Dr. Susan Reckell has been an optometrist for 23 years. She shares some of her knowledge about how our eyes function. She sheds some light on astigmatism, and highlights differences between being ametropic, hyperopic, myopic and presbyopic.
Dr. Reckell describes the various parts of the eye, and the intricacies of their interaction. She discusses some of the options available when our eyes are not functioning perfectly, including the purchase of certain types of glasses and surgery.
(Transcribed from video interview)
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.