Important characteristics of your vision that are not measured on the standard eyechart.

To the unschooled consumer who has not undergone laser eye surgery, or to the patient who has undergone it without any adverse effect, vision "quality" is not a meaningful term, that is, it is indistinguishable from vision as a whole. You either see well or you don't, right? Nonetheless, vision quality is a very important concept in laser eye surgery and plays a key role in patient satisfaction.

Think of vision as having both a quantity and a quality. The quantity is your refractive error, that is, myopia, hyperopia or astigmatism. Refractive error simply means any of the focusing problems which glasses can usually correct. When your refractive error is corrected (whether with glasses or laser eye surgery or both) you can see a certain line on a high-contrast eyechart, and that line determines your visual acuity score (20/20, 20/30, etc.)

Then comes the quality part. Vision quality refers to all the aspects of images you see after they have come into the clearest focus that (for you) they can. Vision quality defects include double vision/ghosting (you may see both images clearly, but there are two of them!); reduced contrast (hard to see where one thing stops and the next starts); and starbursts (where oncoming headlights create spiky optical effects which obscure everything around them), to name a few. It is possible to have excellent visual acuity (quantity) as measured on a high-contrast acuity test chart, but have very poor vision quality, particularly at night, due to the introduction of some of these distortions.

In laser eye surgery, vision quality degradation is usually due to the introduction of aberrations.

Two examples of vision defects associated with laser eye surgery are night vision disturbance and reduced contrast sensitivity.

aberrations

Lawless MA, Guest editorial: Refining visual quality assessment in refractive surgery. J Cat Refract Surg, Aug 1999, Vol 25, p. 1031-1032

Fraenkel G, et al: Development of a questionnaire to assess subjective vision score in myopes seeking refractive surgery. JRS Vol 20:10-19.

Vision Simulations: Website with examples of vision quality problems (static and animated) and simulators to reproduce vision quality disturbances.

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Last updated 30 Nov 2004.