Dr. Reckell explains what a woman should know about her eyes' focusing mechanisms.
The focus of the eye is determined by, first of all, the curve of the cornea, the length of the eye, and the way these line up. The curve of the cornea and the length of the eye have to match for perfect focus. Perfect focus is called ametropia. If the curve of the cornea and the length of the eye don’t perfectly match there can be the light focusing in front of the retina and a person is myopic or the light focusing in back of the retina, they are hyperopic where myopic is near-sighted, hyperopic is far-sighted, then we will need glasses to fix that and help us focus the light properly on the retina.
Now, there can be irregularity of the shape of the cornea where instead of being perfectly round and smooth, has more of a football shaped and that is called astigmatism. So with the astigmatism, some light’s rays will focus on the retina; some will be in front; some will be behind irregularly. So we use special glasses or contacts to correct astigmatism and have all the light rays equally focusing on the back of the eye.
Now another focusing issue is this lens, this crystalline lens in the eye, I am going to turn this around, is attached to a muscle system called the accommodation system. The way this system works in a normal eye is, when we look at things far away, this system is relaxed. This crystalline lens is relatively flat like a pancake and the system is relaxed for distance focus.
Now when we start looking at things up close, about arm’s length or closer, the light rays hit the eye at a different angle and it’s a reflex where this will start to contract to focus the accommodation system. Well, some people have a very inflexible focusing system that could be hereditary that this muscle lens system just is not real flexible, that’s why we sometimes will see children wearing bifocals. So it’s not always age-related; there are just some weak systems that require assistance, but it is an age-related problem as well, usually between 35 and 45 this crystalline lens will start hardening. When we are born it’s very soft and gel-like and when the muscle pushes, it will contract into a ball shape and when we look at things far away it relaxes.
Well as this lens is hardening, it’s no longer real flexible. So when the muscle pushes on it, it still stays relatively flat and won’t flex to the ball shape necessarily to focus up close. That’s called presbyopia. Presbyopia is a normal age change that affects 100% of us and it is easily corrected visually with the proper glasses or contact lenses.
Now a lot of people think that presbyopia is a weak muscle, which it is not. This muscle is a smooth muscle similar to the muscle in our stomach or intestines. It’s a reflex system. It’s not something that weakens, and a lot of people think, “Oh if I just do the right exercise I can strengthen that muscle and I can focus and get rid of my glasses.” That’s not the case with presbyopia.
Presbyopia is, again, where the lens hardens, the muscle is still pushing on it, this lens just is not responding and flexing and at this point, there’s not a surgery that will restore the flexibility or a medication or a special vitamin. The only thing we know, at this point, to correct lens disorders are when there’s a cataract and the lens clouds over and we can no longer see through it, we can remove the cloudy lens, insert a clear, artificial lens to restore the vision from cloudiness.
We are just now coming out with lenses that have some flexibility and a bifocal type lens that have some structural designs that will focus both far and near light sources. So, that is a new development and so when people have cataracts removed, they now have the option to have a type of lens inserted that will correct both the distance and the near and quite often eliminate the need for reading glasses. But other than that, there really isn’t any other surgery or medication to correct the normal age change of the lens system of the eye.
About Dr. Susan Reckell, O.D.:
Dr. Susan L. Reckell graduated from Michigan College of Optometry at Ferris University in 1984. She holds optometry licenses in Arizona and Michigan. With more than 23 year of experience, she currently works as an optometrist at Riviera Opticare Inc.