Improvement of visual function in an adult amblyope

Current Management of Childhood Amblyopia

Amblyopia is defined as the reduction of best-corrected visual acuity of one or both eyes caused by conditions that affect normal visual development. The basic strategy to treat amblyopia is to obtain a clear retinal image in each eye and correct ocular dominance through forced use of the amblyopic eye. Treatment modalities include correcting any underlying organic disease, prescribing appropriate optical correction, and providing occlusion/penalization therapy for the non-amblyopic eye. Given the success of amblyopia treatment declines with increasing age, the detection and management of amblyopia should begin as early as possible during the sensitive period for visual development. Proper management of amblyopia during childhood can reduce the overall prevalence and severity of visual loss. This study aims to provide an update for the management of childhood amblyopia to provide better visual outcomes.

Selective serotonin reuptake inhibitors may lead to improved cataract surgery outcomes in patients with amblyopia

Purpose

To evaluate the effects of selective serotonin reuptake inhibitor (SSRI)/serotonin norepinephrine reuptake inhibitor (SNRI) medications in combination with cataract surgery in treating amblyopia in adult patients.

Patients and methods

A retrospective chart review study was conducted on patients who had undergone cataract surgery at the Johns Hopkins Hospital Wilmer Eye Institute. Six inclusion criteria were used to assess patient eligibility: 1) >18 years of age, 2) diagnosis of amblyopia, 3) diagnosis of cataract and treatment with surgery, 4) electronic medical record contains pre-surgery and post-surgery visual acuity (VA) measurements, 5) electronic medical record contains information on whether the patient was ever prescribed a SSRI/SNRI and the treatment duration, and 6) interocular VA difference of two lines or more on Snellen chart prior to cataract surgery. From each record, preoperative VA, postoperative VA, date of surgery, date at which postoperative VA was measured, and age at surgery were collected.

Results

A total of 237 patients were included, with 38 of them being on SSRI/SNRI. The mean improvement in VA after surgery was not significantly greater in patients on SSRI/SNRI (SSRI/SNRI: −0.276 logMAR, control: −0.192 logMAR, p=0.15). Multivariable regression was subsequently performed and while holding all other variables constant, demonstrated a statistically significant improvement in VA in patients on SSRI/SNRI (95% CI: −0.194, −0.0116, p=0.03). The regression analysis further demonstrated that advanced age has an adverse effect on the change in post-op VA (CI: 3.34×10⁻³ logMAR, 9.77×10⁻³ logMAR, p<0.005). Worse baseline VA is associated with a greater improvement in post-op VA (95% CI: −0.659 logMAR, −0.463 logMAR, p<0.005) but adverse effect on the absolute post-op VA (95% CI: 0.341 logMAR, 0.544 logMAR, p<0.005).

Conclusion

This study suggests that patients with amblyopia undergoing cataract surgery may potentially have a greater visual improvement when treated with SSRI/SNRIs.

Binocular treatment in adult amblyopia is based on parvocellular or magnocellular pathway

INTRODUCTION

Amblyopia is speculated to be an untreatable disease in the patient, who is beyond the critical period of vision; however, currently, it is treatable in adults.

PURPOSE

This study aimed to elucidate whether the treatment is useful in both anisometropic amblyopia and strabismic amblyopia. In addition, the differences were detected between anisometropic amblyopia and strabismic amblyopia after the same perceptual treatment and whether the suppression in anisometropic amblyopia or strabismic amblyopia could be decreased before and after the treatment.

METHODS

A binocular perceptual learning was applied for the treatment, the suppression was measured, and the patients were followed up for 2 months after training. Anisometropic amblyopia and strabismic amblyopia groups were subjected to the assessment of stereo, visual acuity, contrast sensitivity, and suppression before and after the training.

RESULTS

After 6 weeks of "Diploma Gabor Orientation Coherence" training, in the anisometropic amblyopia group, the outcomes of visual acuity (t = 3.114, p = 0.026) and contrast sensitivity (t = 7.786, p = 0.001) were increased significantly. While in the strabismic amblyopia group, the outcomes of stereo (t = 2.987, p = 0.040) and contrast sensitivity (t = 3.638, p = 0.022) were increased significantly.

CONCLUSION

After Diploma Gabor Orientation Coherence training in the same frequency and in the same duration, the anisometropic amblyopia group got an improvement in visual acuity, but the strabismic amblyopia group got an improvement in stereo. As there are evidences to show that anisometropic amblyopia and strabismic amblyopia were injured in different pathways, we think the diverse results might come from the different pathway injury in anisometropic amblyopia and strabismic amblyopia.

Fluoxetine does not enhance the effect of perceptual learning on visual function in adults with amblyopia

Amblyopia is a common visual disorder that is treatable in childhood. However, therapies have limited efficacy in adult patients with amblyopia. Fluoxetine can reinstate early-life critical period-like neuronal plasticity and has been used to recover functional vision in adult rats with amblyopia. We conducted a Phase 2, randomized (fluoxetine vs. placebo), double-blind, multicenter clinical trial examined whether or not fluoxetine can improve visual acuity in amblyopic adults. This interventional trial included 42 participants diagnosed with moderate to severe amblyopia. Subjects were randomized to receive either 20 mg fluoxetine (n = 22) or placebo (n = 20). During the 10-week treatment period, all subjects performed daily computerized perceptual training and eye patching. At the primary endpoint, the mean treatment group difference in visual acuity improvement was only 0.027 logMAR units (95% CI: −0.057 to 0.110; p = 0.524). However, visual acuity had significantly improved from baseline to 10 weeks in both fluoxetine (−0.167 logMAR; 95% CI: −0.226 to −0.108; p < 0.001) and placebo (−0.194 logMAR; 95% CI: −0.254 to −0.133; p < 0.001) groups. While this study failed to provide evidence that fluoxetine enhances neuroplasticity, our data support other recent clinical studies suggesting that improvement of vision can be accomplished in adults with amblyopia.

Optical treatment of amblyopia in older children and adults is essential prior to enrolment in a clinical trial

PURPOSE

Optical treatment alone can improve visual acuity (VA) in children with amblyopia, thus clinical trials investigating additional amblyopia therapies (such as patching or videogames) for children require a preceding optical treatment phase. Emerging therapies for adult patients are entering clinical trials. It is unknown whether optical treatment is effective for adults with amblyopia and whether an optical correction phase is required for trials involving adults.

METHODS

We examined participants who underwent optical treatment in the Binocular Treatment for Amblyopia using Videogames (BRAVO) clinical trial (ANZCTR ID: ACTRN12613001004752). Participants were recruited in three age groups (7 to 12, 13 to 17, or ≥18 years), and had unilateral amblyopia due to anisometropia and/or strabismus, with amblyopic eye VA of 0.30-1.00 logMAR (6/12 to 6/60, 20/40 to 20/200). Corrective lenses were prescribed based on cycloplegic refraction to fully correct any anisometropia. VA was assessed using the electronic visual acuity testing algorithm (e-ETDRS) test and near stereoacuity was assessed using the Randot Preschool Test. Participants were assessed every four weeks up to 16 weeks, until either VA was stable or until amblyopic eye VA improved to better than 0.30 logMAR, rendering the participant ineligible for the trial.

RESULTS

Eighty participants (mean age 24.6 years, range 7.6-55.5 years) completed four to 16 weeks of optical treatment. A small but statistically significant mean improvement in amblyopic eye VA of 0.05 logMAR was observed (S.D. 0.08 logMAR; paired t-test p < 0.0001). Twenty-five participants (31%) improved by ≥1 logMAR line and of these, seven (9%) improved by ≥2 logMAR lines. Stereoacuity improved in 15 participants (19%). Visual improvements were not associated with age, presence of strabismus, or prior occlusion treatment. Two adult participants withdrew due to intolerance to anisometropic correction. Sixteen out of 80 participants (20%) achieved better than 0.30 logMAR VA in the amblyopic eye after optical treatment. Nine of these participants attended additional follow-up and four (44%) showed further VA improvements.

CONCLUSIONS

Improvements from optical treatment resulted in one-fifth of participants becoming ineligible for the main clinical trial. Studies investigating additional amblyopia therapies must include an appropriate optical treatment only phase and/or parallel treatment group regardless of patient age. Optical treatment of amblyopia in adult patients warrants further investigation.

Effectiveness of the addition of citicoline to patching in the treatment of amblyopia around visual maturity: a randomized controlled trial

Aim:

To study the effectiveness of the addition of citicoline to patching in the treatment of amblyopia in the age group of 4-13 years.

Materials and Methods:

A randomized controlled trial, which included patients who were randomly divided into two groups. Both the groups received patching therapy till plateau was achieved in phase 1 of the study. Then in phase 2, group I received citicoline plus patching and group II continued to receive only patching.

Outcome Measures:

Outcome was measured by the visual acuity in logMAR every month in phase 1 till plateau was achieved and then for 12 months in phase 2.

Results:

No significant difference was found in the mean visual acuities in these two groups in phase 1 till plateau was reached. In phase 2, for the initial four months, there was no significant difference in the visual acuities in these two groups, at the respective intervals. However, five months onward, up to 12 months, there was a significant difference in the visual acuities in these groups. The result was the same in younger patients (< seven years of age) as well as in older patients (> seven years of age). In phase 2, the mean proportional improvement in group I was significantly more than that in group II, at two months and onward, at the respective intervals.

Conclusion:

The improvement in visual acuity with citicoline plus patching was significantly more than that with patching alone, in one year of treatment.

Dichoptic training improves contrast sensitivity in adults with amblyopia

Dichoptic training is designed to promote binocular vision in patients with amblyopia. Initial studies have found that the training effects transfer to both binocular (stereopsis) and monocular (recognition acuity) visual functions. The aim of this study was to assess whether dichoptic training effects also transfer to contrast sensitivity (CS) in adults with amblyopia. We analyzed CS data from 30 adults who had taken part in one of two previous dichoptic training studies and assessed whether the changes in CS exceeded the 95% confidence intervals for change based on test-retest data from a separate group of observers with amblyopia. CS was measured using Gabor patches (0.5, 3 and 10cpd) before and after 10days of dichoptic training. Training was delivered using a dichoptic video game viewed through video goggles (n=15) or on an iPod touch equipped with a lenticular overlay screen (n=15). In the iPod touch study, training was combined with anodal transcranial direct current stimulation of the visual cortex. We found that dichoptic training significantly improved CS across all spatial frequencies tested for both groups. These results suggest that dichoptic training modifies the sensitivity of the neural systems that underpin monocular CS.

Global processing in amblyopia: a review

Amblyopia is a neurodevelopmental disorder of the visual system that is associated with disrupted binocular vision during early childhood. There is evidence that the effects of amblyopia extend beyond the primary visual cortex to regions of the dorsal and ventral extra-striate visual cortex involved in visual integration. Here, we review the current literature on global processing deficits in observers with either strabismic, anisometropic, or deprivation amblyopia. A range of global processing tasks have been used to investigate the extent of the cortical deficit in amblyopia including: global motion perception, global form perception, face perception, and biological motion. These tasks appear to be differentially affected by amblyopia. In general, observers with unilateral amblyopia appear to show deficits for local spatial processing and global tasks that require the segregation of signal from noise. In bilateral cases, the global processing deficits are exaggerated, and appear to extend to specialized perceptual systems such as those involved in face processing.

Laser in situ keratomileusis in adult patients with anisometropic amblyopia

AIM

To evaluate the increase in corrected distance visual acuity (CDVA) after laser in situ keratomileusis (LASIK) in adults with anisometropic amblyopia.

METHODS

The medical records of consecutive patients diagnosed with anisometropic amblyopia at the time of refractive evaluation who underwent LASIK were retrospectively reviewed. Patients with at least a two-line difference of visual acuity (VA) between the eyes with a spherical refractive error difference of at least 3.00 diopters (D) or an astigmatic difference of at least 2.00D were included. Patients with any other possible reason for amblyopia other than anisometropia or those who had undergone previous amblyopia treatment were excluded. Amblyopic eyes with myopia or myopic astigmatism were considered as group 1, hypermetropia or hypermetropic astigmatism constituted group 2, and mixed astigmatism patients comprised group 3. Uncorrected distance visual acuity (UDVA), subjective manifest refraction, and CDVA were analyzed at 1 week and 1 month, 3, and 6 months.

RESULTS

The study included 57 eyes of 57 patients. There were 33 eyes in group 1, 12 eyes in group 2, and 12 eyes in group 3. The preoperative mean values for spherical equivalent of subjective manifest refraction (SE) in groups 1, 2, and 3 were (-4.66±1.97)D, (4.40±1.00)D, and (0.15±1.05)D, respectively. Mean CDVA improved 0.1 log units (1 line LogMAR) at 6 months (P<0.05). Sixteen eyes (28%) exhibited an improvement in CDVA in week 1. Fourteen eyes (25%) experienced two or more lines of CDVA improvement at month 6. There were no statistically significant differences among the groups in terms of CDVA (P>0.05). Moreover, age, the amount of preoperative refractive error, and the levels of preoperative corrected and UDVA had no effect on postoperative CDVA improvement (P>0.05).

CONCLUSION

Correction of refractive errors with LASIK produced significant CDVA improvement in adult patients with anisometropic amblyopia and no previous amblyopia treatment.

Can perceptual learning be used to treat amblyopia beyond the critical period of visual development?

BACKGROUND

Amblyopia presents early in childhood and affects approximately 3% of western populations. The monocular visual acuity loss is conventionally treated during the 'critical periods' of visual development by occluding or penalising the fellow eye to encourage use of the amblyopic eye. Despite the measurable success of this approach in many children, substantial numbers of people still suffer with amblyopia later in life because either they were never diagnosed in childhood, did not respond to the original treatment, the amblyopia was only partially remediated, or their acuity loss returned after cessation of treatment.

PURPOSE

In this review, we consider whether the visual deficits of this largely overlooked amblyopic group are amenable to conventional and innovative therapeutic interventions later in life, well beyond the age at which treatment is thought to be effective.

RECENT FINDINGS

There is a considerable body of evidence that residual plasticity is present in the adult visual brain and this can be harnessed to improve function in adults with amblyopia. Perceptual training protocols have been developed to optimise visual gains in this clinical population. Results thus far are extremely encouraging; marked visual improvements have been demonstrated, the perceptual benefits transfer to new visual tasks and appear to be relatively enduring. The essential ingredients of perceptual training protocols are being incorporated into video game formats, facilitating home-based interventions.

SUMMARY

Many studies support perceptual training as a tool for improving vision in amblyopes beyond the critical period. Should this novel form of treatment stand up to the scrutiny of a randomised controlled trial, clinicians may need to re-evaluate their therapeutic approach to adults with amblyopia.

Eye patching as a treatment for amblyopia in children aged 10-16 years

PURPOSE

To investigate the effects of full-time patching regimen on the treatment of amblyopia in children aged 10-16 years.

METHODS

Forty-seven patients with a mean age of 12.09 ± 1.65 years were included in this study. All of the patients received eye patching for the entire day, 6 days a week, during the first 3 months. The patients who achieved visual acuity of 0.00 logMAR at the third month were provided with additional patching treatment (4-6 h/day). On the other hand, the patients who showed no change in their visual acuity or an increase of less than 0.00 logMAR at the third month had 3 more months of eye patching for the entire day, 6 days a week.

RESULTS

Prior to treatment, the best mean visual acuity of the amblyopic eyes was 0.48 ± 0.25 (range 1.00-0.15) logMAR. After follow-up, the visual acuity of the amblyopic eyes was 0.20 ± 0.22 (range 1.00-0.00) logMAR. Thus, visual acuity in the amblyopic eyes improved by 0.2 log unit or more in 38 of 47 patients (81%).

CONCLUSIONS

The present results show that patching in older children with amblyopia improves visual acuity with no serious complications. The use of patching in children to improve amblyopia seems promising.

Amblyopia: a mini review of the literature

Amblyopia is a form of cerebral visual impairment in the absence of an organic cause. It is considered to derive from the degradation of the retinal image associated with abnormal visual experience during the developmental period of the visual system in infancy and early childhood. Amblyopia is a significant cause of unilateral visual deficit in childhood and is still considered as one of the most common causes of persistent unilateral visual impairment in adulthood. The following review aims at presenting the contemporary literature regarding the prevalence, the aetiology, the neural correlates, the period of critical development, the treatment, the prognosis and the disability associated with this visual deficit.

Mechanisms underlying perceptual learning of contrast detection in adults with anisometropic amblyopia

What underlies contrast sensitivity improvements in adults with anisometropic amblyopia following perceptual learning in grating contrast detection? In this paper, we adopted the external noise approach (Z.-L. Lu & B. A. Dosher, 1998) to identify the mechanisms underlying perceptual learning in adults with anisometropic amblyopia. By measuring contrast thresholds in a range of external noise conditions at two performance levels (79.3% and 70.7%), we found that a mixture of internal additive noise reduction and external noise exclusion underlay training induced contrast sensitivity improvements in adults with anisometropic amblyopia. In comparison, normal adults exhibited only small amount of external noise exclusion under the same training conditions. The results suggest that neural plasticity may be more robust in amblyopia, lending further support of perceptual learning as a potential treatment for adult amblyopia.

Perceptual learning as a potential treatment for amblyopia: a mini-review

Amblyopia is a developmental abnormality that results from physiological alterations in the visual cortex and impairs form vision. It is a consequence of abnormal binocular visual experience during the "sensitive period" early in life. While amblyopia can often be reversed when treated early, conventional treatment is generally not undertaken in older children and adults. A number of studies over the last twelve years or so suggest that Perceptual Learning (PL) may provide an important new method for treating amblyopia. The aim of this mini-review is to provide a critical review and "meta-analysis" of perceptual learning in adults and children with amblyopia, with a view to extracting principles that might make PL more effective and efficient. Specifically we evaluate: 1). What factors influence the outcome of perceptual learning? 2). Specificity and generalization - two sides of the coin. 3). Do the improvements last? 4). How does PL improve visual function? 5). Should PL be part of the treatment armamentarium? A review of the extant studies makes it clear that practicing a visual task results in a long-lasting improvement in performance in an amblyopic eye. The improvement is generally strongest for the trained eye, task, stimulus and orientation, but appears to have a broader spatial frequency bandwidth than in normal vision. Importantly, practicing on a variety of different tasks and stimuli seems to transfer to improved visual acuity. Perceptual learning operates via a reduction of internal neural noise and/or through more efficient use of the stimulus information by retuning the weighting of the information. The success of PL raises the question of whether it should become a standard part of the armamentarium for the clinical treatment of amblyopia, and suggests several important principles for effective perceptual learning in amblyopia.

Visual Processing in Amblyopia: Human Studies

Within the last five years, there have been a number of exciting new advances in our knowledge and understanding of amblyopia. This article reviews recent psychophysical studies of naturally occurring amblyopia in humans. These studies suggest that: 1) There are significant differences in the patterns of visual loss among the clinically defined categories of amblyopes. A key factor in determining the nature of the loss is the presence or absence of binocularity. 2) Dysfunction within the amblyopic visual system first occurs in area V1, and the effects of amblyopia may be amplified downstream. 3) There appears to be substantial neural plasticity in the amblyopic brain beyond the "critical period."

Vision 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 (The Cochrane Library Issue 3, 2008), MEDLINE (January 1950 to August 2008) and EMBASE (January 1947 to August 2008). The electronic databases were last searched on 15 August 2008. 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.

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.

Improving the performance of the amblyopic visual system

Experience-dependent plasticity is closely linked with the development of sensory function; however, there is also growing evidence for plasticity in the adult visual system. This review re-examines the notion of a sensitive period for the treatment of amblyopia in the light of recent experimental and clinical evidence for neural plasticity. One recently proposed method for improving the effectiveness and efficiency of treatment that has received considerable attention is 'perceptual learning'. Specifically, both children and adults with amblyopia can improve their perceptual performance through extensive practice on a challenging visual task. The results suggest that perceptual learning may be effective in improving a range of visual performance and, importantly, the improvements may transfer to visual acuity. Recent studies have sought to explore the limits and time course of perceptual learning as an adjunct to occlusion and to investigate the neural mechanisms underlying the visual improvement. These findings, along with the results of new clinical trials, suggest that it might be time to reconsider our notions about neural plasticity in amblyopia.

Perceptual plasticity in damaged adult visual systems

Plasticity appears to be a ubiquitous property of nervous systems, regardless of developmental stage or complexity. In the visual system of higher mammals, perceptual plasticity has been intensively studied, both during development and in adulthood. However, the last few years have seen some significant controversies arise about the existence and properties of visual plasticity after permanent damage to the adult visual system. The study of perceptual plasticity in damaged, adult visual systems is of interest for several reasons. First, it is an important means of unmasking the relative contribution of individual visual areas to visual learning, adaptation and priming, among other plastic phenomena. Second, it can provide knowledge that is essential for the development of effective therapies to rehabilitate the increasing number of people who suffer the functional consequences of damage at different levels of their visual hierarchy. This review summarizes the available evidence on the subject and proposes that visual plasticity may be just as ubiquitous after damage as it is in the intact visual system. However, damage may alter visual plasticity in ways that are still being defined.

Efficacy of neural vision therapy to enhance contrast sensitivity function and visual acuity in low myopia

Purpose

To evaluate the efficacy and safety of neural vision enhancement technology (NVC, NeuroVision, Inc.) to improve visual acuity and contrast sensitivity function in eyes with low myopia.

Setting

Singapore Eye Research Institute, Singapore, Singapore.

Methods

This noncomparative interventional case series comprised 20 Asian adults between 19 and 53 years of age with low myopia (cycloplegic spherical equivalence [SE] from −0.5 diopter [D] to −1.5 D in the worst eye; astigmatism not exceeding 0.5 D in either eye; uncorrected visual acuity [UCVA] ≤0.7 logMAR) who had NVC treatment. The main outcome measures were distance UCVA, uncorrected contrast sensitivity, refraction, accommodative amplitude, and safety.

Results

All eyes had improvement in UCVA and contrast sensitivity. After treatment, the mean distance UCVA improved by a mean of 2.1 lines on the Early Treatment Diabetic Retinopathy Study logMAR chart. The mean contrast sensitivity improved over a range of spatial frequencies on sine-wave contrast sensitivity chart testing (1.5 to 18 cycles per degree). Follow-up data up to 12 months posttreatment showed that the gains were retained. Treatment did not alter refraction (mean spherical equivalent) or accommodative amplitudes. No adverse effects were reported.

Conclusion

Preliminary evidence suggests NVC treatment is safe and improves UCVA and uncorrected contrast sensitivity in adult patients with low myopia.

Optical Analysis of Visual Improvement after Correction of Anisometropic Amblyopia with a Phakic Intraocular Lens in Adult Patients

PURPOSE

To analyze possible reasons for an increase in visual acuity observed in myopic patients with anisometropic amblyopia after implantation of a phakic intraocular lens (PIOL) using a theoretical eye model.

DESIGN

Retrospective case series.

PARTICIPANTS

Fifty-nine eyes of 48 patients with anisometropic amblyopia implanted with an angle-supported PIOL.

METHODS

Inclusion criteria were anisometropia of at least 3 diopters (D) and a best spectacle-corrected visual acuity (BSCVA) of 0.7 or less in the best eye. Follow-up was performed at 1, 3, 6, and 12 months and then annually for up to 10 years. The theoretical analysis of mechanisms to explain the visual improvement was performed using a theoretical eye, based on the Kooijman model, in which the measured values of radii and thickness of the different surfaces were substituted. The magnification and spot size were calculated by a ray tracing process.

MAIN OUTCOME MEASURES

Uncorrected visual acuity, improvement in best spectacle-corrected visual acuity, and spherical equivalent.

RESULTS

Mean gain in visual acuity was 3 lines (range, 0-7 lines). Fifty-four eyes (91.5%) gained at least 1 line of visual acuity, whereas no eyes lost lines of vision. The change in BSCVA did not correlate with preoperative BSCVA (Pearson coefficient, r = 0.19) or with the degree of anisometropia (Pearson coefficient, r = 0.23). The calculations using a Kooijman eye model corrected with spectacles and with a PIOL accounted for the full increase in visual acuity in terms of the magnification (increased by a factor of 1.2) and the spot size (reduced by a factor of 2).

CONCLUSIONS

After implantation of a PIOL, the visual acuity of myopic patients with anisometropic amblyopia showed a significant increase. This increase was explained using a theoretical eye model not only in terms of magnification but also including changes in aberrations. An evident role of neuroprocessing in this visual improvement was not identified.

Amblyopie fonctionnelle : évaluation en IRM fonctionnelle de la réponse corticale visuelle après traitement

PURPOSE

Functional MRI evaluation of the cortical response in treated amblyopic patients.

MATERIAL AND METHODS

Clinical and functional MRI exploration of ten patients, seven men and three women aged from 21 to 59 years, with strabismus management during childhood. Functional evaluations were performed on a 1.5 Tesla MR device, with four monocular functional sessions, two stimulations per eye. Alternating rest and active phases displayed still and flickering black and white checkerboards with spatial and temporal frequencies of 1 degree/8Hz and 15'/4Hz. Anatomical realignment and statistical analysis were performed using SPM99 (Statistical Parametric Mapping) to compare the four sessions in individuals.

RESULTS AND DISCUSSION

In patients presenting a visual acuity of the amblyopic eye less than 0.7, stimulation of this eye induced lower response in V1, V3, and V5 in comparison with the contralateral eye stimulation. Unexpectedly, in patients recovering normal or subnormal acuity, the amblyopic eye gave comparable or enhanced response in these areas. Additional response was found in the secondary visual cortex, the cuneus, the lingual gyrus, and in parietal, frontal, and orbitofrontal areas. These results suggest a variation in cortical response depending on the efficacy of the treatment. Recovered amblyopic eye, even with acuity less than the contralateral eye, may induce a reinforced cortical sensitivity to visual stimulus. Secondary visual areas may contribute to an attentional process in image perception and analysis. Cortical plasticity may be observed several years after amblyopia treatment.

CONCLUSION

Our study substantiates the importance of an effective and early treatment of functional amblyopia, inducing cortical plasticity with reinforced attention and sensitivity to visual perception.

Visual improvement in high myopic amblyopic adult eyes following phakic anterior chamber intraocular lens implantation

PURPOSE

To evaluate the efficacy and safety of angle-supported phakic anterior chamber intraocular lenses in amblyopic adult eyes with very high myopia.

METHODS

We evaluated 12 eyes in nine patients with very high myopic amblyopia who received angle-supported phakic intraocular lenses (Phakic 6H) and followed them for more than six months. Uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), and complications were evaluated. A satisfaction score was rated by patients using a 5-point (1-5) numeric scale.

RESULTS

The mean age of patients was 37.3 +/- 9.4 years, ranging from 29 to 59 years old. The preoperative mean refraction (spherical equivalent, SE) was -20.10 +/- 5.41 diopters (D). The postoperative mean refraction (SE) was -1.75 +/- 0.76 D at six months. The postoperative BCVA improved an average 3.92 +/- 1.24 lines over preoperative values, and mean endothelial cell loss was 8.9% at six months. Development of cataracts, glaucoma, and pupil abnormalities were not demonstrated in any case during the study. The patients were all very satisfied, as the average satisfaction score was 4.3.

CONCLUSIONS

This study indicates that angle-supported phakic anterior chamber intraocular lens implantation may be an effective surgical alternative for the correction of amblyopic adult eyes with very high myopia. However, long-term evaluation is necessary to assess possible complications and long-term safety.

Visual deprivation modifies both presynaptic glutamate release and the composition of perisynaptic/extrasynaptic NMDA receptors in adult visual cortex

Use-dependent modifications of synapses have been well described in the developing visual cortex, but the ability for experience to modify synapses in the adult visual cortex is poorly understood. We found that 10 d of late-onset visual deprivation modifies both presynaptic and postsynaptic elements at the layer 4-->2/3 connection in the visual cortex of adult mice, and these changes differ from those observed in juveniles. Although visual deprivation in juvenile mice modifies the subunit composition and increases the current duration of synaptic NMDA receptors (NMDARs), no such effect is observed at synapses between layer 4 and layer 2/3 pyramidal neurons in adult mice. Surprisingly, visual deprivation in adult mice enhances the temporal summation of NMDAR-mediated currents induced by bursts of high-frequency stimulation. The enhanced temporal summation of NMDAR-mediated currents in deprived cortex could not be explained by a reduction in the rate of synaptic depression, because our data indicate that late-onset visual deprivation actually increases the rate of synaptic depression. Biochemical and electrophysiological evidence instead suggest that the enhanced temporal summation in adult mice could be accounted for by a change in the molecular composition of NMDARs at perisynaptic/extrasynaptic sites. Our data demonstrate that the experience-dependent modifications observed in the adult visual cortex are different from those observed during development. These differences may help to explain the unique consequences of sensory deprivation on plasticity in the developing versus mature cortex.

Intermediate spatial frequency letter contrast sensitivity: its relation to visual resolution before and during amblyopia treatment

We examined the loss of letter contrast sensitivity (LCS) measured using the Pelli-Robson chart, and the extent to which any such loss was modulated by spectacle wear and occlusion therapy in children participating in an amblyopia treatment trial. Their initial mean interocular difference in logMAR acuity was approximately three times that of their LCS (0.45 vs 0.14 log units). Log LCS was weakly though significantly correlated with logMAR visual acuity (VA) for all VAs better than 0.90 (r = -0.19, 95% CI: -0.28 to -0.10) whereas for all VAs of 0.90 or poorer, log LCS was markedly and significantly correlated with VA (r = -0.72, 95% CI: -0.83 to -0.53). LCS in those children with a > or =0.1 log unit interocular difference on this test improved commensurately with VA during treatment. We conjecture that the spatial visual loss in all but the most severe amblyopes occurs in an area of resolution and contrast space that lies beyond that sampled by the Pelli-Robson chart.

Repeated measurements of contrast sensitivity reveal limits to visual plasticity after early binocular deprivation in humans

Contrast sensitivity improves in visually normal children until 7 years of age and is impaired in children who experienced early visual deprivation from bilateral congenital cataracts. Here, we investigated whether the deficits after early visual deprivation change during childhood by retesting the contrast sensitivity of seven patients treated for bilateral congenital cataract who had been first tested before 7.5 years of age, and of two patients first tested after 11 years of age. For the younger group, contrast sensitivity at low spatial frequencies improved after 1- and 2-year intervals, while their sensitivity at mid and high spatial frequencies did not change. There was no systematic change in the two older patients. The results indicate that early visual input sets up the neural substrate for later improvement in contrast sensitivity at mid and high spatial frequencies. However, there is sufficient plasticity during middle childhood to allow some recovery at low spatial frequencies. The results shed new light on the role of early visual experience and the nature of developmental plasticity.

Can We Utilize Photorefractive Keratectomy to Improve Visual Acuity in Adult Amblyopic Eyes?

PURPOSE

To report the results of photorefractive keratectomy (PRK) in adult amblyopic patients.

DESIGN

Noncomparative case series.

PARTICIPANTS

Thirty-eight amblyopic eyes of 36 adult patients who had undergone PRK ranging from -14.63 diopters (D) to +3.75 D (mean, -6.38+/-4.10) were analyzed.

METHODS

Preoperative and postoperative (1, 3, and 6 months) refractions and measurements of the best spectacle-corrected visual acuity (BSCVA) were reviewed. Statistical evaluation was performed using a paired Student's t test.

MAIN OUTCOME MEASURES

Best-corrected visual acuity before and after PRK.

RESULTS

Before PRK, BSCVA ranged between 0.2 and 0.7 lines (mean, 0.60+/-0.13). One month after PRK, BSCVA ranged between 0.2 and 1.2 lines (mean, 0.77+/-0.24), with a significant difference (P = 3x10(-5)). Three months after PRK, BSCVA ranged between 0.15 and 1.15 lines (mean, 0.84+/-0.23), with a significant difference (P = 5x10(-7)). Six months after PRK, BSCVA ranged between 0.25 and 1.3 lines (mean, 0.88+/-0.25), with a significant difference (P = 8x10(-8)).

CONCLUSIONS

Our study does not imply that refractive surgery should or may be performed in young children but, rather, that adults wishing to undergo refractive surgery may undertake such procedures despite an amblyopic eye thought to be refractory to visual rehabilitation by conventional methods, such as spectacles and contact lenses.

Perceptual learning improves contrast sensitivity and visual acuity in adults with anisometropic amblyopia

To evaluate the effects of perceptual learning on contrast-sensitivity function and visual acuity in adult observers with amblyopia, 23 anisometropic amblyopes with a mean age of 19.3 years were recruited and divided into three groups. Subjects in Group I were trained in grating detection in the amblyopic eye near pre-training cut-off spatial frequency. Group II received a training regimen of repeated contrast-sensitivity function measurements in the amblyopic eye. Group III received no training. We found that training substantially improved visual acuity and contrast-sensitivity functions in the amblyopic eyes of all the observers in Groups I and II, although no significant performance improvement was observed in Group III. For observers in Group I, performance improvements in the amblyopic eyes were broadly tuned in spatial frequency and generalized to the fellow eyes. The latter result was not found in Group II. In a few cases tested, improvements in visual acuity following training showed about 90% retention for at least 1 year. We concluded that the visual system of adult amblyopes might still retain substantial plasticity. Perceptual learning shows potential as a clinical tool for treating child and adult amblyopia.

Perceptual learning in adults with amblyopia: a reevaluation of critical periods in human vision

Critical periods for experience-dependent plasticity are ubiquitous. The idea that experience-dependent plasticity is closely linked with the development of sensory function is still widely held; however, there also is growing evidence for plasticity in the adult nervous system. This article reviews the notion of a critical period for the treatment of amblyopia in light of recent experimental and clinical evidence for neural plasticity. Specifically, adults with amblyopia can improve their perceptual performance via extensive practice on a challenging visual task, and this improvement may transfer to improved visual acuity. Amblyopes achieve this improvement via the mechanisms that have been shown to explain perceptual learning in the normal visual system. It is hypothesized that these same mechanisms account for at least some of the improvement that occurs in the treatment of amblyopia.

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.

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.

Amblyopia characterization, treatment, and prophylaxis

Amblyopia has a 1.6-3.6% prevalence, higher in the medically underserved. It is more complex than simply visual acuity loss and the better eye has sub-clinical deficits. Functional limitations appear more extensive and loss of vision in the better eye of amblyopes more prevalent than previously thought. Amblyopia screening and treatment are efficacious, but cost-effectiveness concerns remain. Refractive correction alone may successfully treat anisometropic amblyopia and it, minimal occlusion, and/or catecholamine treatment can provide initial vision improvement that may improve compliance with subsequent long-duration treatment. Atropine penalization appears as effective as occlusion for moderate amblyopia, with limited-day penalization as effective as full-time. Cytidin-5'-diphosphocholine may hold promise as a medical treatment. Interpretation of much of the amblyopia literature is made difficult by: inaccurate visual acuity measurement at initial visit, lack of adequate refractive correction prior to and during treatment, and lack of long-term follow-up results. Successful treatment can be achieved in at most 63-83% of patients. Treatment outcome is a function of initial visual acuity and type of amblyopia, and a reciprocal product of treatment efficacy, duration, and compliance. Age at treatment onset is not predictive of outcome in many studies but detection under versus over 2-3 years of age may be. Multiple screenings prior to that age, and prompt treatment, reduce prevalence. Would a single early cycloplegic photoscreening be as, or more, successful at detection or prediction than the multiple screenings, and more cost-effective? Penalization and occlusion have minimal incidence of reverse amblyopia and/or side-effects, no significant influence on emmetropization, and no consistent effect on sign or size of post-treatment changes in strabismic deviation. There may be a physiologic basis for better age-indifferent outcome than tapped by current treatment methodologies. Infant refractive correction substantially reduces accommodative esotropia and amblyopia incidence without interference with emmetropization. Compensatory prism, alone or post-operatively, and/or minus lens treatment, and/or wide-field fusional amplitude training, may reduce risk of early onset esotropia. Multivariate screening using continuous-scale measurements may be more effective than traditional single-test dichotomous pass/fail measures. Pigmentation may be one parameter because Caucasians are at higher risk for esotropia than non-whites.

Improvement in best corrected visual acuity in amblyopic adult eyes after laser in situ keratomileusis

PURPOSE

To evaluate improvement in best spectacle-corrected visual acuity (BSCVA) after laser in situ keratomileusis (LASIK) in adult patients with amblyopia.

SETTING

Refractive Eye Surgery Center, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.

METHODS

The charts of consecutive patients with a diagnosis of amblyopia at the time of refractive evaluation who had LASIK were reviewed retrospectively. The preoperative and postoperative uncorrected visual acuity (UCVA) and BSCVA were analyzed.

RESULTS

Twenty-one eyes of 19 patients were identified as having amblyopia and LASIK surgery. Eight patients (42.1%) were diagnosed with amblyopia only, 6 patients (31.6%) had anisometropic amblyopia, 4 patients (21.1%) had strabismic amblyopia, and 1 patient (5.2%) had anisometropic and strabismic amblyopia. Eleven eyes (52.4%) had myopic astigmatism, 7 eyes (33.3%) were hyperopic, and 3 eyes (14.3%) had mixed astigmatism. Seven eyes (33.3 %) experienced more than a 1-line improvement in postoperative UCVA compared with the preoperative BSCVA. Nine eyes (42.8%) experienced more than a 1-line improvement in postoperative BSCVA compared with the preoperative BSCVA. The BSCVA was unchanged in 11 eyes (52.4%) and was worse by 2 lines in 1 eye (4.8%).

CONCLUSION

After LASIK, the postoperative BSCVA was better than preoperatively in 42.8% of eyes with a history of amblyopia and the postoperative UCVA was better than the preoperative BSCVA in 33.3%.

Laser in situ Keratomileusis Improves Visual Acuity in Some Adult Eyes With Amblyopia

PURPOSE

To report the results of laser in situ keratomileusis (LASIK) in a series of adult patients with amblyopia.

METHODS

A retrospective noncomparative review was performed on patients with amblyopia who underwent LASIK for correction of ametropia, using the Summit Krumeich Barraquer microkeratome and the Nidek EC-5000 excimer laser. Data were collected on uncorrected visual acuity, best spectacle-corrected visual acuity, manifest refraction, anterior segment evaluation, intraocular pressure, corneal topography, and dilated fundus examination (preoperative and postoperatively on day 1, months 2 and 6).

RESULTS

Eight eyes of seven patients were included, with a mean patient age of 30 +/- 10 years (range 21 to 49 yr). Mean preoperative spherical equivalent refraction was -4.70 D (range -12.62 to +4.71 D) and the best spectacle-corrected visual acuity varied from 20/32 to 20/80. At 2 months after LASIK, mean spherical equivalent refraction was -0.37 +/- 0.60 D (range -1.37 to + 0.60 D), uncorrected visual acuity ranged between 20/20 to 20/30, and a mean gain of 3 Snellen lines (range 2 to 4 lines) was observed. All patients reported significant subjective improvement in their perception of vision. The visual acuity and subjective improvement were maintained throughout 6 months postoperatively.

CONCLUSIONS

LASIK with the Nidek EC-5000 laser for correction of ametropia in adult amblyopic eyes provided encouraging results for visual acuity improvement beyond correction of the refractive error.

A survey of pediatric visual assessment by optometrists in New South Wales

BACKGROUND

The importance of early vision care in the prevention and treatment of amblyopia is clear from an abundance of literature on visual development. Optometrists possess the necessary skills to detect and manage amblyogenic factors and thus have an important role to play in paediatric visual assessment and management. The present study investigates the role that optometrists in New South Wales are taking in paediatric vision care and the methods and strategies used in this role.

METHODS

Questionnaires were sent to 400 optometrists practising in New South Wales; 179 completed questionnaires were returned.

RESULTS AND DISCUSSION

Our findings reveal a number of associations between practice characteristics (such as location) and the management of paediatric patients. In general, practitioners in rural locations, in full-time practice or self-employed were more likely to treat patients and less likely to refer them elsewhere than those in city locations, in part-time practice or employed by others. In addition, our findings suggest the possibility of a changing pattern of collaboration between optometrists and ophthalmologists in the management of paediatric patients.

Possible role of corticosteroids in nervous system plasticity: improvement in amblyopia after optic neuritis in the fellow eye treated with steroids

OBJECTIVE

Amblyopia consists of reduced visual function in the absence of organic disease, caused by deficient visual stimulation, most commonly due to squint or refractive error. Amblyopia is thought to be reversible up until the age of approximately 8 years (critical period) and is usually treated with occlusion of the fellow eye. There is recent evidence for visual system plasticity extending beyond the critical period, supported by reports of improvement in visual acuity in the amblyopic eye after loss of vision in the contralateral eye. This suggests that the adult visual system exhibits sufficient plasticity to allow such improvement. We describe here improvement in visual acuity in three amblyopic patients after they received high-dose intravenous glucocorticoids for optic neuritis in the contralateral eye.

METHODS

Clinical and neurological evaluation added.

RESULTS

In all cases, the improvement was sustained, even after the recovery from the optic neuritis.

CONCLUSIONS

Because steroids affect neural plasticity, we hypothesize that they facilitate and enhance visual improvement in amblyopia, a quality that may be tested in future controlled trials.

The present and potential impact of research on animal models for clinical treatment of stimulus deprivation amblyopia

OBJECTIVE

With the benefit of hindsight based on an additional 20 years of research, we review a question posed originally by Marg of whether animal models for stimulus deprivation amblyopia in children are valid or useful for clinical application.

METHOD

Following a review of relevant research on animal models, the human clinical literature on treatment of stimulus deprivation amblyopia has been reviewed with respect to past and current impact of animal research on clinical treatment. In addition, we speculate on the potential future clinical impact of animal work on developmental plasticity in the visual cortex that is directed towards an understanding of its underlying molecular basis.

CONCLUSIONS

Animal research that has begun to define the timing, nature and sites of critical periods in the central visual pathways with greater precision than was known 20 years ago has had a demonstrable impact on clinical practice. In turn, these changes in clinical practice have produced far better outcomes than prior to 1980, for both the acuity of the amblyopic eye and for binocular functions such as stereopsis.

Effect of late surgery for acquired esotropia on visual evoked potential

PURPOSE

To asses the effect of strabismus surgery on visual evoked potential (VEP) amplitude after age 5 years in children with acquired esotropia.

METHODS

Visual evoked potentials to binocular and monocular pattern reversal stimulation were recorded in 10 children aged 5 to 6 years before and 3 months after surgical correction of their esotropia. Visual function (fusion) was tested by synoptophore after strabismus surgery. Electrophysiological and clinical data were correlated following surgical intervention.

RESULTS

A significant increase in pattern VEP amplitudes was noted following strabismus surgery. Visual evoked potential changes were most prominent on binocular stimulation. Binocular fusion showed similarly significant improvement after intervention. Postoperative VEP data, however, were not consistently correlated with functional improvement.

CONCLUSION

Surgical intervention in esotropia, even if performed years beyond the end of the classical critical period, can have a strong effect on binocular VEPs and a beneficial effect on the development of binocular fusion.

Amblyopia: is visual loss permanent?

AIM

To ascertain whether recovery of visual function in amblyopic eyes is likely to occur when the fellow eye is lost as a result of age related macular degeneration.

METHODS

The records of 465 patients with an established diagnosis of age related macular degeneration who had attended a specialist macular clinic between 1990 and 1998 were scrutinised. A full clinical examination and standardised refraction had been carried out in 189 of these cases on a minimum of two occasions. Cases were looked for where an improvement of one or more lines of either distance or near acuity was recorded in the eye unaffected by macular disease. In each one of these cases the improvement in visual acuity could not be attributed to treatment of other existing pathology.

RESULTS

12 such cases were detected. In nine of these the eye showing improvement of acuity had a history of amblyopia. The mean improvement in distance and near acuity in amblyopic eyes by 12 months was 3.3 and 1.9 lines logMAR respectively. The improvement in acuity generally occurred between 1 and 12 months from baseline and remained stable over the period of follow up.

CONCLUSIONS

Older people with a history of amblyopia who develop visual loss in the previously normal eye can experience recovery of visual function in the amblyopic eye over a period of time. This recovery in visual function occurs in the wake of visual loss in the fellow eye and the improvement appears to be sustained.