19 Nov The Cornea and How We See
The cornea is the clear tissue at the front of the eye. A contact lens rests on the cornea. It is normally crystal clear, focuses light and permits light to be focused on to the retina. A healthy retina absorbs light, transmits this information to our brain……..and voila………it gives us vision.
The Cornea and Focusing Power of the Eye The cornea is more than just a clear window to the inside of the eye. The cornea is actually responsible for about 70% of the focusing power of the eye! For those that remember physics, the combination of the air/water interface along with a specific radius of curvature……………..
Anyway, this is why laser vision correction works so well. By reshaping the surface of the cornea, the focusing strength of the cornea can be calibrated to refocus light onto the retinal surface. No more need for glasses!
Ever have a scratch on your cornea? It hurts and can cause significant loss of vision. Why? The surface of the cornea is usually smooth, but when scratched this critical focusing surface is now rough and uneven, resulting in significant loss of vision. With patching, the surface usually can heal quickly with full restoration of vision.
The natural lens inside the eye also contributes a small portion to the overall focusing power of the eye, but remember most is due to the cornea.
Nearsighted vs. Farsighted Nearsighted individuals have a natural focusing point in front of the retinal surface. Glasses/contact lenses are used to push the focusing point back to the retinal surface. Nearsighted (not nearsightless) individuals can take their glasses off and read without glasses.
Farsighted individuals have their focusing point in back of the retinal surface. Glasses are required to bring this focusing point forward to the retinal surface.
Measuring Your Visual Acuity of 20/20 occurs when a focused image is on the surface of the retina and the retina is healthy. A healthy retina is required to transmit all of the focused light to the brain.
In cases of macular degeneration and diabetic retinopathy, if the disease has caused some damage to the macula, perfect vision is not possible simply because the retina is not functioning completely.
Corneal Disease is usually unassociated with diabetic retinopathy and macular degeneration, that is, there are usually no related corneal findings in these two retinal diseases. There is a slight chance of spontaneous abrasions, but no true disease.
Randall V. Wong, M.D.
Ophthalmologist, Retina Specialist