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Volume 2 - Vision Screening Primer
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Lecture 3 of 24 NEXT»
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The purpose of vision screening is to identify chldren with one or more of the following conditions:
1) Decreased vision in one or both eye(s) (below an arbitrary standard)
2) Eye conditions which could lead to decreased vision in one or both eye(s)
3) Strabismus (crossed or wall eye)
4) Other eye related conditions such as: ptosis (droopy lid), nystagmus (dancing eyes), head tilt, etc.
The best age for vision screening:
1) As near as possible to the 3rd birthday
2) Should be done no later than by the 5th birthday - preschool between ages 3 and 5 yrs. (for volunteer screening)
3) Should be done at the first visit after the 3rd birthday in pediatrician or primary care doctor's office
The principles of vision screening:
1) To find out if a child can see an object of a given size with each eye.
20/20 vision means a person can see an object that fills an angle of 5 minutes, with component parts of 1 minute at a distance of 20 feet. This is a complicated but necessary standard. The 20/20 letter is about 1 inch at 20 feet. The 20/20 letter is about 1/2 inch at 10 feet which is the minimum distance for checking distance vision. It is logical that the 20/40 letter is twice as big, the 20/60 letter 3 times as big, the 20/100 letter 5 times as big. When saying that a child has 20/40 vision, it means that the smallest letter that can be seen at 20 feet is the letter twice as big as the 20/20 letter, or about 2 inches. 20/40 is passing for a preschooler. If the smallest letter seen is 20/60 (3 x the 20/20) or 20/100 (5 x the 20/20), vision is definitely reduced.
If a child can see the 20/40 letter in each eye while wearing corrective glasses, the child passes. One of the important goals of vision screening is to find out if a child needs correction with glasses for far or near sightedness or astigmatism.
CONDITION
| Far sighted |
Near sighted |
Astigmatism |
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Light rays focus behind the retina (back of the eye like the film in a camera) |
Light rays focus in front of the retina |
Some light rays focus in front of the retina and some behind. |
| REMEDY |
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The eye can focus the lens to remedy small and equal amounts |
Near objects can be seen well, all distance objects are blurred. Squinting helps distance vision some. |
The blur is always present. |
| TREATMENT |
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plus lens |
minus lens |
cylinder lens |
A very important problem when a child has a refractive error is when the errors are different between eyes. This is called anisometropia and leads to amblyopia.
Amblyopia occurs in infants and children who are learning how to see. It is a decrease in vision in one or both eyes from a constant blurred vision being sent to the brain by an out of focus eye or eyes or a crossed eye.
How can you tell if these children have normal vision? Test children beginning at age 3 yrs. and before 5 yrs. for vision in each eye - each eye should see at least 20/40 with no more than 2 lines difference (20/20 - 20/40 is failure)
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Observe for:
a) eye crossing
b) droopy lids
c) nystagmus (dancing eyes)
d) head tilt
e) red eyes |
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All causes for failure |
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Children who fail should receive an examination by an eye doctor - a professional who treats eye problems in children.
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crossed or "wall" eye |
nystagmus (dancing eyes) |
droopy lid |
head tilt |
The screening test can also include a test for stereopsis or depth perception at near: passing this test ensures good cooperation between the eyes (binocular vision).
Eye health screening for conditions other than vision, such as cataract, glaucoma, tumor, etc. begins at birth with informed parents and primary care doctors. These are discussed in The Strabismus Minute, Vol. 2, No. 1 & 2. Photoscreening is a purely objective (requiring no cooperation) method of discovering possible refractive errors and misalignment which could lead to amblyopia.
How photoscreening works:
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1) A camera photographs the eyes producing the "red eye" which we usually try to avoid.
2) Study of the appearance of the "red eye" tells about the state of refractive error: normal - farsighted, near sighted, astigmatism, equal? unequal? |
For example:
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an unequal reflex indicates unequal refraction and suggests that amblyopia could develop (or has developed) |
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high - near sightedness, etc. |
Photoscreening can be done on children as young as 2 yrs. old or even younger - a disadvantage is the expense of equipment, film, and expert interpretation.
The referral process in vision screening:
1) Identify children day care/preschool classes - open screening
2) Screen
3) Refer as needed
4) Eye doctor examines and treats appropriately
5) Reports to screener
6) Failure to receive report from examining doctor results in follow up
Once a child has demonstrated 20/40 or better vision in each eye and aligned eyes, there is virtually no chance that serious eye health problems will occur on a developmental basis. After an initial normal screening either by volunteers or by a doctor's examination (one eye doctor examination is recommended but not essential), regular screening in school and parental awareness is all that is required. “Annual” examinations confirming that a child's vision is remaining normal is a waste of time and money. Volunteer and primary care physician vision screening is effective for both health and financial considerations.
The Strabismus Minute
, Vol.2, No. 3 Copyright (C) 2000 Eugene M. Helveston All Rights Reserved
Editor-in-Chief: Eugene M. Helveston, M.D.
Associate Editor: Faruk H. Orge, M.D.
Editorial Board: Bradley C. Black, M.D.
Edward R. O'Malley, M.D.
David A. Plager, M.D.
Derek T. Sprunger, M.D.
Daniel E. Neely, M.D.
Naval Sondhi, M.D.
Senior Editorial Consultant: Gunter K. von Noorden, M.D.
Graphics: Michelle L. Harmon
Technical Support: George J. Sheplock, M.D.
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