examination of visual system

1. Examination of the Visual System
Introduction
Good morning everyone. Today, we will discuss the examination of the visual system,
focusing on visual acuity assessment, an essential part of ophthalmic evaluation. Visual acuity
testing not only helps determine the function of the eye and the extent of disability, but it also
has medicolegal implications, particularly in cases of workplace injuries, assaults, or fitness
to drive assessments.
1. Visual Acuity Assessment
Visual acuity is commonly tested using the Snellen chart in the UK. This chart is placed 6
meters away, or, if space is limited, a mirror setup at 3 meters can be used.
• The numerator (6 in 6/6) represents the testing distance in meters.
• The denominator represents the distance at which a person with normal vision can read
that line.
• Example: 6/60 vision means the patient can read at 6 meters what a normal-sighted
person can read at 60 meters.
If the patient cannot read the top line (6/60), further assessment is done:
1. Move the patient closer to the chart.
2. If still unable to read, test for:
o Counting fingers (CF) at a short distance.
o Hand movements (HM) detection.
o Light perception (PL or NLP)—distinguishing between light and darkness.
o No light perception (NLP)—indicates complete blindness.
These distinctions are important, as a person with CF vision may still manage independently,
while only light perception (PL) may mean complete dependency.
In the United States, a different notation system is used:
• 20/20 vision = 6/6 vision
• 20/200 vision = 6/60 vision
Another common system is the LogMAR chart, which is logarithmic and provides greater
accuracy. It is particularly useful in clinical trials and pediatric screenings, but it takes longer
to perform.

2. Testing Conditions
• Vision should be tested with the patient’s usual glasses or contact lenses.
• If vision is poor, using a pinhole helps determine whether the issue is due to refractive
error or an underlying ocular condition.
Near Vision Testing
• Near vision is assessed using a standard reading chart or even newspaper print.
• Conditions such as presbyopia (age-related loss of near vision) can lead to a
discrepancy between near and distance vision.
2. Additional Visual Function Tests
Colour Vision
• Tested using Ishihara plates for red-green colour deficiencies (common in inherited
conditions).
• Other tests may detect blue-yellow defects seen in conditions like glaucoma or optic
neuropathies.
Contrast Sensitivity
• Assessed using the Pelli-Robson chart.
• Important in conditions like cataracts, where a patient may have good visual acuity but
poor contrast sensitivity—leading to difficulties in low-light conditions.
Conclusion
Visual acuity testing is a fundamental part of ophthalmic assessment, providing essential
diagnostic information. It should be performed systematically, considering both distance and
near vision, colour vision, and contrast sensitivity. Proper assessment can help diagnose
refractive errors, cataracts, glaucoma, and optic nerve diseases, ensuring appropriate
management and intervention.
Thank you! Any questions?