Low vision assessment

Low vision is both a subspeciality and a condition. Optometrists, Opticians, Orthoptists and Ophthalmologists after their training may undergo further training in Low vision assessment and management. There are various classifications for low vision, this varies from country to country and even from state to state. It must however be noted that the work of a low vision specialist is very important as they aid individuals with reduced vision even in the presence of conventional lenses to be able to make use of their residual vision. People benefitting from low vision assessment must be motivated to make use of the residual vision and must again be willing to use the various aids that would be prescribed.

Purpose

The purpose of a low vision assessment is to determine a person's functional or residual vision. This will reveal how a person uses their eyesight in real life settings and the visual aids which are most appropriate to support their functional vision. Functional vision is assessed by six different fields (visual acuity, visual field, contrast sensitivity, colour discrimination, and oculomotor control), meaning every person's results will be different and require an individualised support plan.^[1]

After a low vision assessment, an assessor will work with the person to discuss their goals for mobility, navigation, technology, and more. They will be able to suggest low vision aids, including technology and mobility supports, as well as practical tips and strategies for daily tasks.

Classification

The World Health Organization classifies^[2][3] people with low vision as follows:

• 1. 6/18 (20/60) [0.5] to 6/60 (20/200) [1.0]
• 2. 6/60 (20/200) [1.0] to 3/60 (20/400) [1.3]
• 3. 3/60 (20/400) [1.3] to 1/60 (20/1200) [1.8]

readings from left to right are in metres, feet and LogMAR values

Examinations

Low vision visual acuity examinations are done using the LogMAR chart. The advantage that this presents with is that it allows for more accurate measures of the individual's vision to be recorded. Other tests done and their significance are as follows:

• Amsler's grid test - to locate scotomas on the visual field of the individual
• Colour sensitivity test - to assess the function of the Optic nerve
• Contrast sensitivity test - to assess the function of rods photoreceptors
• Visual field test - to know the extent of the individual's field that is sensitive
• Near visual acuity - to assess the reading ability at near