Eye and Vision
Why Do People Wear Glasses But Animals Don’t?
Most animals have good vision, but many humans do not. Somewhere in this very simple statement may be the answer to the question of why many people need glasses or contact lenses to see well, but more importantly, what can be done to prevent poor vision in people. The eye is a marvelously simple, yet incredibly complex organ. In some ways, the eye is like a camera, with a lens (actually two lenses consisting of a cornea and a lens) whose job it is to focus light onto the film (retina) at the back of the eye. It is more like a digital camera in that the image focused on the retina gets processed or interpreted by the brain and then seen. It is this processing that results in an image that we see that is the incredibly complex part.
Types of Vision Problems
When the eye can see images perfectly clearly at a far distance, optometrists would call it emmetropia, but most people would say that eye has perfect vision or they might say 20/20 vision. Alternatively, the eye might see poorly at distance, but perhaps quite well at near, known as myopia or nearsightedness. This word tends to confuse a lot of people because they don’t connect good near vision with poor distance vision. A better term, that would be more easily understood, would be distance blurredness, but it is not a great word in the English language, so we are stuck with nearsightedness.
Another type of blurred vision that the eye might have is hyperopia or farsightedness. This might be better named near blurredness, as farsightedness usually means blurred vision up close. Even more confusing than nearsightedness, farsightedness could also result in blurred vision far away if the amount of the farsightedness is high enough or the person is old enough, but almost always, farsightedness affects near vision more than distance vision.
Astigmatism is even more confusing, but it occurs when the eye focuses images differently in different directions. A letter “E” might be better focused for the horizontal bars of the “E” than the vertical bar or vice versa, when the eye has astigmatism. This occurs when either the cornea, or the lens or both surfaces are shaped more like a football than a baseball. Astigmatism is usually combined with either myopia or hyperopia, just to make it more confusing.
Presbyopia is a terrible word, that practically no one has heard of, but everyone gets it at some point after age 40. Presbyopia is the term for the difficulty that most people over the age of 40 have when they try to focus on near objects. It affects different people differently depending on whether they have emmetropia, myopia, hyperopia and/or astigmatism. When presbyopia happens to someone with good natural distance vision (emmetropia), they start to have difficulty focusing near and they usually need reading glasses to see well. When it happens to people with myopia (or here is where the word nearsightedness works well), they can often remove their glasses in order to see near, because they are near-sighted, that is what they do well without glasses. Occasionally, people with astigmatism can also remove their glasses to read, but they can only see parts of the letter well, but they sometimes find that having part of the letter clear is better than having none of the parts of the letter clear. When presbyopia happens to people with hyperopia, it just makes their usually poor near vision even worse, so here thinking of hyperopia as “near blurredness” might get the point across that presbyopia is most annoying to people with hyperopia.
Does Myopia Always Have to Get Worse and Worse?
The causes of myopia have been debated for hundreds of years, however, recent research findings are helping to convince practitioners that attempting to control myopia may be worth a serious look. Many optometrists and ophthalmologists were taught in school that myopia was a genetic condition resulting in a gradually increasing level of myopia until the “age of cessation” somewhere in the late teens. While many private practitioners may be convinced that myopia frequently changes well into adulthood or may onset in adulthood, there is still a lot of skepticism that myopia can change in adults. Moreover, despite the innumerable correlations between academics and myopia there are very few studies, if any, that can reliably link levels or progression of myopia to any type of measure of reading or near work hours. These debates will not be settled by this discussion; however, I will argue that there are reliable ways with currently available optical treatments to dramatically slow the myopia progression rates in many myopic children and adults. Some may question the value of controlling myopia progression but with serious eye diseases linked to higher levels of myopia, not to mention the visual disability associated with high levels of myopia, that’s an issue that shouldn’t even merit a debate.
Bifocal Eyeglasses and Progressive Multifocals for Myopia Control
A myopia control treatment that has been used for maybe a hundred years is the use of bifocal glasses. There have been a number of studies over the years on the use of bifocals to control myopia and most of the studies show little or no effect when used on a general population of children. Bifocal glasses and progressive multifocals (bifocals without lines) have been shown to reduce myopia progression by anywhere from 20 to 40%, when used in children who have a slight tendency to cross their eyes excessively while reading (esophoria.) There also seems to be some reliable effect on children who have a tendency to focus insufficiently while reading, though children with esophoria tend to under-focus their eyes as well. A very recent study with Chinese-Canadian children showed that bifocal glasses slowed myopia progression a little better than most bifocal studies have shown. This was a select group of children, that all were worsening rapidly in their myopia before being fitted with bifocal glasses and that may have accounted for the apparent increased effect.
How About Reading Glasses?
A similar treatment for myopia progression has fewer studies to show its effectiveness, but there are good enough reasons to expect it to work that it can be considered for children. For the same children that bifocal glasses should work for (esophoria, and perhaps also poor focusing at near) reading glasses should also work. Reading glasses can be less convenient than bifocals, for while they make near vision clearer and/or more comfortable, they do make the distance vision blurrier, until they are removed and a distance pair of glasses is put on. Even for children that are wearing bifocals or progressives, a separate pair of reading glasses may still be advisable for viewing the computer. The reason for this is that the reading portion of a bifocal eyeglass is in the lower part of the lens, and most kids would have to raise their chins a lot in order to look at computer screens through the lower part of the lens. Most children will not view computers this way and they would be better served to use an eyeglass designed to make the computer screen clear with a comfortable head position.
Can Orthokeratology Correct Myopia and Slow Progression?
Another treatment that has been shown in a few studies to slow myopia progression in children is orthokeratology. Orthokeratology is known by several names (Ortho-K, Corneal Refractive Therapy, Gentle Corneal Molding, Corneal Reshaping, etc.) Ortho-K involves wearing highly gas permeable contact lenses only while sleeping. The lenses are specially designed to reshape the eye overnight to correct the vision, providing good vision during the day without the lenses. This is a good non-surgical option to correct poor vision caused by myopia, but it may have some additional benefits. Two small studies have shown that children that undergo this Ortho-K procedure not only have good daytime vision because of the corrective lenses, they also seem to have their myopia progression slowed by 50% compared to children of the same age that wear standard contact lenses.
If Bifocal Eyeglasses Work, What About Bifocal Contacts?
This is my favorite question, because it was the question that I asked myself almost twenty years ago and I have been researching the answer ever since. To boil down all of the research including two retrospective studies, one identical twin study and a randomized controlled clinical trial, bifocal soft contact lenses have been shown to reduce myopia progression in children or adults by an average of 90%. Most of my research has been on people with esophoria at near, but lately I have been using bifocal contacts on most nearsighted people that are experiencing continual worsening of their vision, and they appear to work well on most people with myopia. There are a number of other studies ongoing throughout the world that should come out soon that will offer further evidence of the tremendous myopia control effect of these lenses.
How Do Bifocal Contacts Work?
This is another very interesting question. The type of bifocal contact lenses that I have used in my practice and in the various studies over the years are known as “simultaneous vision bifocals.” They are quite different than eyeglass bifocals in that they typically have a distance focus lens in a center circular zone which is surrounded by a ring zone of near focus power. Alternatively, they can have a central near zone surrounded by a distance zone. The cool thing about bifocal contact lenses is that the brain is presented with the distance vision in focus by the distance zone and simultaneously out of focus by the near zone. After a short learning period, the brain learns how to pay attention to the clear image and ignore the blurred image. Similarly, while viewing a near object, the brain chooses to pay attention to the clear image provided by the near zone, while ignoring the blurred image provided by the distance zone. Incredibly, most children and young adults see quite well with these lenses and usually have 20/20 vision.
Why Do Bifocal Contact Lenses Control Myopia So Well?
It may be as simple as simultaneous vision bifocal contact lenses work at all angles, and children don’t have to be instructed how to properly hold their head to get the beneficial effects. So, they work like bifocal eyeglasses, but they work all of the time, no matter how the wearer uses them. There is a very popular theory lately that myopia worsens in many cases because regular glasses and contact lenses only focus images properly in the central part of the back of the eye, while allowing the peripheral focus to fall behind the retina. Numerous researchers have shown that in every animal species studied, if the images are focused behind the retina in a young animal, the eye grows to where the image is. This growth of the eye creates myopia. If, on the other hand, the images are manipulated to fall in front of the retina, the eye growth slows to try to match the focus. This slowing of growth causes hyperopia. From these animal studies comes the theory that if a contact lens or eyeglass lens could be designed to focus properly on the central part of the retina to provide good clear vision, while at the same time bring the focus in the periphery of the retina either on the retina or in front of the retina, the eye will stop growing, and myopia progression will cease. Studies are ongoing on the optimal designs for these anti-myopia lenses, and they should be introduced somewhere in the world in the year 2010.
Can Anything be Done Now, or Do We Have To Wait for Anti-Myopia Lenses?
There is no reason to wait for these lenses to hit the market as there are quite effective ways to control myopia right now. Consider taking the following steps for your child depending on their current situation. Start by scheduling comprehensive eye examinations prior to age 5 and annually thereafter. Particularly important are the years around age 7 when myopia may start to show signs of developing and age 8 or 9 where it commonly starts. Ask the optometrist to carefully look for esophoria at near, as this condition tends to cause myopia. This is the general approach that I recommend for managing and controlling myopia:
1. For young children with gradually reducing hyperopia, resulting in +0.75 or less hyperopia, with esophoria, and particularly with a strong family history of myopia, consider starting with reading glasses. These glasses should be used for all near vision tasks, reading, handheld video games, computers, homework, etc.
2. For children with low amounts of myopia along with esophoria, still consider reading glasses, instead of correcting the distance vision. Young children with 20/30 vision or so, see quite well in class and may not really need their distance vision corrected. The problem with distance glasses in this type of child is that the distance vision lens causes increased eye crossing while reading, and even if you tell the child to remove the glasses while doing near work, some kids just don’t listen to parental advice.
3. For children with a little bit more myopia, maybe -0.75 or worse, consider a progressive multifocal eyeglass. My personal preference is to slightly undercorrect the distance portion and add a little bit of prism. These modifications help to insure that if the child does near work through the top of these glasses instead of using the reading portion, their eyes will still be less crossed than they would be otherwise with a standard bifocal prescription. My advice to doctors is to make the bifocal power strong enough to eliminate the tendency for the eyes to cross, specifically to eliminate something called fixation disparity. For a child that uses the computer frequently, additional myopia control can be provided by a supplemental reading or computer glass. The prescription should also be selected to properly control the eye crossing tendency.
4. For the same child as in number 3, as soon as the parent or the child thinks that they are mature enough to take proper care of contact lenses, switch them to bifocal soft contact lenses. Keep in mind that most children can do quite well with contact lenses even at ages as low as 5 or 6, and a number of studies have shown that contact lenses are quite safe for young children. Because bifocal contact lenses are so much more effective in controlling myopia than any other method, the sooner you can get a child to wear these lenses, the better and more effective control of myopia progression.
5. Any person with continually worsening myopia, child or adult with or without esophoria should consider bifocal contact lenses as well. There are at least two or three theories that support this approach, and it is well worth a try.
6. For a child or adult without esophoria, but with some progression of myopia, who wants to eliminate their myopia without surgery, consider Orthokeratology. For the right candidate, the results are fantastic and there will likely be an additional benefit of slowing myopia progression. I think the existing evidence would still argue for bifocal contacts instead of Ortho-K for people with esophoria, because of better control of progression.
Any Other Advice?
Several studies are starting to show that there may be some protective anti-myopia effect just from playing outdoors. Whether this is because kids that are playing outside are not reading as much, or whether it has something to do with some unique controlling effect from viewing distance images, or whether sunlight actually plays some role is still unknown. Worst case scenario, your child will discover that it can be more fun to play outdoors than playing video games indoors, and they will get more exercise.
Animal studies suggest that when researchers are trying to create myopia by blurring retinal images, short periods of clear distance vision can counteract the myopia effect. This might mean that taking frequent visual breaks from close work, by looking off in the distance, might be beneficial. There are no studies in humans that show this behavior protects against myopia, however.
What About Gas Permeable Contact Lenses?
Many optometrists and ophthalmologists have thought over the years that people that wear rigid gas permeable contact lenses experience less myopia progression than other people. Several studies, including a very good one recently pretty much have proven that there is actually no significant slowing of myopia caused by wearing rigid gas permeable lenses. What is a little tricky is that gas permeable lenses usually cause the shape of the cornea to change resulting in a temporary reduction in myopia, and this can cause an appearance of a slowing of myopia over the years. Once the lenses are removed, most of the hidden myopia reappears. What is different about using gas permeable lenses overnight with Orthokeratology, is that the shape change caused by Ortho-K seems to slow myopia.
What About Exercises to Improve Vision?
There have been numerous attempts over the years to study whether there were any effective ways to control myopia with eye exercises and unfortunately there doesn’t seem to be a way to reduce myopia or slow myopia progression with eye exercises. Certain techniques can cause the eye’s focusing system to relax and this might cause an improvement in temporary forms of myopia known as psuedomyopia, causing an improvement in vision. Other techniques can train people with blurred vision to learn to interpret their blurred vision, giving them an apparent improvement in vision, though their actual prescription does not change after the exercise program.
Where Can I Find More Information?
There are more details about Dr. Aller’s myopia progression research and clinical methods on his websites: www.draller.com You can also email him with questions through this site.