What is Visual Acuity?
Visual acuity refers to the measure of the eye’s ability to resolve detail at both short and long distances. Each eye has its own level of visual acuity and the two measures can vary considerably. Often there is a third measure noted in eye reports – this is the measure with both eyes open (BEO).
Distance Visual Acuity
The capacity of the eye to resolve fine detail is measured by determining the smallest size print/picture that the student is able to read from an eye chart. The student’s visual acuity is often recorded as a Snellen fraction, the numerator (first number) representing the testing distance and the denominator (second number) indicating the smallest letter/picture size the student is able to identify.
For example, a student who has a visual acuity of 6/24 sees at 6 metres what the ‘normal’ eye, with 6/6 vision, can see at 24 metres.
Near Visual Acuity
Determining near visual acuity involves assessing the capacity of the eye to resolve fine detail. Near visual acuity is recorded as an N point size. Specialists at the Educational Vision Assessment Clinic assess near vision acuity using the Near Vision Test for Children (NVTC) by Gayle Lamb. The ‘normal’ eye can generally read print which is N6 (newspaper print) or even N5.
The N point size indicated on the Educational Vision Assessment Clinic reports (and other ophthalmologist’s reports) generally refers to the minimum size print a student can resolve – usually a larger print size will be required for sustained reading.
For more information visit: Vision and Vision Impairment.