Sunglass Fundamentals

SUNGLASS FUNDAMENTALS

Sunglasses are now available in more styles, brands, materials and colours than ever before. Today's sunglasses are both functional and fun. Sunglasses can be worn as a fashion accessory to compliment a 'look', give greater visual performance and comfort outdoors, and offer protection against the elements. Whatever reason you wear sunglasses, all sunglasses should improve your visibility against bright light and glare, and protect your eyes against ultraviolet (UV) radiation. 

The Importance of UV Protection

The most common misconception about sunglasses is that the darker the lens, the higher the UV protection. However, the darkness of the lens has little to do with protecting your eyes from potentially harmful UV radiation. In fact, dark lenses without UV protection can do more harm because the pupils dilate in very dim conditions, allowing more UV rays to enter the eye. The cornea, lens and retina are all vulnerable to UV rays and research shows that continuous exposure to UV light contributes to the development of cataracts or macular degeneration and can cause a form of corneal sunburn called photokeratitis. Consequently, it is important that the sunglasses we wear protect us against UV rays. Proper UV absorption is either an integral part of the lens material or must be added as a coating on the lens. 

Inexpensive sunglasses are available from retail stores and street-side vendors, especially in the summer. Knowing the level of protection or the optical quality of these sunglasses is not always possible at the point of purchase. Your eyecare professional will ensure you are getting the proper sun product that meets your specific needs.  

Reducing Glare

Glare is a phenomenon in which reflections from horizontal surfaces such as water, roads, snow, and sand create polarized light to be reflected into the atmosphere. This polarized glare washes out detail and colour, and makes viewing difficult and uncomfortable. Similarly, hazy conditions also cause glare, because light bounces off dust particles in the air. Glare causes impaired vision outdoors as well as distorting colour and depth perception that can lead to eyestrain. Glare can be painful and dangerously distracting while driving or playing sports. The most effective way to eliminate glare is by wearing polarized sunglass lenses. The addition of the polarized material to a sunglass lens blocks reflections that cause glare. Reducing glare provides comfortable viewing, increases visual clarity, depth and colour perception. Polarized lenses also provide 100 percent UV protection and are ideally suited for anyone who is going to spend time outdoors. Special lens treatments such as mirrored coatings and back surface anti-reflection coatings are also effective to reduce glare and reflect bright light.

Shades and Tints

The varieties of lens tints available today are staggering and can be confusing. The importance of colour choice depends on the specific 'sun' need. The traditional greys, browns and greens provide specific benefits such as, colour neutrality, colour contrast and eye comfort. Amber, yellow, orange and red filters can increase depth perception and colour contrast by absorbing blue and green wavelengths. These colours are beneficial for low vision conditions like cataracts, macular degeneration, and glaucoma. The pinks, blues, and violets are fashion colours that project a fashion trend, mood or are just fun to wear. Some manufacturers provide tints that are specific to sports activities such as golf and tennis. These lenses increase contrast and enhance colours such as the green of the golf course or the yellow of a tennis ball. Check with your eyecare professional to ensure you are wearing the right tint and colour density for your needs.

Eighty percent of our lifetime UV exposure occurs by the time we are 18, so an early start to wearing sunglasses is ideal.  However, UV exposure is cumulative over time, so it is never too late to start practicing good sun protection habits!

Suffering from seasonal allergies?

ALLERGIES AND YOUR EYES

WHAT IS AN ALLERGY?

Allergic reactions occur when the immune system overreacts to an ordinarily harmless or foreign substance that it perceives to be an invader, known as an allergen.  The immune system mounts a defensive attack against the allergen with various antibodies, which results in the release of high quantities of chemicals (including histamine).  The release of these chemicals causes an inflammatory response that leads to the classic ocular symptoms of itching, tearing, redness, swelling, irritation, stringy discharge and soreness. 

Seven percent of the Canadian population is estimated to suffer from eye allergies, of which there are two common types.  Seasonal allergic conjunctivitis is caused by specific allergens such as ragweed, grass or tree pollens that occur seasonally at approximately the same time each year.  In British Columbia, tree pollen occurs in the months of February through May; grass pollen in June and July; and ragweed in August and September.  July and August tend to be the worst months for allergy sufferers because the presence of grass and ragweed overlaps.  Perennial (year-round) allergic conjunctivitis is often caused by animal hair, dust, mold, wool, feathers and other allergens that tend to be present throughout the year.

HOW ARE EYE ALLERGIES TREATED?

Unfortunately, there is no known cure for an allergy.  Treatment consists of avoiding allergy triggers and using medications to provide prevention or relief of symptoms.  Avoiding an allergen can be quite difficult, but some tips on how to do so are:

·   Watch the pollen forecasts. When pollen counts are high, try to stay indoors particularly when pollen release is at its peak (usually early morning hours) and on dry, windy days.

·   Keep your household windows closed so pollens are kept outside, and when driving in your car, use your air conditioning with your windows rolled up.

·   Avoid direct exposure to grasses.  Keep your lawn short during the summer.

·   Molds thrive in dampness, so reduce humidity in your home with an air conditioner or dehumidifier.  Change or clean the filtration unit often to prevent mold build-up.

·   Keep dust to a minimum; keep carpets, rugs and blankets as clean as possible, and clean under beds and couches where dust builds up.

When exposure to an allergen cannot be avoided, several treatment options are available.  The use of artificial tears to help wash away and reduce contact with an allergen, and cool compresses to constrict blood vessels can often be helpful.  The two main types of ocular medications for allergies are anti-histamines and mast-cell stabilizers.  Different formulations are available both over-the-counter and by prescription, including various combination medications. 

Anti-histamine eye drops provide immediate but temporary relief of symptoms related to an allergy response.  Over-the-counter preparations are typically combined with a decongestant (vasoconstrictor) ingredient.  These OTC medications should not be used for more than three to five consecutive days to prevent rebound redness problems, and thus are best for occasional use only.  Mast-cell stabilizers help to prevent an allergic response from occurring by blocking the release of chemicals that trigger allergy symptoms.  In order to be effective, the medication must be taken on a continual basis and can take up to two to three weeks to be maximally effective.  Thus, this type of anti-allergy medication provides a good choice for sustained, long-term relief.  These drops can be started just prior to the usual allergy season to allow time for the medication to achieve full effectiveness. 

It is not recommended that you diagnose and treat your allergy symptoms on your own.  Several different eye conditions can mimic the symptoms of allergies, and anti-allergy medications are not without possible side effects or reactions with other systemic medications.  Your eye care professional is specially trained in this area and is best qualified to recommend the right treatment for you.

How 3D televisions work

HOW 3D TELEVISIONS WORK

Why we perceive in 3D

The simple reason why we perceive in 3D is because we have two forward facing eyes working together as a team to observe the world around us (binocular vision). Our eyes are separated from each other by about 3 inches. As a result, one eye perceives a slightly different image than the other eye. For example, if you look at a word on this page with only your left eye open, and then your right eye, you will see pretty much the same image, except that each eye gives you a slightly shifted perspective of the same object. This is referred to as parallax and is crucial in our ability to perceive depth. The human brain is wired such that when it simultaneously receives images from the left and right eye each possessing a slightly shifted perspective, it is able to combine these images such that we are able to perceive the depth or distance of an object (stereopsis or stereoscopic vision). 

In order for us to perceive a 3D image on a flat surface such as a television, it needs to utilize some form of technology that provides a slightly different image for viewing to each eye.  Let’s explore those options below.  As an interesting side note, approximately ten percent of people are unable to appreciate this 3D imagery, most commonly due to strabismus (crossed eyes that don’t work together as a team) or amblyopia (a lazy eye that sees very poorly).

Polarized Glasses

Polarized glasses are the technology of choice when it comes to commercial 3D projectors that are used in 3D movie theaters around the world. Polarization of light is a unique property that enables us to selectively screen out light using materials called polarizing films. 

Two overlapping but slightly skewed images with different polarization are projected on a special screen.  The polarizing glasses worn by the viewer consist of two polarizing films that allow light of different polarizations through. As a result, one eyepiece allows one image through, while the other eyepiece allows the other image through due to the differing polarizations of the incoming light.  The end result is that each eye perceives a different image and as explained earlier, this results in the brain perceiving a 3D effect.

This technology provides one of the best 3D viewing experiences with rich colors and great detail, and the glasses required are inexpensive.  Unfortunately, the polarized glasses you brought home with you from the movie theater likely won’t work with the new 3D television that you plan on purchasing, because most consumer electronics companies are using a different technology for their first generation models.

Active Shutter Glasses

Active shutter display technology is the primary technology that is being utilized by a number of the big name electronic manufacturers. In this method, the left and right images are displayed alternatively in a sequential manner on a regular LCD TV, and “shutter glasses” are used to discriminate between the images.  These special glasses alternately shut off the left eye and right eye in a synchronized manner so that each eye only sees the corresponding image being displayed on the 3D TV set. The active shutter glasses are maintained in sync with the television set using bluetooth, infrared or radio technology. The main drawback to this technology is that the shutter glasses are expensive and require batteries.  A screen with high refresh rate is required for a smooth view of fast moving sports and movie scenes.

3D TVs without glasses

This is considered the holy grail when it comes to 3D technology, and involves the use of special optical elements between the television screen and the viewer so that each eye of the viewer receives a different image thus producing the illusion of depth (“autostereoscopy”). This can typically be achieved in flat panel displays either using lenticular lenses or parallax barriers.

A lenticular lens is an array of magnifying lenses, designed so that when viewed from slightly different angles, different parts of the underlying image are magnified.  This unique grooved shape on the surface of the television allows a different view to be projected to each eye, thus causing a 3D image.  A parallax barrier consists of a layer of material with a series of precision slits, which controls the direction in which light is transmitted through the LCD panel.  This allows each eye to see a different set of pixels, generating the three dimensional effect.  One advantage of this technology is that using a switchable liquid crystal barrier allows it to be turned off so that the television can also display regular 2D content.

The major disadvantages are an effective reduction in screen resolution, and that there is an optimal viewing distance or position for these screens (the quality of the 3D image can degrade significantly if outside this “sweet spot”).  Autostereoscopic technology is still mostly in the prototype and commercial market phase, but if the demand for 3D technology continues to grow and improve, these televisions will likely become mass-produced consumer products.

The Case of the Lazy Eye

Amblyopia or “lazy eye” is a disorder of the visual system characterized poor vision in an eye that is otherwise normal in structure. This condition often occurs during early childhood and results from poor stimulation from the eye to the brain. This visual stimulation is required to reinforce the visual centres in the brain to allow the brain to pay attention to the signals being received.  The two main causes of the poor stimulation are a strabismus (turned eye) and anisometropia  (unequal refractive errors). 

In the case of a strabismus the amblyopia is caused by the brain suppressing the image from the turned eye (otherwise double vision occurs). In the case of anisometropia the brain ignores the blurry or poorly corrected eye and only pays attention to the good eye. It is this latter case that is often the most surprising to parents when amblyopia is detected in the early childhood years by an eye care professional. There exists a “plastic period” where those reinforcements loops from the eye to the brain are formed. This plastic period exists from birth until about the age of 8 or 9 which is where the window of treatment exists.

The goal of treatment is to break the amblyopia by providing the brain with a clear image from each eye.  Let’s use a real life example. Eric was three years old when I first examined him. He could see perfectly all of the animals from the Children’s Allen chart in his right eye but he could not see anything from his left eye. His mother suspected that he was kidding with us but after I refracted him to plano in the right eye and +6.00 in the left eye. I assured his mother that Eric was not joking around. The corrected visual acuity in the left eye was 20/60, still quite a bit weaker than the plano right eye. We decided to fit Eric with an continuous wear silicone hydrogel contact lens in his left eye only. We instituted a patching regimen of the right eye for several hours per day in order to facilitate the proper feedback loop for the lazy left eye. Today Eric is 12 years old and is best corrected to 20/25+ in the left eye. He is still wearing a continuous wear contact lens with great results. Eric’s parents were an integral part of the successful rehabilitation of Eric’s lazy eye. Diligence with patching is critical to the long term success of this therapy.

Alternatives to Patching

Some practitioners have started using atropine eye drops to treat amblyopia instead of an eye patch. Atropine blurs the good eye and forces the child to use the amblyopic eye and thereby strengthen it.

Research is ongoing into improving vision in older amblyopic patients. It appears that long standing amblyopia can be improved by computer programs that stimulate neural changes leading to improvements in visual acuity and contrast sensitivity.

Acupuncture may eventually become another optional treatment apart from patching for lazy eye, especially among older children who have a poorer response to patching, say researchers from China in Archives of Ophthalmology. More studies are required but initial results are positive.

Detection is Key

The biggest take home message is that all children should have a full eye health examination by the age of three and every year afterwards. It is critical to promote routine eye examinations to all of your clients and by doing so you may be helping a lazy eye to see again.