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PubMed2000

[Unilateral amblyopia without strabismus and with anisometropia].

PURPOSE OF THE STUDY: To evaluate a group of patients with unilateral isometropic amblyopia according to presence of possible amblyogenic factors. MATERIAL AND METHODS: 37 patients (18 girls and 19 boys) with unilateral amblyopia without strabismus and with anisometropia of less than 1 D in any of the meridians were analysed according to such possible risk factors of amblyopia as age of examination, age of mother on delivery, sex, family history, puerperal complications, birth weight, refraction error, left or right eye. Depth of amblyopia, state of binocular vision and results of optical and pleoptical treatment were also evaluated. RESULTS AND DISCUSSION: No significant risks were found regarding the age of patient, sex, left or right eye, birth weight, age of mother on delivery, puerperal complications and family history. Refraction error was not high. Depth of amblyopia did not correlate with amount of refraction error. Central fixation was present only in 50% and stereopsis only in 42% of patients. 10 patients revealed no significant defect of fixation or binocular vision. All patients responded significantly poorly to treatment. CONCLUSIONS: Presence of amblyopia in patients with isometropia cannot be explained by genetic or puerperal risk factors. It might have developed in the period sensitive for amblyopia as a result of anisometropia that was later diminished by the process of emmetropisation or microstrabismus which was spontaneously cured. Some cases can be described as idiopathic because no defect can be detected. Early in life screening is necessary to successfully diagnose and treat amblyopia in childhood.

Amblyopia↗
PubMed1994

Social deprivation and age at presentation in amblyopia.

BACKGROUND: Amblyopia is the most common visual disability in children. Early treatment is thought to be more effective, and therefore factors affecting the age at presentation are important. A relationship between social deprivation and access to health care and screening services is well known. We hypothesized that social deprivation might be associated with later presentation of amblyopia, particularly of anisometropic amblyopia which depends on vision screening for referral. METHODS: Data from a historical cohort of 897 children with amblyopia, from seven UK orthoptic clinics, were used to test this hypothesis. Social deprivation was measured by the Townsend score of the ward in which the child lived. RESULTS: A relationship between social deprivation and age at presentation was found in children with anisometropic amblyopia even after adjusting for differences between clinics (p = 0.01) but no similar association was evident in children with amblyopia associated with strabismus. There was a difference of 22 months in the average age at presentation between children with anisometropic amblyopia in the most deprived and least deprived areas of the study. CONCLUSIONS: If screening for anisometropic amblyopia is to be undertaken, priority should be given to screening children from areas of social deprivation.

Age Factors↗
PubMed2006

Causes and associations of amblyopia in a population-based sample of 6-year-old Australian children.

OBJECTIVES: To describe the prevalence of amblyopia and associated factors in a representative sample of 6-year-old Australian children. METHODS: Logarithm of minimum angle of resolution visual acuity (VA) was measured in both eyes before and after pinhole correction, correcting cylindrical refractive components greater than 0.50 diopter (D), and with spectacles (if worn) in a population-based sample of 1741 schoolchildren. Retinal pathological abnormalities were excluded based on photographs. Amblyopia was defined using various best-available corrected VA measures in the absence of significant organic pathological abnormalities. RESULTS: Using the criteria of corrected VA less than 20/40 and at least a 2-line difference between eyes, amblyopia was diagnosed in 13 children (0.7%). The inclusion of children with amblyopia who had been successfully treated (n = 19) increased the amblyopia prevalence to 1.8%. Strabismus or strabismus surgery history was present in 37.5% of the children with amblyopia, anisometropia in 34.4%, both conditions in 18.8%, and isoametropia in 6.3%. Mean corrected VA in amblyopic eyes was 37.7 logarithm of minimum angle of resolution letters (Snellen VA equivalent < 20/40), ranging from 0 to 48 logarithm of minimum angle of resolution letters (Snellen VA equivalent < 20/200-20/25). Most amblyopic eyes (58.7%) were significantly hyperopic (spherical equivalent > or = +3.00 D); 8.7% were myopic. CONCLUSIONS: A relatively low prevalence of amblyopia in a sample of 6-year-old children is documented. The majority of these children had already been diagnosed and treated for this condition.

Amblyopia↗
PubMed2005

Screening for amblyopia in childhood.

BACKGROUND: Amblyopia is a reversible deficit of vision that has to be treated within the sensitive period for visual development. Screening programmes have been set up to detect this largely asymptomatic condition and refer children for treatment while an improvement in vision is still possible. The value of such programmes and the optimum protocol for administering them remain controversial. OBJECTIVES: The objective of this review was to evaluate the effectiveness of vision screening in reducing the prevalence of amblyopia. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), which contains the Cochrane Eyes and Vision Group Trials Register, on The Cochrane Library Issue 2, 2005, MEDLINE (1966 to May 2005 week 1) and EMBASE (1980 to 2005 week 19). No language restrictions were placed on these searches. No handsearching was done. SELECTION CRITERIA: We planned to analyse data from randomised controlled trials and cluster-randomised trials comparing the prevalence of amblyopia in screened versus unscreened populations. DATA COLLECTION AND ANALYSIS: Two authors independently assessed study abstracts identified by the electronic searches. Full text copies of appropriate studies were obtained and, where necessary, authors were contacted. No data were available for analysis and no meta-analysis was performed. MAIN RESULTS: Despite the large amount of literature available regarding vision screening no trials designed to compare the prevalence of amblyopia in screened versus unscreened populations were found. Data currently under preparation may be available for updates to the review. AUTHORS' CONCLUSIONS: The lack of data from randomised controlled trials makes it difficult to analyse the impact of existing screening programmes on the prevalence of amblyopia. The absence of such evidence cannot be taken to mean that vision screening is not beneficial; simply that this intervention has not yet been tested in robust trials. To facilitate such trials normative data on age-appropriate vision tests need to be available and a consensus reached regarding the definition of amblyopia. In addition, the consequences of living with untreated amblyopia have yet to be quantified and a cost-benefit analysis carried out.

Amblyopia↗
PubMed2006

Successful treatment of anisometropic amblyopia with spectacles alone.

BACKGROUND: The efficacy of treating anisometropic amblyopia with occlusion therapy is well known. However, this form of treatment can be associated with risks. Spectacle correction alone may be a successful and underutilized form of treatment. METHODS: The records of 28 patients treated successfully for anisometropic amblyopia with glasses alone were reviewed. Age, initial visual acuity and stereoacuity, and nature of anisometropia were analyzed to assess associations with time required for resolution, final visual acuity, and stereoacuity. Incidence of amblyopia recurrence and results of subsequent treatment, including patching, were also studied. RESULTS: Mean time to amblyopia resolution (interocular acuity difference <or=1 line) was 5.8 months (range 2 to 15 months). Worse best corrected initial visual acuity was associated with longer time to resolution (Spearman's rho = 0.37, P = 0.05), while age, initial stereoacuity, amount, and type of anisometropia were not (P = 0.43, 0.68, 0.26, 0.47, respectively). None of the astigmatic or myopic patients achieved visual acuity of 20/20 in the amblyopic eye, while seven (39%) of the hyperopic patients did. This difference was significant (P = 0.03). Better initial stereoacuity predicted good final stereoacuity (P = 0.01). Only four (14%) patients developed amblyopia recurrence over an average follow-up period of 1.7 years. All were successfully treated with updated spectacles or patching. CONCLUSIONS: Treatment of anisometropic amblyopia with spectacles alone can be a successful option. Patients treated with spectacles alone may experience a lower amblyopia recurrence rate than those treated with occlusion therapy.

Amblyopia↗
PubMedDate not supplied

Amblyopia.

Over the past thirty years, much has been learned about the physiological basis for amblyopia. For many years amblyopia was considered to be a retinal disorder; it has now been well established through animal studies that amblyopia represents functional and morphological effects of visual deprivation on the visual cortex and the lateral geniculate nucleus. With this knowledge has come the recognition of a "sensitive period" of development of the visual system, during which time visual deprivation causes amblyopia. The best approach to managing amblyopia is to detect amblyogenic factors before the age of two years and prevent it through eliminating the causes of visual deprivation. When amblyopia exists, it can be cured if adequately treated in children less than 6-7 years of age. Even in older patients, visual improvement can be achieved with therapy. Current research is aimed at developing substances and delivery modes that will allow the sensitive period of visual development to be manipulated, increasing the period during which it can develop and enhancing preventative and therapeutic measures. In this review selected literature contributing to current understanding of causes, prevention and treatment of amblyopia is discussed. Although many new treatment modalities have been tried, occlusion still seems to be the most successful therapy.

Amblyopia↗
PubMed1997

Automated pupil perimetry in amblyopia: generalized depression in the involved eye.

OBJECTIVE: This study was designed to determine whether the relative afferent pupillary defects observed commonly in amblyopic eyes are associated with a uniform depression of the pupillary light reflex throughout the visual field or solely by a focal decrease in pupillary response near fixation. DESIGN: The authors used pupil perimetry to evaluate the contraction amplitude of the pupil in response to focal light stimuli at 76 points throughout the 30 degrees field in each eye of 28 patients with amblyopia. The "pupil fields" were recorded using a computerized infrared pupillograph linked to a Humphrey Field Analyzer, so that the pupil contraction could be recorded in response to perimetric light stimuli. PARTICIPANTS: Nine patients had strabismic amblyopia, ten had anisometropia, six had a combination of anisometropia and strabismus, and three had deprivation amblyopia due to monocular congenital cataract. MAIN OUTCOME MEASURES: Mean pupillary contraction amplitude for the entire field and focal amplitudes at each tested location were compared. Mixed-model analysis of variance was used to assess effects of perimetry location, type of amblyopia, and interaction effects. RESULTS: The overall average of all the pupil contractions throughout the 30 degrees field was less for the amblyopic eye compared with that of the fellow eye. This decrease in focal pupil response for amblyopic eyes was present in each type of amblyopia and was greatest for deprivation amblyopia. The contraction amplitude was depressed diffusely throughout the pupil field and showed neither focal deficits nor a selective depression about fixation. CONCLUSION: Amblyopia produces a global depression of focal pupillary responses across the entire 30 degrees field.

Adult↗
PubMed2002

The frequency of amblyopia among visually impaired persons.

PURPOSE: To investigate the frequency of amblyopia among visually handicapped patients. METHODS: The study is a retrospective investigation of all living patients registered in four Visual Rehabilitation Centres in a region in southern Sweden. The area's total population numbered 865,612 persons of whom 11,365 were registered as visually handicapped (with visual acuity < or = 0.3 in the better eye). RESULTS: Amblyopia was the main cause of decreased visual acuity in one eye in 1.72% (195 of 11,365) of the patients. The average age of the patients with amblyopia was 69 years (9-95 years) and 28.2% of these patients were less than 65 years old (the age for retirement in Sweden). The median visual acuity in the amblyopic eye among these patients was 0.1. The median visual acuity in the nonamblyopic eye was 0.2. The most common cause of decreased vision in the nonamblyopic eye was macular degeneration (39.5%). Bilateral amblyopia was present in 13 (6.7%) of the amblyopic patients. By comparing this study with earlier studies, we can calculate that about 1.2% of the persons with amblyopia 0.3 or lower will eventually become visually handicapped. CONCLUSION: A small but considerable number of patients who attend the Visual Rehabilitation Centres have amblyopia as a cause of their visual impairment. Since amblyopia can be treated if detected in childhood, later visual rehabilitation of these patients can be avoided or delayed, thereby reducing rehabilitation costs for society.

Adolescent↗
PubMed2003

Astigmatic axis and amblyopia in childhood.

PURPOSE: This study is part of a larger project whose aim is to evaluate the relationship between refractive errors and amblyopia. In an earlier study, we showed that there is a substantial increase in the prevalence of amblyopia among children with oblique astigmatism. To further evaluate this relationship, we examined children with astigmatisms of 1 dioptre or more and varying directions of the astigmatic axes. METHODS: Two groups of astigmatic children, with oblique and orthogonal astigmatism, respectively, were selected for the study at 1 year of age via a general health screening programme. The most emmetropic axis was identified in each child and used in the study. Visual acuity (VA) was tested when the children were between 4 and 4.5 years of age. The presence of amblyopia, defined as difference in VA between the eyes of 0.1 log unit or more, and any increase in acuity following occlusion therapy were noted. RESULTS: The angle of the astigmatic axis strongly relates to the risk of developing amblyopia. Axes +/- 15 degrees from the main axes did not affect the risk of amblyopia but oblique astigmatism significantly increased the risk of developing amblyopia (p = 0.0024). CONCLUSIONS: The results accord with earlier findings that oblique astigmatism increases the risk of developing amblyopia.

Amblyopia↗
PubMed1980

Contrast perception above threshold is only minimally impaired in human amblyopia.

Amblyopia is a condition occurring at birth, or in early childhood, which affects up to 5% of the population and is characterized by degraded vision in one eye not able to be corrected by spectacles and having no observable lesion in the eye itself. Its cause is therefore uncertain, yet indirect evidence suggests a neural one, very likely in the visual areas of the brain. Ambyopia is usually associated with either a strabismus (eye misalignment) or anisometropia (unequal refractive error). Investigation into its neural basis has involved two approaches: psychophysical research in humans with amblyopia has shown marked contrast deficits for threshold stimuli, suggesting deficient contrast coding at and above threshold in amblyopia. Neurophysiological research on animals deprived in early life with either a surgically induced squint or an optically induced anisomeropia has suggested that 'blur' may be the common etiological basis for these two amblyopias. We have investigated here whether amblyopes exhibit contrast deficiencies for other than threshold stimuli. Our measurements show that the threshold deficits measured in amblyopia bear no simple relationship to what happens above threshold. There is no contrast coding abnormality in amblyopia in the high-contrast range typical of everyday vision. We also give suprathreshold evidence for anisometropic and strabismic amblyopia having different neural bases.

Amblyopia↗
PubMed1994

The presentation of children with amblyopia.

This study reports the presentation of 961 children who underwent amblyopia treatment at seven orthoptic centres in the United Kingdom. We confirmed previous authors' findings of a small but significant increased incidence of left-sided compared with right-sided amblyopia overall. For pure anisometropic amblyopia this difference was very marked and a possible pathophysiological mechanism is proposed. The mean age of presentation for anismetropic, strabismic and mixed amblyopia was 5.6, 3.3 and 4.4 years, respectively. Neither sex nor race affected the age of presentation. Despite their older age, children with pure anisometropic amblyopia had the best initial visual acuity, with 25% of anisometropes having an initial visual acuity of less than 6/18 compared with 39% of strabismics and 50% of mixed amblyopes. The ages and initial acuities of the strabismic patients in this series are at least as favourable as those of patients reported from outside the UK. There were variations in the age and proportion of patients presenting with anisometropic amblyopia at the different centres, suggesting a failure in the referral of anisometropic amblyopia of importance in interpreting epidemiological studies.

Age Factors↗
PubMed1994

Factors affecting the outcome of children treated for amblyopia.

The outcome of treatment for amblyopia and the factors that affect this are not well understood. A major reason for this has been the exclusion from previous large studies of a sometimes unknown number of patients because of failure to comply with treatment. This paper analyses the outcome of amblyopia treatment in a retrospective review of the orthoptic records of a cohort of 961 children treated for amblyopia at seven centres who first attended in 1983. The final visual acuity was recorded by Snellen or matching methods in 894 children (93%). Of these, 48% achieved 6/9 or better, 35% less than 6/9 but better than or equal to 6/18, and 17% achieved less than 6/18. The outcome was best for pure anisometropic amblyopia, intermediate for pure strabismic amblyopia and least good for mixed strabismic and anisometropic amblyopia with a final visual acuity of 6/10.2, 6/12.8 and 6/14.8 respectively. While the age at start of treatment did not correlate with final visual acuity both poor initial visual acuity and poor compliance were associated with poor outcome. The main factor affecting the outcome of amblyopia treatment is the initial visual acuity. Comparison with the literature suggests that the results of treatment in this country may be falling far short of what would be possible in ideal circumstances with unlimited resources.

Age Factors↗
PubMed2005

[Cost-effectiveness of screening for amblyopia].

BACKGROUND: The effectiveness of a screening program for amblyopia has been discussed controversely for several years. While the medical profit is obvious, little is known on the cost-effectiveness of such a screening program. METHODS: By literature research all important variables were determined: incidence of amblyopia, sensitivity of different screening modalities, effectiveness of therapy, costs as well as the loss of utility and life quality by an existing amblyopia. Based on those data in a simple model the costs of a screening program for amblyopia were determined per quality adjusted life year (QALY). The result was analyzed for its stability by sensitivity analysis and compared to the costs of other therapies. RESULTS: Amblyopia occurs with an incidence of approximately 2 % (1.3 - 12 %). Most Screening programs reach a sensitivity of 60 - 90 % and cause costs of 900 - 1400 Euro per detected case. By appropriate therapy with mean costs of 2300 Euro approx. 60 % of the cases obtain useful vision of > 20/40. However, therapy results vary considerably. After discounting the incremental cost-effectiveness ratio (ICER) reaches 7684 Euro/QALY for a screening and treatment program for amblyopia. This is well comparable with other therapies and accepted to be cost-efficient. Sensitivity analysis yielded 24 700 Euro/QALY and 57,633 Euro/QAL with higher discounting for worst case scenarios. CONCLUSION: Screening for amblyopia meets the basic requirements of cost-effectiveness.

Amblyopia↗
PubMed1993

Amblyopia induced by anisometropia without shrinkage of ocular dominance columns in human striate cortex.

Amblyopia can be induced by opacity of the ocular media (e.g., cataract), misalignment of the ocular axes (strabismus), or unequal refractive error in the eyes (anisometropia). Experiments in monkeys have shown that early monocular eyelid suture, a model of amblyopia caused by cataract, results in shrinkage of the eye's ocular dominance columns in striate cortex. This reduction of the geniculocortical projection from the deprived eye has been thought to explain in part the mechanism of amblyopia. We labeled the ocular dominance columns in monkeys with amblyopia by using cytochrome oxidase histochemistry. In animals rendered amblyopic by early unilateral eyelid suture, no pattern of cytochrome oxidase activity appeared in layer IVc. Outside layer IVc, alternating rows of light and dark patches were present; the pale patches fit in register with the shrunken ocular dominance columns of the deprived eye, which were labeled by autoradiography. Subsequent removal of one eye caused a striking cytochrome oxidase pattern to emerge in layer IVc that correlated precisely with the shrunken (deprived eye) and expanded (normal eye) ocular dominance columns. This correlation was shown by injecting one eye with [3H]proline. It has remained unsettled whether other forms of amblyopia are accompanied by shrinkage of ocular dominance columns. To address this issue, in an analogous clinical case, we examined the pattern of cytochrome oxidase activity in a human subject with a history of anisometropic amblyopia who suffered a lesion of one optic nerve shortly before death. The ocular dominance columns were normal in width, indicating that some forms of amblyopia occur without shrinkage of ocular dominance columns.

Amblyopia↗
PubMed2002

The history of research into the disorders of reading and accommodation in strabismic amblyopia.

During the past 150 years, research on amblyopia and nystagmus has developed in five different waves (W1-W5). Amblyopia was initially regarded to be enigmatic and believed to be related to eccentric fixation (W1, after 1850); later, it was ascribed to disorders in refraction or accommodation (W2, around 1900). After 1900 (W3), phylogenetic explanations appeared, and after 1945 (W4) concepts based on successful orthoptic practice came to the fore. Since 1965 (W5), research on amblyopia has been guided by modern insights into neuroanatomy and neurophysiology. In contrast to amblyopia, nystagmus has always been a well-defined symptomatic entity. Even though amblyopia and nystagmus are both symptoms of strabismus, their understanding has therefore developed along different paths. In juvenile strabismus, defects in binocularity lead to monolateral amblyopia, while defects in contour vision lead to bilateral nystagmus. In the present paper, these five waves of amblyopia research are described in more detail, with particular attention to the concepts of adaptation, visual fields, and sensory and motor functions as related to disorders in reading and accommodation.

Accommodation, Ocular↗
PubMed2005

Haphazard neural connections underlie the visual deficits of cats with strabismic or deprivation amblyopia.

Identification of the neural basis of the visual deficits experienced by humans with amblyopia, particularly when associated with strabismus (strabismic amblyopia), has proved to be difficult in part because of the inability to observe directly the neural changes at various levels of the human visual pathway. Much of our knowledge has necessarily been obtained on the basis of sophisticated psychophysical studies as well as from electrophysiological explorations on the visual pathways in animal models of amblyopia. This study combines these two approaches to the problem by employing similar psychophysical probes of performance on animal models of two forms of amblyopia (deprivation and strabismic) to those employed earlier on human amblyopes (Hess & Field, 1994, Vis. Res., 34, 13397-13406). The tests explore two competing explanations for the visual deficits, namely an evenly distributed loss of neural connections (undersampling) with the amblyopic eye as opposed to disordered connections with this eye (neural disarray). Unexpectedly, the results in animal models of deprivation amblyopia were not in accord with expectations based upon an even distribution of lost connections with the amblyopic eye. However, the results were similar to those observed in a strabismic amblyopic animal and to strabismic amblyopic humans. We suggest that deprivation amblyopia may be accompanied by an uneven loss of connections that results in effective neural disarray. By contrast, amblyopia associated with strabismus might arise from neural disarray of a different origin such as an alteration of intrinsic cortical connections.

Amblyopia↗
PubMed2004

Consequences of amblyopia on education, occupation, and long term vision loss.

AIMS: To describe the effect of amblyopia on education, occupation, and 5 year incident vision loss. METHODS: 3654 participants aged 49 years or older participated in the Blue Mountains Eye Study (BMES I, 1992-4) and 2335 (75.1% of survivors) were re-examined (BMES II, 1997-9). All participants underwent detailed eye examination. Amblyopia, defined as best corrected visual acuity of less than or equal to 6/9 and not attributable directly to any underlying structural abnormality of the eye or the visual pathway, was identified in 118 participants (3.2%) in BMES I, of whom 73 were re-examined in BMES II. Occupation and educational classifications used definitions of the Australian Bureau of Statistics. RESULTS: The mean age of people with amblyopia seen at baseline was 67.0 years. Amblyopia did not affect lifetime occupational class (p = 0.5), but fewer people completed higher university degrees (p = 0.05). In people with amblyopia, there was an increased risk of 5 year incident visual impairment in the better seeing eye worse than 6/12, relative risk (RR) 2.7, 95% confidence interval (CI) 1.6 to 4.6. One of 11 (9.1%) people with amblyopia showed significant improvement in visual acuity in the poorer seeing eye after a two line (10 logMAR letter) vision loss in the better seeing eye. CONCLUSION: This study further documents the longitudinal history of amblyopia using population based data.

Aged↗
PubMed1999

Preschool vision screening: negative predictive value for amblyopia.

BACKGROUND/AIMS: Single optotype tests of visual acuity are widely used for preschool vision screening in order to optimise cooperation with testing. These tests may, however, underestimate the visual acuity deficit in amblyopia because they lack visual crowding. This study assessed the resultant negative predictive value (NPV) for amblyopia. METHODS: Cohort study of 936 children in the Cambridge Health District selected by date of birth. The presence of amblyopia among children who had passed preschool vision screening was determined using Snellen line acuity as the reference test. Preschool vision screening was conducted at 3.5 years of age by community orthoptists. The screening assessment comprised Sheridan-Gardiner single optotype test of visual acuity (referral criterion 6/9 or worse in either eye), cover test, ocular movements, 20(Delta) prism test, and TNO stereotest. RESULTS: The overall NPV of preschool vision screening for amblyopia was 100% (95% CI 99.4% to 100%). Most children with amblyopia were detected by the Sheridan-Gardiner single optotype test of visual acuity, but the other screening tests were necessary to prevent any false negatives. In isolation, the Sheridan-Gardiner single optotype test of visual acuity has a NPV for amblyopia of only 99.6% (95% CI 98.7% to 99.9%). CONCLUSION: Preschool vision screening using a single optotype test of visual acuity does achieve a high NPV for amblyopia, but only under certain conditions. These comprise a low threshold for referral (6/9 or worse in either eye) and the inclusion of a cover test and tests of binocular function in the screening assessment.

Amblyopia↗