An estimated one in four school-aged children and seven in 10 juvenile offenders have an undiagnosed visual problem that affects school performance.1 Also, in a study on a clinical population of 1,650, patients ages 6 to 18, 0.7% had ocular motility disorders, 16.3% had nonstrabismic binocular vision disorders, and 6% had accommodative disorders.2 As primary eye care providers, we can play a vital role in improving academic performance. This starts with knowing the appropriate tests to determine what visual condition is interfering with a childs academic success.
In this third and final installment of our series, Pediatric Practice, I will discuss the various tests needed to assess eye movements, vergence and accommodation in the school-aged child.
Assessing Eye Movements
A child who has poor reading comprehension, skips lines or frequently loses his place while reading may have eye movement problems. To assess eye movement, test fixation, saccades and pursuits. We observe a patients ability to fixate throughout our usual entrance testing, especially while watching him attend to a fixation target during cover testing. These four tests can help you evaluate saccades. (The NSUCO/Maples Oculomotor Test evaluates both saccades and pursuits.)
|The patient performs near cover testing, so I can watch how he fixates on the target and assess his eye movements.|
To observe saccades, hold two target sticks in front of the patient. Ask him to move his eyes back and forth between the two sticks without moving his head or body.
|The patient performs the saccades portion of the NSUCO/Maples Oculomotor test by moving his eyes back and fourth between the two target sticks without moving his head or body.|
|Table 1. Scoring Criteria for the NSUCO/Maples Oculomotor Test4|
|Ability||1||Completes less than two roundtrips (the patient cannot go from one target to the other and back more than once).|
|2||Completes two roundtrips.|
|3||Completes three roundtrips.|
|4||Completes four roundtrips.|
|5||Completes five roundtrips.|
|Accuracy||1||Large over- or undershooting is noted one or more times.|
|2||Moderate over- or undershooting is noted one or more times.|
|3||Constant slight over- or undershooting noted more than 50% of the time|
|4||Intermittent slight over- or undershooting noted less than 50% of the time.|
|5||No over- or undershooting noted.|
|Head and body movement||1||Large movement of the head or body at any time.|
|2||Moderate movement of the head or body at any time.|
|3||Slight movement of the head or body more than 50% of the time.|
|4||Slight movement of the head or body less than 50% of the time|
|5||No movement of the head or body.|
|Ability||1||Cannot complete 1/2 rotation in either clockwise or counterclockwise direction.|
|2||Completes 1/2 rotation in either direction.|
|3||Completes one rotation in either direction but not two rotations.|
|4||Completes two rotations in one direction but less than two rotations in the other direction.|
|5||Completes two rotations in each direction.|
|Accuracy||1||No attempt to follow the target or requires greater than 10 fixations.|
|2||Refixations five to 10 times.|
|3||Refixations three to four times.|
|4||Refixations two times or less.|
|Head and Body Movement||1||Large movement of the head or body at any time.|
|2||Moderate movement of the head or body at any time.|
|3||Slight movement of the head or body more than 50% of the time.|
|4||Slight movement of the head or body less than 50% of the time.|
|5||No movement of head or body.|
Visagraph III Eye-Movement Recording System (Taylor Associates) or the Readalyzer. These computer-based programs evaluate the number of fixations and regressions, duration of fixations, reading rate, efficiency and grade equivalence based on age-related reading material.5 These tests offer an objective assessment of saccades and reading behavior. (If you do not have either system, refer the patient to a pediatric/binocular vision specialist.)
During the test, the patient wears infrared goggles that plug into the computer; the program does the rest. These systems then provide detailed reports on the above areas.
Problems with the vergence system fall into two major categories: problems at near (e.g., convergence insufficiency or convergence excess) and problems at distance (e.g., divergence excess or divergence insufficiency). Convergence insufficiency and convergence excess are more prevalent than divergence excess and divergence insufficiency in school-aged children, so you want to thoroughly evaluate the patient for these two conditions.2
Eyestrain or fatigue while reading or using the computer, diplopia and near blur often result from convergence insufficiency and convergence excess. If you suspect one of these, evaluate the following:
Eye alignment. The two most common ways to measure eye alignment are the cover test and the Von Graefe technique, both at distance and near. The latter is subjective and, therefore, usually better suited for children ages 7 and older.
One concern about cover testing: how to get the child to focus on the target long enough to control his attention. I have found that a detailed sticker placed on a stick is small and detailed enough to control for accommodation, and it yields excellent results for near testing. I ask the child specific questions about the sticker, forcing him to attend to it longer.
To perform the Von Graefe technique, have the child sit behind the phoropter with his appropriate correction in place. Place a card with the appropriate-sized print, which is based on his acuity, at the appropriate working distance (usually 16 inches) on the nearpoint rod in front of the phoropter. (If the patient is able to read 20/20 at 16 inches, a target such as 20/30 letters is a good choice.) Place prisms in front of the patients eyes so that the image becomes doubled. Move the lens dial and instruct the patient to tell you when one image lines up above the other (horizontal testing) and when the images line up side by side (vertical testing). The expected norms for phoria testing are 1pd of exophoria at distance (1pd) and 3pd of exophoria at near (3pd) for every patient.6
AC/A ratio. There are two methods for determining the ratio of accommodative convergence (AC) to accommodation (A).
The calculated method uses the formula AC/A = interpupillary distance in cm + near fixation distance in meters (near phoria far phoria). Esophoria receives a (+) number and exophoria receives a (-) number. For example, if a patient has an interpupillary distance of 60 mm, with 4 pd of esophoria at distance and 10 pd of esophoria at a near distance of 40 cm, the AC/A would be: AC/A = 6 + 0.4(10 4) = 8.4/1.
Or, you can use the gradient method. Place -1.00D lenses over your patients distance correction (or a trial frame), while performing this test. Repeat your chosen method for phoria testing, and compare the results with and without the lenses. For example, if the patient initially had 8pd exophoria at 40cm and 2pd exophoria with the added lenses, the AC/A ratio would equal 6/1. The expected normal AC/A ratio is 4/1 (2pd) for every patient.5
Vergence ability. To evaluate vergence ability, measure either smooth vergence using Risley prisms in the phoropter or step vergence using prism bars outside of the phoropter.
To test smooth vergence using Risley prisms, seat the patient behind the phoropter, dial in his appropriate correction, and align a target card at 40cm on the near-point rod. The patient initially will see one vertical target. Dial the prism in the base-in direction over both eyes until the patient sees blur, break (when one eye drifts out) and finally, recovery of the target. Repeat the test with the same target dialing the prisms in the base-out direction. Perform the test in the same manner for distance, using a distance target.
To test step vergence using prism bars out of the phoropter, have the patient wear his correction (or use a trial frame) and sit facing an appropriate-sized near point target. Place the prism bar with the bases-in before one eye, and move it step by step as the patient attends to a distance or near target. Ask the patient to tell you when he sees a blur, break and recovery point.
|To evaluate the patient for convergence insufficiency and convergence excess, you can test step vergence using prism bars out of the phoropter.|
If the patient cannot report this, watch for his eyes to flick off of the target. This is his break point. The point at which you see his eyes point in the same direction (as before the test began) is his recovery point.
Repeat this test with the prisms facing base-out. Compare your results to the norms. (See Normal Values for Vergences).
|Normal Values for Vergences5|
|Base-in||x/7/4 where x = no blur point|
Nearpoint of convergence (NPC). This is an important test for convergence insufficiency. Have the patient wear his nearpoint correction (or a trial frame if he does not wear a correction). Place a small detailed target, such as the one used for cover testing, 40cm from the patient. Slowly move the target toward him until he sees two target images (the break point). Move the target further toward the patient, then pull the target away until the patient sees only one image again (the recovery point).
If you think the patient will show an increase in the break and/or recovery values due to his case history or other exam findings, repeat the test five to 10 times to try to fatigue the patient. The normal values for this test are 5cm break and 7cm recovery for every patient.7
Based on the above tests, you may diagnose the child with convergence insufficiency or convergence excess. Patients who have the former generally exhibit greater exo-phoria at near than at distance, a low AC/A ratio (less than 4/1) base-out vergence values at near and a receded NPC. Patients who have the latter generally exhibit greater esophoria at near, a high AC/A ratio, low base-in vergence values at near and a normal NPC. To diagnose the patient correctly, evaluate these results and consider your exam findings, the patients complaints and your prior experience.
Children who complain of near blur, fatigue while reading, eyestrain at near or blur in the distance after reading may have an accommodative problem. To determine whether such a problem exists, evaluate the following:
Amplitude of accommodation. Evaluate the patient using the push-up test or the minus lens test.
The push-up test, performed in open space, is suitable for children who cannot give good subjective responses at the phoropter. Have the patient wear his best correction (or a trial frame), patch one eye, and place a target (20/30 letter if the child can read at 20/20) 40cm away. Move the target toward the patient until it becomes blurry, then measure the distance from the object to the patient and convert it to diopters. For example, if the patients vision blurs at 4cm, the amplitude would equal 1/.04, or 25.00D. Patch the other eye, and repeat the test.
To perform the minus lens test, place the patient behind the pho-ropter, program his correction into the phoropter, and cover one eye. Ask the patient to read the appropriate letters from a target card at 40cm away under good illumination. For example, if the patient can read 20/20, the letters should appear 20/30 in size. Slowly add different minus lenses until the print he sees becomes blurry yet remains readable. When the patient first reports blur, encourage him to focus on the object until it is no longer blurry. End the test when the patient tells you he cannot clear the blur but that the letters are still readable. Repeat with the other eye.
Calculate your findings based on the amount of minus lenses added until your stopping point and the working distance. For example, if you added 8.00D of lenses until blur to the right eye and the working distance was 40cm, the final amplitude of accommodation for the eye is 8.00 + 2.5 = 10.5.
If your patients values are lower than expected for his age or the values between his two eyes are unequal by a value of 0.50D, be concerned. The expected value for the amplitude of accommodation for the push-up test is based on Hofstetters amplitude formula. I use Hofstetters for minimum amplitudes, which is stated as 15-0.25(age). So, if your patient is eight years old, the minimum amplitude expected for the push-up test is 15-0.25(8) = 13. Due to the minification effects of the minus lenses, the expected value for the minus lens test is always 2.00D less than the value for the push-up test. For example, an eight-year-old childs minimum acceptable amplitude of accommodation would be 13 - 2 = 11.
Accommodative response. To evaluate accommodative response, use one of two tests: the monocular estimation method (MEM) or the fused cross-cylinder test (FCC).
Perform the MEM test in normal illumination. Attach an MEM card that is appropriate for your patients grade level to your retinoscope. While holding your retinoscope at the childs Harmon working distance (i.e., the distance from the middle knuckle of the childs second finger to his elbow), perform retinoscopy on each eye as the child reads the letters/words on the card. Quickly place a plus or minus lens in front of the eye to neutralize the reflex. Measure the reflex along the horizontal and vertical axis, and repeat with the other eye. The expected values for the accommodative response for the MEM test are +0.25 to +0.50D for every patient.5
You probably are familiar with the FCC test. Perform this test in dim illumination. Place the cross cylinder lenses in front of the patient. Add plus lenses to the phoropter if the patient tells you that horizontal lines are darker and clearer when looking at the target. (Darker and clearer vertical lines imply a lead of accommodation.) The expected values for the FCC are +0.50D for every patient.5
Accommodative facility. This test is particularly important in children ages 7 and older who complain of distance blur yet have 20/20 visual acuity at distance.
Perform this test using 2.00D lens flippers. I prefer to test binocularly first and then monocularly to determine if there is a difference between the two eyes. For monocular testing, the room should have good illumination. Place an appropriate target, such as accommodative rock cards, 40cm from the patient. Have the patient wear his best correction (or trial frame) with one eye covered.
Using a double-sided lens holder, flip the 2.00D lenses in front of the patient as he reads each letter/word off of the card. Continue the test for one minute, then calculate the amount of cycles (a cycle equals one plus and one minus flip) the child achieved. To perform this test binocularly, use suppression control (such as red/green suppression strips held over the target as the child wears red/green glasses) to be sure the patient is actually performing binocularly.
|Accommodative facility testing is a particularly important test to perform on children ages 7 and older who complain of distance blur, yet have 20/20 visual acuity at distance. The test employs a double-sided lens holder that contains 2.00D lenses.|
There are many different norms for this test, depending on which study you refer to. I usually use 11 cycles per minute for binocular testing and eight cycles per minute for monocular testing.5 However, I believe that its more important to watch your patients responses than memorize a set value of norms for this test. For example, did the patient have trouble with the plus or minus sides of the flippers? Was he slow throughout the test? Did he start out fast and fatigue rapidly? The answers to such questions will allow you to evaluate his responses more accurately from a functional point of view.
The results of the above tests may reveal one of four problems:
Accommodative insufficiency. These patients generally exhibit low amplitudes of accommodation for their age and a large lag of accommodative response. They fail the minus lens side of monocular and binocular accommodative facility testing.
Accommodative excess. These patients generally exhibit normal amplitudes of accommodation and a low lag or lead of accommodation for the accommodative response. They fail the plus lens side of monocular and binocular accommodative facility testing.
Accommodative infacility. These patients generally exhibit normal amplitude of accommodation and a normal accommodative response, but have difficulty with monocular and binocular accommodative facility testing.
Ill-sustained accommodation. These patients generally exhibit normal amplitude of accommodation and a high lag of accommodative response. They fail the minus lens part of the monocular and binocular accommodative facility test.5
The ability to assess eye movements, vergence and accommodation enables you to diagnose the visual problem that may be hampering your patients academic success. And, once you have determined what is responsible for his problems in school, you can initiate a treatment plan that will enable him to enjoy learning again.
Dr. Allison is an associate professor at the Illinois College of Optometry and is program coordinator for the colleges Binocular Vision and Pediatric Optometry Residency. She is also a diplomate in binocular vision, perception and pediatric optometry of the American Academy of Optometry and a fellow of the College of Optometrists in Vision Development.
1. PAVE (Parents Active for Vision Education) Vision and Learning. www.paveeye.com/vision/
visionandlearning.htm. (11 May 2005).
2. Scheiman M, Gallaway M, Coulter R, et al. Prevalence of vision and ocular disease conditions in a clinical pediatric population. J Am Optom Assoc 1996 Apr;67(4):193-202.
3. Maples WC, Ficklin TW. Interrater and test-retest reliability of pursuits and saccades. J Am Optom Assoc 1988 Jul;59(7):549-52.
4. Maples WC. NSUCO oculomotor test. Santa Ana, CA: Optometric Extension Program, 1995.
5. Scheiman M, Wick B. Clinical Management of Binocular Vision, 2nd ed. Philadelphia: Lippincott, Williams & Wilkins, 2002:3-50, 74.
6. Morgan MW. The clinical aspects of accommodation and convergence. Am J Optom Arch Am Acad Optom 1944;21:301-13.
7. Scheiman M, Gallaway M, Frantz KA, et al. Nearpoint of convergence: test procedure, test selection, and normative data. Optom Vis Sci 2003 Mar;80(3):214-25.