Optic Nerve – Visual Acuity

Examination Technique:

• each eye is tested separately.
• test best corrected vision using eyeglasses.
• any patient with uncorrected visual acuity of less than 20/20 should be examined with a pinhole. Improvement of vision through a pinhole indicates that the error is refractive.
• test distant vision using a Snellen chart at 10 or 20 feet.

or test near vision using a near vision card at 14 inches.
the patient is instructed to read progressively smaller lines of letters until they can go no further.

Normal Response:

• most young healthy individuals have vision of 20/20, i.e. at 20 feet, the patient reads a line that a normal eye sees at 20 feet.
• record for each eye separately, right eye = OD, left eye = OS.

Abnormal Response: (Examples)

• 20/30 – 2: The patient missed two letters of the 20/30 line.
• 20/200: Legally blind. At 20 feet the patient reads a line that a normal eye could see at 200 feet.
• CF: If a patient is unable to read the top line, have him count fingers at maximal distance.
• HM: If a patient cannot count fingers, ask them to determine direction of hand motion.
• LP: If a patient cannot perceive hand motion, see if they can perceive a light.
• NLP: No light perception