Check Visual Acuity
We use eye charts consisting of optotypes (letters or pictures) to test visual acuity. If a patient’s visual acuity is known from a prior examination, start at that line of the eye chart. Otherwise, first cover the left eye, and ask the patient to read the 20/40 line on the eye chart with the right eye (Figure I-21A). Go up or down the eye chart to find the line your patient can just barely read. Then cover the right eye and repeat the process to measure the acuity of the left eye.
Figure I-21 Eye charts for testing visual acuity. A, ETDRS-type chart with Sloan letters; B, Allen Symbols (not recommended).
(Part A Courtesy of Precision Vision; part B courtesy of Vision Training Products.)
If visual acuity is subnormal, try a pinhole occluder, a device with 1 or more small apertures used to reduce the eye’s effective aperture (Figure I-22). Note: Best-refracted vision may be better than, worse than, or the same as pinhole-corrected vision! Failure to improve with a pinhole does not exclude refractive error and does not justify omitting the refraction.
Figure I-22 Pinhole occluder.
If the patient has distance glasses, there is rarely any reason to check the visual acuity without them, unless the patient requests it or acuity with the existing glasses is very poor. A patient may inadvertently use reading glasses while attempting to see at distance!
Check visual acuity at near (ie, reading vision) routinely only in the following cases: potential presbyopes (with age-related loss of near vision), latent hyperopia suspects, patients (especially children) suspected of amblyopia, and patients with a near-vision or an asthenopic complaint.
Asthenopic complaints are various symptoms associated with accommodative effort—that is, with the ability of the eye to increase the optical power of the crystalline lens.
Patients over the age of 40 or so should routinely be checked for presbyopia. It is better to allow such patients to hold the near-card at their own preferred reading distance (with or without reading glasses, according to the patient’s typical reading habits), and record the smallest legible line, and the distance at which the patient chose to hold the near-card, than to enforce the standard reading distance. Use “Jaeger notation,” optotype size in “points,” or both to record the patient’s near vision.
Obtain a Visual History
As in any other patient care encounter, obtaining an accurate history is a vital initial step in clinical refraction. Understanding the patient’s visual complaints, if any, is often critical to providing a satisfactory refractive solution. For example, the patient may benefit from glasses suitable for specific activities, such as using a computer, playing a musical instrument, or going shopping. Prescribing glasses for a patient without visual complaints is rarely helpful.
Seek the following items if they are not volunteered:
decreased visual acuity: At distance? At near? Both?
presbyopia (difficulty reading at comfortable distance)
occupation (computer work, in particular)
hobbies (eg, music, sewing)
other ocular history (eg, amblyopia, trauma, glaucoma, prior eye surgery)
Review Indications for Refraction
Which patients need to be refracted?
those with subnormal visual acuity. Remember, 20/25 is not normal visual acuity. Patients with acuity of 20/25 or worse should generally be refracted, unless a credible refraction documenting a stable best-corrected visual acuity of 20/25 or worse is already present in the medical record. Patients with acuity of 20/30 or worse should be refracted routinely
those with asthenopic symptoms
those with decreased visual acuity since their previous visit
postoperative patients (especially after cataract surgery)
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.