If you have been to an eye care provider because you wanted to know if glasses would help you to see better, you’ve probably been asked this question … more than once.
This question is asked while performing a refraction and it can be a nerve racking question. You feel like you don’t want to give the wrong answer and sometimes you just cannot tell which is better. Rest assured, if you cannot tell which is better, then “I cannot tell” is the right answer!
What is a “refraction”?
The refraction is a process that begins with the use of a retinoscope or an autorefractor. These do not require any responses from you. They provide a starting point for the subjective refraction.
Typically during the subjective refraction a phoropter is used (shown above). The phoropter is the piece of equipment that you sit behind, looking through holes (that have lenses) at the visual acuity chart across the room. The phoropter allows the lenses to be changed easily and quickly as the question is asked, “Which is better, 1 or 2?”
However, there is another way to do a refraction. That is with a trial frame and loose lenses (see below). If you have low vision, this is the best way to have a refraction performed.
More on Refraction
Technically, refraction is the bending of light that takes place within the human eye. The goal of the light bending is to put the visual image (of the object that you are looking at) on the retina in the back of the eye.
As with almost all aspects of human anatomy and function, there are many variations and occasional malfunction. This can result in refractive errors. The shape of the cornea, the shape of the lens and the length of the eyeball are the main components that determine the distance refraction of the eye. Lenses are used to compensate for these refractive errors.
Typical Refractive Errors
Myopia (Nearsighted): Visual images come to a focus in front of the retina of the eye. This means you cannot see far away. A concave lens is used in your glasses to compensate for the myopia by moving the image back to the retina.
Hyperopia (Farsighted): Visual images come to a focus behind the retina of the eye. This means your eye muscles have to work harder to see, so it usually affects your close up vision first. A convex lens is put in your glasses to compensate for hyperopia by moving the image forward to the retina.
Astigmatism: Visual images do not focus in just one spot. This means you can have blurry vision both far away and close up. The lens in your glasses will bring the image into one focal point.
Presbyopia: When looking at an object close up, your eye cannot bring it into focus. This is due to aging. A convex lens compensates for the problem.
Does macular degeneration cause refractive disorders?
No, macular degeneration does not cause you to have refractive disorders. Macular degeneration affects the retina, but not the focusing apparatus of the eye. However, most people with macular degeneration are older so they have presbyopia. If this is not corrected by wearing lenses to refocus the image, the difficulty with vision caused by the macular degeneration will be aggravated, making seeing up close even more difficult.
Therefore, it is important for all with macular degeneration to see their eye doctor regularly and have a good refraction done.
Cheri Glaus OD, Optometrist
Joe Fontenot MD, CLVT Medical Director
Community Services for Vision Rehabilitatin(CSVR)