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PubMed2003

Amblyopia.

Amblyopia is a serious medical condition affecting tens of millions of individuals around the world. For the most part it is correctable, assuming that it is promptly recognized and vigorously treated. Amblyopia may result from form deprivation, anisometropia, or strabismus in infants and young children. Basic research in animal models has shown that the major pathologic changes in amblyopia occur in the visual cortex of the brain. The mainstay of treatment remains patching, although penalization has a role to play in the management of moderate degrees of amblyopia. Better methods for early identification of patients with amblyopia are being developed, along with newer novel methods of treatment.

Amblyopia↗
PubMed2002

A cost-utility analysis of therapy for amblyopia.

OBJECTIVE: Evaluation of the incremental cost-effectiveness of therapy for amblyopia. DESIGN: Cost-utility reference-case analysis. METHODS: A cost-utility analysis was performed from a third-party insurer perspective by using decision analysis, evidence-based data from the literature, and patient preference-based time trade-off utility values. DATABASE: Patient-derived time trade-off ocular utility values and the American Academy of Ophthalmology Preferred Practice Pattern guidelines for the treatment of amblyopia. INTERVENTION: Treatment of childhood amblyopia using medical and surgical therapies per the American Academy of Ophthalmology Preferred Practice Pattern. MAIN OUTCOME MEASURE: Dollars (year 2001 nominal U.S. dollars) expended per quality-adjusted life-year ($/QALY) gained. RESULTS: Treatment for amblyopia resulted in a $/QALY gained of $2281 with a discount rate of 3% for costs and outcomes. Sensitivity analysis, varying costs and utility values by 10%, resulted in a $/QALY gained range from $2053 to $2509. CONCLUSIONS: When compared with other interventions in health care, therapy for amblyopia seems to be highly cost-effective. This information is increasingly important for health care policy makers.

Amblyopia↗
PubMed2004

[Importance of occlusion therapy for amblyopia in partial unilateral congenital cataracts that are discovered late].

PURPOSE: The aim of this study is to investigate the importance of occlusion therapy for amblyopia in patients with partial unilateral congenital cataracts that were discovered after 24 months of age. MATERIAL AND METHODS: A retrospective study was conducted on 11 patients, each of whom underwent a clinical examination including a cycloplegic refraction with atropine. The average age when the cataract was diagnosed was 35 months. The average distance visual acuity was 6/78 and the average near visual acuity was 35/175. Occlusion therapy using adhesive patches was started after refractive error correction. In two cases, observance was mediocre. RESULTS: Ametropia was found in every patient, with anisometropia in nine patients (alpha < 0.02). This anisometropia included an astigmatism that was always greater on the side with the cataract (alpha < 0.001), averaging 2.7 diopters. After occlusion therapy for amblyopia, the average visual acuity significantly improved to 6/22 in distance vision (alpha < 0.02) and 35/45 in near vision (alpha < 0.01). The average follow-up period was 28 months (5-60 months). CONCLUSION: Amblyopia is related to lens opacities as well as frequently associated anisometropia. Functional improvement is greater in near vision than in distance vision. With occlusion therapy for amblyopia, accommodation is preserved. This factor is of utmost importance as near vision is preferential in young children. This study provides an opportunity to recall the importance of refraction and occlusion therapy for amblyopia, which must be systematically attempted in cases of partial unilateral congenital cataracts before considering a surgical procedure.

Amblyopia↗
PubMed1997

Unifying concepts in mechanism of amblyopia.

Most of the evidence of formation of amblyopia is derived traditionally from electrophysiological studies. Recently, there have been many discoveries from genetics, histopathology, biochemistry, immunology and interventional studies. On the basis of evidence gathered in the last five years, the various types of amblyopia (strabismic and non-strabismic amblyopia) can be seen not only as disturbance of the development of the visual system at different points but as basically different pathologic processes. It is postulated here that strabismic amblyopia is initiated as a maladaptive differentiation in the ocular dominance columns, whereas the non-strabismic amblyopia may be initiated from the ganglion cell population of the amblyopic eye. The total clinical picture is confusing because of secondary changes in other parts of the central nervous system. The manifested features can be due to a slower, more enduring type of change (pooling, loss and re-wiring of the neurones) as well as a more transient, adaptive type of response (such as suppression of diplopia). Neurotransmitter replacement has a potential therapeutic application.

Amblyopia↗
PubMed2004

Laser-assisted subepithelial keratectomy and photorefractive keratectomy versus conventional treatment of myopic anisometropic amblyopia in children.

PURPOSE: To evaluate the visual and refractive results of photorefractive keratectomy (PRK) and laser-assisted subepithelial keratectomy (LASEK) for high myopic anisometropia with amblyopia and contact lens (CL) intolerance in children. SETTING: Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic. METHODS: This prospective comparative study comprised 27 children with high myopic anisometropia and amblyopia. The mean age of the children was 5.4 years (range 4 to 7 years). Multizonal PRK (13 eyes) or LASEK (14 eyes) was performed in the more myopic eye under general anesthesia using the Nidek EC-5000 excimer laser. After surgery, the dominant eye was patched. The postoperative visual and refractive outcomes were analyzed; all children had a 2-year follow-up. The 27 children (Group A) were compared with a control group of 30 children (mean age 5.1 years) (Group B) in whom myopic anisometropia and amblyopia were treated conventionally by CLs and patching the dominant eye. The visual acuity and binocular vision outcomes in both groups were analyzed and compared. RESULTS: In Group A, the mean spherical equivalent refraction was -8.25 diopters (D) +/- 2.37 (SD) (range -6.00 to -11.25 D) preoperatively and -1.61 +/- 0.73 D (range +0.50 to -2.25 D) postoperatively. The mean best corrected visual acuity (BCVA) was 0.23 +/- 0.21 preoperatively and 0.78 +/- 0.19 at 2 years. In Group B, the mean BCVA was 0.16 +/- 0.19 at the start of CL correction and amblyopia therapy and improved to 0.42 +/- 0.15 after 2 years. The mean BCVA at the final examination was significantly better in Group A (P<.05). Binocular vision improvement expressed by the proportion of patients who gained fusion and stereopsis was better overall in Group A (78%) than in Group B (33%) (P<.05). There were no complications postoperatively. CONCLUSIONS: Photorefractive keratectomy and LASEK were effective and safe methods for correcting high myopic anisometropia and improving amblyopia in children aged 4 to 7 years who were CL intolerant. Visual acuity and binocular vision outcomes were better in children who received permanent surgical correction of anisometropia than in those who were treated conventionally by CLs.

Amblyopia↗
PubMedDate not supplied

Pattern of ocular dominance columns in human striate cortex in strabismic amblyopia.

Previous experiments in animals have shown that early unilateral eyelid suture, a model of amblyopia induced by cataract, causes shrinkage of ocular dominance columns serving the deprived eye in the striate cortex. It is unknown whether the ocular dominance columns are affected in amblyopia produced by strabismus. We examined specimens of striate cortex obtained postmortem from a 79-year-old woman with a history of amblyopia in her left eye (20/800) since age 2 from accommodative esotropia. Four years prior to her death, she suffered an ischemic infarct of the left optic disc. This injury to the left optic disc made it possible to label the ocular dominance columns using cytochrome oxidase histochemistry. The pattern of ocular dominance columns was reconstructed throughout most of the right striate cortex. No shrinkage of columns was found. In the left cortex only half the column mosaic was labelled, because the patient had some residual vision in the temporal retina of her left eye. The columns within the labelled portion of the overall mosaic appeared normal. These findings indicate that shrinkage of ocular dominance columns does not occur in humans with amblyopia caused by accommodative esotropia. The ocular dominance columns are probably no longer susceptible to shrinkage at the age when most children with this condition begin to develop amblyopia.

Aged↗
PubMedDate not supplied

Pattern of ocular dominance columns and cytochrome oxidase activity in a macaque monkey with naturally occurring anisometropic amblyopia.

Unilateral eyelid suture, a model for amblyopia induced by congenital cataract, produces shrinkage of the deprived eye's ocular dominance columns in the striate cortex. Loss of geniculocortical projections are thought to account for the poor vision in the amblyopic eye. It is uncertain whether ocular dominance columns become shrunken in other forms of amblyopia. We examined the striate cortex in a pigtailed macaque with natural anisometropia discovered at age 5 months. Amblyopia in the left eye was documented at 1 year by behavioral testing. At age 6 years, the left eye was injected with [3H]proline and the striate cortex was processed for autoradiography and cytochrome oxidase (CO). The ocular dominance columns in layer IVc labelled with [3H]proline were normal. CO staining showed a novel pattern of thin dark bands in layer IV. These bands occupied the core zones at the center of the ocular dominance columns. Their appearance resulted from relative loss of CO activity along the borders of the ocular dominance columns, regions specialized for binocular processing. These findings indicate that not all forms of amblyopia are accompanied by shrinkage of ocular dominance columns. The unusual pattern of CO staining in layer IVc reflected a subtle alteration in metabolic activity which may have resulted from impairment of binocular function in anisometropic amblyopia.

Amblyopia↗
PubMed1991

Microtropia versus bifoveal fixation in anisometropic amblyopia.

Microtropia with identity is a unique condition in which amblyopes have parafoveal eccentric fixation in the amblyopic eye in either monocular or binocular viewing, plus a macular scotoma. The condition has previously been described in anisometropic amblyopia. The records of 55 consecutively presenting anisometropic amblyopes were scrutinised and the cases divided into microtropes or non-microtropes (bifoveal fixators). The features of the two groups were then compared to identify factors associated with microtropia and to determine whether microtropes or bifoveal patients responded better to amblyopia therapy. Results show that 45% of anisometropic amblyopes have microtropia rather than bifoveal fixation. There appears to be no association between the microtropic phenomenon and age, depth of amblyopia or amount of anisometropia. Bifoveal patients may respond better to amblyopia therapy although the difference between groups was not great. The sensitive period during which amblyopia may be treated is the same for each group.

Age Factors↗
PubMed2002

The assessment and management of strabismus and amblyopia: a national audit.

AIMS: To determine what systems are in place within ophthalmic services for the assessment and management of children suspected of having amblyopia and strabismus. To find out what methods are used for the assessment of these children. METHODS: A questionnaire-based study auditing 288 orthoptic departments in the UK. RESULTS: Responses were received from 75% orthoptic departments. Most hospitals employ more than one system for the assessment of strabismus and amblyopia, which is generally dependent on route of referral. These include 'orthoptic assessment without refraction' (66%), 'combined orthoptist and ophthalmologist assessment' (66%), while 22% have an entirely orthoptist/optometric system. Ophthalmologists are involved in the initial assessment in 145 units (67%), whereas some units involve an ophthalmologist only if response to treatment is poor (15%), or if surgery is required (6%). Fourteen per cent of units reviewed all children, with discharge criteria being based on normal visual acuity (52%), accurate visual acuity (39%) and a normal orthoptic assessment (42%). Seventy-six per cent of units review some children, commonly as a result of family history (55%), parental concern (43%), poor co-operation (30%) and young age (72%). In the absence of squint or amblyopia children are discharged at the first visit, in only 8% of units. There is considerable variation in the tests used to assess visual acuity. LogMAR-based tests (eg EDTRS) are not routinely used in 75% of units. CONCLUSION: Different systems exist for the assessment and management of squint and amblyopia across the country. While much of this variation is to be expected given their possible aetiologies, some could be reduced to produce a more cohesive service. There is also considerable scope for rationalising the tests used to screen infants and children for amblyopia and strabismus.

Amblyopia↗
PubMed2006

Modified virtual reality technology for treatment of amblyopia.

PURPOSE: The conventional patching/occlusion treatment for amblyopia sometimes gives disappointing results for a number of reasons: it is unpopular, prolonged, frequently resulting in poor or noncompliance, and also disrupts fusion. The aim of this research was to develop a novel virtual-reality (VR)-based display system that facilitates the treatment of amblyopia with both eyes stimulated simultaneously. METHODS: We have adopted a multidisciplinary approach, combining VR expertise with a team of ophthalmologists and orthoptists to develop the Interactive Binocular Treatment (I-BiT) system. This system incorporates adapted VR technology and specially written software providing interactive 2D and 3D games and videos to the patient via a stereo (binocular) display, and a control screen for the clinician. RESULTS: We developed a prototype research system designed for treatment of amblyopia in children. CONCLUSIONS: The result is a novel way to treat amblyopia, which allows binocular treatment. It is interactive, and as it is partially software based, can be adapted to suit the age/ability, and needs of the patient. This means that the treatment can be made captivating and enjoyable. Further research is on-going to determine the efficacy of this new modality in the treatment of amblyopia.

Amblyopia↗
PubMed1981

[Diagnosis and differential diagnosis of hysteric amblyopia using psychophysical and electro-ophthalmological examination methods (author's transl)].

In three patients with psychogenic amblyopia the computerized visual field, the ERG, the flash light (H-EP) and pattern reversal stimulated (M-EP) cortical potentials were recorded. Differential diagnosis between psychogenic amblyopia on the one hand, and functional amblyopia and organic lesions of the retrobulbar visual pathways on the other was shown to be possible. In the cases with organic retrobulbar lesions of visual pathways, visual field defects and pathologic H-EP's and M-EP's were found. In functional amblyopia only the M-EP responses are diminished in amplitude. In psychogenic amblyopia only the computerized visual field shows pathologic changes.

Adolescent↗
PubMed2001

The Amblyopia Treatment Index.

OBJECTIVE: To develop a questionnaire to assess the acceptability of amblyopia treatment and its effect on the child and family. METHODS: A 20-item parental survey was developed and pilot tested on 64 subjects, aged 3 to 6 years, participating in the Amblyopia Treatment Study, a randomized trial comparing patching and atropine as treatments for moderate amblyopia. The survey was administered after 4 weeks of treatment. A descriptive item analysis and an internal consistency reliability analysis were performed. RESULTS: Nineteen of the 20 items demonstrated adequate variability as evidenced by the frequency distributions for item responses. Only 4 (<1%) of 1280 possible item responses were missing, one each by 4 different respondents. Factor analysis identified 3 treatment-related factors--"adverse effects," "compliance," and "social stigma"--among 11 of the 20 items. The internal-consistency reliability alpha for the 5-item adverse effects subscale was 0.82, the 4-item compliance subscale alpha was 0.81, and the 2-item social stigma subscale alpha was 0.84. CONCLUSIONS: The Amblyopia Treatment Index appears to be a useful instrument for assessing the impact of amblyopia treatment in 3- to 6-year-old children.

Amblyopia↗
PubMed2002

Functional magnetic resonance imaging as a tool for investigating amblyopia in the human visual cortex: a pilot study.

PURPOSE: This study investigates interocular differences in the level and extent of cortical activation in amblyopic and normal subjects. SUBJECTS AND METHODS: Blood oxygenation level dependent functional magnetic resonance imaging (FMRI) was performed at 1.5 T. A total of 5 subjects with amblyopia and 6 control subjectswere recruited. Visual stimuli included a homogeneous field flickering at 8 Hz and vertical sinusoidal gratings with spatial frequencies of 0.5, 1, and 2 cycles per degree of visual angle (counterphased at 8 Hz). Baseline images were taken in darkness. Stimuli were presented monocularly and binocularly. Data analysis was constrained to the occipital cortex, including striate and extrastriate areas. An absolute percent difference measure defined interocular differences in terms of total area, average level of activation, and a pooled activation parameter. RESULTS: Subjects with amblyopia exhibited a significantly larger (P <.05) interocular activation difference compared to controls. The level of activation driven by monocular stimulation of the amblyopic eye was reduced by 8.25% +/- 1.3% relative to the dominant eye. Controls showed an interocular difference in level of activation of 4.82% +/- 0.74%. The total area of activation driven by the amblyopic eye was reduced by 34.86% +/- 6.25% relative to the dominant eye. Controls showed an interocular difference in total area of activation of 20.80% +/- 3.67%. Subjects with amblyopia also manifested significantly greater (P <.05) cortical area and level of activation differences between the binocular and monocular states; the dominant eye response differed less from the binocular response than did the amblyopic eye response. CONCLUSION: FMRI is sensitive to amblyopia-related deficits in the human occipital cortex and, therefore, has potential as a tool for basic amblyopia research.

Adolescent↗
PubMed2005

Location coding by the human visual system: multiple topological adaptations in a case of strabismic amblyopia.

Amblyopia, a major cause of vision loss, is a developmental disorder of visual perception commonly associated with strabismus (squint). Although defined by a reduction in visual acuity, severe distortions of perceived visual location are common in strabismic amblyopia. These distortions can help us understand the cortical coding of visual location and its development in normal vision, as well as in amblyopia. The history of retinotopic mapping in the visual cortex highlights the potential impact of amblyopia. Theories of amblyopia include topological disarray of receptors in primary visual cortex, undersampling from the amblyopic eye compared with normal eyes, and the presence of anomalous retinal correspondence or multiple cortical representations of the strabismic fovea. We examined the distortions in a strabismic amblyope, using a pop-out localization task, in which normal observers made errors dependent on the visual context of the stimulus. The localization errors of the strabismic amblyope were abnormal. We found that none of the available theories could fully explain this one patient's localization performance. Instead, the observed behavior suggests that multiple adaptations of the underlying cortical topology are possible simultaneously in different parts of the visual field.

Adult↗
PubMed1980

An unexpected role for normal accommodative vergence in strabismus and amblyopia.

Accommodative vergence was measured using the Müller experimental paradigm in which target movement along the line of sight of the viewing eye results in large movement of the fellow (covered) eye. Our paper demonstrates an unexpected predominance of accommodative vergence over disparity vergence in patients with constant strabismus amblyopia, intermittent strabismus, and amblyopia without strabismus. Comparison of accommodative vergence responses in these patients with responses from normal subjects using symmetrical and asymmetrical targets under binocular and monocular conditions established the normal character of the patients' accommodative vergence and the absence of disparity vergence in most of them. The intermittent absence of disparity vergence in certain of our patients--some with surgically corrected strabismus, some with moderate amblyopia, and some with amblyopia treated with orthoptics--raises questions of clinical and neurophysiological interest. Preliminary results on the effects of amblyopia on accommodative responses are also presented.

Accommodation, Ocular↗
PubMed1982

Prentice-Memorial Lecture: Is the animal model for stimulus deprivation amblyopia in children valid or useful?

The animal models are not, strictly speaking, valid for clinical application to children, primarily because of the large differences in the duration of the critical or sensitive period. However, they do provide a useful conceptual framework to follow, especially while determining the waxing and waning of the amblyopia in each eye by preferential looking or visual evoked potential acuity methods. These methods allow us to detect or determine the degree of amblyopia and guide the treatment or prevention of stimulus deprivation amblyopia in each child by direct measurement. The reciprocal effect of amblyopia found by Thomas, Mohindra and Held in infants by the preferential looking method and confirmed and extended in age by our group with the visual evoked potential acuity method could have been predicted by the animal modelers from the cross-suturing experiments. It appears that more harm than good may be done by patching infants for the treatment of amblyopia without measuring the acuity of each eye to avoid the significant loss of connections to the patched eye and to both eyes (binocular units).

Amblyopia↗
PubMed1997

Detection, prevention, and rehabilitation of amblyopia.

The necessity of visual preschool screening for reducing the prevalence of amblyopia is widely accepted. The beneficial results of large-scale screening programs conducted in Scandinavia are reported. Screening monocular visual acuity at 3.5 to 4 years of age appears to be an excellent basis for detecting and treating amblyopia and an acceptable compromise between the pitfalls encountered in screening younger children and the cost-to-benefit ratio. In this respect, several preschoolers' visual acuity charts have been evaluated. New recently developed small-target random stereotests and binocular suppression tests have also been developed with the aim of correcting the many false negatives (anisometropic amblyopia or bilateral high ametropia) induced by the usual stereotests. Longitudinal studies demonstrate that correction of high refractive errors decreases the risk of amblyopia and does not impede emmetropization. The validity of various photoscreening and videoscreening procedures for detecting refractive errors in infants prior to the onset of strabismus or amblyopia, as well as alternatives to conventional occlusion therapy, is discussed.

Amblyopia↗
PubMed2004

Amblyopia treatment studies.

PURPOSE OF REVIEW: Amblyopia continues to be a major cause of vision loss in children. Several different treatment modalities exist. Research in the field of amblyopia has been very active over the past few years, and clinical practice patterns are changing. RECENT FINDINGS: Atropine has been found to be effective in the treatment of amblyopia. Less intense patching regimens have been found to be effective as well. Many other aspects of amblyopia therapy are being investigated. SUMMARY: Herein are current reviews of the major clinical amblyopia studies. Various treatment options are reviewed, and controversies in the field are discussed.

Amblyopia↗