Pattern reversal visual evoked potentials following early treatment of unilateral, congenital cataract

Sensory experience during early sensitive periods shapes cross-modal temporal biases

Typical human perception features stable biases such as perceiving visual events as later than synchronous auditory events. The origin of such perceptual biases is unknown. To investigate the role of early sensory experience, we tested whether a congenital, transient loss of pattern vision, caused by bilateral dense cataracts, has sustained effects on audio-visual and tactile-visual temporal biases and resolution. Participants judged the temporal order of successively presented, spatially separated events within and across modalities. Individuals with reversed congenital cataracts showed a bias towards perceiving visual stimuli as occurring earlier than auditory (Expt. 1) and tactile (Expt. 2) stimuli. This finding stood in stark contrast to normally sighted controls and sight-recovery individuals who had developed cataracts later in childhood: both groups exhibited the typical bias of perceiving vision as delayed compared to audition. These findings provide strong evidence that cross-modal temporal biases depend on sensory experience during an early sensitive period.

VEP estimation of visual acuity: a systematic review

Purpose

Visual evoked potentials (VEPs) can be used to measure visual resolution via a spatial frequency (SF) limit as an objective estimate of visual acuity. The aim of this systematic review is to collate descriptions of the VEP SF limit in humans, healthy and disordered, and to assess how accurately and precisely VEP SF limits reflect visual acuity.

Methods

The protocol methodology followed the PRISMA statement. Multiple databases were searched using “VEP” and “acuity” and associated terms, plus hand search: titles, abstracts or full text were reviewed for eligibility. Data extracted included VEP SF limits, stimulus protocols, VEP recording and analysis techniques and correspondence with behavioural acuity for normally sighted healthy adults, typically developing infants and children, healthy adults with artificially degraded vision and patients with ophthalmic or neurological conditions.

Results

A total of 155 studies are included. Commonly used stimulus, recording and analysis techniques are summarised. Average healthy adult VEP SF limits vary from 15 to 40 cpd, depend on stimulus, recording and analysis techniques and are often, but not always, poorer than behavioural acuity measured either psychophysically with an identical stimulus or with a clinical acuity test. The difference between VEP SF limit and behavioural acuity is variable and strongly dependent on the VEP stimulus and choice of acuity test. VEP SF limits mature rapidly, from 1.5 to 9 cpd by the end of the first month of life to 12–20 cpd by 8–12 months, with slower improvement to 20–40 cpd by 3–5 years. VEP SF limits are much better than behavioural thresholds in the youngest, typically developing infants. This difference lessens with age and reaches equivalence between 1 and 2 years; from around 3–5 years, behavioural acuity is better than the VEP SF limit, as for adults. Healthy, artificially blurred adults had slightly better behavioural acuity than VEP SF limits across a wide range of acuities, while adults with heterogeneous ophthalmic or neurological pathologies causing reduced acuity showed a much wider and less consistent relationship. For refractive error, ocular media opacity or pathology primarily affecting the retina, VEP SF limits and behavioural acuity had a fairly consistent relationship across a wide range of acuity. This relationship was much less consistent or close for primarily macular, optic nerve or neurological conditions such as amblyopia. VEP SF limits were almost always normal in patients with non-organic visual acuity loss.

Conclusions

The VEP SF limit has great utility as an objective acuity estimator, especially in pre-verbal children or patients of any age with motor or learning impairments which prevent reliable measurement of behavioural acuity. Its diagnostic power depends heavily on adequate, age-stratified, reference data, age-stratified empirical calibration with behavioural acuity, and interpretation in the light of other electrophysiological and clinical findings. Future developments could encompass faster, more objective and robust techniques such as real-time, adaptive control.

Registration

International prospective register of systematic reviews PROSPERO (https://www.crd.york.ac.uk/PROSPERO/), registration number CRD42018085666.

Occlusion for stimulus deprivation amblyopia

BACKGROUND

Stimulus deprivation amblyopia (SDA) develops due to an obstruction to the passage of light secondary to a condition such as cataract. The obstruction prevents formation of a clear image on the retina. SDA can be resistant to treatment, leading to poor visual prognosis. SDA probably constitutes less than 3% of all amblyopia cases, although precise estimates of prevalence are unknown. In high-income countries, most people present under the age of one year; in low- to middle-income countries, people are likely to be older at the time of presentation. The mainstay of treatment is correction of the obstruction (e.g., removal of the cataract) and then occlusion of the better-seeing eye, but regimens vary, can be difficult to execute, and traditionally are believed to lead to disappointing results.

OBJECTIVES

To evaluate the effectiveness of occlusion therapy for SDA in an attempt to establish realistic treatment outcomes and to examine evidence of any dose-response effect and assess the effect of the duration, severity, and causative factor on the size and direction of the treatment effect.

SEARCH METHODS

We searched CENTRAL (2018, Issue 12), which contains the Cochrane Eyes and Vision Trials Register; Ovid MEDLINE; Embase.com; and five other databases. We used no date or language restrictions in the electronic searches. We last searched the databases on 12 December 2018.

SELECTION CRITERIA

We planned to include randomized controlled trials (RCTs) and controlled clinical trials of participants with unilateral SDA with visual acuity worse than 0.2 LogMAR or equivalent. We specified no restrictions for inclusion based upon age, gender, ethnicity, comorbidities, medication use, or the number of participants.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We identified no trials that met the inclusion criteria specified in the protocol for this review.

AUTHORS' CONCLUSIONS

We found no evidence from RCTs or quasi-randomized trials on the effectiveness of any treatment for SDA. RCTs are needed in order to evaluate the safety and effectiveness of occlusion, duration of treatment, level of vision that can be realistically achieved, effects of age at onset and magnitude of visual defect, optimum occlusion regimen, and factors associated with satisfactory and unsatisfactory outcomes with the use of various interventions for SDA.

Impairments of Visual Function and Ocular Structure in Patients With Unilateral Posterior Lens Opacity

PURPOSE

We investigate visual function impairment and ocular structure in patients with unilateral posterior lens opacity, a type of congenital cataract (CC) in our novel CC category system.

METHODS

We studied patients aged 3 to 15 years who were diagnosed with unilateral posterior CC. Best corrected visual acuity (BCVA) and visual evoked potentials (VEP) were examined. Corneal astigmatism (CA), mean keratometry, central corneal thickness, anterior chamber depth (ACD), and axial length were measured by Pentacam and IOL-Master. Variations between two eyes were compared by paired t-tests.

RESULTS

Among the 25 patients involved, BCVAs (logMAR) of cataractous and contralateral healthy eyes were 0.8 ± 0.4 (range, 0.1-1.7) and 0.1 ± 0.1 (range, -0.1 to 0.4). Compared to contralateral healthy eyes, larger CA (1.8 ± 1.2 vs. 0.9 ± 0.4 diopters [D], P = 0.002) and deeper ACD (3.7 ± 0.3 vs. 3.5 ± 0.4 mm, P = 0.009) were found in cataractous eyes. No significant positive or negative linear relationship was found between BCVA and parameters of VEP. Peak time of P100 of pattern VEP-60' in cataractous eyes was longer than that in contralateral healthy eyes (114.9 ± 18.8 vs. 105.0 ± 12.4 ms, P = 0.013). Amplitudes of P100 of patterns VEP-60' and -15' in cataractous eyes were smaller than those in contralateral healthy eyes (PVEP-60', 15.2 ± 5.3 vs. 19.9 ± 10.4 μV, P = 0.023; PVEP-15', 10.4 ± 7.0 vs. 22.1 ± 11.9 μV, P = 0.012).

CONCLUSIONS

Impaired visual function and ocular structure were detected in patients with posterior lens opacities.

TRANSLATIONAL RELEVANCE

This study provides evidence-based clinical recommendations for unilateral posterior CC patients with controversial treatment options.

Fractal Dimension Analysis of Transient Visual Evoked Potentials: Optimisation and Applications

PURPOSE

The visual evoked potential (VEP) provides a time series signal response to an external visual stimulus at the location of the visual cortex. The major VEP signal components, peak latency and amplitude, may be affected by disease processes. Additionally, the VEP contains fine detailed and non-periodic structure, of presently unclear relevance to normal function, which may be quantified using the fractal dimension. The purpose of this study is to provide a systematic investigation of the key parameters in the measurement of the fractal dimension of VEPs, to develop an optimal analysis protocol for application.

METHODS

VEP time series were mathematically transformed using delay time, τ, and embedding dimension, m, parameters. The fractal dimension of the transformed data was obtained from a scaling analysis based on straight line fits to the numbers of pairs of points with separation less than r versus log(r) in the transformed space. Optimal τ, m, and scaling analysis were obtained by comparing the consistency of results using different sampling frequencies. The optimised method was then piloted on samples of normal and abnormal VEPs.

RESULTS

Consistent fractal dimension estimates were obtained using τ = 4 ms, designating the fractal dimension = D2 of the time series based on embedding dimension m = 7 (for 3606 Hz and 5000 Hz), m = 6 (for 1803 Hz) and m = 5 (for 1000Hz), and estimating D2 for each embedding dimension as the steepest slope of the linear scaling region in the plot of log(C(r)) vs log(r) provided the scaling region occurred within the middle third of the plot. Piloting revealed that fractal dimensions were higher from the sampled abnormal than normal achromatic VEPs in adults (p = 0.02). Variances of fractal dimension were higher from the abnormal than normal chromatic VEPs in children (p = 0.01).

CONCLUSIONS

A useful analysis protocol to assess the fractal dimension of transformed VEPs has been developed.

Pediatric cataract: challenges and future directions

Cataract is a significant cause of visual disability in the pediatric population worldwide and can significantly impact the neurobiological development of a child. Early diagnosis and prompt surgical intervention is critical to prevent irreversible amblyopia. Thorough ocular evaluation, including the onset, duration, and morphology of a cataract, is essential to determine the timing for surgical intervention. Detailed assessment of the general health of the child, preferably in conjunction with a pediatrician, is helpful to rule out any associated systemic condition. Although pediatric cataracts have a diverse etiology, with the majority being idiopathic, genetic counseling and molecular testing should be undertaken with the help of a genetic counselor and/or geneticist in cases of hereditary cataracts. Advancement in surgical techniques and methods of optical rehabilitation has substantially improved the functional and anatomic outcomes of pediatric cataract surgeries in recent years. However, the phenomenon of refractive growth and the process of emmetropization have continued to puzzle pediatric ophthalmologists and highlight the need for future prospective studies. Posterior capsule opacification and secondary glaucoma are still the major postoperative complications necessitating long-term surveillance in children undergoing cataract surgery early in life. Successful management of pediatric cataracts depends on individualized care and experienced teamwork. We reviewed the etiology, preoperative evaluation including biometry, choice of intraocular lens, surgical techniques, and recent developments in the field of childhood cataract.

Occlusion for stimulus deprivation amblyopia

BACKGROUND

Stimulus deprivation amblyopia (SDA) develops due to an obstruction to the passage of light secondary to a condition such as cataract. The obstruction prevents formation of a clear image on the retina. SDA can be resistant to treatment, leading to poor visual prognosis. SDA probably constitutes less than 3% of all amblyopia cases, although precise estimates of prevalence are unknown. In developed countries, most patients present under the age of one year; in less developed parts of the world patients are likely to be older at the time of presentation. The mainstay of treatment is removal of the cataract and then occlusion of the better-seeing eye, but regimens vary, can be difficult to execute, and traditionally are believed to lead to disappointing results.

OBJECTIVES

Our objective was to evaluate the effectiveness of occlusion therapy for SDA in an attempt to establish realistic treatment outcomes. Where data were available, we also planned to examine evidence of any dose response effect and to assess the effect of the duration, severity, and causative factor on the size and direction of the treatment effect.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2013, Issue 9), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to October 2013), EMBASE (January 1980 to October 2013), the Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to October 2013), PubMed (January 1946 to October 2013), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com ), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 28 October 2013.

SELECTION CRITERIA

We planned to include randomized and quasi-randomized controlled trials of participants with unilateral SDA with visual acuity worse than 0.2 LogMAR or equivalent. We did not specify any restrictions for inclusion based upon age, gender, ethnicity, co-morbidities, medication use, or the number of participants.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study abstracts identified by the electronic searches.

MAIN RESULTS

We did not identify any trials that met the inclusion criteria specified in the protocol for this review.

AUTHORS' CONCLUSIONS

We found no evidence on the effectiveness of any treatment for SDA. Future randomized controlled trials are needed in order to evaluate the safety and effectiveness of occlusion, duration of treatment, level of vision that can be realistically achieved, effects of age at onset and magnitude of visual defect, optimum occlusion regimen, and factors associated with satisfactory and unsatisfactory outcomes with the use of various interventions for SDA.

Changes in interocular axial length after pediatric cataract surgery

PURPOSE

To explore the hypothesis that preoperative interocular axial length difference changes after pediatric cataract intraocular lens implantation surgery to meet the measurement of the fellow eye.

METHODS

Retrospective chart review. Eyes with traumatic and secondary cataract, lens subluxation, or postoperative glaucoma were excluded. In bilateral cataract cases, only right eye data were included. In addition, eyes were included only if axial length data for both eyes were available before surgery and at follow-up equal to or greater than the age at surgery.

RESULTS

Forty-seven eyes fit the inclusion criteria. Average age at surgery and follow-up was 2.2 +/- 2.2 and 5.6 +/- 2.9 years, respectively. Three groups were formed based on the preoperative interocular axial length difference: < -0.2, group 1; >or= -0.2, and <or=0.2, group 2; >0.2, group 3. Average age at surgery between these three groups was not significantly different (p = 0.82), nor was age at follow-up between the groups (p = 0.66). The change in interocular axial length difference (postoperative interocular axial length difference minus preoperative interocular axial length difference) was significant between the three groups (0.3, 0.2, -0.4 mm, respectively; p = 0.02). The average rate of axial length growth was significantly different between three groups (3.7, 2.4, 2.5 mm, respectively; p = 0.03).

CONCLUSIONS

Eyes with a shorter axial length than the fellow eye showed postoperative rate of axial growth that exceeded the growth rate of eyes with a longer interocular axial length. These growth rates resulted in a postoperative trend of intraocular axial length difference toward zero.

Interventions for stimulus deprivation amblyopia

BACKGROUND

Stimulus deprivation amblyopia (SDA) develops due to an obstruction to the clear passage of light, preventing clear formation of an image on the retina for example, cataract, ptosis (droopy eyelid). It is particularly severe and can be resistant to treatment and the visual prognosis is often poor. Stimulus deprivation amblyopia is rare and precise estimates of prevalence difficult to come by; it probably constitutes less than 3% of all cases of amblyopia. In developed countries most patients present under the age of one; in less developed parts of the world presentation is likely to be significantly later than this.The mainstay of treatment is patching of the better-seeing eye but regimes vary, treatment is difficult to execute and results are often disappointing.

OBJECTIVES

The objectives of this review were to evaluate the effectiveness of occlusion treatment for SDA, determine the optimum treatment regime and factors that may affect outcome.

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 (2006, Issue 1), MEDLINE (1996 to April 2006), EMBASE (1980 to April 2006) and LILACS (Latin American and Caribbean Literature on Health Sciences) (to November 2004). There were no date or language restrictions.

SELECTION CRITERIA

We aimed to include randomised and quasi-randomised controlled trials of subjects with unilateral SDA defined as worse than 0.2 LogMAR or equivalent. There were no restrictions with respect to age, gender, ethnicity, co-morbidities, medication use, and the number of participants.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study abstracts identified by the electronic searches.

MAIN RESULTS

No trials were identified that met the inclusion criteria.

AUTHORS' CONCLUSIONS

It is not possible to conclude how effective treatment for SDA is or which treatment regime produces the best results. There is a need for further study in this area.

Estimating chromatic contrast thresholds from the transient visual evoked potential

Chromatic contrast thresholds may be estimated from transient VEPs by measuring the peak-to-peak amplitude at a range of stimulus levels followed by extrapolation to zero amplitude. However, there have been reports of failure of this technique when applied to the transient chromatic VEP due to variability of amplitude, difficulties with component identification and poor correlation of amplitude with stimulus level. The aim of our study was to compare methods of transient VEP chromatic contrast threshold estimation in terms of success rate and comparison with psychophysical threshold. We found each of the methods we investigated to have a high success rate, and in most cases VEP and psychophysical thresholds did not differ significantly.

Multiple sensitive periods in human visual development: Evidence from visually deprived children

Psychophysical studies of children deprived of early visual experience by dense cataracts indicate that there are multiple sensitive periods during which experience can influence visual development. We note three sensitive periods within acuity, each with different developmental time courses: the period of visually-driven normal development, the sensitive period for damage, and the sensitive period for recovery. Moreover, there are different sensitive periods for different aspects of vision. Relative to the period of visually driven normal development, the sensitive period for damage is surprisingly long for acuity, peripheral vision, and asymmetry of optokinetic nystagmus, but surprisingly short for global motion. A comparison of results from unilaterally versus bilaterally deprived children provides insights into the complex nature of interactions between the eyes during normal visual development.

Which ocular and neurologic conditions cause disparate results in visual acuity scores recorded with visually evoked potential and teller acuity cards?

PURPOSE

We investigated whether disparity between visually evoked potential (VEP) acuity scores and Teller Acuity Card (TAC) scores varied according to presence of ocular or neurologic conditions.

METHODS

Charts from 175 children (mean age, 34.8 months; range, 3 to 158 months) referred for visual acuity testing were examined. All children had been tested with pattern-alternation VEP and TAC and had undergone a complete eye examination. VEP and TAC acuity scores were relative to age-expected acuity scores for each acuity test. The absence and degree of macular abnormality, retinal abnormality, optic nerve hypoplasia, optic nerve atrophy, cortical visual impairment, developmental delay, cerebral palsy, seizures, and nystagmus were noted. Analysis of variance models were used to determine whether differences between VEP and TAC scores varied according to the presence of specific deficits. Logistic regression analysis determined whether degree of specific deficits was associated with a greater chance of inconsistency between VEP and TAC scores (>0.3 log unit difference).

RESULTS

Inconsistent scores were found in 48% of children. Developmental delay was associated with relatively poorer TAC than VEP score, and the chance of inconsistency increased with severity of developmental delay.

CONCLUSIONS

Diagnosis-dependent variability exists between TAC and VEP scores. Therefore knowledge of the clinical picture is necessary in interpretation of VEP and TAC scores. It is not clear which test is more useful when a disparity exists, either from this or previous studies. When visual acuity is assessed longitudinally in a given child, then consistency in method for acuity assessment is important.

Visual acuity in unilateral cataract

BACKGROUND

Patching the fellow eye in infancy is a well recognised therapy to encourage visual development in the lensectomised eye in cases of unilateral congenital cataract. The possibility of iatrogenic deficits of the fellow eye was investigated by comparing the vision of these patients with untreated unilateral patients and binocularly normal controls.

METHODS

Sweep visual evoked potentials (VEPs) offer a rapid and objective method for estimating grating acuity. Sweep VEPs were used to estimate acuity in 12 children aged between 4 and 16 years who had had a congenital cataract removed in the first 13 weeks of life. The acuities of aphakic and fellow phakic eye were compared with the monocular acuities of similarly aged children who have good binocular vision, and with children with severe untreated uniocular visual impairment. Recognition linear acuities were measured with a linear Bailey-Lovie logMAR chart and compared with the sweep VEP estimates.

RESULTS

A significant difference was found between Bailey-Lovie acuity of the fellow eye of the patient group and the right eye of binocular controls, and the good eye of uniocular impaired patients (one way ANOVA, p < 0.01). However, this was not evident for a similar comparison with sweep VEP estimates. There was no significant difference between the right and left eye acuities in binocular controls measured by the two techniques (paired t test).

CONCLUSION

A loss of recognition acuity in the fellow phakic eye of patients treated for unilateral congenital cataract has been demonstrated with a logMAR chart. This loss was not apparent in children who have severe untreated uniocular visual impairment and may therefore be an iatrogenic effect of occlusion. An acuity loss was not apparent in the patient group using the sweep VEP method. Sweep VEP techniques have a place for objectively studying acuity in infants and in those whose communication difficulties preclude other forms of behavioural test. The mean sweep VEP acuity for the control groups is 20 cpd--that is, about 6/9. When acuities higher than this are under investigation--for example, in older children, slower transient VEP recording may be more appropriate, because higher spatial frequency patterns are not as visible at higher temporal rates (for example, 8 Hz used in sweep VEP recordings).

Infantile cataracts

Cataracts are one of the most treatable causes of visual impairment during infancy. Recent epidemiological studies have shown that they have a prevalence of 1.2 to 6.0 cases per 10,000 infants. The morphology of infantile cataracts can be helpful in establishing their etiology and prognosis. Early surgery and optical correction have resulted in an improved outcome for infants with either unilateral or bilateral cataracts. While contact lenses continue to be the standard means of optically correcting an infant's eyes after cataract surgery, intraocular lenses are gaining in popularity as an alternative means of optically correcting these eyes. Post-operative complications occur more commonly after infantile than adult cataract surgery and many of these complications do not develop until years later. As a result, it is critical that children be followed closely on a long term basis after infantile cataract surgery.

Assessment of visual acuity in multiply handicapped children

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Balanced translocation (t 2q; 10p) and ocular anomalies. A possible HOX gene defect

The authors report a child with a phenotype typical of a first branchial arch defect. The patient has a balanced translocation involving chromosome 2. They propose a defect that has occurred during the translocation in a gene mapped to chromosome 2 and belonging to the HOXD family. HOX gene defects can perturb the expression of other genes important for head development.