SCREENING

Vision

Screening

of

Preschool Children

How To Check on Visual Acuity and Routine Physical Examination

Heterophoria

as

Part of a

Marie Scott Brown, R.N., Ph.D.

ALTHOUGH

it is easy for parents to child is suffering from recognize severe vision loss, it-is difficult to detect less incapacitating, yet important losses. And when a child’s vision has always been poor or has become poor gradually, he is usually unaware that the problem exists. that

A

problems and 20 to 30 per cent of the schoolage children have such problems. Many of these conditions are not being currently detected, particularly in the preschool age group among whom only 25 per cent of the

a

preschooler

with lowered visual

or about one in four, receive any type of visual examination.’ The rest would never be found without some type of visual examination, as shown by the report of the 1964-65 rejection list of the Armed Forces. Of those volunteers and draftees who were rejected because of vision defects, 75 per cent had lesions which could have been prevented or treated in childhood .4 Visual acuity, far-

total,

acuity

will miss many of the experiences that are important in his perceptual and cognitive development. His eye-hand coordination may be poor. He may not learn to distinguish important aspects of pictures that should lay the foundation for later reading ability. The most dramatic situation is the very young child with a minor degree of crossed eyes (strabismus), who if caught early could have perfect vision for the rest of his life, but if missed, may totally lose the vision in one eye by school age. Then, as a school-age child who cannot see well, he will miss important parts of his education that he may never be able to make up. Vision impairment is the fourth most common disability in the United States and the leading cause of handicapping conditions in childhood. Five to 10 per cent of the preschoolers in this country have vision *

Assistant

Graduate

sightedness, nearpoint vision, heterophoria, color vision, and visual fields can all be clinically assessed in the office. Only the two most important of these-visual acuity and heterophoria-will be discussed in this article.

Testing

The Snellen

of Colorado, 4200

East Ninth Avenue, Denver, Colo. 80220.

Acuity

Alphabet

Visual

.

Chart

acuity is arbitrarily measured in of the ability to see a standardized symbol at a standardized distance. Classically, this refers to a Snellen &dquo;E&dquo; or alphabet chart viewed at 20 feet. The Snellen Chart, by far the most accurate of the charts, should be used whenever possible, and is generally applicable with children in and above third terms

Professor, Maternal-Child Nursing

Department, University

for Visual

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able to read the 20/30 line accurately with both eyes. Children younger than this are expected to read the 20/40 line. Any child who can not read with each eye the line appropriate for his age should be referred for more detailed

school settings. It is important that the chart be used properly, with the lighting measured by a light meter. The illumination should fall evenly across the chart without shadows or glare and should measure between ten and 30 foot-candles. Adequate lighting can be supplied by a 75-watt bulb in a gooseneck lamp, situated five feet away at a 45

grade

testing.

degree angle. Each child should be tested separately, that the next in line cannot memorize the chart while waiting. One examiner should be stationed at the chart and one with the child. The examiner usually begins with the 20/30 or 20/40 foot line and works either up or down, depending on how good the response is. Each child should be tested as far down the chart as he is able to read. A passing score for a line consists of reading the majority of letters on that line. so

preschooler with

lowered visual acuity will miss many of the experiences that are important in his perceptual and A

cognitive development. With small children, it is important to expose the entire line at once, rather than a single letter at a time, since some authorities9 feel that exposing one letter at a time may miss certain children with amblyopia. Furthermore, vision tested by the single letter method can seem up to one and one-half lines better than when tested by exposure of the whole line. Since the vision in both eyes when tested together will never be poorer than that of either eye singly, most workers do not begin by testing of both eyes at once except with very young children in order to get them accustomed to the test first. Some, however, suggest beginning the test with both eyes since this may reveal a phoria,6 but when near and far cover tests are done (these should always be done), such a phoria will be detected at that time. Fourth-grade children should be able to read the 20/20 line. Children from the age of four years through the third grade should be &dquo;

Furthermore, any child who shows a two line difference between lines, even though the worst eye is seeing at a level appropriate for his age (for instance, a three year old who has 20/20 vision in one line eye and 20/40 in the other), should also be referred, since this difference may lead the child to suppress the vision in the poorer eye and eventually lose the sight in that eye completely. For this reason, all children should be tested as far down the chart as they are able to see. If the building in which the testing is being done does not have a space long enough to utilize the 20-foot chart, two alternatives exist. The Snellen chart is also made in a ten-foot version which, though less desirable since it has been less thoroughly standardized, is generally quite adequate. A second possibility is to use the 20-foot chart with a mirror. In this situation, the examiner sits next to the child with the 20-foot chart between them. Both the examiner and the child face directly into a mirror ten feet in front of them in which they can see each other and the chart. This arrangement needs only one examiner who remains close to the child, helping to maintain rapport. An alphabet chart if used must be specially designed for use with a mirror; the letters though of standard size are printed backwards so that when seen in the mirror they appear normally oriented. The Snellen &dquo;~’g Chart for Very Young Children .

With children

too young for an alphabet best standardized chart is the Snellen &dquo;E’g-sometimes called the &dquo;Illiterate E&dquo; since it does not require knowledge of letters. Some feel that this is slightly inferior since no curves or complicated letters are used which might detect certain forms of astigmatism. Nonetheless, in practice it works out almost as well as the alphabet chart. Most &dquo;E&dquo; charts have the letter &dquo;E&dquo; oriented in four directions: up, down,

chart, the

next

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right and left. Oblique angles are usually too developmentally advanced for the child of age who must use the &dquo;E&dquo; chart. The mechanics of testing with the &dquo;E&dquo; chart are basically the same as those for the alphabet chart, though with some problems of their own. The child is generally asked to point his finger, hand, or entire arm in the direction an

impairment is the fourth most common disability in the United States and the leading cause of handicapping Vision

conditions in childhood. which the &dquo;E&dquo; is pointing (or in which the &dquo;legs of the table&dquo; are pointing). This requires the preschool child not only to see the letter, but also to comprehend the idea of direction, to match this direction to the direction of his hand, and to be reasonably agile in making his hand or arm conform to the direction in his mind. In other words, this approach evaluates not only vision, but several other complicated skills. When a child gives an incorrect answer, one cannot be sure that it is his vision which is at fault. Several tricks may help determine whether he is having difficulty with directionality. One is to paste colorful easily recognized pictures (e.g., dog, rabbit, boy, or girl) on the wall at the top, bottom, and each side of the chart and then ask the child to tell you which picture the &dquo;E&dquo; is pointing to. This eliminates the difficulty in

feet with the use of a mirror is partichere. Children of this age may have difficulty in looking at one letter at a time, and this may mask amblyopia. Accordingly, it is always important to record which method was used in at ten

ularly applicable

testing. With children over two and one-half years of age, mothers may be able to test the eyes with an &dquo;E&dquo; chart at home long before an unfamiliar examiner can do so. With the National Society for the Prevention of Blindness card for such testing at home,’ more visual problems were discovered by mothers than later by institutional and office nurses, and the rate of overreferrals was only 4.6 per cent. Trotter compared testing by mothers to testing by volunteers and found mothers much more accurate.12 This approach can be an important adjunct to the office visits. An estimated 95 per cent of all preschool children in this country have never received a vision screening examination. Mothers their own children could find many testing disturbances early. Cards for home testing are available at no cost from local Chapters of the National Society for Prevention of Blindness. Tests for

Younger

Children

Because the two Snellen charts are the best standardized charts, they should be used whenever feasible. The accuracy of the results justify the extra time it may take in having the child practice with his mother or setting up a ten-foot mirror arrangement or any other measures that may be useful. The next best set of tests utilize certain figures from the Snellen. The &dquo;E&dquo; is the most common example of this. Another similar one is the Landholt rings, which utilizes the letter &dquo;C.&dquo; It has the same problems of directionality, difficulty in keeping the child’s interest, etc. as does the &dquo;E&dquo; chart and the author has found no advantage in it. The Ffooks chart, somewhat similar, utilizes geometric figures-a square, circle and

motor maneuvering and in mentally matching the direction of the letter to the direction of his body. It does not eliminate the problem of directionality, however. A very helpful step is to ask mother to practice with the child at home during the week before the test. This considerably enhances the ease of testing. The National Society for the Prevention of Blindness has prepared printed forms of the &dquo;E&dquo; chart, made for the purpose of having mothers test their own children at home. Some examiners send such a chart, with an explanatory letter, to the parents of children three years of age triangle (because these figures are developand up in advance. mentally recognized first). Their standardizaGaining rapport is another difficulty in . tion is less accurate than the Snellen approach. By far the best test the author has found testing preschool children. The 20-foot chart

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for younger children is the Stycar test manufactured in England by the NFER Publishing Company.* The basic idea behind its several forms is to use letters which can be recognized at a developmentally early stage. After working with several thousand young children, Sheridan and Gardiner settled on V, A, T, C, 0, L, H, U, and X as the letters most With these letters they chart similar to the Snellen alphabet chart, but since the children are not yet able to name the letters they are given a key card with the letters on it. The child holds this card on a table in front of him and indicates the letter which matches the letter on the chart being pointed to. For children over four years of age, the test uses nine letters; for four-year-olds, seven letters; for threeyear-olds, five letters; and for two-year-olds, only four letters. The younger children are given individual cards each with a single letter, rather than a single chart with all the letters. This approach has the disadvantage of testing by the single letter exposure as discussed before. Sheridan has advised that the test be given at ten feet with the use of a mirror. It has been found that 100 per cent of four-year-olds are testable with the sevenletter method; 80 per cent of three-year-olds with the five-letter method; and 30 per cent of two-year-olds with the four letters. This is an extraordinarily high rate of testability for these age groups. Lippman’ compared the &dquo;E&dquo; test at 20 feet, the &dquo;E&dquo; test at ten feet, the Allen cards (to be discussed later), the Stycar test, and the Starcar test (to be discussed later) and found the Stycar easiest to learn and highly accurate. Although in the first attempt, testability was similar to the &dquo;E&dquo; at ten feet, it became much higher with the Stycar on the second attempt than it did with the &dquo;E&dquo; at ten feet. It seems unfortunate that such a useful test as this is not more widely used in the United States.

easily recognized.10 constructed

a

Picture Charts

If

none

of the

more

standardized

tests

(i.e., the Snellen Alphabet, &dquo;E,&dquo; Landholt, *

2

Berks,

Fleury

Thames Avenue, Windsor, from Jean-Marc Chevier, 34 Street West, Montreal.

Jennings Building, England; available

Stycar) can be used with a child, choice is one of the picture charts. Not only are they less standardized, and therefore far less accurate, but many children are not familiar with all the pictures used. Lippman found the testability rates three times lower with children from lower economic groups than with those from higher economic groups. Some of the picture charts are also put out in color; though this may add interest, it makes them even less standardized than the black and white charts. Probably the best of the available picture tests is the Allen cards, since greater effort has been put into their standardization than with the other picture cards. The Allen cards consist of a series of black and white pictures

Rings, the

or

next

(e.g,, a telephone, a birthday cake, a man on a horse, a Christmas

tree, etc.) which are shown child by an examiner who is slowly coming toward the child. The distance at which the child is first able to recognize three of the pictures is used as the numerator, over a denominator of 30. A three-year-old should achieve a score of 15/30; a four-year-old a score of 20/30. Any child who misses the appropriate pictures or who shows a difference of five feet between individual eyes should be referred for more precise testing. to a

With children too young for an alphabet chart, the next best standardized chart is

the Snellen &dquo;~f’--sometirne~ called the &dquo;Illiterate E&dquo; since it does not require knowledge of letters. Other

charts available are the Danish chart of black and white figures such as a swan, house, Christmas tree, man, and key; the Kindergarten chart with its colored pictures of a circle, heart, flag, sailboat, and cross; the A.~9. and B & L test which is similar in black and white; and the California Clown test in which the clown’s hand points in various directions. Other tests which might be included under this category of picture tests are the Sjogren’s Hand Test and Withnell’s Block Test. Sjogren’s Hand Test is a picture of a hand very much like the illiterate &dquo;E.&dquo; However,

picture

Osterberg chart,

a

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distance of ten feet, and seeing whether the child will follow them. Sheridan says that a baby from six to nine months of age can be expected to follow the one-fourth inch ball. A ten-month-old will follow the oneeighth inch ball. By 12 months, the child should follow all the balls. Specific information is available from the NFER Publishing Company. This test is difficult to do monocularly since babies often object to having one eye covered, but it is sometimes worth

the &dquo;E&dquo; into the more of a hand, the standardiinteresting picture zation has been lost. Often the thickness of the palm will determine the correct answer rather than the child’s ability to distinguish between the fingers. %Vithnell’s Blocks are inexpensive and portable. The cards show one, two, or three rectangles in both horizontal and vertical positions (in order to detect certain types of astigmatism). This test still lacks the exact standardization of the Snellen and, in addition, lacks the attention-holding interest of picture charts. The child must be able to count up to three in order to report how many blocks he sees. in the attempt

at a

to turn

trying. Testing for Heterophoria

acuity testing, the most important component of vision screening is to check for heterotropia and heterophoria. These Next to

Toy Tests The Starcar Test. For very young children, the picture tests will suffice, and their vision can only be roughly estimated. For this age group, Sheridan has devised the Starcar test. This utilizes seven small toys: a car, plane, chair, knife, spoon, fork, and doll. The examiner holds these one at a time against a black background. The child has a similar set of toys, though in different colors so that the child is unable to match by color. He matches and holds up the one chosen by the examiner who is ten feet away. This test cannot be exactly equated with the Snellen standards, but Sheridan advises that the child who can distinguish between the small knife and fork at ten feet has vision equal to 20/20. If he cannot distinguish between the large fork and knife, he should be referred for further evaluation. This is a more difficult test to administer and the clinician himself should do it rather than delegating it to ancillary personnel. Sheridan has been able to use these test materials from about 21 months until the Stycar letters are usable. Directions for this test are obtainable from the NFER

Publishing Company. The Rolling Ball Test. For children below 211 months, there is only one rough test available-again, one that is seldom used in this country. It was originated by Worth in the early 1900’s, and since then the only one to attempt to standardize it has been Mary Sheridan.li This test consists of rolling . standard sized balls across a dark background

the most serious visual conditions that the clinician is likely to encounter with any degree of frequency, particularly in preschool children. Heterotropia is a condition in which a child’s eyes do not focus together in such a way as to transmit good coordinated binocular vision. Heterophoria is a tendency, not always overt, towards the same problem. It results from some type of inequality between the eyes or the eye muscles which prevents each eye from focusing on exactly the same point at the same time. Sometimes this is obvious as with severely crossed eyes, but more often it is subtle and requires careful screening procedures to become evident. This is extremely important to detect, since if left unrecognized and untreated the child may suppress the vision in one eye completely. If neglected until school years, it is likely that the lost vision will never be regained. Since neither the child nor the parents are ordinarily aware of this difficulty, search for it by routine screening is essential. Hatfield found that 21 per cent of the eye problems found in his series of three-year-olds were of this type.’ During infancy, many babies will exhibit intermittently crossed eyes. When such a muscle imbalance is horizontal rather than vertical, when it is not continuous, and when it gradually becomes better, up to the age of six months it can be looked upon as normal. Beyond this age it may still be normal, but the infant should nevertheless be referred to are

not even

&dquo;

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an

ophthalmologist

in

eye is blocked completely so that it , focus. The occluder is held over the eye from five to ten seconds and then removed fairly abruptly. The examiner watches the eye which was covered to see if it moves. In the presence of a phoria, this eye while covered will wander while it is not able to

for careful evaluation. history of

Indeed, after age six months any

one

cannot

eyes which cross during fatigue or illness or for unknown reasons is an indication for an ophthalmologic consultation. When such crossing (strabismus) is overt and constant, it is referred to as ~ro~i~z.. Where there is merely a tendency to such crossing, this is called phoria, and usually has to be unearthed by screening ,techniques. These -

All children should be tested as far down the chart as they are able to see.

should be incorporated into every well-child examination.

screening techniques

focus

Hirschb~:rg Reflex The first is the Cornel

Light

the

designated

spot. As

is removed it will attempt

cover

soon as

to

the

refocus

sharp, jerky movement. This movesignifies to the examiner that the eye has a phoria. The procedure is performed twice with each eye-once at the nearpoint of 14 inches and once at the farpoint of 20 feet.

with

Reflex (or

a

ment

Hirschberg’s Reflex) and should be _ looked for in both the nearpoint (i.e., about 14 inches) and farpoint (i.e., at 20 feet) positions. In this procedure, the child is asked to fix his eyes straight ahead on a particular spot designated by the examiner. The examiner then shines a penlight into each eye separately and notes where mthe light reflex is seen. It should be seen in exactly the same position in each eye. Any asymmetry is the signal for further consultation. During the procedure,

Neither the eye nor the eyelashes should be touched during the maneuver, since otherwise the child may blink when the cover is moved and obscure the response of the pupil. Since the consequences of underreferral are so grave (i.~., amblyopia with possible irreversible loss of sight in one eye), it is always better to err on the side of overreferral.

it is essential that the child hold his eyes absolutely still, so that the examiner has enough time to determine where the light reflexes are falling. Older children can usually cooperate when asked to. With young babies, a bright, flashing, moving toy will generally fix their attention long enough for such a determination. It is often necessary to turn out the room lights, inasmuch as overhead lights will also be reflected in the eyes, and the examiner may not be sure which reflected -light is coming from the room lights and which from his penlight. The Cover Test

on

&dquo;

References 1.

Green, Morris, and Richmond, Julius B.: Pediatric

and London, W. B. Saunders Co., 1960. 2. Hatfield, Elizabeth Macfarlane: A year’s record of preschool vision screening. The Sight Saving Review 36: 194, 1966. 3. Krupke, Sidney S., Dunbar, Constance A., and Zimmerman, Vivian: Vision screening of preschool children in mobile clinics in Iowa. Public Health Rep. 85: 41, 1970. 4. —: ibid., pp. 41-45. 5. Lippman, Otto: Vision screening of young children.

Diagnosis. Philadelphia

.

Another test which should also be done at each visit is &dquo;the cover test.&dquo; This is another method of making manifest a phoria which is not ordinarily apparent. This test is begun by having the child focus on a specified spot,’ first 14 inches away and then 20 feet away. While the child is focusing on a spot, the vision &dquo;

AJPH 61: 1598, 1970. 6. : — pp. 1598-1601. ibid., 7. — ibid., pp. 1598-1601. : 8. Press, Edward: Screening of preschool children for amblyopia. JAMA 204: 109, 1968. 9. Sheridan, M. D., and Gardiner, P. A.: SheridanGardiner test for visual acuity. Br. Med. J. 2: 108, 1970. 10. —: ibid., pp. 108-109. 11. —: ibid., pp. 108-109. 12. Trotter, Robert R., and Phillips, Ruth M., and Shaffer, Kennetta: Measurement of visual acuity of preschool children by their parents. The Sight Saving Review 36: 80, 1966.

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Vision screening of preschool children. How to check on visual acuity and heterophoria as part of a routine physical examination.

SCREENING Vision Screening of Preschool Children How To Check on Visual Acuity and Routine Physical Examination Heterophoria as Part of a Mar...
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