Resources:How Your Eyes Work


How Your Eyes Work

The "white part" of the eye is known as the sclera.

Light enters your eye through the cornea, which is made of transparent tissue. The cornea focuses and bends the light, allowing it to pass through the pupil.

The pupil is the dark, round opening in the center of the colored iris. It acts as an aperture to regulate the amount of light entering your eye. The pupil becomes smaller in bright light and larger in dim light.

Directly behind the pupil is the lens. Muscles in the eye adjust the lens to focus the light rays on to the retina, especially during the reading process.

The retina is made of photosensitive cells. It captures light images and translates them into electrical impulses which travel to the brain via the optic nerve.

There is a clear "gel-like" substance, vitreous, inside the eye's cavity which helps maintain the spherical shape of the eye.
The Causes of Blurry Vision
The contour of your cornea, the power of your lens, and the length of your eye determine how clearly you can see. If all three of these elements are matched together perfectly, light rays are properly focused and you can see clearly.

If even one of these elements does not coordinate with the others, light will not focus correctly. These "refractive" or focusing problems are referred to as myopia, hyperopia, astigmatism, and presbyopia.

The measuring unit used when describing refractive problems of the eye is the diopter. Diopters express the focusing power of the corrective lenses that are needed to make the vision normal. The higher your prescription in diopters, the more nearsighted or farsighted you are.

Visual acuity often changes over time, usually declining with age. Certain illnesses, such as diabetes, can also cause changes in vision. Therefore, general health plays a role in how well you see, and should be monitored regularly by a family physician.
Myopia (Nearsighted)
Otherwise known as nearsightedness, myopia is the most common refractive vision problem. People with myopia can see near objects more clearly but have difficulty focusing on distant objects.

Nearsightedness is either caused by a cornea that has more curvature than normal or an eye that is too long. These conditions cause the light rays to focus at a point in front of the retina
Hyperopia (Farsighted)
Hyperopia is more commonly referred to as farsightedness and is the opposite of myopia. Farsighted people have difficulty focusing on nearby objects.

Farsightedness is either caused by a cornea that is flatter than normal or an eyeball that is too short. These conditions cause the light rays to focus at a point behind the retina.
Astigmatism often occurs along with myopia or hyperopia. This condition is caused by a cornea that has an uneven or asymmetrical curvature. This prevents the eye from properly focusing at any distance and causes a ghosting or doubling effect.
Understanding Presbyopia and Dysfunctional Lens Syndrome
For hundreds of years the prevailing concept of presbyopia has been that, by our mid 40s, our natural lens has become less flexible and can no longer provide the near focusing power that we need to be able to shift our focus from distance vision to near, allowing us to read. This resulted in the need for reading glasses or bifocals. This process continued for a number of years until there was no flexibility left and reading glasses have reached their maximum power.
Another, but related process, was that of cataract formation. As the natural lens ages it also begins to change density and become cloudy. At first, this has little significance on vision but as time goes by our vision suffers, finally reaching a point that requires the removal of the natural lens, known as cataract surgery. A new, artificial lens, known as an intraocular lens, is placed in the eye and the distance vision is returned. The most common type of lens implant, however, has no flexibility therefore does not provide separate reading power. There are more advanced intraocular implants that do provide various amounts of near focus and reading power. The following is a classification of the changes that occur to our natural lens over the second half of our lifespan, and available treatments.

Level One

At the approximate age of 43 years old, the lens is still clear but the flexibility has dropped and reading help becomes necessary. Treatment at this point usually involve some form of monovision, the concept of arranging one eye to handle distance vision and the other assigned to near vision. This is most commonly achieved with contact lenses or laser eye surgery. There are newly approved corneal inlays known as the Raindrop and the Kamra lens that, in appropriate cases, can restore a certain amount of reading vision in this first level of Dysfunctional Lens Syndrome (DLS). We will discuss these inlays further within this wesite.

Level Two

This level typically occurs in our 50s and 60s. The natural lens is now becoming yellowed and loosing transparency. This causes a progressive loss of optical quality, more difficult night vision, increase in night glare and the need for more light to read. Lasik with or without monovision can still be performed at this stage but it will be more of a temporary solution as the process will continue to progress. Optical quality at this stage is not good enough to use the corneal inlay process. The permanent treatment for this is the removal of the clouding internal natural lens and replace it with an artificial lens implant. Since, at this stage, the lens clouding is not severe enough to be classified as a cataract, insurance will not cover these procedures.

Level Three

This stage is reached at the average age of 73, when the natural lens becomes clouded to the point of decreased everyday vision and the lens is classified as a cataract. The treatment for this is natural lens removal and replacement with an intraocular implant. Standard procedures for cataract removal are covered by insurance, although some combined with more advanced lens implants styles may require additional payment.

Anyone considering refractive surgery should be aware of the impact of presbyopia. Even after a person's distance vision has been corrected to normal, he or she can expect presbyopia to develop with age. At some point, reading glasses will be required for clear sight up close.
As mentioned above, for patients who would like to delay the use of reading glasses, there is an option known as monovision. This process has been used for years in the fitting of contact lenses. The most common technique is to correct the dominant eye for distance vision and the leave the non-dominant eye somewhat nearsighted so that it can be used for reading. The amount of nearsightedness left can be varied for different purposes. The disadvantage of leaving significant amounts of nearsightedness is that the reading eye will not have good distance vision. This may cause a decrease in depth perception, which is based on the input of sharp visual information to the brain from both eyes.

Some people readily adapt to this condition, while others never become completely comfortable using each eye for different tasks. If a person previously achieved successful monovision with contacts, he or she should have good results with surgical correction as well. Even monovision cannot permanently eliminate the need for reading glasses, but it can definitely increase the length of time that a person can function without corrective lenses.

There are always FDA trials underway in an attempt to surgically improve our ability to focus after forty. Several devices such as the KAMRA lens and RAINDROP lens have been recently approved but it will be a number of years before the results of ongoing tests are known.
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