Visual Acuity Test: Practical Optometry Guide
- maudoptical
- 7 days ago
- 2 min read
Objective
To evaluate the eye’s ability to distinguish details, in both distance vision and near vision.
Principle
The patient reads letters, numbers or symbols of decreasing size, successively:
one eye at a time (monocular vision),
then with both eyes (binocular vision),
with or without correction,
at distance and then at near.
Visual acuity results are typically expressed in decimal notation.
Testing Conditions
Appropriate testing distance depending on the type of test (distance or near vision)
example: for the Galinier test, the testing distance is 40 cm
example: for the Optoprox test, the testing distance is 33 cm
Adequate and uniform lighting, without glare or shadows
Proper use of an occluder to measure monocular visual acuity (right eye, then left eye), followed by binocular visual acuity
example: the occluder is placed over the right eye to assess the monocular visual acuity of the left eye, and vice versa
Types of Optotypes Used to Measure Visual Acuity
Letters (alphabetical optotypes): used for literate patients (e.g., Snellen or Monoyer charts)
Words or text: used for near vision (e.g., Parinaud chart), allowing assessment of reading ability
Numbers: an alternative to letters, useful for certain patients or to vary testing
Landolt C (Landolt ring): a ring with a gap in different orientations; the patient indicates the direction of the gap (up, down, left, right)
Snellen E (tumbling E): the patient indicates the direction of the limbs of the letter E
Pediatric optotypes: simple symbols or pictures (animals, objects, shapes), adapted for children or non-literate patients (e.g., Lea symbols)
What Is Considered Good Visual Acuity?
Visual acuity evaluates the quality of vision at both distance and near. But what is considered “good” visual acuity? Reference values depend on the testing distance and the scale used.
Distance Vision : Distance visual acuity is commonly expressed in decimal notation. A visual acuity of 1.0 (10/10) corresponds to very good vision, allowing fine detail discrimination at distance.
Conversely, a visual acuity around 0.1 (1/10) indicates significantly reduced vision. In clinical practice, 1.0 is often considered normal, although some patients may achieve higher values (e.g., 1.2 or more).
Near Vision : Near visual acuity is typically assessed using the Parinaud chart, based on reading text of decreasing size.
This scale generally ranges from P1.5 (very good near visual acuity) to P28 (very poor). Normal near vision is usually around P2, corresponding to comfortable reading under standard conditions.
Conclusion
The visual acuity test is a fundamental examination used to measure the eye’s ability to resolve fine details at both distance and near. It represents the starting point of visual assessment with a phoropter, following objective measurements obtained with an autorefractor.
Simple to perform, it guides the subsequent subjective refraction and helps determine the most accurate optical correction.
It is an essential test in daily practice and in exams, particularly for optometry students and orthoptics students.
Mastering the visual acuity test ensures reliable measurements, a well-structured eye examination, and greater confidence, both in exams and in real clinical situations.
