Welcome to question of the day #229

Eyteools question of the day #229

One of the other eye specialists in the practice where I work measures visual acuity with the room lights low. I was always told to measure visual acuity with the room lights up. What should I do?

Measurement of visual acuity looks and sounds like a simple measurement to make. You point to some letters and ask the person to read them. It is, of course, much more complicated than that. So many times I have come across cases where poor or absent visual acuity measurements led to a patient suffering harm.

Accurately assessing visual acuity is very very important for many reasons. It allows the eye specialist to:

Determine unaided visual acuity (also known as vision) which gives an indication of the refractive error, especially helpful with new patients.

Determine the optimum refractive correction.

Detect eye disease.

Monitor the effect of treatment or disease progression.

Verify eligibility for tasks such as driving.

Verify eligibility as legally blind.

When measuring distance visual acuity, measuring in a darkened room is no longer necessary. In the past, when projected charts were used, the room lights had to be lowered for better contrast on the chart. With high-definition retro-illuminated charts and LCD monitor charts poor contrast is not an issue.

Also, it’s not a good idea to take patients from a normally-lit waiting room into a darkened exam room, as this will artificially lower the visual acuity, particularly for those people who have difficulty adjusting to low-light conditions.

Because so many clinical decisions are based on visual acuity measurements, accurate assessment of each person’s monocular and binocular visual acuity is critically important.

In my opinion, all visual acuity testing should be done with the overhead lights on in the exam room. I am aware, however, if the patient complains of photophobia and asks for the lights to be lowered I will do so but make a note in the clinical records that the visual acuities were measured in low light conditions and the reasons for doing so.

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