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The Effectiveness of Vision Therapy in Improving Visual Function
Documentation on the Clinical Research and Scientific Support Underlying Vision Therapy
Note: There is a tremendous amount of literature available which documents the effectiveness of vision therapy in treating binocular vision (eye coordination and alignment), oculomotor (tracking and eye movements), and accommodative (focusing) problems. The following is a copy of a report published by the American Optometric Association entitled “The Efficacy of Vision Therapy.” Please note over two hundred references listed at the end of the paper. The clinical research, scientific studies, and professional articles listed in the bibliography were first published in “refereed” scientific journals, meaning each were examined by outside experts before publication to validate their science, value, and research methodology. Please refer to the Bibliography of Research for a more complete list of studies and clinical reports underlying the science supporting vision therapy.
"The Efficacy of Optometric Vision Therapy" The
purpose of this paper is to offer supporting documentation for the efficacy
and validity of vision therapy for modifying and improving vision functioning.
Optometry
is an independent primary health care profession. Its scope of practice
includes the prevention and remediation of disorders of the vision system
through the examination, diagnosis, treatment, and/or management of visual
efficiency and eye health as well as the recognition and diagnosis of related
systemic manifestations, all of which are designed to preserve and enhance the
quality of our lives and environment. Optometrists
examine the eyes and related structures to determine the presence of vision
problems, eye disease, and other abnormalities. They gather information on the
vision system during the optometric examination, diagnose any conditions
discovered, and prescribe individual or combinations of interventions such as
corrective lenses, prescription drugs, contact lenses, and vision therapy. The
American Optometric Association considers vision therapy an essential and
integral part of the practice of optometry (1). Forty-three states
specifically describe vision training, orthoptics, or some synonym in their
definitions of the profession of optometry .The Institute of Medicine of the
National Academy of Sciences (2), the Dictionary of Occupational Titles of the
Employment and Training Administration (3), the U .S. Public Health Service
(4), the U.S. Dept. of Labor, Employment and Training Administration (5), the
National Center for Health Statistics (6), the Bureau of Labor Statistics (7),
The Dept. of Health and Human Services (8) and the Association of Academic
Health Centers (9) all include vision therapy in their definitions of the
profession of optometry. The
theory and procedures underlying the diagnosis and management of vision
disorders are taught in all the schools and colleges of optometry (9). In
addition, the National Board of Examiners in Optometry (10) and the majority
of the various state licensing agencies examine applicants for their
theoretical and clinical knowledge in vision therapy. What
is vision therapy /
visual training? Vision
therapy (also called vision training, orthoptics, eye training, and eye
exercises) is a clinical approach for correcting and ameliorating the effects
of eye movement disorders, nonstrabismic binocular dysfunctions, focusing
disorders, strabismus, amblyopia, nystagmus, and certain visual perceptual
(information processing) disorders. The practice of vision therapy entails a
variety of non-surgical therapeutic procedures designed to modify different
aspects of visual function (11). Its purpose is to cure or ameliorate a
diagnosed neuromuscular, neurophysiological, or neurosensory visual
dysfunction. Vision
therapy typically involves a series of treatments during which carefully
planned activities are carried out by the patient under professional
supervision in order to relieve the visual problem. The specific procedures
and instrumentation utilized are determined by the nature and severity of the
diagnosed condition. Vision therapy is not instituted to simply strengthen eye
muscles, but rather is generally done to treat functional deficiencies in
order for the patient to achieve optimal efficiency and comfort. The
treatment may appear to be relatively uncomplicated, such as patching an eye
as part of amblyopia therapy. Or, it may require complex infrared sensing
devices and computers, which monitor eye position and provide feedback to the
patient to reduce the uncontrolled jumping of an eye with nystagmus. Treatment
of strabismus, or turned eye, can involve complex optical and electronic
instruments or such simple devices as a penlight or a mirror. The particular
procedures and instruments are dependent on the nature of the visual
dysfunction and the doctor's clinical judgment. Who
can benefit? Vision
therapy is utilized for conditions, which include oculomotor dysfunctions,
non-strabismus binocular coordination problems, accommodative disorders,
strabismus, amblyopia, and nystagmus. These
disorders and dysfunctions have a prevalence rate second only to refractive
conditions, such as myopia and hyperopia, and are far greater than most ocular
diseases (12-16). Graham (17) reports overt strabismus in almost 4% of over
4,000 school children. Among clinical cases, Fletcher and Silverman (18) found
8% of 1,100 to be strabismic. Other studies have generally found rates between
these two levels (19). The
reported prevalence of amblyopia varies somewhat depending upon the specific
criteria used, with low estimates at approximately 2% (20), and ranging up to
8.3% in the Rand HIE report (21), and also in the study by Ross, Murray and
Steed (22). The National Society to Prevent Blindness estimates 127,000 new
cases of amblyopia per year in the United States (23). Non-strabismic
binocular coordination anomalies have an even higher incidence. Convergence
insufficiency is reported in 15% of adults by Duke-Elder (24). Graham (l5)
reports high heterophorias in over 13%, while Hokoda (25) found fusion or
accommodative problems in 21% of a non-presbyopic clinical population. The
recently developed New York State Vision Screening Battery probes oculomotor,
binocular, accommodative, and visual perceptual function. Testing of 1,634
children with this battery revealed a failure rate of 53% (27). When
"special" populations are considered, the incidence of ocular
coordination and visual processing problems becomes very high. Among children
who are reading disabled, as many as 80% show deficiency in one or more basic
visual skills (26). Grisham (28) has recently reported that children with
reading problems showed greater than a 50% prevalence of visual deficiencies
in accommodation, fusional vergence or gross convergence, compared to their
normally achieving peers. Cerebral palsied patients show an incidence of
strabismus as high as 50%. (29,30) The
hearing impaired (31.32), emotionally impaired (33), and developmentally
disabled (34,35) also demonstrate unusually high prevalence rates of visual
problems. This is of particular importance because almost 11% of the school
population has been identified as having one of the above handicapping
conditions (36). Our
culture continues to foster higher educational standards and produces work
related tasks, which are increasingly visually demanding. This is evident in
the difficulties encountered by video display terminal (VDT) operators. A
majority of surveys have shown that more than 50% of VDT workers report they
experience some type of ocular discomfort or blurring (37,38). The National
Academy of Sciences (39) concluded that the oculomotor and binocular vision
changes noted at video display terminals are similar to those that occur
during standard nearpoint tasks. What
are oculomotor skills and oculomotor dysfunctions?
[Tracking
and eye movements] Clear
vision occurs when a precisely focused image of the object of regard is
centered on the fovea and when accurate eye movements maintain this
relationship. The components of the oculomotor or eye movement system include
fixations, vestibular and optokinetic movements, saccades, and pursuit
movements (40). Each
one of the components has its own distinct and different neuroanatomical
substrate and functional neurophysiology (41).
There are times when several components interact. An example of this
occurs when the pursuit system interacts with other systems to create the
ocular stabilization or position maintenance system (42) to hold the eyes
steady. Nystagmus,
a to-and-fro involuntary movement of the eyes, is caused by disturbances in
the mechanisms that hold images steady (position maintenance) and may be
exhibited in over a dozen different clinical patterns of movement (43). This
loss of ability to maintain central fixation and eye position with the foveal
area is one of the characteristics of pathological nystagmus. Patients
with amblyopia represent another class of individuals with impaired central
fixational ability. Lack of ability to steadily fixate with the fovea is
accompanied by reduced visual acuity and is commonly observed in anisometropic
and especially strabismic amblyopes. Their characteristics have been described
extensively (44-46). Abnormal
saccadic and pursuit eye movements are exhibited in strabismic amblyopes and
appear to be related to dysfunctions in the monocular motor control center for
position maintenance (47-49). When
nystagmus or nystagmoid movements are present, the clinical identification of
fixation pauses, regressions, and progressions during reading become
difficult. The erratic eye movements interfere with efficient visual
information processing (50,51). During
reading, the function or behavior of the eye movement system involves more
than the physical movement of the eyes alone. This functional component
involves the integration of the eye movements with higher cognitive processes
including attention, memory, and the utilization of the perceived visual
information (52). Clinical
and research evidence strongly suggest that many children and adults who have
difficulty with both reading and non-reading visual information processing
tasks exhibit abnormal eye movements (53-66). Numerous
studies (67-69) indicate that there is a distinct difference in the oculomotor
(eye movement) patterns between children with reflective strategies or styles
of processing visual information and those with impulsive styles. There is
evidence that children and adults with attentional difficulties and
hyperactivity exhibit inefficient eye movement patterns that interfere with
visual information processing (70-74). In
summary, there are a variety of dysfunctions in the oculomotor system. Their
clinical manifestations are quite often related to problems with functional
visual performance and the efficient processing of information. Can
eye movement skills be modified? Improvement
in eye movement control and efficiency has been reported in individual case
studies following vision therapy (75-77). Wold
et al (78) reported on 100 consecutive optometric vision therapy patients
whose eye movement skills were rated on the Heinsen-Schrock Performance Scale
(79). This is a 10-point observational scale for scoring saccadic and pursuit
eye movement performance. Only 6% of the children passed the eye movement
portion prior to therapy. Post-therapy
reevaluation revealed that 96% of the children were able to pass. Heath
(80) discussed the influence of ocular-motor proficiency on reading. Sixty
third and fourth graders who scored below the 40th percentile on the
Metropolitan Reading Test and failed the ocular pursuit subtest of the Purdue
Perceptual Motor Survey were divided into control and experimental groups.
Results of the study showed significant improvement in ocular pursuit ability
for the experimental compared to the control group. In addition, those
children receiving therapy were found to score significantly better on a
post-test of the Metropolitan Reading Test. Fujimoto
et al (81) compared the use of various techniques for saccadic fixation
training. In this controlled clinical trial, both of the treated groups showed
a statistically significant improvement in speed and accuracy of eye movements
compared to an untreated control group. A
controlled study of pursuit eye movements was conducted by Busby (82) in an
enhancement program for special education students. The subjects were rated on
their ability to maintain fixation on a moving target. The rating procedure
was shown to have a high interrater reliability. The results showed
statistically significant improvement by the experimental group in pursuit eye
movement and persistence of the therapeutic effect on retesting at a 3-month
interval after conclusion of the therapy. Punnett
and Steinhauer (83) conducted a controlled study investigating the effects of
eye movement training with and without feedback and reinforcement. There were
clear post-training differences between the eye movement skills of the control
and experimental group of reading disabled students. This demonstrated that
the use of reinforcement in training oculomotor facility could improve those
skills. There was an improvement in reading performance following the
oculomotor training as well. Similar results demonstrating the trainability of
eye movements have been obtained in studies employing behavior modification
and reinforcement (84,85). Modifying
and improving the oculomotor ability to maintain central fixation and eye
position in nystagmus patients has been reported over the years in various
studies. The
use of after-images (86,87) and Emergent Textual Contour training to provide
visual biofeedback regarding eye position and stability has had some success
in improving fixational ability. Orthoptics, as well as verbal feedback
techniques, have helped some patients in reducing their nystagmus (88-90). More
recently, the application of eye movement auditory biofeedback in the control
of nystagmus has shown positive results. Ciufredda et al (91) demonstrated a
significant reduction in the amplitude and velocity of eye movements in
congenital nystagmus patients. Vision was improved, and positive cosmetic and
psychological changes were reported as well. Abadi et al (92) reported
reduction in nystagmus and improvement of contrast sensitivity after auditory
biofeedback training. In addition to nystagmus, the use of auditory
biofeedback has been successfully used in expanding the range of eye movement
in gaze limitations (93). There
is evidence (94) that large and unsteady eye movements occur in the eyes of
amblyopic patients during attempted monocular fixation. A number of studies
report the successful treatment of amblyopia resulting in improved vision and
oculomotor control (95-98). Occlusion therapy, a passive procedure, has been a
standard and relatively successful approach for many years (99-111).
However, there are individuals that either do not or cannot respond to
occlusion therapy. There is evidence that occlusion with active vision therapy
is more effective than occlusion alone (112).
Pleoptics (113,114) is an active vision therapy procedure in which
patients receive visual feedback about their position of fixation and
direction of gaze. These procedures are designed to correct the positional
fixation problem and thereby improve the vision of the patient. Pleoptics has
been used successfully in treating eccentric fixation in individuals not
responding to regular occlusion therapy (115-118). Vision
therapy for amblyopia incorporates a broad spectrum of procedures, including
occlusion techniques, pleoptic techniques, and visual-motor spatial
localization feedback techniques using after-images and entoptic phenomena
(45,79) with a high success rate (119-124). The
question of age and its influence on the efficacy of amblyopia therapy has
been addressed in a number of studies and reviews. These indicate that a
significant improvement in oculomotor and vision function can be achieved even
in adulthood (125). It is clear
from the evidence that amblyopia and its oculomotor components can be
successfully treated with occlusion and active vision therapy for a wide range
of patients of all ages. Studies
have demonstrated that it is possible to change and improve inefficient and
inadequate visual information processing strategies and visual attention
patterns. Many of these changes have been accompanied by enhanced eye
movements (126-138). A
number of techniques used to improve these poor visual scanning and attention
problems in children and adults, e.g., tachistoscopic procedures, pursuit and
fixation activities, and eye-hand coordination techniques have been described
and utilized professionally for many years (79,139-143). What
are accommodative dysfunctions and their remediation?
[Focusing] Accommodative
(focusing) dysfunctions have been described in detail (144-146) in numerous
sources and are clinically classified as accommodative spasm, accommodative
infacility, accommodative insufficiency, and ill-sustained accommodation.
There are also clearly defined syndromes associated with accommodative
dysfunctions (147-155). The
literature discusses many symptoms common to accommodative dysfunctions as a
group. These have been described as reduced nearpoint acuity, a general
inability to sustain nearpoint activity, asthenopia, excessive rubbing of the
eyes, headaches, periodic blurring of distance vision after prolonged near
activities, periodic double vision at near, and excessive fatigue at the end
of the day (152,154,156-160). The
efficacy of applying vision therapy procedures in improving accommodative
functioning has considerable basic science and clinical research support.
Studies have shown that accommodative findings, although under
autonomic nervous system control, can respond to voluntary command (161-163)
and can be conditioned (164). These
studies demonstrate that voluntary control of accommodation can be controlled,
trained, and transferred. Once
pathological or iatrogenic causes have been eliminated, the treatment of
accommodative deficiencies includes plus lenses for near work and vision
therapy aimed at improving the functioning of the accommodative mechanism
(165-168). Levine et al (156) established baseline statistics for diagnostic
accommodation findings which differentiate symptomatic from asymptomatic
patients. Their findings were in close agreement with a similar study by
Zellers and Rouse (152). The significant element of these studies is the
relationship between symptoms and inadequate accommodative facility. Wold
(78) reported on 100 children who had undergone accommodative vision therapy
procedures. These clinically selected cases showed an 80% rate of improvement
in accommodative amplitude and 76% in accommodative facility using a pre- and
post-treatment ordinal criterion referenced scaling method. These results are
similar to those reported by Hoffman and Cohen (168) a in which 70 patients
were successfully treated for accommodative insufficiency and infacility based
on clinical findings. Liu
et al (169) investigated accommodative facility disorders by objective
laboratory methods using a dynamic optometer with an infrared photomultiplier.
They objectively identified the dynamic aspects of the accommodative response
that were improved by vision therapy. Young adults with symptoms related to
focusing difficulties were treated by procedures commonly used in orthoptic or
vision therapy practice. Significant improvement in their focus flexibility
occurred and these changes correlated with marked reduction or elimination of
symptoms. Standard clinical measures of accommodative facility were found to
correlate well with the more objective measures. Bobier
and Sivak (l70) replicated the work of Liu et al (169) using a greater degree
of recording precision with a dynamic photorefractor (television camera and
monitor with light-emitting diodes}. They found no evidence of regression in
improved focusing flexibility during an l8-week interval after cessation of
training. The subjects' symptoms also abated as accommodative function
normalized. Hung et al (l71) demonstrated the efficacy of accommodation,
vergence, and accommodative vergence orthoptic therapy using a dynamic
binocular simulator. This experiment objectively validated optometric vision
therapy procedures through use of photoelectric eye movement recording systems
and an optometer. There
is a higher prevalence of accommodative insufficiencies and infacilities in
persons with cerebral palsy (172). Duckman demonstrated that accommodative
abilities can be modified and improved in a cerebral palsy population using
vision therapy techniques (173,174). Since
accommodative changes take place when looking from near to far and back to
near, Haynes and McWilliams (175) investigated the effects of training this
near-far response on school age and college students. Their results indicate
that this near-far response ability is trainable and can be improved with
vision therapy. Weisz
(l76) has shown that improvement in accommodative ability transfers to
improvement in near point task performance. In a double blind clinical study
following vision therapy, her experimental group was found to improve
significantly in accuracy of performance on a Landolt-C resolution task as
compared with the controls. Hoffman
(160) investigated the impact of accommodative deficiencies on visual
information processing tasks. He compared the results of vision therapy for
the accommodative problems in an experimental and control group of school age
children. This study indicated that by improving accommodative skills, there
was a concomitant improvement in his subject's visual perceptual skills. Recently,
in a detailed series of analyses involving retrospective studies, Daum
(177-180) investigated the full range of accommodative disorders. He used a
stepwise discriminant analysis of regression variables in patient care
records, to establish a model to determine the length of treatment necessary,
and to predict the success of treatment for accommodative disorders. In
conclusion, these studies demonstrate that accommodative disorders can cause
significant discomfort, inefficiency or avoidance of nearpoint tasks. They
further demonstrate that when diagnosed and treated appropriately, these
dysfunctions may be ameliorated or eliminated through vision therapy. What
are binocular vision disorders and their remediation?
[Eye
coordination and alignment] Normal
and efficient binocular vision is based on the presence of motor alignment and
coordination of the two eyes and sensory fusion. The range of binocular
disorders extends from constant strabismus with no binocular vision present to
non-strabismic binocular dysfunctions, e.g., convergence insufficiency (146). The
first category is non-strabismic binocular disorders. Standard techniques and
diagnostic criteria in the assessment of the vergence system and binocular
sensory fusion ability have been described in detail elsewhere (181-185). Patients
exhibiting non-strabismic anomalies of binocular vision quite often report
feeling ocular discomfort and asthenopia (186).
Some of the patient complaints include eyestrain, soreness of the eyes,
frontal and occipital headaches, and ocular fatigue which result in an
aversion to reading and studying (187,187a). Vision
therapy has long been advocated as a primary intervention technique for the
amelioration of non-strabismic anomalies of binocular vision (188-194).
Suchoff and Petito (l46) have concluded that vision therapy for these
conditions is directed toward several therapeutic goals: First, to increase
the efficiency of the accommodative system so as to facilitate a more
effective interaction between this system and the vergence system. Second, to
maximize the functioning of the fusional vergence system (i.e., divergence and
convergence) and the binocular sensory system. Since the training of
accommodation has been covered in the previous section, the remainder of this
section will be devoted to the evidence of the modifiability of the vergence
system. Clinical
vision therapy procedures are intended to improve the patient's ability to
compensate for fusional stress which may result in asthenopia, headache,
and/or diplopia. A number of studies will be reviewed showing that
improvements can be made in fusional vergence skills by vision therapy
procedures. The
clinical assumption that fusional vergences can be trained is not a new one.
Over 50 years ago, Berens et al advocated the use of this aspect of orthoptics
for all non-strabismic anomalies of binocular vision (195). Within the past
several years a number of investigators have sought to determine
experimentally whether the clinical assumption of the trainability of the
vergence system was a valid one. Daum
(196) prospectively studied a group of 35 young adults. The results of daily
vision therapy showed statistically significant improvement in convergence
ranges. The gains persisted on post-testing 24 weeks after completion of the
therapy program. The conclusion was that relatively short periods of training
can provide long-lasting increases in vergence ability. Daum
(l97) conducted a retrospective study of 110 patients who received treatment
for convergence insufficiency. The patients were classified according to the
effectiveness of the treatment program into total success, partial success or
no success categories. Post training diagnostic findings and changes in
patient symptomatology were used to define the classification categories. A
comparison of pre- and post-training findings revealed statistically
significant improvement. In a companion report, (198) a portion of the above
data (l97) was used to investigate and identify which of 14 common diagnostic
measures best predicted the success of the vision training program. These
measures were 75% accurate in predicting efficacy of the vision therapy
program. Another
study (l99) utilized tonic and phasic vergence training and demonstrated
impressive changes in convergence and divergence abilities. The 34 subjects
were randomly assigned in a double crossover design, wherein subjects served
as their own controls, and learning effects were controlled. In
another study, Veagan used a motor-driven prism stereoscope (ophthalmic
ergograph) to train divergence and convergence (200). Forty- seven adults were
divided into convergence and divergence experimental and control groups. The
findings led Veagan to conclude that sustained divergence and convergence
training showed large and significant immediate and stable improvement in the
trained vergence ranges of the experimental groups. Vaegan
and McMonnies (201) utilized a recording device that measured eye movements
during vergence activity. They were able to objectively demonstrate that
convergence training with prism-induced changes resulted in sustained
improvement of convergence ability. In a companion study, Vaegan (202)
demonstrated substantial long-lasting gains in convergence and divergence
ability from both tonic and phasic vergence training. Pantano
(203) studied over 200 subjects with convergence insufficiency who underwent
vision therapy and evaluated them 2 years later. The majority remained
asymptomatic with normal clinical findings. Those subjects who had learned to
control convergence and accommodation together had the best success. Grisham
(204, 205) used vergence latencies, velocity, and step vergence tracking rate
by measuring them objectively with infra-red eye monitor recordings; He
reported improved step vergence tracking after vision therapy of 4 to 8 weeks.
Cooper
and Duckman, in their extensive review of convergence insufficiency, stated
that 95% of the patients reported in these studies responded favorably to
vision therapy for this binocular disorder (206). Cooper
and Feldman (207) investigated the role and clinical use of operant
conditioning in vision therapy based on random dot stereograms (RDS). They
demonstrated that response-contingent positive reinforcement, immediate
feedback, and preprogrammed systematic changes during discrimination learning
improves convergence ability. Control and experimental groups were formed with
subjects matched in baseline convergence ability and randomly assigned to each
group. The convergence ranges of the experimental group improved significantly
while there were little or no increases for the control group. Cooper
et a1 (208) conducted a controlled study of vision therapy and its
relationship to symptomatology for a group of patients with convergence
insufficiency. A vision therapy program of fusional vergence activities was
administered in a matched-subjects control group crossover design to reduce
placebo effects. They used a written assessment scale for rating asthenopia in
terms of discomfort and/or fatigue, and conclusively demonstrated that the
symptoms were eliminated or relieved. Clinical findings also improved,
corroborating the subjective assessments. Dalzie1
(209) reported on 100 convergence insufficiency patients who did not meet
Sheard's criterion, and were given a program of vision therapy. After vision
therapy, clinical findings were again assessed and 84% of the patients
successfully met Sheard's criterion. Eighty-three percent of the patients
reported they had symptoms of discomfort or loss of efficiency prior to
treatment. Only 7% reported these symptoms after therapy. The post-training
group who failed to meet Sheard's criterion correlated well with those still
reporting subjective symptoms. Wold
(78) reported on the results of 100 patients who underwent vision therapy.
Based on standard clinical tests, only 25% of the children had adequate
binocular sensory fusion prior to vision therapy and 9% had adequate binocular
fusional vergence. Post-training evaluation showed 96% had achieved
appropriate sensory fusion findings and 75% demonstrated adequate fusional
vergence ranges. Wittenberg
et al (210), along with Saladin and Rick (211), used slightly different
techniques and demonstrated that stereopsis thresholds could be improved in
normal subjects. In Dalziel's (212) study there was a statistically
significant improvement in stereopsis after vision therapy. Another
category of binocular vision disorders is strabismus. Strabismus may be
described as a misalignment of the eyes (referred to as crossed-eyes, eye
turn, weak eye muscle, etc.). Many forms and variations of strabismus exist,
depending upon direction and amount of the eye turn, the number of affected
nerves or muscles, and the degree to which it is associated with reduced
vision. The clinical characteristics and diagnostic criteria have been
described in detail (212-215). Numerous
comprehensive reviews and studies relating to the success of vision therapy
for strabismus exist. Flom (216) reviewed studies and used detailed
multifactorial analysis. This revealed an overall functional cure rate for
strabismics receiving vision therapy of 50%, with esotropia less responsive
than exotropia. Ludlam (217) evaluated a sample of 149 unselected strabismics
who received vision therapy and determined a 73% overall success rate
utilizing the rigorous criteria established by Flom. In
a longitudinal follow-up study of this population, Ludlam and Kleinman (218)
found 89% of these patients had retained their functional cure (binocular
vision present). The long-term overall success rate of vision therapy was
calculated at 65%. If one adopts a less stringent definition of "success,
" such as the cosmetic criterion of "straight-looking eyes"
employed in some less precise studies, the success rate increases to 96% of
the re-analyzed population, or a 71% long- term success rate. Flax
and Duckman, (219) in their literature review of treatment for strabismus,
found strong support for the efficacy of vision therapy for strabismus. They
gathered data from numerous studies, each of which met rigorous criteria for
success, and reported an overall success rate of 86%. In
a controlled study of 100 cases (220) Gillan reported that 76% of strabismic
patients attained a cosmetic cure with orthoptics. None of those in the
control group, treated with glasses alone, showed a spontaneous cure. In
a series of controlled studies conducted by Guibor (221-223), 50% of the
experimental group achieved alignment of the eyes with glasses and vision
therapy (orthoptics) as compared with only 12.5% of the control group who
received glasses without vision therapy. More
recently, Ziegler et al (224) conducted a literature review of the efficacy of
vision therapy for strabismus. An important contribution is their comparative
analysis of published papers using the functional cure criteria defined by
Flom. They noted the study conducted by Etting (225) in which he reported a
65% overall success rate in patients with constant strabismus (57% of
esotropes and 82% of exotropes), 89% success rate with intermittent strabismus
(100% of esotropes and 85% of exotropes), and a 91% success rate when retinal
correspondence was normal. In
a study designed to investigate the effectiveness of vision therapy utilizing
computer generated stereo graphics for subjects with strabismus, Kertesz and
Kertesz (226) reported a 74% success rate in 57 strabismics. They combined
traditional vision therapy techniques with computer generated stimuli as
successfully applied by CooperO7 to the remediation of non-strabismic
binocular vision anomalies. The functional cures obtained persisted on
long-term follow-up visits for a period of up to 5 years. Sanfilippo
and Clahane (227) designed a prospective study of the results of orthoptic
therapy for divergent strabismus (exotropia). Of the patients who completed
the study, 64.5% attained a functional cure upon completion, and 51.7%
retained this status on an average follow-up interval of 5 years and 4 months.
In
two studies on the effectiveness of orthoptics (vision therapy) for
intermittent and constant exotropes, Altizer (228) and Chryssanthou (229)
found the majority of their patients had significant improvement in clinical
findings as well as relief of symptoms. Goldrich
(230) reviewed records of patients completing a vision therapy program for
exotropia of the divergence excess type. Of the patients reviewed, 71.4%
attained a functional cure following approximately 5 months of standardized
sequential therapy procedures used in-office as well as at home. Several
studies have applied biofeedback in vision therapy to assist in training
patients to align their eyes (231-236). The use of biofeedback to enhance
traditional vision therapy, provide reinforcement, and increase motivation was
supported in these studies. Strabismic
patients exhibiting esotropia with anomalous correspondence tend to be the
most difficult to successfully treat. The use of more aggressive and
sophisticated techniques for vision therapy has been reported with a better
success rate for anomalous correspondence and esotropia than earlier studies
(237,238). In general, the treatment period tends to be longer for
anomalous correspondence and esotropia than other types of strabismus. Summary
and conclusion Vision
is not simply the ability to read a certain size letter at a distance of 20
feet. Vision is a complex and adaptable information gathering and processing
system which collects, groups, analyzes, accumulates, equates, and remembers
information. In
this review, some of the essential components of the visual system and their
disorders which can be physiologically and clinically identified. i.e., the
oculomotor, the accommodative, and the fusional vergence systems have been
discussed. Any dysfunctions in these systems, can lessen the quality and
quantity of the initial input of information into the visual system. Deficiencies
in one or more of these visual subsystems have been shown to result in
symptoms, such as blurred or uncomfortable vision or headaches, or behavioral
signs such as rubbing of the eyes, eyes turning inward or outward, reduced job
efficiency or reading performance, or simply the avoidance of near point
tasks. In addition, these signs/symptoms may contribute to reducing a person's
attention and interest in near tasks. The goal of vision therapy is to
eliminate visual problems, thereby reducing the frequency and severity of the
patient's signs and symptoms. Vision therapy should only be expected to be of
clinical benefit to patients who have detectable visual deficiencies. In
response to the question, "How effective is vision therapy in remediating
visual deficiencies?," it is evident from the research presented that there
is sufficient scientific support for the efficacy of vision therapy in
modifying and improving oculomotor, accommodative, and binocular system
disorders, as measured by standardized clinical and laboratory testing
methods, in the majority of patients of all ages for whom it is properly
undertaken and employed. The
American Optometric Association reaffirms its long-standing position that
vision therapy is an effective therapeutic modality in the treatment of many
physiological and information processing dysfunctions of the vision system. It
continues to support quality optometric care, education, and research and will
cooperate with all professions dedicated to providing the highest quality of
life in which vision plays such an important role (1). Corresponding
author: Allen H. Cohen, O.D. SUNY State College of Optometry 100 E. 24th St.,
New York. NY 10010
Acknowledgment
The
Task Force would like to acknowledge Jack E. Richman, O.D., Nathan Flax, O.D.,
and Leonard Press, O.D. for their major contributions to the research and
preparation of this document. A number of editorial revisions were based on
the recommendations of the following individuals and organizations: Arol
Augsburger, O.D., Louis G. Hoffman, O.D., Mike Rouse, O.D., Ralph T. Garzia,
O.D., the College of Optometrists in Vision Development, and the Optometric
Extension Program Foundation. The members of the 1985-86 Task Force also
contributed to the initial development of this document: Donald J. Getz, O.D.,
chairman; Paul A. Harris, O.D.; Paul J. Lederer, O.D.; Ronald L. Bateman. O.D.;
and D. Gary Thomas. O.D. Members
of the task force Allen
H. Cohen, O.D., chairman; Sue E. Lowe, O.D.; Glen T. Steele, O.D.; Irwin B.
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