The refraction is the process of determining a glasses or contact lens prescriptions. To many people, the refraction is just the number on the lens that allows one to see the 20/20 visual acuity line. After one reaches adulthood, many people assume that this number should not change much just like their shoe size. Many low vision patients do not have 20/20 vision. In fact, their best corrected visual acuity may be 20/200 or worst, but they still can appreciate a good refraction.

What can influence Refractions?

Ocular Health.

Cornea, retina, and ocular surface health can impact the quality of a refraction. Some examples can include: blur from cataracts, distortion from low vision conditions (such as macular degeneration), and surface and irritation compromises from dry eye syndrome.

Systemic Health.

Poor control of diabetes can result in acute swelling of the lens that can drastically change a refraction. Diabetes can also cause retina bleeding and diabetic macular edema that can impact the image. Multiple sclerosis, albinism, and premature birth are other common systemic health problems that can result in physical changes to how vision operates.

Neurology.

This comes as a surprise many, but many of our brain injury patients report fluctuating vision. Dr. Ho often purposely modifies a prescription to get patients more functional i.e. to reduce dizziness or help reconcile visual spatial differences or modify posture. Therapeutic tints and prism glasses help increase patient comfort when their nervous system is unstable. Supports sometimes need to be altered over time during the course of rehabilitation and recovery.

Eye Alignment, Eye Teaming (vergence), and Eye Focusing (accommodation).

These visual skills can all contribute to changes in one’s refraction. Each prescription has a sweet spot for a certain distance. This may be different for someone who spends a lot of time on the computer vs a cell phone or a work bench. Some patients require multiple prescriptions for the different tasks they do every day. As we age, our eye focusing naturally loses power so many people will need reading glasses.
Sometimes a disease may cause severe distortion in one eye’s image. In this case, refracting to optimize clarity to this distorted vision may not be purposeful. Instead, it may be more comfortable to create blur to allow the brain to favor the other eye more readily.
Dr. Ho takes into consideration: ocular alignment, eye teaming, visual acuity, visual strategy, balance, light sensitivity, and task specific distances to name a few.
The picture above is a high prescription lens. It appears to create a lot of distortion for some, but for this patient who it was designed for, this offers clarity to help them go through their activities of daily living.
Prescription holds the power to change visual behavior and alter visual function.
Purposeful prescriptions are a critical piece to vision rehabilitation. Prescribing is much of an art as a science. Dr. Ho frequently jokes with her patients that “a prescription is a negotiation between me and what your brain wants to do.”