Strabismus and Amblyopia: Experimental Basis for Advances in Clinical Management

Von Noorden, Gunter K. 1928-
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Ninety-four of the patients completed treatment. To determine whether the results obtained were durable, the investigator examined mean accommodative amplitude data on 24 patients followed-up for various durations after completing vision therapy Daum, The mean accommodative amplitude had fallen 2 diopters on average from a mean of 12 diopters to a mean of 10 diopters , but the mean amplitude of these patients was higher than that for patients before vision therapy 8 diopters.

Patients received 1 year of standard vision therapy conducted 3 to 4 days per week for 10 to 30 mins. Of the 60 children, only 36 completed therapy. Thirty-four of the 36 children were reported to show a significant increase in accommodative amplitude. The author concluded that the results suggested that accommodative amplitude and facility could be improved in children with cerebral palsy by standard vision therapy techniques, although he admitted that this study had important deficiencies.

A third line of studies have sought to prove that the improvements in accommodation brought about by vision therapy translate into improvements in performance on various tasks. Weisz examined the results of vision therapy on nearpoint performance in children with deficiencies in accommodation. One group received accommodative vision therapy and the other received perceptual-motor training without accommodative therapy.

Both groups were given two min sessions per week, and were treated for an equal length of time. A pen and paper task requiring fine nearpoint discrimination was given to all patients before and after training to assess transfer effects of accommodative therapy on this task. The group provided with accommodative therapy reached normal levels of accommodation within an average of 4.

Although this study has been cited to support the conclusion that accommodative training improves accuracy on tasks involving nearpoint performance, there are a number of problems that make the study by Weisz difficult to interpret. Fourth, there is no demonstration that the pen and paper test used to measure progress has a valid relationship between practical reading and writing tasks. The symptomatic patients were then given vision therapy and then retested after its completion.

Symptomatic patients with disorders of accommodation or vergence were given weekly min in-office vision therapy sessions, supplemented with daily min at-home exercises, for 8 to 16 weeks. Symptomatic patients who had both accommodation and vergence disorders were given twice as much weekly vision therapy and daily at-home therapy. All symptomatic patients had had higher monocular accommodative flipper rates a measure of accommodative facility following vision therapy. Also, the measures of accommodative ability that changed after vision therapy were not the same as the measures of accommodative ability that were found to be significantly different between asymptomatic and symptomatic subjects.

Scheiman et al showed that accommodative infacility was substantially less common in older children than younger children, suggesting either that this condition resolves spontaneously with age in most afflicted children, or that measurement of accommodative deficiency in younger children is unreliable. The fact that the verbal and numerical format of the tests of accommodative facility caused problems for younger children suggested that pre- and post- training measures of accommodative deficiency were more reliable in older children and young adults than in younger children.

The literature on the effectiveness of vision therapy for ocular motor disorders and for deficiencies in accommodation has largely been characterized by anecdotes, case reports, or case series with small sample sizes. Because case series are by definition uncontrolled, their results to not allow one to determine whether any improvements that occur are due to therapy or whether they are an artifact of maturational effects, test-retest effects, and the non-specific gains accrued simply by bestowing more attention on a child Levine, The interpretation of these case series is also made difficult by the relative lack of knowledge about the natural history of untreated disorders of visual efficiency.

A non-strabismic disorder of binocular vision is defined as a condition where an individual must exert an undue amount of effort in sustaining continuous singular binocular vision Suchoff, Non-strabismic disorders of binocular vision are related to deficiencies of accommodation, problems with fusional vergences i. Binocular vision dysfunction always occurs secondary to these diagnoses. A diagnosis of binocular dysfunction is secondary to diagnoses of convergence, divergence, or accommodative function.

A non-strabismic disorder of binocular vision is distinguished from intermittent strabismus, a condition where there is overt eye turn at least some of the time. In practice, a patient who has comfortable and continuous single binocular vision may exhibit a non-strabismic disorder of binocular vision when fatigued or because of the optical or cognitive demands of a particular situation.

Similarly, a patient with a non-strabismic disorder of binocular vision may exhibit intermittent strabismus in demanding situations, such as prolonged reading. The major consequence of a patient having a non-strabismic disorder of binocular vision is asthenopia, a feeling of ocular or visual discomfort Suchoff, The patient with asthenopia may complain of eyestrain, soreness of the eyes, frontal and occipital headaches, and eyes that easily fatigue. According to the optometric literature, non-strabismic disorders of binocular vision are related to deficiencies of accommodation, problems with fusional vergences i.

Thus, the efficacy of vision therapy for a non-strabismic disorder of binocular dysfunciton would depend upon its efficacy for the underlying causative disorder. Early uncontrolled studies had shown that convergence insufficiency rapidly and reliably responds to simple exercises, such as "push-ups", in almost all cases Mann, ; Cushman, ; Lyle, ; Hirsch, ; Duthie, ; Mayou, ; Mellick, ; Passmore, ; Norn, ; Hoffman, ; Wick, ; Dalziel, ; Kertesz, ; North, ; Patano, ; Cohen, ; Daum, ; Deshpande, a; Deshpande, b. More recently, controlled clinical studies have demonstrated the effectiveness of vision therapy for convergence insufficiency.

Only Hoffman reported a much higher average number of office visits 24 ; all vision therapy exercises were conducted in the office. The orthoptic ophthalmology literature reports successful treatment of convergence insufficiency with fewer office visits than are reported in the optometric vision therapy literature.

Although not all of these studies described the particular vision therapy methods that were used, many reported successful treatment using simple exercises that can be performed at home after brief instruction. Griffin and Grisham recommend office visits once per week to monitor the patient's progress, prescribe and teach new training procedures, and to continue motivating the patient. Treatment of convergence insufficiency can be completed in less than 12 weeks. Christenson reported on a case example of a patient with convergence insufficiency who was treated with weekly office visits and home exercises over a week period cited in Griffin and Grisham, Patano reported successfully treating convergence insufficiency patients with min daily home exercises for 1 month.

Cohen and Soden reported treating patients with convergence insufficiency with weekly min office sessions accompanied by home therapy. The average number of office therapy sessions was Daum analyzed the results of vision therapy in convergence insufficiency patients, ranging in age from 2 to 46 years. Most of the training in this patient series was completed at home. The average training time was 4. Dalziel reported on the success of treating convergence insufficiency patients with weekly office visits and daily home exercises.

The investigators reported that the average duration of therapy was 6 weeks, and ranged from 2 to 16 weeeks, but noted that the average patient received only two min office sessions. Exercises for convergence insufficiency can be accomplished at home, and patients with convergence insufficiency should be transferred to a home program.

The comparative efficacy of home therapy versus office treatments was studied by Deshpande and Ghosh , who reported on the success of vision therapy in 2, patients with convergence insufficiency. Patients received either 10 office visits or 3 weeks of home exercises. They concluded that response to therapy was "comparably equal" between the 2 therapies. Convergence excess is a vergence anomaly where the esophoria or esotropia is greater at near than at far. Diagnosis generally includes the presence of an eso deviation at near of at least 2 to 6 prism diopters Shorter, Symptoms of convergence excess include diplopia, headache, asthenopia eye stain , blurred vision, and avoidance or inability to sustain near visual tasks.

Symptoms are often elicited after prolonged near vision tasks AOA, Vision therapy has been advocated as a treatment for convergence excess in textbooks and in anecdotal reports see Shorter, The AOA states that 28 to 36 hours of vision therapy are usually required, but that longer durations of treatment may required for convergence excess complicated by esotropia, oculomotor dysfunction, an accommodative disorder, other visual anomalies, or associated conditions such as stroke, head trauma, or systemic diseases AOA, Few clinical reports have been published on the effectiveness of vision therapy for convergence excess.

Subjects received different types and durations of vision therapy treatment, and were treated by different clinicians. Subjects received vision therapy office visits at a frequency ranging from once per week to once per month, with home exercises prescribed for 4 to 6 days per week in addition to office therapy.

Clifton M. Schor, Vision Research

Three of the subjects were also treated with bifocals. Median duration of vision therapy was 4 months. However, there was no statistically significant improvements in vergence ranges after vision therapy. Because of the limitations of the study design, no conclusions could be reached about the effectiveness of vision therapy for convergence excess. The term oculomotor dysfunction refers to difficulties in eye movements.

Vision therapy has been used in patients with problems with saccades and pursuits. Eye movements have been a concern of optometrists because of their importance in the act of reading. Eye movements include saccades and pursuits. Saccades are eye movements that enable us to rapidly redirect our line of sight so that the point of interest stimulates the fovea Scheiman and Wick, Saccadic eye movements are made in reading, as the reader moves along a line of print.

Most symptoms related to deficient saccadic movements are thought to be associated with reading, such as head movement, frequent loss of place, omission of words, skipping lines, slow reading speed, and poor comprehension Scheiman and Wick, Short attention span is also alleged to be related to problems with saccadic movements.

Pursuits involve eye tracking, and allow us to have continuous clear vision of objects moving in space Scheiman and Wick, Pursuits may be stimulus-generated or voluntary. Stimulus-generated pursuits are elicited when a child is instructed to follow a moving target, whereas voluntary pursuits are elicited when the child is instructed to track a stationary path. Although pursuit difficulties have been reported in children who have reading problems, pursuit dysfunction is probably more likely to interfere with activities such as sports Scheiman and Wick, Press described the tests used to diagnose ocular motility problems in a school-aged child.

Tests of ocular motility are concerned with saccadic fixations and pursuits. These include objective eye movement recording devices like the Visagraph and Eye-Trac, standardized tests such as the Developmental Eye Movement DEM test, and direct observations by the clinician. Although eye movement recording devices like the Visagraph and the Eye-Trac provide objective and precise measurements of eye movement, they are expensive, time consuming, and difficult to use with young children.

The DEM and other tests using a visual-verbal format assess oculomotor function on the basis of the speed in which a series of numbers can be seen, recognized, and verbalized with accuracy; these tests are inexpensive, easily administeredand provide a quantitative evaluation of eye movements in a simulated reading environment. Procedures have been developed to measure stimulus-generated and voluntary pursuit eye movements. The most commonly used procedure for eliciting stimulus-generated pursuit movement is to ask the child to follow a penlight or a bright object Scheiman and Wick, Movements are made horizontally, vertically, diagonally, rotationally, and in-out z-axis.

The examiner notes how accurately the child tracks the target. A commonly used clinical test of voluntary pursuit movement is Groffman Visual Tracings. This test, in which the child must trace a path visually between a letter on one side of the page and a number on the opposite side of the page, involves a significant degree of visual-perceptual skill. A shortcoming of the Groffman Visual Tracings test, however, is that there has been no study of its reliability and validity.

Press described the vision therapy techniques used to improve oculomotor performance. These include pursuit training and saccadic activities. Pursuit training involves oculorotatory exercises, such as pie pan rotations, where the child follows the circular path of a marble tilting about the inner axis of a pie pan, and the Marsden ball, where the child tracks the perpendicular path of a ball suspended from the ceiling.

Another commonly used pursuit training exercise is the vertical rotator, where the child tracks a visual target, placed on a tripod stand, which rotates in clockwise or counterclockwise directions. Saccadic activities are done with the large Hart chart Press, The child begins with large angle saccades by calling out the first letter and last letter on each line. The child then does smaller angle saccades by reading each letter aloud in sequence. Both pursuits and saccades may be trained with activities involving hand-eye coordination Press, There are a large number of such activities, such as the Wayne Saccadic Fixator and the pegboard rotator.

The Wayne Saccadic Fixator involves a central fixation point and a circular array of lights. The child is asked to touch the button adjacent to whichever light is illuminated. The pegboard rotator involves a rotating board with holes into which pegs are inserted. The child is instructed to align the peg visually over the hole and follow it for one revolution before placing the peg into the hole. Scheiman and Wick noted that vision therapy for eye movement skills generally involves more than simply treatment techniques for saccades and pursuits.

As a general rule, accommodative and binocular vision techniques are incorporated into the therapy program because eye movement anomalies are usually associated with accommodative, binocular, or visual-perceptual disorders. Wold and colleagues evaluated the records of a series of consecutive patients with learning disabilities who had completed a course of vision therapy for a variety of problems including deficiency in accommodation, binocular dysfunction, and oculomotor dysfunction.

Vision therapy consisted of three 1-hour visits per week, which were continued for 22 to 53 weeks. Eye movements were rated on the Heinsen-Schrock scale, a point ordinal scale for observing and scoring pursuit and saccadic eye movement performance. Almost all of the patients, however, had accommodative and binocular vision problems in addition to eye movement disorders. The study by Wold was a retrospective uncontrolled study of consecutive cases seen in a private practice; the uncontrolled and retrospective nature of the study makes it subject to substantial bias.

Possible sources of bias include maturation effects, test-retest bias, placebo effects, and regression toward the mean. The author was able to report statistically significant results by inappropriately using statistical tests that apply to ratio or interval scales to the point ordinal scale of visual functioning that the author created.

Hence, we are not sure of the effectiveness of these techniques on patients who have the specific diagnosis of oculomotor dysfunction. Finally, there is no information on whether any of these learning disabled patients had symptoms related to vision, or the effects of vision therapy on these symptoms. Solan studied the results of vision therapy on 63 normal high school students. Although the investigators found increased reading rate, less fixations, and less regressions after treatment, the subjects received other forms of treatment along with vision therapy.

There is no information in this report on the efficacy of vision therapy for alleviation of symptoms related to oculomotor dysfunction. Subsequent papers by Solan a; b have been cited to support the efficacy of vision therapy in oculomotor disorders; these papers report on small numbers of selected cases, thus no conclusions about the efficacy of vision therapy in oculomotor dysfunction can be drawn from them. Rounds and colleagues examined reading eye movements before and after eye movement therapy in 12 adults with reading problems, and compared these results to that for 9 adults with reading problems who received no interventions.

The investigators used a Visagraph to assess reading eye movements before and after therapy. Although the treatment group showed significant improvements in certain eye movement measures compared to the untreated group, there were no statistically significant differences between the treated and untreated groups at the end of the study in terms of reading efficiency and comprehension.

Other problems with the study have to do with the fact that the the control group was given no treatment, rather than sham treatment. First, there was no masking of subjects, observers or therapists. Third, this study examined improvements in reading efficiency from vision therapy; this study does not address whether vision therapy is effective in alleviating symptoms from oculomotor dysfunction.

Young assessed the impact of vision therapy on 13 children from a learning center who had failed a vision screening. There is no report that any of these children reported any symptoms related to vision. Exercises were administered by a school teacher. Eye movement were recorded before and after therapy using and Eye-Trac. After therapy, the schoolchildren were found to have a significant decrease in the number and duration of fixations and an increase in their reading speed.

Two major flaws of this study were the lack of a control group and the fact that the investigators measured eye movement efficiency, and not reading comprehension and reading efficiency. Also, this study sought to measure the efficacy of vision therapy on improving reading ability, not on alleviating symptoms related to oculomotor dysfunction. The purpose of measuring vision parameters in the asymptomatic subjects was to establish norms for the dynamic tests developed by the authors.

Statistically significant differences between symptomatic subjects and asymptomatic subjects were identified for only one variable: the slope of the fixation-disparity curve with accommodation open-looped. There was a statistically insignificant difference between symptomatic and asymptomatic subjects in the slope of the accommodative response to stimulus. The symptomatic patients were then given vision therapy, and were retested after completion of therapy. The asymptomatic subjects, however, were not later retested at the end of the study, and hence were not a true control group.

There are several problems with the study by Hung and colleagues that make its results difficult to interpret. First, because this study is uncontrolled, we do not know whether improvements in symptoms were attributable to vision therapy. Second, the variables found to be significantly different between asymptomatic and symptomatic subjects were not the ones that changed significantly with orthoptic therapy.

Finally, although this study has been cited as support for the effectiveness of vision therapy for oculomotor dysfunction, the study only measured changes in accommodation and vergences with vision therapy. Punnett and Steinhauer compared the results of eye movement vision therapy with and without feedback in 6 children, aged 9 to 12, who were found to have oculomotor problems and were reading substantially below their grade level. Although reading compehension and reading level appeared to increase more in the children who received vision therapy, no statistical analysis could be performed because of the small number of subjects in each group.

The study did not specify whether the children were randomly assigned to the groups, and the children in the control group did not receive placebo or sham treatment. The study examined the effectiveness of vision therapy in improving the reading abilities of learning disabled children with oculomotor dysfunction, and did not examine the effectiveness of vision therapy in alleviating symptoms related to oculomotor dysfunction. Busby examined the efficacy of vision therapy in improving eye-movement control, eye-hand coordination, and figure and form copying capabilities in 59 special education students, aged 7 to 10 years, who had neurological impairments and language difficulties.

Students received twice-weekly, min group vision therapy sessions over a 9-month period. Vision therapy was performed by teachers in the classroom. Students generally improved on each of the tests after vision therapy. During this period, students were also attending other classes, so it is uncertain how much of the improvement on these test can be attributed to vision therapy.

There was no control group, so one does not know whether the improvements could be due to maturational effects. Finally, the study examined the effectiveness of vision therapy on eye-movement control, eye-hand tasks, and visual-motor skills, and not on symptoms from oculomotor dysfunction. Heath and colleagues examined the effectiveness of oculomotor and convergence exercises on 80 second- and third-grade children who had scored below the 40th percentile on a reading test and in the deficient range on an oculomotor tracking examination.

Subjects were randomly assigned to 4 groups: group 1 received oculomotor and convergence exercises with propioceptive touch reinforcement; group 2 received exercises without reinforcement; group 3 received perceptual exercises sham treatment ; and group 4 received no treatment. Seventeen of the 80 subjects dropped out before the end of the study; however, intention-to-treat analysis was not performed. Subjects were treated over a week period; the frequency of vision therapy visits was not specified.

Group 1 exercises with propioceptive showed significantly larger improvements in measurements of pursuits and convergence than the other groups, including group 2 which received vision therapy exercises alone. On tests of reading and eye tracking, group 1 scored significanly better than the group receiving no treatment group 4 ; differences in improvments in reading between group 1 and groups 2 and 3 were not statistically significant. The study did not determine whether the group receiving vision therapy alone group 2 scored statistically significantly better on each of these variables than the group receiving sham treatment group 3 and the group receiving no treatment group 4.

It is unclear whether the improvements in group 1 were a result of convergence exercises or exercises to improve oculomotor function. Finally, this study examined the effectiveness of vision therapy in improving skills related to reading ability, and not the effectiveness of vision therapy in relieving symptoms related to oculomotor dysfunction. Two studies by Schroeder and Holland ; have been cited in support of the effectiveness of biofeedback to improve oculomotor ability.

None of these students had oculomotor dysfunctions. Thus, no conclusions can be drawn from these studies about the effectiveness of vision therapy for patients with oculomotor dysfunction. Other investigators have used biofeedback to improve oculomotor ability in patients with nystagmus and eccentric fixation, which is discussed in separate sections below. The literature on the effectiveness of vision therapy for ocular motor disorders has largely been characterized by anecdotes, case reports, or uncontrolled studies with small sample sizes. These case series are unable to determine whether bias has occurred due to maturational effects, test-retest effects, and the non-specific gains accrued simply by bestowing more attention on a child Levine, In a review of the literature on vision therapy for reading problems, Beauchamp found that oculomotor pursuit or "tracking" deficiencies are alleged.

However, there is evidence that these "deficiencies" disappear when content is corrected for reading level, and "oculomotor control of dyslexic children is similar to that of normal children" Black, Reports that show abnormal pursuit in samples of children having reading problems provide no unbiased sample measurements of abnormal pursuit problems in the general population for comparison Sherman, Most controlled studies of the effectiveness of vision therapy have not used random assignment, and the comparison groups that are used in non-randomized studies have not been carefully matched for factors affecting the outcome of therapy.

The studies also report their findings in terms of averages, and fail to provide subgroup or cluster analysis to allow one to identify the characteristics of patients that most likely to respond to vision therapy. According to Keogh, there is also "inconsistency and confounding in the nature of the samples used" in studies of vision therapy Keogh, that limits the inferences that can be drawn from research on vision therapy in children with reading problems.

In addition, the investigators frequently fail to demonstrate and quantify the visual dysfunctions in patients undergoing treatment Beauchamp, Studies of such vision therapy regimens are difficult to interpret, because effectiveness of these regimens may be due to the non-optometric interventions, such as standard remedial educational techniques, that are employed, rather than due to the vision therapy itself. Beauchamp notes that "[o]ne may legitimately question the ability of an optometrist to function in such complex substantive areas" outside of optometry Beauchamp, There is also a paucity of information on whether the results achieved with vision therapy are durable i.

Beauchamp concluded that it is insufficient to recommend an intervention, such as optometric vision therapy for reading disabilities, on a speculative basis because "time and financial resources are finite. The AOA concluded that up to 18 hours of vision therapy are needed for the most common oculomotor dysfunction.

However, the AOA has provided no evidence or rationale to support this conclusion. In most of the studies of vision therapy for oculomotor dysfunction, home exercises were emphasized. Optometric orthoptic therapy has focused on office therapy, whereas orthoptist orthoptic therapy has emphasized home exercises.

However, there is no evidence that office orthoptics are superior to home exercises. Esotropia, or convergent strabismus, is a manifest inward deviation of the eye s. It may be present at birth congenital or appear later in life acquired. Esotropia may be constant or intermittent. Alternating esotropia refers to shifting of esotropia from one eye to the other.

Handbook of Pediatric Strabismus and Amblyopia

Active vision therapy also called vision trining, orthoptics, eye training, and eye exercises includes a variety of non-therapeutic approaches, including biofeedback, eye movement exercises, and more complex training involving optical and electronic instruments Hoffman, Strabismus is a manifest deviation of the visual axes, commonly referred to as turned eyes or crossed eyes. Esotropia is a type of strabismus where there is manifest inward deviation of the eyes. The deivation in strabismus may occur in various directions, may occur at distance, near, or both, and may be intermittent or constant.

There is a lack of evidence of the effectiveness of vision therapy for esotropia. Several authors of reviews of the optometric literature on the effectiveness of vision therapy in esotropia have drawn conclusions about the overall effectiveness by adding together the success rates" from observational studies of vision therapy in esotropia, grouping together studies of various designs, strengths, and weaknesses Flax, No attempt is made to critically evaluate the inherent limitations of these studies, or the difficulties of drawing conclusions about the effectiveness of vision therapy from them.

The authors make reference to "controlled" studies, implying that these studies are controlled clinical trials, whereas in actual fact, these studies were observational studies with noncontemporaneous comparison groups. Studies should be grouped by design, with the greatest weight given to the strongest studies i. The only prospective randomized controlled clinical trial of optometric vision therapy in esotropia published to date has found no benefit from active vision therapy Fletcher, This study has been ignored in reviews of the effectiveness of optometric vision therapy for esotropia.

Published case series on vision therapy for esotropia report widely varying durations of treatment and frequencies of office visits, without any consistent relationship between increased duration of treatment and frequency of office visits with improved outcomes. Cooper and Medow noted that "[o]rthoptist orthoptic therapy is primarily given to the patient to do at home while optometric orthoptic therapy utilizes both office and home therapy.

Although the AOA states that office treatment of intermittent esotropia requires 40 to 52 hours of visits, and the most commonly encountered constant esotropia usually requires 60 to 75 hours of office therapy, their guideline provides no evidence to support this assertion. The literature on the effectiveness of vision therapy has reported on orthoptic treatment of esotropia reuiring far fewer office visits are sufficient.

Wick , in a report on the outcomes of treatment of 57 patients with esotropia, reported a mean length of treatment of intermittent esotropia of 4. He noted that "constant strabismics had a significantly longer treatment course [average 6. They state that in basic esotropia, doctors can determine which patients require surgery and which do not after 1 to 2 months of vision training, and state that, "if the strabismic patient has not achieved satisfactory binocular vision result within a 6-month period of active vision training with full compliance, we suggest a surgical evaluation and support the surgeon's recommendation in most cases.

Kertesz and Kertesz report on esotropia treatment completed in 9 orthoptic therapy visits. Layland reported esotropia treated in 15 visits. Fletcher and Silverman , reporting on the success rate in treatment of a series of over 1, consecutive cases of esotropia, stated that "no long-term orthoptics has been used. Mann reported that treatment of esotropia averaged 9 visits. Weinstein reported needing only 5 to 6 sessions necessary for treatment of esotropia and exotropia with the opto-illuminator. There is no evidence that optometric orthoptic therapy, performed largely in the office, is superior to orthoptist orthoptic therapy, which is primarily given to the patient to do at home.

Outcomes of long-term office-based treatment of constant or intermittent esotropia have not been demonstrated to be superior to home therapy with periodic followup. Intermittent exotropia is a nonconstant outward deviation of one eye. It is a type of strabismus cross eyes. Horizontal strabismus may be exotropic or esotropic. Exotropia is less common, and less well understood than esotropia, except in cases with an obvious cause, such as paralysis of the muscle that pulls the eye outward. As a general rule, exotropia is found most frequently at older ages, and is expressed in an intermittent fashion Daw, The investigators identified and summarized the evidence of effectiveness of treatments for intermittent exotropia, including optical correction, prisms, occlusion, strabismus surgery, and vision therapy.

The investigators concluded that the pooled success rates for vision therapy were greater than for any other treatment. The number of office visits necessary and duration of treatment for a given indication is also significantly different between orthoptists and vision therapists. The AOA, in their Clinical Practice Guideline on Strabismus stated that optometric vision therapy generally requires 25 to 75 hours of office visits.

However, treatment durations reported in the literature vary widely, with no consistent relation of number of office visits, duration of treatment, or transfer to home exercise programs, to results of treatment. In a series of studies on the effectiveness of optometric vision therapy, Daum reported on mean durations of treatment of intermittent exotropia of 4.

In the largest study of vision therapy for intermittent exotropia published to date, Patano reported an average treatment duration of 1 month. The second largest study of vision therapy for intermittent exotropia, by Cooper and Leyman , reported a treatment duration ranging from 12 to 15 weeks. The longest average treatment durations were reported by Newman and Mazow , who reported an average treatment time of 12 months.

Their reported success rate, however, was below the average for all studies of vision therapy in intermittent exotropia. Vertical deviations refer to disconjugate movements of the eyes in the vertical up and down plane. They are an unusual type of strabismus cross-eyes. Vision therapy has been used to correct vertical deviations. Hyperphoria or hypertropia occurs if one visual line is higher than the other.


It is present on the right if the right visual line is higher than on the left, and on the left if the left visual line is on the right. A hypertropia is also known as a vertical strabismus. Movshon JA, Kiorpes L. Biological limits on visual developments in primates. In: Simons K, editor. Early visual development, normal and abnormal. Oxford: Oxford University Press, ; — Ikeda H, Wright MJ. Properties of LGN cells in kittens reared with convergent squint: a neurophysiological demonstration of amblyopia.

Exp Brain Res ; 25 : 63— Ikeda H, Tremain KE. Amblyopia occurs in retinal ganglion cells in cats reared with convergent squint without alternating fixation. Exp Brain Res ; 35 : — Normality of spatial resolution of retinal ganglion cells in cats with strabismic amblyopia. Neural site of strabismic amblyopia in cats: X-cell acuities in the LGN. Exp Brain Res ; 72 : —9.

Metrika članka

A study involving strabismic, refractive and mixed both, aged 3—12 years old, were included in these trials. A new treatment for congenital nystagmus. The matter of contention is the claim, by some, that visual training can improve athletic performance. American Journal of Optometry and Physiological Optics All of these symptoms are associated with reading or other close work. Optometric orthoptic therapy has focused on office therapy, whereas orthoptist orthoptic therapy has emphasized home exercises. This practice, however, is contradictory to the recent evidence.

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London: Macmillan Press, — Travers T. Suppression of vision in squint and its association with retinal correspondence and amblyopia. Br J Ophthalmol ; 22 : — Sireteanu R, Fronius M. Naso-temporal asymmetries in human amblyopia: consequence of long-term interocular suppression. Vision Res ; 21 : — Sireteanu R. Binocular vision in strabismic humans with alternating fixation. Vision Res ; 22 : — Human amblyopia: consequence of chronic interocular suppression.

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Sengpiel F, Blakemore C. However, this does not tend to occur in myopia, as there is always a distance Atropine and optical penalisation for each eye at which a clear image may be obtained without Atropine penalisation is an alternative to patching for amblyopia accommodation Jampolsky et al.

Bilateral high refractive errors can Holmes and Clarke In patients with high hypermetropic refractive be used instead Wu and Hunter Patching has been errors, accommodation may also lead to strabismic amblyopia. For this reason, they simply reduce their working distance to focus the image atropine has been reserved for cases when compliance with Wu and Hunter Meridional amblyopia results from occlusion therapy is poor or if patching cannot be undertaken uncorrected bilateral astigmatism which causes a blurred for any reason Holmes and Clarke Atropine treatment, image in a specific meridian Dobson et al.

Induced astigmatism or anisometropia can is gained once the drop is instilled whereas a patch can be result from pressure on the cornea which disturbs its curvature easily removed by the child , peripheral binocularity is allowed due to a haemangioma, chalazion or ptosis or as a result of with atropine but is completely impaired by patching and lens structural changes anterior polar cataracts , which may distress to the child during treatment is rare with atropine.

There are also some disadvantages: atropine effects last up to 2 weeks from instillation, while patching can be immediately In anisometropic amblyopia the correction of refractive stopped if required. Rarely systemic side-effects can occur error eliminates the unilateral blur, which should improve with atropine: flushing, dry mouth, hyperactivity, tachycardia, neuronal sensitivity and therefore stimulate visual recovery.

The atropine therapy, to ensure that no iatrogenic reverse study included children aged 3—7 years with acuities of amblyopia has taken place. Improvement was faster in the patching group. The by full hypermetropic correction Holmes and Clarke At the 2-year follow-up examination, the VA in the occurring in only one of patients treated PEDIG , amblyopic eye had improved similarly in both groups by three ; Repka et al. This effectively blurs the vision at both distance and near, since accommodation Occlusion and dose cannot correct the blur Wu and Hunter , but may increase the risk of secondary amblyopia in the non-amblyopic The amount of occlusion to prescribe for a given reduction eye Morrison et al.

PEDIG compared weekend atropine in acuity has largely been driven by anecdotal evidence augmented by a plano lens for the sound eye with weekend until recent years. It was concluded that, as an initial treatment accurately assessing the level of compliance. This was overcome for moderate amblyopia, the augmentation of weekend by the development of an objective device, the occlusion atropine with a plano lens does not substantially improve the dose monitor ODM , which monitors actual occlusion wear amblyopic eye acuity when compared with atropine alone.

An had reduced sound eye acuity towards the end of the trial at alternative device, based on measuring the temperature 18 weeks ; however there were no cases of persistent reverse difference between the internal and external surfaces of the amblyopia PEDIG A study involving strabismic, refractive and mixed both, aged 3—12 years old, were included in these trials. In trial 2, 40 children than 2 hours daily did not affect the final outcome Stewart 7—12 years of age were randomised to weekend atropine or et al.

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In terms of the number of hours of cumulative 2 hours of daily patching. The VA outcome was assessed at dose, the majority of improvement occurs after — 18 weeks in trial 1 and 17 weeks in trial 2. The acuity of the hours, with a gain of 0.

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This finding differs from that of Cleary types of treatment in trial 1 4—5 lines and trial 2 1. The discrepancy is likely to be as a result improve VA in children between 3 and 12 years of age with of the fact that the former study used an ODM and therefore severe amblyopia. Improvement may be greater in younger more accurately reflects the actual dose worn. Previous unpopularity of atropine could also be related to a belief that the treatment would not be effective The number of hours of prescribed occlusion as opposed to unless fixation switched to the amblyopic eye.

Similarly, there were no Studies have proved that a fixation switch is not required differences in efficacy for 6 hours versus 12 hours of daily for atropine to be successful Holmes and Clarke The results are not without their limitations, given at a younger age. For example, treatment has been however, as the follow-up time was relatively short, the shown to be significantly more effective in children under 4 actual dose was not known though this is the same in clinical years compared to those over 6 years of age Stewart et al.

Secondly, whilst it is relatively straightforward to treat during treatment, which does not necessarily reflect standard refractive amblyopia in older children or young adults, treating practice. The findings for severe amblyopia were partly strabismic amblyopia where there is an absence of fusion supported by research involving ODMs, where no significant presents a potential risk of intractable diplopia.

The very nature of intractable diplopia means that it cannot be eliminated by surgical realignment of the eyes or Neural plasticity and the upper age limit correcting the angle with prisms, and it presents important for treatment quality-of-life issues for the individuals affected. Elimination of the diplopic image can only be achieved by occluding one It is acknowledged in clinical practice that the critical period of the eyes. A variety of methods have been employed, such limits the age to which amblyopia can be successfully treated, as using Blenderm tape on glasses, Bangerter filters, occlusive yet clinicians in the UK tend to be rather conservative regarding contact lenses, inducing ptosis via Botox, corneal tattooing this, which perhaps results in some patients being unnecessarily and opaque intraocular lenses.

These methods are often denied treatment. Newsham This practice, however, is contradictory to the recent evidence. A small study involving 16 patients aged Assessment of the risk of intractable diplopia is undertaken 9—14 years found that all but one had an improvement of in the UK by means of the Sbisa bar.

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Strabismus and Amblyopia: Experimental Basis for Advances in Clinical Management (Wenner-Gren International Symposium Series, Vol 49). Strabismus and Amblyopia: Experimental Basis for Advances in Clinical Management (Wenner-Gren International Symposium Series, Vol 49) by Gunnar .

Other than a small at least two lines following occlusion treatment Park et al. Similarly, a larger study of 11—year-olds found all undertaken to indicate how the results of this test should be patients showed an improvement, with a mean acuity gain interpreted to guide management. It is not surprising therefore of 0.

Even slightly older children that a recent study of current UK practice demonstrated up to young adulthood have shown significant responses considerable variability in areas such as the age from which the to treatment Scheiman et al. The issue of assessing and interpreting the risk via Firstly, although it appears that amblyopia can still improve evidence-based research is currently being addressed by the later in life than was originally thought, it does not indicate authors and the results will be available in the near future.

Treatment success and factors affecting A variety of factors may be related to compliance. There the prognosis appears to be disagreement as to whether non-compliance It is clear that treatment can provide a significant improvement decreases with age Nucci et al. It is also uncertain whether the common types of amblyopia.

Many children, however, do not VA at the start of treatment has an effect on non-compliance, achieve normal acuity in the amblyopic eye after treatment. Another issue related to key areas of amblyopia and its treatment, such as the critical disappointing results is the recurrence of the amblyopia after period, prognosis, urgency of the treatment and the treatment the treatment has been stopped.

To address this lack of understanding, a atropine Holmes et al. This was reinforced by a later study that additionally gave suitably designed educational material to the children as well The findings of a recent randomised controlled trial however as to the parents and reported significant improvements in do not support this approach Walsh et al. Other risk factors related to recurrence Compliance cannot be expected to be improved in all parents include the age of the patient at the time of treatment, with by the introduction of educational material, though it is clearly age showing an inverse relationship to the level of risk Bhola an effective strategy to adopt and may help in many cases.

Other effect on recurrence Tacagni et al. Amblyopic patients may also be at risk on the career choice, giving a day off occlusion every 2 weeks, from permanent loss of acuity in the healthy eye which will use of arm bands to prevent removal of occlusion, hospital result in reduced quality of life.