Visual Acuity Examination

    • Assessment of high-resolution central (foveal) achromatic vision
    • Complements visual field testing, which assesses low-resolution peripheral (non-foveal) achromatic vision
    • Step 1: measure distance visual acuity in one eye at a time, at a test distance of 20 feet (6 meters), with the patient’s customary distance glasses or contact lenses in place
    • Step 2: if distance visual acuity cannot be tested, assess near visual acuity with the patient’s customary near correction in place
    • Step 3: Grade Snellen acuity with the numerator designating testing distance and the denominator designating the smallest line on which the patient can identify most letters
    • Step 4: if the patient cannot identify the largest letter on the Snellen chart, grade visual acuity as follows
      • Counts fingers: identifies the number of fingers displayed at 1 foot from the eye
      • Hand movements: distinguishes horizontal from vertical hand movements displayed at 1 foot from the eye
      • Light perception: identifies a bright light you have shined on the eye
      • No light perception: does not identify a bright light you have shined on the eye
    • Step 5: in pre-literate or other language-challenged patients, test visual acuity with
      • Tumbling E's visual acuity test or...
      • Picture visual acuity test
    • Step 6: if visual acuity is subnormal, use the pinhole test to detect uncorrected refractive errors or media opacities such as cataract
    • Step 7: perform a refraction (or get someone skilled to do it!)
    • Tip: designate “best-corrected visual acuity” as visual acuity assessed with the optimal refractive correction in place
    • Snellen distance acuity test is the international standard
      • For patients aged 3 to 5 years, normal visual acuity is at least 20/40 and at most 1 Snellen line difference in visual acuity between eyes
      • For patients aged more than 5 years, normal visual acuity is 20/25 and no difference in acuity between eyes
    • For patients aged 3 years or less, fixing and following a face, toy, or light is an acceptable screening standard
    • Trap: results of visual acuity testing are subjective--patients report what they say they see. If they are not cooperative or truthful, watch out!
    • Tip: there are 4 reasons for reduced visual acuity
      • Optical: uncorrected refractive error, corneal or lens irregularities
      • Amblyopic: monocular reduction in visual acuity based on lack of a clearly focused image presented to the fovea within the first 5 years of life (ocular misalignment, anisometropia, ptosis, opaque ocular media)
      • Neural: lesions of the retina, optic nerves, optic chiasm, or bilateral retrochiasmal pathway
      • Psychogenic: poor cooperation, malingering, conversion, or somatoform disorder
    • Trap: errors in distinguishing between these 4 reasons are common and lead to misdirected evaluations and diagnoses!

    Additional Examination Techniques

    Visual Acuity Examination Color Vision Examination Pupil Examination Eye Movement Examination Eye Alignment Examination