total misrepresentation. I could never own (or allow myself to be owned by) a cat, because they kill too many birds!

Safety glasses

Bluewear Cobra safety glasses.

Glasses are the simplest form of eye protection. They come with a rod/ temple on each side that are bent, and end in an ear piece. These are worn over the ear. The main advantage with them is that they are simple and cheap. However, they are not particularly effective in preventing saw dust from reaching eyes. Thus, I seldom use them when working with electric saws.

One can buy 10 Bluewear Cobra safety glasses for the price of a single 3M brand equivalent. We have four, suitable for visitors to the workshop, not undertaking any work. They cannor be adjusted, are more easily scratched, and can fog up. We also have two pairs of slightly better Bluewear Atrax safety glasses, that are less easy to scratch, avoid fogging and are adjustable. They cost about three times more than the Cobra model. These can be used by people working, in the workshop or elsewhere.

Safety goggles

Googles are similar to glasses, but offer increased protection. They are typically fastened with a strap. The main advantage with them is that prescription glasses can be worn inside them. So people with this need should probably use them. However, it should be noted that safety protection equipment worn over glasses may transmit forces through the eye glasses, placing the user at risk! Goggles are effective in preventing saw dust from reaching eyes.

Personally, I use Raptor PPEEs (see photo at top of post) that are somewhere between goggles and glasses, have both temples and straps. These cannot be combined with glasses. These are most often worn when working with electrical tools in a workshop situation, especially with mitre saws and rip saws.

Face shields

Some face shields are inappropriate despite meeting EN166 standards. They may protect eyes, but they prohibit the wearing of ear protection, often called ear defenders. I refuse to buy/ use these. Instead I have a combined helmet with hearing protection, a poly-carbonate face shield and a mesh = metal netting face shield, only one of these last two can be worn at a time.

In addition to meeting the EN166 standard, these meet the EN 397 (industrial hard hats), EN 1731 (mesh protectors for chain saws), and EN 352-3 (Hearing protectors that are designed to be attached to industrial safety helmets) standards. This equipment is suitable for working outdoors with chainsaws, clearing saws, trimmers but even less dangerous equipment such as lawn mowers. The total price of such equipment is about half that with the three products bought separately.

Sunglasses

Bluewear Nepture safety glasses with dark lenses.

There are two types of safety glasses with dark lenses available at Cliff Cottage. Bluewear Achillo and Bluewear Neptune. Both have partial frames and dark lenses that have been specially treated to give a scratch-free and fog-free surface. Both have rubber-coated rods make the frame comfortable to wear and keep the glasses in place. These can be used when using a lawn mower or garden trimmer. I use a Neptune for outdoor construction work. It fits larger faces. The Achillo fits smaller adult faces; Neptune fits larger faces.

Note: This post was started on 2024-04-27 at 18:00. It was based, in part, on notes taken as an employee at assorted schools. In addition, for five years I commuted with Victor Nilsen (1953 – ), who was chief steward at Romsdal upper secondary school. Our conversations provided me with a lot of anecdotal information about health and safety issues.

Welding helmet

Modern welding helmets are described as automatic. This means that they are fitted with a glass cassette containing liquid crystals typically activated (auto-darken) by an electronic control unit within 100 – 400 µs. The legal limit is 10s which is up to 10 000 times shower, and totally unacceptable in real life. The field of view varies, but many welders find 100 x 67 mm window acceptable, although larger sizes are available, at increased price. The degree of darkness is easily adjustable (5-13 DIN) with 13 being the darkest. There is usually an adjustment knob on the side of the helmet. Some helmets have a lower angle grinder mode with dimming to 4 DIN. Fieldwork and high amperages require helmets with fixed darkening.

Most welding activities undertaken by amateurs can use auto-darkening. Low amperage tungsten inert gas (TIG) welding is a precise and versatile process used to create high-quality welds. It joins metals using a non-consumable tungsten electrode while protecting the welding area from atmospheric contamination with an inert gas such as argon. The shielding gas prevents oxides and nitrides from forming in the weld. Metal inert/ active gas (MIG/MAG) are similar. The most important active gas is CO2. Manual metal arc welding (MMA) uses a flux for shielding. A variety of light sensors can be used to activate darkness.

Welding helmets provide other features. Cheater lenses magnify the view of the work.

Rechargeable batteries can be used to power sensors and liquid crystal cassettes. Some helmets can be plugged in to be recharged or use solar cells. In the future, smart welding helmets will have cameras, and bluetooth connectivity, allowing the welder to communicate through other devices.

Respiratory welding helmets = Powered Air Purifying Respirator (PAPR) masks protect lungs while allowing the welder to breathe normally. They are equipped with external blower units with changeable filters connected by a thick hose for sufficient airflow. Most people prefer an adjustable helmet, with a padded headband.

Welding helmets are often made of ABS plastic. It is cheap, lightweight, sturdy, durable and is a poor thermal conductor. It comes in a matt finish. The alternative is fibreglass. It has high tensile strength, absorbs vibrations and insulates sounds. Given a choice and a large enough budget most welders choose fibreglass!

Favourites

Bluewear Raptor safety glasses pictured at the top are my favourite because they are comfortable, and meet most of my needs. They have soft padding around the eyes and a removable strap. Both are useful to prevent the glasses from moving/ slipping off. The safety glasses are equipped with scratch-resistant and anti-fog-treated clear glass, so that the glasses provide good visibility and have a long lifespan. Unfortunately, because of my light sensitivity, I prefer not to wear these outdoors. Instead, I use Bluewear Nepture dark lens safety glasses.

Welding is not an activity I engage in often, so I do not have a valid opinion about safety equipment.

Note: Originally, this post contained general information about household health and safety stewardship. On 2024-06-21 at 07:30, this content was moved to its own post to be published on 2024-07-27 at 12:00 (Norwegian time).

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Optics 4

This weblog post is the fourth of a series of nine about optics and optical equipment. This post is about eyeglasses, including sunglasses. Towards the end I also make some comments on glasses for reading, as well as being used with assorted screens.

Eyeglasses

Both Trish and I have used eyeglasses since we were 13. Yes, since puberty.

We have renounced the discount optical retailers found everywhere in the world, locally in Levanger and Steinkjer, cities 40 km south and 35 km north of us, respectively. We now patronize the optician located at our former bank building in Straumen, about 13 km east of our house. Husby Optikk was founded in 1854 in Steinkjer. Anne Sofie Staven Husby, the niece of a neighbour, has run the Inderøy branch since it opened in 2020. I suspect she met her husband, Terje, who runs the larger, Steinkjer branch, while they both studied to be opticians in Copenhagen.

Trish’s regular eyeglasses are in frames made by Kuno-Qvist. a Swedish firm founded in 2004, and located in the Norra Sorgenfri industrial area of Malmö. Its motto is Always in character. Her Khantra 52-18 model offers metal frames with blue and brown highlights: with a feather like pleated metal pattern,… [that] will evoke a feeling of movement in the frame when the wearer moves. Trish always enjoys blue, and in this case it matches the colour of her eyes.

My regular eyeglasses are housed in frames made by Face a Face, Paris. It calls itself an audacious, non-conformist eyewear brand. That definitely suits my personality. Despite its French origins in 1995, it now has its headquarters in Aarhus, Denmark. The model I use is called Kieth 3, and is made in opaque fluid yellow. These frames are an extreme bright yellow. I had asked Anne Sofie to find frames in signal yellow, and I am more than pleased with the result.

Sunglasses

Both Trish and I use sunglasses made to our individual prescriptions, with polarized glass. We may need these to drive legally with sunglasses, but also prefer to view the world through corrected lenses.

As usual, Trish invested in Maui Jim Koki Beach sunglasses first. I would describe these sunglasses as basic. Trish’s eyes still function as intended/ designed. She does not need extreme features. These provide everything that is needed, but nothing more, including a clear, glare-free view of the world. The name comes from a beach on Maui’s east shore.

I have started to prioritize the selection and care of sunglasses, because of the challenges I have with my eyes. I want sunglasses that feel comfortable, and are kind to my eyes. I use sunglasses for driving, more often than I use conventional glasses. Compared to Trish, I need greater protection from glare. This includes winter glare from snow. Thus, I felt that Maui Jim Southern Cross = Hanaiakamalama (Hawaiian) with their polarized wrap were better at meeting my sunglass needs. Other features, such as a triple-injected nylon frame in Soft Black with Sea Blue and Grey, were nice to have.

In 1980, Jim Richards, a fisherman, began selling sunglasses on the beaches of Maui, Hawaii. Some years later, the company developed polarized sunglasses to protect eyes from glare and UV light. In 1991, Walter Hester, a boat captain, purchased and rebuilt the company, calling it Hester Enterprises, Inc. By 1994, the company was named Maui Jim Sunglasses, and allowed Illinois-based RLI Vision to become its mainland distributor. In 1996, Maui Jim Sunglasses bought RLI Vision from its parent company, Peoria, Illinois-based RLI Corporation to form Maui Jim Inc. The corporate headquarters is in Peoria, but there is a branch office in Maui. In 2004, the company opened a distribution center in Braunschweig, Germany. It later became its European headquarters.

Part of the reason why I think I will stick with Maui Jim as a brand was an earlier work related trip to Sicily when people with fake Ray-Ban sunglasses were issued an €800 fine by the customs authorities in Italy. At the time, I was wearing real Ray-Bans, but I found the incident so offensive, that I vowed never to buy Ray-Bans again. I haven’t.

Other eyeglasses

There are several other types of glasses available. At one time, I used reading glasses. As I aged I found it better just to remove the glasses. I was able to read just as well. Many people experience the opposite. They need some form of reading glasses.

My former employer, Nord-Trøndelag county, encouraged the use of device/ computer glasses. There was a claim that using them make made work with a screen more comfortable. One point that is often taken up involve blue light. Electronic device screens radiate many colours, including blue, with wavelengths from about 400 nm to 495 nm. Some people are affected by blue light. Blue light can be divided into two bands, blue-violet light (400-455 nm) and blue-turquoise light (465-495 nm). Sleep/wake = circadian cycles are impacted by blue-turquoise light, but not blue-violet light. The main source of all forms of blue light is sunlight. Device glasses typically filter blue-violet light, but not blue-turquoise light, that impacts the circadian rhythm. My experience of using device glasses, is that they are not particularly helpful. I do not currently use them.

Displays/ Screens

I use three very different displays/ screens with my computing devices: a hand-held device/ smart phone with a 5.9″ display = 1080 x 2400 pixels; a laptop with a 14″ display = 1920 x 1080 pixels; and a desktop with a QHD 27″ display = 2560 × 1440 pixels. The last one is best when my eyes feel strained. About four years ago it replaced another 27″ display with HD resolution = 1920 x 1080 pixels, that I had used for twelve years. I find that the increased resolution, rather than the screen size, most helpful. For me, the most effective improvement comes from using a dark background.

Trish does not use glasses when working with computer screens, either. She has almost identical devices to mine, but on her desktop machine she but prefers to use a 24″ HD display. Yes, she was offered an identical QHD 27″ display, but declined. In addition, she uses two Kobo e-readers, a black Glo HD (N437) with a 6″ display = 1448 x 1072 pixels (for fiction) , and a white Libra H2O (N873) with a 7″ display = 1680 x 1264 pixels (for non-fiction). I have tried to use Kobos, but prefer to read paper books.

The main rule seems to be that everyone is different.

Note: This post was originally written early in the morning of Monday 2024-03-18, under the title Magnification. Later in the day that was changed to Optics. It was saved using that new title, for the first time, at 18:10. It was then split into four posts, later expanded to five, on 2024-03-23. On 2024-04-09 at 20:00 the first post was scheduled to be published 2024-06-01 at 12:00.

Note: I appreciate detailed information. At times, I even refer to myself as a detailist. When it comes to products I own and use, including eyeglasses, I want to know who designed it, and why it was designed the way it was. I want to know product history, how and why a product evolved. I am fascinated by the techniques used to fabricate items. Of course, I want to know where things are made. The name of a country is seldom enough of an answer. I want a much more specific location, if possible a street address, and – for the past couple of decades – an image of that location, if only from Google Streetview.

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Optics 3

This weblog post is the third of a series of nine about optics and optical equipment. This post is about deviations from normal sight, that can be corrected with eyeglasses, including sunglasses, or contact lenses.

Eye correction is important because many optical devices, such as telescopes, microscopes and cameras require manual adjustments to optimize results. This situation may not be too important if the device is being used directly to look at objects. However, if the device is being used indirectly to create images, uncorrected eyes may result in out of focus = blurred images, that may be anywhere from difficult to impossible to correct.

In the early 1970s, I spent a lot of time taking photographs with a friend who was losing his sight. He used photography to see his world before it dimmed forever. This situation has had a major impact on my attitudes toward vision, and photography.

In 2019, I wrote a weblog post about visual acuity, Optotypes. Acuity tests measure how sharp a person’s vision is at a distance. In many places it is tested using a Snellen eye chart, with rows of letters in decreasing sizes. It is read at a distance of 6m = 20′, although if mirror reflection is used, the distance can be reduced to 3m = 10 feet. I remember, at the age of 13, I asked the school nurse about my blurred vision. She gave me a Snellen test and said I should have my eyes tested. Shortly after this, I was wearing glasses. In many places, especially in Europe, the Landolt C test has replaced the Snellen test. This asks a patient to tell where the opening of a letter C is. The letter can be orientated in any of eight different positions, at 45 degrees from each other. Acuity tests, with the patient using her/ his ordinary prescription lenses, are used in many jurisdictions to prohibit people from driving. Unacceptable results in a darkened room, can be used to prohibit driving after dark.

In Optics 1, it was noted that Ibn al-Haytham in his Book of Optics (1021) along with Roger Bacon‘s written works on optics, described the function of corrective lenses for vision.

Reading stones, often used by monks when they illuminated manuscripts, were invented at some point between the 11th and 13th century. These were primitive plano-convex lenses (see illustration above) initially made by cutting a glass sphere in half. As the stones were experimented with, it was slowly understood that shallower lenses magnified more effectively. Around 1286, possibly in Pisa, Italy, the first pair of eyeglasses were made, although it is unclear who the inventor was.

There are several types of eye care/ health professions. The distinctions between them varies, depending on the jurisdiction regulating them. The text below is intended to give a flavour of the various professions, not rigorous legal definitions.

Ocularists make and fit ocular prostheses for people who have lost eyes due to trauma or illness.

Opticians make and fit ophthalmic lenses, spectacles = eyeglasses, contact lenses, low vision aids and ocular prosthetics.

The most problematic term is optometrist. In some jurisdictions it is a person with medical education, with an authorization to perform eye surgery. In others, the scope is more limited. Thus, some are trained and licensed to manage any eye disease, including infections, glaucoma and macular degeneration. Many can prescribe topical medications = eye drops, fewer can prescribe controlled ingested substances. Some may order imaging tests (CT/MRI), remove ocular foreign bodies and perform some laser procedures. Some are also qualified to perform some surgical procedures.

Orthoptists diagnose and manage eye movement and coordination problems, such as misalignment of the visual axis, binocular vision problems, convergence and accommodation problems, and pre/post surgical care of patients with: amblyopia (see below) and strabismus = a vision disorder in which the eyes do not properly align with each other when looking at an object. They treat patients using optical aids and eye exercises, but not with medications or surgery.

An ophthalmist is a physician who specializes in serious eye conditions, but is not a surgeon.

Ophthalmology is a surgical subspecialization that handles the diagnosis and treatment of eye disorders. Ophthalmologists are physicians that undergo subspecialty training in medical and surgical eye care.

Eyewear prescriptions

Corrective lenses are typically prescribed by an ophthalmologist or an optometrist. The prescription consists of all the specifications necessary to make the lenses, typically two! Typically the following information is included: the strength of each lens in quarter-diopter steps (0.25 D). Most people cannot generally distinguish between smaller increments. The use of improper corrective lenses may not be helpful and can even exacerbate binocular vision disorders. The goal is to provide the clearest, most comfortable, and most efficient vision, avoiding double vision and maximizing binocularity.

Eyewear is fragile. Many people have a service card they carry with them when travelling that specifies their eyeglass prescription. Hopefully, this will allow new glasses to be made anywhere in the world.

An eyewear prescription is a written order by an eyewear prescriber, that specifies the value of all parameters the prescriber has deemed necessary to construct appropriate corrective lenses for a patient. In Norway, and many other jurisdictions, most often the person performing the eye examination is also the same person selling you the glasses.

The parameters specified on eyewear prescriptions vary, but typically include the patient’s name, power of the lenses, any prism to be included, the pupillary distance, expiration date, and the prescriber’s signature. The prescription is typically determined during a refraction, using a phoropter and asking the patient which of two lenses is better, or by an automated refractor, or through the technique of retinoscopy. A dispensing optician will take a prescription written by an optometrist and order and/or assemble the frames and lenses to then be dispensed to the patient.

Sphere component

Because its shape minimizes some aberrations, convex-concave lenses (see the diagram at the beginning of this post) are most commonly used in corrective lenses. These can be defined as transmissive optical devices worn in front of the eye to improve visual perception.

Eyeglasses = spectacles are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted, most commonly after cataract removal.

Every corrective lens prescription includes a spherical correction in diopters. Convergent powers are positive (e.g., +4.00 D) and condense light to correct for farsightedness/long-sightedness (hyperopia) or allow the patient to read more comfortably (see presbyopia and binocular vision disorders). Divergent powers are negative (e.g., −3.75 D) and spread out light to correct for nearsightedness/short-sightedness (myopia). If neither convergence nor divergence is required in the prescription, “plano” is used to denote a refractive power of zero.

The term sphere comes from the geometry of lenses. Lenses derive their power from curved surfaces. A spherical lens has the same curvature in every direction perpendicular to the optical axis. Spherical lenses are adequate correction when a person has no astigmatism. To correct for astigmatism, the “cylinder” and “axis” components specify how a particular lens is different from a lens composed of purely spherical surfaces.

Cylinder component

Patients with astigmatism need a cylindrical lens, or more generally a toric lens to see clearly. The geometry of a toric lens focuses light differently in different meridians. A meridian, in this case, is a plane that is incident with the optical axis. For example, a toric lens, when rotated correctly, could focus an object to the image of a horizontal line at one focal distance while focusing a vertical line to a separate focal distance.

The power of a toric lens can be specified by describing how the cylinder (the meridian that is most different from the spherical power) differs from the spherical power. Power evenly transitions between the two powers as you move from the meridian with the most convergence to the meridian with the least convergence. For regular toric lenses, these powers are perpendicular to each other and their location relative to vertical and horizontal are specified by the axis component. By convention, a horizontal axis is recorded as 180° meridians. The 90° meridian defines the vertical axis.

There are two different conventions for indicating the amount of cylinder: “plus cylinder notation” and “minus cylinder notation”. In the former, the cylinder power is a number of diopters more convergent than the sphere power. That means the spherical power describes the most divergent meridian and the cylindrical component describes the most convergent. In the minus cylinder notation, the cylinder power is a number of diopters more divergent than the sphere component. In this convention, the sphere power describes the most convergent meridian and the cylinder component describes the most divergent. Europe typically follows the plus cylinder convention while in the United States the minus cylinder notation is used by optometrists and the plus cylinder notation is used by ophthalmologists. Minus cylinder notation is also more common in Asia, although either style may be encountered there. There is no difference in these forms of notation and it is easy to convert between them:[1]

  • Add the sphere and cylinder numbers together to produce the converted sphere
  • Invert the sign of cylinder value
  • Add 90° to axis value, and if the new axis value exceeds 180°, subtract 180° from the result

For example, a lens with a vertical power of −3.75 and a horizontal power of −2.25 could be specified as either −2.25 −1.50 × 180 or −3.75 +1.50 × 090.

Axis component

The axis defines the location of the sphere and cylinder powers. The name axis comes from the concept of generating a cylinder by rotating a line around an axis. The curve of that cylinder is 90° from that axis of rotation.

The most common use is to treat refractive errors: myopia = near-sightedness = short-sightedness = a condition where incoming light focuses in front of, instead of on, the retina; hypermetropia = hyperopia = far-sightedness = long-sightedness = a condition where incoming light focuses behind, instead of on, the retina; condition of the eye where distant objects are seen clearly but near objects appear blurred ; astigmatism = rotational asymmetry resulting in distorted or blurred vision. If it occurs in early life and is left untreated, it may result in amblyopia = lazy eye = a disorder where the brain fails to fully process input from one eye and favors the other eye, over time resulting in decreased vision in an eye that typically appears normal in other aspects; and presbyopia = age-related farsightedness = physiological accommodation insufficiency associated with aging (typically people aged over 40) resulting in a progressively worsening ability to focus clearly on close objects.

Contact lenses

There are five types of contact lenses, based on type of lens material: 1) Polymethyl methacrylate (PMMA) lenses have excellent optics, but they do not transmit oxygen to the eye and can be difficult to adapt to. They are considered old fashioned. 2) Rigid gas permeable lenses (RGP) look and feel like PMMA lenses but are porous and allow oxygen to pass through them. They can be fit closer to the eye than PMMA lenses, making them more comfortable. They were introduced in 1978. 3) Hydrogel lenses are thin and pliable = soft, and conform to the front surface of the eye. These were introduced in the early 1970s. They made contact lens wear much more popular because they typically are immediately comfortable. 4) Silicone hydrogel lenses are an advanced type of soft contact lenses that are more porous than regular hydrogel lenses and allow even more oxygen to reach the cornea. These were introduced in 2002, and are now the most popular lenses prescribed in economically advanced countries. 5) Hybrid contact lenses provide wearing comfort similar to soft or silicone hydrogel lenses, but combine this with the clear optics of gas permeable lenses, due to a skirt of hydrogel or silicone hydrogel material. These lenses are difficult to fit and are more expensive to replace than other types. Only a small percentage of people wear hybrid contact lenses.

Once again there is a distinction made between spherical and toric lenses. Spherical contact lenses have the same lens power throughout the entire optical part of the lens. This means they can be used to correct myopia (nearsightedness) or hyperopia (farsightedness). Toric lenses allow contact lenses to correct for astigmatism.

At one time, contact lenses had to be changed every day. They were then cleaned, then stored in an appropriate container, with solution, over night. Then the maximum duration extended, soon becoming once a week, for certain types. Now 30 days is considered the legal maximum.

In our nuclear family, the use of contact lenses is extremely limited. Non-existent is incorrect, because one person decided that it would be best to use these at her wedding, so that her glasses would not date the event.

Notes

Recently, I was asked why I write weblog posts that remind people of Wikipedia articles. They suggested I should spend my time writing autobiographical materials about my life. Part of the reason has to do with my career as a teacher. My main task was to explain how the world operates. In addition, I am perpetually creating user manuals, usually for an audience of one. However, publishing them as blogs, allows more people to access the content.

Because the content is originally produced just for my own consumption, sources are seldom specified.

On 2024-04-27, this post, also called Optics 3, was started. By the end of the day, it had been divided into three, with this section being about eye prescriptions. The next post was renamed Optics 4, about eyeglasses. It is to be published on 2024-06-22. Optics 5 is about various types of safety glasses. This post is to be published on 2024-06-29.

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Optics 2

Eyes. Photo: Manuel Meurisse, 2017-11-17, Tasmania, Australia

This is the second of nine posts about optics.

Optical devices interact with eyes and a brain, so that the content being observed can be interpreted relevantly. Cameras, binoculars, microscopes and other analogue optical devices, can subject eyes to excessive strains. For example, looking even indirectly at the sun during a solar eclipse using inappropriate aids, invites permanent damage to the eyes. Optics mediated through a digital screen are less problematic, because the screens come equipped with limits on their optical capabilities. That said, screen brightness settings can be excessive, either too low or too high for the eyes using them. Personally, I routinely set my digital devices to 20% of the maximum allowable. I also select black backgrounds. I have often wondered if this light sensitivity is related to my blue eyes. Other people may have completely different needs.

Vision changes

As a person ages, it is common for them to find that they can’t see as well as they once did. That’s a normal development. They will probably need glasses or contacts. If a person already uses them, they may need a stronger prescription. Some people may choose to have Laser-Assisted in Situ Keratomileusis (LASIK), commonly referred to as laser eye surgery or laser vision correction. There are mixed opinions (and little scientific evidence, as far as I can find) about the suitability of LASIK.

Presbyopia is the name given to the situation where a person loses the ability, despite good distance vision, to see close objects and small print clearly. After age 40 or so, people may have to hold a book or other reading material farther away from their eyes to make it easier to read. Many complain that their arms are too short. Reading glasses, contact lenses, and other procedures can be used to restore good reading vision.

Other, more serious conditions also happen as people age. Eye diseases like macular degeneration, glaucoma and cataracts, can cause vision problems. Symptoms vary a lot among these disorders.

Colour blindness

When a person cannot see certain colors, or can’t tell the difference between them (usually reds and greens), that person may be colour blind. It happens when the cone cells, used to distinguish colour, are absent or fail to work. When it is most severe, a person can only see in shades of gray, but this is rare. Most people who have colour blindness are born with it, but one can get it later in life from certain drugs and diseases. Men are much more likely to be born with it than women.

Paddy, the father of my wife, Trish, had red-green colour blindness, so I have been concerned about people inheriting this. There are free online colour blindness tests. I have taken one here, and found that I have normal vision. There’s no treatment if a person is born colour blind, but special contacts and glasses can help some people tell the difference between certain colors.

My son, Alasdair, has also taken numerous colorblindness tests with no indication of colour blindness. In middle school he created such a test and was able to diagnose one of his peers as colour blind. Until then, this child was unaware of his condition. My daughter, Shelagh, informs me that it’s common practice in web development to check designs to ensure they pass colour blindness tests.

Eyestrain

Eyes can be overused. They get tired and need to rest. Give eyes that feel strained time off.

Red Eye

The surface of eyes is covered in blood vessels that expand when they’re irritated or infected. That gives eyes a red look. It can be caused by eyestrain, a lack of sleep, allergies, or something more serious: an injury, conjunctivitis (pinkeye) or sun damage. Over-the-counter eye drops can sometimes help, along with rest.

Amblyopia

Amblyopia = Lazy eye is a situation where one eye does not develop properly. Vision is weaker in that eye, and it tends to move “lazily” around while the other eye stays put. It’s found in infants, children, and adults, but rarely affects both eyes. Treatment needs to be sought immediately for infants and children.

Lifelong vision problems can be avoided if this is detected and treated during early childhood. Treatment includes corrective glasses or contact lenses and using a patch or other strategies to make a child use the lazy eye.

Strabismus

If both eyes aren’t lined up with each other when one is looking at something, the problem could be strabismus = crossed eyes = walleye. This problem is often corrected using vision therapy, where weak eye muscles are strengthened. At other times, surgery is necessary.

Nystagmus

With nystagmus, an eye moves/ jiggles all the time on its own. Vision therapy is one treatment option. Surgery is another.

Uveitis

Uveitis is the name for a group of diseases that cause inflammation of the uvea, the middle layer of the eye that contains most of the blood vessels. These diseases can destroy eye tissue, and even cause eye loss. People with immune system conditions like AIDS, rheumatoid arthritis, or ulcerative colitis may be more susceptible to uveitis. Common ymptoms include: blurred vision; eye pain; eye redness; and, light sensitivity. Treatments vary, dependent on the type of disease.

Floaters

These are tiny spots or specks that float across a field of vision. Most people notice them in well-lit rooms or outdoors on a bright day.

Floaters are usually normal, but they sometimes can be a sign of a more serious eye problem, like retinal detachment. That’s when the retina at the back of an eye separates from the layer underneath. When this happens, a person might also see light flashes along with the floaters or a dark shadow come across the edge of their sight.

If a person notices a sudden change in the type or number of spots or flashes they see or a new dark “curtain” in appears in their peripheral vision, it is advisable to see an eye doctor as soon as possible.

Dry Eyes

This happens when eyes can’t make enough good-quality tears. A person might feel like something is in their eye or that it is burning. Rarely, in severe cases, extreme dryness can lead to some loss of vision. Some treatments include:

  • Using a humidifier
  • Special eye drops that work like real tears
  • Plugs in tear ducts to lessen drainage
  • Lipiflow, a procedure that uses heat and pressure to treat dry eyes
  • Testosterone eyelid cream
  • Nutritional supplements with fish oil and omega-3

If a dry eye problem is chronic, it could indicate dry eye disease. A doctor could prescribe medicated drops like cyclosporine (Cequa, Restasis), lifitegrast (Xiidra), or Tyrvaya nose spray to stimulate tear production.

Excess Tearing

It has nothing to do with feelings. A person might be sensitive to light, wind, or temperature changes. Try to protect eyes by shielding them or wearing sunglasses (go for wraparound frames — they block more wind than other types).

Tearing may also signal a more serious problem, like an eye infection or a blocked tear duct. An eye doctor can treat or correct both of these conditions.

Cataracts

These are cloudy areas that develop in the eye lens.

A healthy lens is clear like a camera’s. Light passes through it to the retina — the back of the eye where images are processed. With a cataract, light can’t get through as easily. The result: A person can’t see as well and may notice glare or a halo around lights at night.

Cataracts often form slowly. They don’t cause symptoms like pain, redness, or tearing in the eye.

Some stay small and don’t affect sight. If they do progress and affect vision, surgery almost always works to bring it back.

Glaucoma

An eye is like a tire: Some pressure inside it is normal and safe. But if levels are too high it can damage the optic nerve. Glaucoma is the name for a group of diseases that cause this condition.

A common form is primary open angle glaucoma. Most people who have it don’t have early symptoms or pain. This is often part of a regular eye examination.

Glaucoma can be caused by:

  • An injury to the eye
  • Blocked blood vessels
  • Inflammatory disorders of the eye

Treatment includes prescription eye drops or surgery.

Retinal Disorders

As previously noted, the retina is a thin lining on the back of the eye that is made up of cells that collect images and pass them on to the brain. Retinal disorders can damage retinal cells and block this transfer. There are different types:

  • Age-related macular degeneration refers to a breakdown of a small portion of the retina called the macula.
  • Diabetic retinopathy is damage to the blood vessels in the retina caused by diabetes.
  • Retinal detachment happens when the retina separates from the layer underneath.

It’s important to get an early diagnosis and have these conditions treated.

Conjunctivities (Pinkeye)

In this condition, tissue that lines the back of the eyelids covering the sclera gets inflamed. It can cause redness, itching, burning, tearing, discharge, or a feeling that something is in one’s eye.

People of all ages can get it. Causes include infection, exposure to chemicals and irritants, or allergies.

Wash hands often to lower chance of getting it.

Corneal Diseases

The cornea is the clear, dome-shaped “window” at the front of an eye. It helps to focus the light that comes in. Disease, infection, injury, and exposure to toxins can damage it. Signs include:

  • Red eyes
  • Watery eyes
  • Pain
  • Reduced vision, or a halo effect

The main treatment methods include:

  • A new eyeglasses or contacts prescription
  • Medicated eye drops
  • Surgery

Eyelid problems

Eyelids are important for: protecting eye, spreading tears over its surface, and limiting the amount of light that can enter.

Pain, itching, tearing, and sensitivity to light are common symptoms of eyelid problems. One might also have blinking spasms or inflamed outer edges near eyelashes.

Treatment could include proper cleaning, medication, or surgery.

Some vision changes can be dangerous and need immediate medical care. Anytime a person has a sudden loss of vision, or vision becomes blurry seek medical advice.

Contact Lenses

I have never used, nor wanted to use, contact lenses. However, I understand that cleanliness is essential for their use. Users are advised to follow the care guidelines that came with their prescription. There is a need for users to

  • Wash their hands before touching contact lenses.
  • Never use saliva to wet them.
  • Ensure the lenses fit properly, to avoid scratches.
  • Use eye drops that say they’re safe for contact lenses.
  • Never use homemade saline solutions. Even though some lenses are FDA-approved for sleeping in them, doing so raises the risk of a serious infection.

If a person does everything right and still have problems with contacts, see an eye doctor. The person might have allergies or dry eyes. Once the problem is known, a person can decide the best course of action, which could include opting to use glasses.

Night Blindness

Night blindness is more of a symptom, than a problem. Nearsightedness, cataracts, keratoconus, or a vitamin A deficiency can all provoke these symptoms, that can be treated. At other times it is a symptom of a degenerative retinal disease that usually can’t be treated.

Note: This post started as my personal checklist about eye health issues. However, it has been augmented with additional problems, that people may encounter. The content has been accumulated over a number of years from unremembered sources, including Wikipedia. Some of these issues will need medical attention, while others are more trivial. The challenge is distinguishing between the two. So if what appears to be a trivial complaint persists, it could be appropriate to seek medical attention, to make sure it is not a more serious problem.

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Optics 1

Structure of the Eye. Image: OpenStax College, 2013-06-19.

This weblog post is the first of a series of nine about optics and optical instruments. Five of these will be posted in 2024-06, and four in 2025-01. This post presents some definitions, and some elementary theory behind optics. #Optics 2 is about eyes and eye diseases; #3 is about eye prescriptions; #4 is about eyeglasses. Later topics include: #5 is about safety glasses; # 6 is about cameras; #7 is about binoculars and monoculars; # 8 is about astronomical telescopes; and, #9 is about microscopes.

There are two approaches to optics that can be taken: Here it is about visual perception, the eyes, and how they sense, rather than on the natural (or even the artificial) production of phenomena, such as light and colour, that can be observed.

Readers are advised against starting any study of optics with Greek philosophers. This will be discussed later in this weblog post. Instead, it they want a historical approach, an appropriate place to begin is The Book of Optics (1011-1021), a seven-volume treatise on optics and some other subjects by Ibn al-Haytham, (965–c. 1040) = Alhazen/ Alhacen, a medieval Arab scholar.

Ibn al-Haytham was the first to correctly explain the theory of vision, and to argue that vision occurs in the brain, noting that it is subjective and affected by personal experience. He stated the principle of least time for refraction that links ray optics and wave optics: the path taken by a ray between two given points is the path that can be traveled in the least time = Fermat’s principle. He made major contributions to catoptrics = the branch of optics dealing with the reflection of light from plane or curved mirrors, and dioptrics = refraction, especially by lenses. More generally, Ibn al-Haytham contended that a hypothesis must be supported by experiments based on confirmable procedures and/ or mathematical reasoning.

Content. Book I: theories about light, colours and vision; Book II: theory of visual perception; Book III: ideas on the errors in visual perception; Book IV and Book V provide experimental evidence for theories about reflection; Book VI: errors related to reflection; Book VII: the concept of refraction.

An appropriate next stop is the English bishop Robert Grosseteste (c. 1175–1253) who wrote on a wide range of scientific topics, that included On Light (1235), which is viewed from four different perspectives: epistemology, metaphysics/ cosmogony, etiology/ physics and theology. All of these take their inspiration from Genesis 1:3: God said, let there be light, Creation is seen as a natural physical process arising from an expanding/ contracting sphere of light.

A third stop is Roger Bacon (c. 1214–1294), an English Franciscan, who was influenced by Grosseteste’s writings. Perspectiva, Tractatus de multiplicatione specierum (<1267) = Tract on the Multiplication of Species, and De speculis comburentibus = On Burning Lenses are all writings about optics. His mathematical analysis of light/ vision was influenced by Ibn al-Haytham.

An erect image = one that appears right-side up. The opposite is an inverted image = one that appears upside down. Some telescopes and other devices including the camera obscura present an inverted image. Mirrors and compound prism elements can be used to transform an inverted image into an erect image.

Popularizations

Many times theorists have a difficult time explaining their subject so that it is understandable for a broader audience. At that point it is good to have other people around who are able to communicate ideas. Here are some of those people in the field of optics.

Peter of Limoges (1240–1306), in Tractatus Moralis de Oculo = A Moral Treatise on the Eye, popularized Bacon’s writings on optics.

John Pecham (ca. 1230 – 1292 ) wrote the most widely used optics textbook in the Middle Ages: Perspectiva communis. His book centered on the question of vision, on how we see. Pecham followed the model set forth by Ibn al-Haytham, but interpreted Ibn al-Haytham’s ideas in the manner of Roger Bacon.

Pseudoscience

When it comes to optics, early Greek philosophers are to be avoided. Empedocles (c. 494 – c. 434 BC) believed Aphrodite made the human eye out of the four elements = earth, air, fire, and water. She lit the fire in the eye which shone out from it, making sight possible. This would mean that it should be possible to see equally well in darkness as in light, which is not the case. He believed there were two different types of emanations that interacted: one from an object to the eye, another from the eye to an object.

In philosophy, William of Ockham (ca. 1287 – 1347) postulated Ockham’s razor , a problem-solving principle that recommends searching for simple explanations = the principle/ law of parsimony. It is expressed as: Entities must not be multiplied beyond necessity. It is often paraphrased as the simplest explanation is usually the best one. These Greek explanations contradict this advice.

There are few contemporary references to Euclid (c 300 BC) about optics. There are questions about the attributions of many of his works. He is believed to have written two books related to optics. Catoptrics, about the mathematical theory of mirrors, particularly images formed in plane and spherical concave mirrors. Optics is the earliest surviving Greek treatise on perspective, including an introduction to geometrical optics and basic rules of perspective.

Claudius Ptolemy (c. 100 – c. 170) of Greco-Egyptian ethnicity and Roman citizenship, flourished in Alexandria. Robert R. Newton (1918 – 1991) in The Crime of Claudius Ptolemy (1977) challenged Ptolemy’s observations and asserted that Ptolemy fabricated many of these to fit his theories. Newton accused Ptolemy of systematically inventing/ doctoring data, and called him the most successful fraud in the history of science.

Winer et al (2002) have found that up to 50% of adults in the early years of this millennium believed in emission theory. The easiest way to refute it is to note that if emission theory were true, it would be possible to observe objects in the dark equally well as objects in the daylight. I find there is a significant difference between these.

Note: In 2024-03 and 2024-04 I systematically investigated various topics related to optics. Much of it had to do with Trish having an eye examination on 2024-04-18. By 2024-04-09 at 20:11 I had decided where this series was going, and scheduled this post to be published 2024-06-01 at 12:00. We also decided that we needed new and lighter binoculars and a spotting scope so that we could be better oriented about the wildlife in our neighbourhood. In particular, I wanted to follow a pair of cranes (Grus grus), birds that live near us during the summer.

Corrections: On 2024-06-08, at about 18:40, the number of posts about optics in 2024-06 was increased from 4 to 5, while the number was decreased from 5 to 4 in 2025-01.