Vision Screening Processes: Acuity Chart vs Photorefractor
Traditional Screening: Acuity Chart
Three (3) minutes average for a complete vision screening by experienced personnel.
The visual acuity test is used to determine the smallest letters the child can read on a standardized chart (Snellen chart) or a card held 20 feet (6 meters) away. Special charts are used when testing at distances shorter than 20 feet (6 meters). The chart is calibrated from very large letters to smaller representing the visual acuity for the test subject on a 20-foot equivalent.
Alternative Names
Eye test – acuity; Vision test – acuity
How the traditional screening is performed
This test may be done in a health care provider’s office, a school, workplace, or elsewhere.
The child will be asked to remove glasses or contact lenses and stand or sit 20 feet (6 meters) from the eye chart, with both eyes open.
The child will be asked to cover one eye with the palm of the hand, a piece of paper, or a small paddle while reading out loud progressing from the largest letters to the smallest line of letters which can be seen on the chart. Numbers, lines, or pictures are used for people who cannot read, especially very young children.
If the child is not sure of the letter, they may guess. This test is done on each eye, and one at a time. If needed, it is repeated while the child wears glasses or contacts.
The visual acuity is determined by the line with the smallest letters the child can correctly identify. A child is referred if the smallest line which is read is out of range for age-appropriate acuity.
The person administering the vision screening must watch carefully observing the child’s behavior while validating the responses from the child. A child can be referred if they are peeking around the eye that is covered, looking sideways, or squinting etc. Eye misalignment problems can only be detected when the child is using both eyes and unless one eye displays a significant misalignment it may not be detected.
Photorefractor
Thirty second (30 second) average for a complete screening
Alternative Names
Autorefractor
How the screening is performed
The photo refractor is an automatic screening device no feedback is required from the child.
1. The screener verifies the child’s name in the photorefractor.
2. The child sits in a chair (or stands) approximately 1 meter from the person holding photorefractor,
3. The child is instructed to look at the camera-like device (photorefractor).
4. Holding the photorefractor at eye height the screener identifies the child’s eyes in the viewing screen. When the child is in range and is in focus, the capture process is underway usually 1-3 seconds.
5. The photorefractor automatically captures the reading of both child’s eyes (binocularly).
6. The Photorefractor immediately indicates if the child passed or failed an age-appropriate screening.
7. A child is referred when one or more of the eight items the refractor measures is out range for the age-appropriate measurements.
The items the photorefractor measures are:
• nearsightedness
• farsightedness
• unequal power
• astigmatism (irregular shape of the cornea, or curvature of the lens)
• amblyopia (lazy eye)
• strabismus (crossed eyes)
• anisometropia (a comparative analysis for unequal refractive power)
• anisocoria (unequal pupil size)
The same screening may be performed if the child is wearing contacts or glasses and will determine if any additional visual correction is required
Screening with Photorefractor
Traditional Screening with Acuity Chart
| Capability | Acuity Chart | Photorefractor |
|---|---|---|
| Results | 3 Minutes | <15 Seconds |
| Identifies Near-Sightedness (Myopia) | X | |
| Identifies Far-Sightedness (Hyperopia) | X | |
| Identifies Unequal Refractive Power (Anisometropia) | X | |
| Identifies Blurred Vision, Eye Structure Problem (Aniscordia) | X | |
| Identifies Eye Misalignment (Strabismus) | X | |
| Testing Calibrated to Child’s Age | X | X |
| Does not require feedback from subject (requiring language, cultural, and verbal skills) | X | |
| Can be administered by anyone (minimal training required) | X | |
| Objective process (computerized system with no human intervention) | X | |
| Subjective Process (manually administered by skilled professional) | X | |
| Documentation of Vision Screening and Referral | Manual | Automatic |
These are examples of a referral from two photorefractor manufacturer:
