Visual Acuity
Examination
- Checks acuity with Snellen and from proper distance
- Checks acuity both eyes separately
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Typically measured by Snellen acuity but there are many optotypes (letters, tumbling E, pictures)
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May be tested at any distance started by 6 meters (20 feet)
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Recorded as fraction (numerator is testing distance, denominator is distance at which person with normal vision would see figure) e.g., 6/60
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Measured without & without glasses (BCVA & UCVA).
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Occlude one eye, children need to be patched
- 20/20 to 20/400, CF (counting fingers), HM (hand motion), LP (light perception), NLP (no light perception)
Examples of Visual Acuity Charts
- (A) Snellen chart.
- (B) Landolt C chart.
- (C) Illiterate E chart.
Hand-Held Eye Chart
- Hold card approx 14” from pt’s nose
- Read smallest line
- Ask pt to cover one eye
- Cover other eye and repeat
Pinhole View
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Difference between refraction or not
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Use: 1 A 1
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The pinhole (PH) exam can show refractive error
- Need a pinhole occluder
- Central rays of light do not need to be refracted
Near Visual Acuity
Examination
- Ask patient to wear glasses
- Hand-held card at 14 inches or 40 cm
- Assess both eyes separately
- Direct the patient to read the smallest letter that he can see
Hand Held Acuity Card
Near Vision
VISUAL ACUITY
Definition:
- 20/20: You can see at 20 feet what should normally be seen at 20 feet
- 20/100: You can see at 20 feet what a normal person can see at 100 feet
Visual Acuity Scales
| Foot | Metre | Decimal | LogMAR |
|---|---|---|---|
| 20/200 | 6/60 | 0.10 | 1.00 |
| 20/160 | 6/48 | 0.125 | 0.90 |
| 20/125 | 6/38 | 0.16 | 0.80 |
| 20/100 | 6/30 | 0.20 | 0.70 |
| 20/80 | 6/24 | 0.25 | 0.60 |
| 20/63 | 6/19 | 0.32 | 0.50 |
| 20/50 | 6/15 | 0.40 | 0.40 |
| 20/40 | 6/12 | 0.50 | 0.30 |
| 20/32 | 6/9.5 | 0.63 | 0.20 |
| 20/20 | 6/6 | 1.00 | 0.00 |
| 20/16 | 6/4.8 | 1.25 | -0.10 |
| 20/12.5 | 6/3.8 | 1.60 | -0.20 |
| 20/10 | 6/3 | 2.00 | -0.30 |
Visual Acuity Testing
Abbreviations and Definitions
| Abbreviation | VA | Definition |
|---|---|---|
| CF | Counting Fingers | Counting fingers at a specific distance |
| HM | Hand Motion | Distinguishing hand motion in front of the patient’s face |
| LP | Light Perception | Ability to perceive any light |
| NLP | No Light Perception | Inability to see any light; Total blindness |