 MANAGING PATIENT REQUIREMENTS DURING VISUAL ACUITY  USING TOOLS FOR TESTING DISTANCE AND NEAR VISUAL ACUITY  HAND HELD CARD  SNELLENS CHART  DISTANCE CORRECTION AND OCCLUSION

Factors governing Normal vision (6/6) Both eyes in alignment (extraocular muscles functioning) Clear cornea Clear lens of the eye Clear ocular media (aqueous and vitreous) Intact retina, optic nerve, visual pathway

What is Visual acuity? The resolving power of the eye used to assess and quantify the eye’s ability to resolve varying letter sizes. Visual acuity is a measurement of central vision only. Assessment of total visual system from cornea to occipital cortex. Visual acuity can be tested for both distance and near vision. Distance visual acuity is the most common test.

Why need a visual acuity test? Diagnostic tool Baseline data Measures progression of disease Evaluates treatment To measure the patient’s progress visual acuity must be assessed at every presentation.

Patient Requirements Patient’s co-operation Patient’s comprehension of what is required Ability to recognise images used on the various charts (letters, numbers or pictures) Distance correction (glasses or contact lenses)

Standard Test Distances Distance visual acuity (DVA)  20ft or 6M is equivalent to optical infinity Near visual acuity (NVA)  40cm

Types of Distance Visual Acuity Charts Wall charts  Testing VA in literate adults  Printed on cardboard and mounted on a wall  Well-suited for vision screenings and doctors’ offices  Variations: Tumbling E chart, Landolt C chart, Bailey-Lovie chart

Examples of visual acuity charts. (A) Snellen chart. (B) Landolt C chart. (C) Illiterate E chart.

Tumbling E Chart

Bailey-Lovie Chart

Hand-held visual acuity cards  Primarily for children in vision screenings  Simplest form is the letter E in different sizes printed onto hand-held cards  Free space testing

Visual acuity by Hand held card

Near Visual Acuity Testing the VA at close range (usually 40cm) The purpose is to detect people with near vision difficulties (e.g., uncorrected high hyperopia, accommodative dysfunction) In patients over 40 years old, the reduced near visual acuity is one of the symptoms of presbyopia

Near Vision Charts Types  Reduced Snellen Acuity card  Test distance at 16in (or 40cm)  Jaeger Acuity Card  Point system  M notation

Bailey-Lovie Reading Card

Lea Symbols

The visual acuity categorized (10th Revision of the WHO International Statistical Classification of Diseases).WHO 1 Good vision = 6/6 to 6/18. 2 Low vision = 6/24 to 3/60 (CF3m). 3 Blind = 3/60 (CF3m) to PL (perception of light). 4 Blind to light - NPL (no perception of light). Legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less in the better eye with best correction possible.visual acuity In many areas, people with average acuity who nonetheless have a visual field of less than 10 degrees (the normal being 180 degrees) are also classified as being legally blind.visual fielddegrees