Sunglasses are a healthy accessory to have along on a sunny summer day. They

Sunglasses. Credits : FreeDigitalPhotos.net

reduce glare from the bright sunlight and also  shield the eye from ultraviolet radiation and visible light.

The ultraviolet radiation from the sun may be related to eye conditions such as cataracts, pterygiums, pinguecula and skin cancers around the eyelid such as basal cell carcinoma, squamous cell carcinoma and melanoma.

Visible light (e.g. blue or violet) may also have a role in causing age related macular degeneration.

Sunglasses Protection

Sunglasses may not all be the same in terms of the amount of ultraviolet light they block out. The tint or color of the lens may also not be a good gauge when the tint  is light or medium. In general, dark or very dark lenses block out more ultraviolet light but also visible light.  Check if they comply to the American standard, European standard or Australian standard and you can determine the amount of protection they provide.

However, there are more considerations when choosing sunglasses. The size of the lens should not be too small. Also the fit of the frame should be such that it is not too distant from the forehead or light may leak in. Side shades or wrap around designs will also reduce light leakage.

Common colors of the sunglasses lens include gray, brown and green. These colours tend to not distort colors.

Sunglasses can also be made with prescriptions in built but these would tend to be expensive. An alternative would be to make photochromatic prescription glasses which change color when exposed to ultraviolet light. Be aware though that if you intend to also  reduce glare while driving,  photochromatic glasses will not change color as the windscreen glass will block out ultraviolet light. Sunglasses which clip on to existing glasses or fit over existing glasses are a cheap but good solution too.

Monovision is a method of correcting presbyopia. In monovision, the right eye (or dominant eye) is corrected for distance and the other eye is corrected for near vision.

This correction may be by means of spectacles, contact lenses, refractive surgery or during cataract surgery by intraocular lenses.

Monovision concept

The concept generally is that the dominant eye is made slightly myopic while the other eye is given a correction for near. There are 2 images, one clear and one blur for a given distance and the brain ignores the blurrer image. Thus vision with both eyes open is equal to the vision of the better seeing eye for the given distance. However, this may not be so for all people.

Each eye has a depth of focus which extends the range of clear vision. This depth of focus is affected in part by the pupil size. Monovision for intermediate vision would thus be better with a small pupil. This occurs in bright lighting conditions. Conversely, the intermediate range of vision may be worse in poor lighting conditions.

Tolerance of monovision correction can first be tested by use of the trial frames for spectacle correction or contact lenses if refractive surgery or intraocular lenses are contemplated.

Contact lenses are an alternative to glasses for those with short sightedness, long sightedness, astigmatism and presbyopia.

Types of contact lenses

Soft contact lens

There are 2 main types of contact lenses:

• Rigid gas permeable lenses
• Soft contact lenses

Soft contact lenses are used by 90% of contact lens wearers. There are 2 main kinds:

• hydrogels
• silicone hydrogels

Silicone hydrogels are the newer generation and have a lower water content than hydrogels. There are at least 15 different silicone hydrogel materials with newer materials having higher water content and being more flexible to try and improve comfort. In general, they have a higher oxygen permeability than hydrogels. They were initially conceived as extended wear contact lenses but even daily disposable versions are available now.

In general, the comfort of hydrogels and sillicone hydrogels is similar although studies may be conflicting. Hydrogels tend to accumulate proteins and silicone hydrogels lipids. Good contact lens care regimes are equally important for both.

Soft contact lenses come in daily, bi weekly and monthly disposable versions. Conventional soft contact lenses can be used for 1 year or so before replacement. The disposable versions are meant to reduce the inconvenience of contact lens care regimes. Daily disposables require no cleaning and are disposed off after a single use. However, the on going cost will be higher for the convenience.

Rigid gas permeable lenses have high oxygen permeability, easier maintenance, excellent vision and safety. The main drawback is short term discomfort in the new user which may take 3 months to adjust to. Over the medium and longer term though, comfort levels are comparable to soft lenses. They are a good choice for those who develop allergy to soft contact lenses and who still want to continue wearing contact lenses.

Newer uses of contact lenses include cosmetic uses like changing the colour of the eye , making the eye more prominent and some contact lenses have graphics printed on them.

Top: Clear lens when born. Bottom: Brown lens in older eyes. Credit: AAO

Cataract surgery is the removal of the cloudy lens of the eye by surgery and replacement of the lens with an artificial lens implant.

The “history of cataract surgery” is found in this website.

Cataract surgery is arguably the most successful surgery throughout medicine today in terms of safety and outcome. It is the most commonly performed surgery worldwide.

Cataract surgery is most commonly performed when vision is not compatible with the person’s activities of daily living e.g work, hobbies, reading, driving etc.

Method of cataract surgery

The main method today remains extracapsular cataract extraction by means of

Phacoemulsification handpiece inside the eye. Credits: AAO

phacoemulsification. The key elements of this gold standard technique are a small wound size, use of an ultrasound probe to break of the lens and use of foldable artificial lenses that can be put into the eye through the small wound size. The small wound size facilitates a faster recovery after the operation. Videos explaining modern cataract surgery can be found here.

Advances

New advances in surgical technique include the use of femtosecond laser assisted cataract surgery.  The technique however comes with additional surgical time  and cost to patient.   Additional resulting improvements in clinical outcome for the cost incurred are currently controversial.

The more important advance in cataract surgery is the widened range of artificial lenses to be put into the eye – Intraocular lenses.

There are now Toric lenses to correct astigmatism and Multifocal lenses to correct presbyopia and Toric multifocals to correct both astigmatism and presbyopia. Other advances include Aspheric lenses which reduce what are called higher order abberations of the eye.

These make cataract surgery much more then dealing with a cloudy lens. It can be a refractive surgery as well where short sightedness, long sightedness, astigmatism and presbyopia can all be corrected at the same time.

Preparing for cataract surgery

Before cataract surgery, your eye surgeon will take a full history and perform a comprehensive eye examination to make sure you are fit for surgery and determine if there are any other eye conditions  present apart from cataract.

Your surgeon will also look out for any eye conditions or general health conditions that will increase the risk of complications during cataract surgery.

Your surgeon will also discuss with you preferences regarding glasses wear after surgery. A full explanation is found in my post – “Before cataract surgery”

From your surgeon, you should understand the risks of cataract surgery, the benefits to be expected from undergoing the procedure and complications that can occur from surgery. Ask if there are any alternatives to surgery e.g. trying  glasses first. Make sure your questions are answered.

Determining the artificial lens choice

Your eye will be measured for its corneal curvature and axial length to determine the correct artificial lens to implant into your eye.  Good equipment such as IOL Master and Lenstar are used to measure the eye.

Surgery Day

Refrain from eating and drinking as instructed. This is usually for 6 to 8 hours before the surgery time.

Take your other regular oral medications as specifically instructed by your surgeon.  Some medications e.g. blood thinners may be stopped before surgery day.

Put dilating eye drops and other eye drops as prescribed.

Arrange to have somebody take you home. Do not drive yourself home.

Recovering from Cataract Surgery

You will have to use antibiotic and steroid eye drops after cataract surgery. Follow the instructions given.  These are used for at least 1 month.

For at least 2 weeks

Use an eye shield while sleeping  to protect the eye.

Avoid strenuous exercise and swimming.

No dirty water or other contaminants should be allowed to enter the eye.

Avoid pressure or injury to your eye.

Use sunglasses should you experience glare from sunlight when going out of the house. Sunglasses can also serve as eye protection in crowded places.

1 month after surgery

New glasses will be prescribed if necessary.

If at any point after surgery you experience increasing eye pain, increasing redness of the eye or worsening of vision, you should seek medical help immediately. These may indicate serious infection or inflammation in the eye.

If you should run out of eye drops before you are due to stop them, get a refill of the eyedrops.

Children’s glasses are prescribed when the child does not have perfect vision and is unable to see near, far or both distances clearly.  This condition is called a refractive

Choosing children’s glasses. Credits: AAO

error. Examples are short sightedness, long sightedness or astigmatism.

Below the age of 9, children’s glasses may be particularly important to prevent lazy eye (amblyopia) developing.

They may also be prescribed to treat some types of squints called accommodative squints.

Children’s glasses should be sized well to the child’s face. The frames can me made of plastic or metal but a non-corrosive material may be preferable.

Spring loaded hinges are a feature on some frames and reduce the likelihood of accidental damage at the junction of the end-pieces and temples.

To prevent the frame slipping down the nose, plastic frames with well fitting bridges should be chosen. Metal frames usually come with adjustable nose pads.  Silicone nose pads reduce slipping well.

Temple tips/loops can also be added on to hold the glasses close to the face.

Children’s glasses lens should be made of plastic. Glass may crack with damage and lead to glass fragments injuring the eye. Polycarbonate lenses are harder than plastic  and provide good protection for the sporty child.

UV protection and scratch resistant coatings are desirable features of the lens are fairly standard from manufacturers these days.

Since it is important that the child wears the glasses, it is best to choose a style and color that the child likes.

Progressive glasses are used for the treatment for presbyopia or old age sight. Presbyopia occurs from the age of 40 years old and up.

Progressive glasses are designed to give the wearer both clear vision for distance as well as clear vision for varying distances of near vision.

Progressive glasses are however not recommended for everyone. They may be unwise in occupations which involve climbing  or uneven surfaces and in the elderly who have  recurrent falls.

The usual design of a progressive glasses lens is such that the upper portion of the lens is used for viewing distance. The lower portion of the lens has a central transition corridor of increasing power for near vision from top to bottom. The lowest portion is for near viewing. The portions of the lens to either side of the central corridor have been called ‘zones of confusion’.

There are many manufacturers of progressive lenses in the marketplace.

These include Essilor, Hoya and Carl Zeiss to name a few. The choice is bewildering.

They are all to some extent governed by the same laws of physics.

Depending on the manufacturer and design, the progressive elements of the lens may be built into the front, back or both front and back of the progressive lens.

Astigmatism at the edges of the  central transition corridor result in visual distubances.  One way to minimise this might be to choose designs with more gradual transition zones. However, consumer information for such comparisons is lacking.

Choosing the appropriate height of the lens will also help optimise vision. Seek advice from your eye care professional.

Lastly, it may make some sense to start wearing progressives early when the near addition is low so that the transition  to progressive glasses is easier.  Some re-learning of daily tasks may be required e.g. the way we check the side mirrors when driving. Patience and persistence is required to get used to them.

What is presbyopia or old age sight?

People might first notice presbyopia around the age of 40 when they notice that their near vision is not as good as before. This might be in subtle ways at first such as difficulty looking at the time on your watch, reading your mobile phone or  reading

Reading glasses required for day to day activities. Credit : AAO

fine print on labels.

The worsening of near vision  or presbyopia is a natural ageing process that continues till about age 65.

Overcoming Presbyopia

In the beginning, options to overcome presbyopia can include simple changes such as increasing font sizes on smartphones and personal computers. Instead of paper books,  e books are a good alternative  where font sizes can be increased. E-ink based readers like the Amazon Kindle or Barnes & Noble Nook are good choices.

For the  short sighted,  an optician or optometrist could weaken prescriptions to give more near reading ability but at the slight expense of distance vision.

At some point of time, reading glasses, bifocals or progressive glasses may become inevitable.

There are alternative methods of spectacle correction too called “monovision” where the power of (usually the left eye) is corrected for reading distance while the other eye is corrected for distance. However, binocular vision is sacrificed. Also not everyone can tolerate monovision.

There are also surgical procedures to treat presbyopia such as laser refractive surgery, corneal inlays and corneal pin hole inlays. These are still not perfect solutions.

The most successful surgical way to correct presbyopia currently is when significant cataracts (cloudiness of the lens) are also present in the eye. At the time of cataract surgery, multifocal intraocular lens implant can be implanted. These give the eye again the ability to see distance, near and sometimes intermediate vision. The trade off with some of the multifocal intraocular lens implants is glare and haloes from light sources.

Why do we want to prevent myopia from increasing?

An obvious reason is that the higher your myopia, the greater the blurring of vision for distance without correction. In addition, high myopia (degree more than 600, or -6D) can result in complications in the eye such as myopic macular degeneration, choroidal neovascularisation and retinal tears and detachment. These can result in permanent loss of vision.

How can we prevent myopia from increasing?

Atropine eye drops have been found to be effective in slowing down the increase in myopia or short-sightedness in children.

Atropine eye drops are however not new. They have been used in the treatment of eye diseases for a long time.

The main effect of atropine eye drops is widening of the pupil and loss of near reading ability.

The eye drops come in different concentrations such as 1%, 0.5% and more recently 0.01%. The eye drop is usually applied once a night but once weekly dosing may be effective for the higher concentrations.

Treatment with atropine may necessitate the use of photochromatic glasses to reduce glare in bright sunlight and progressive glasses to restore near reading ability

Other side effects of atropine may include eye irritation, dry mouth, skin allergy, constipation, palpitations, fever and flushing.

For the child that is experiencing a rapid increase in the power of their myopia, at least there is now a relatively safe method to slow down that increase.

Reference

Ophthalmology. 2012 Feb;119(2):347-54. Atropine for the treatment of childhood myopia: safety and efficacy of 0.5%, 0.1%, and 0.01% doses (Atropine for the Treatment of Myopia 2). Chia A, Chua WH, Cheung YB, Wong WL, Lingham A, Fong A, Tan D.