A pilot study of contrast sensitivity assessment of the CAM treatment of amblyopia

Spatially and Temporally Regulated NRF2 Gene Therapy Using Mcp-1 Promoter in Retinal Ganglion Cell Injury

Retinal ganglion cell degeneration triggered by axonal injury is believed to underlie many ocular diseases, including glaucoma and optic neuritis. In these diseases, retinal ganglion cells are affected unevenly, both spatially and temporally, such that healthy and unhealthy cells coexist in different patterns at different time points. Herein, we describe a temporally and spatially regulated adeno-associated virus gene therapy aiming to reduce undesired off-target effects on healthy retinal neurons. The Mcp-1 promoter previously shown to be activated in stressed retinal ganglion cells following murine optic nerve injury was combined with the neuroprotective intracellular transcription factor Nrf2. In this model, Mcp-1 promoter-driven NRF2 expression targeting only stressed retinal ganglion cells showed efficacy equivalent to non-selective cytomegalovirus promoter-driven therapy for preventing cell death. However, cytomegalovirus promoter-mediated NRF2 transcription induced cellular stress responses and death of Brn3A-positive uninjured retinal ganglion cells. Such undesired effects were reduced substantially by adopting the Mcp-1 promoter. Combining a stress-responsive promoter and intracellular therapeutic gene is a versatile approach for specifically targeting cells at risk of degeneration. This strategy may be applicable to numerous chronic ocular and non-ocular conditions.

Positive and negative polarity contrast sensitivity measuring app

Contrast sensitivity (CS) quantifies an observer's ability to detect the smallest (threshold) luminance difference between a target and its surrounding. In clinical settings, printed letter contrast charts are commonly used, and the contrast of the letter stimuli is specified by the Weber contrast definition. Those paper-printed charts use negative polarity contrast (NP, dark letters on bright background) and are not available with positive polarity contrast (PP, bright letters on dark background), as needed in a number of applications. We implemented a mobile CS measuring app supporting both NP and PP contrast stimuli that mimic the paper charts for NP. A novel modified Weber definition was developed to specify the contrast of PP letters. The validity of the app is established in comparison with the paper chart. We found that our app generates more accurate and a wider range of contrast stimuli than the paper chart (especially at the critical high CS, low contrast range), and found a clear difference between NP and PP CS measures (CSNP>CSPP) despite the symmetry afforded by the modified Weber contrast definition. Our app provides a convenient way to measure CS in both lighted and dark environments.

A comparison between different contrast sensitivity tests in the detection of amblyopia

Twenty adult patients with strabismic amblyopia were examined with seven different contrast sensitivity tests in order to determine which of these tests is the most sensitive in the detection of amblyopia. Both grating tests (Vistech, Arden, Cadwell, and Cambridge) and optotype tests (LH, Regan, and Pelli-Robson) were used. The following parameters of the contrast sensitivity function (CSF) were measured: maximum contrast sensitivity, total area of CSF and the area of 8 different spatial frequency bands in the CSF. Based on non-parametric tests, it was found that separations of the normal from the amblyopic eye by means of CSF could be done with: - maximum contrast sensitivity using the Vistech test; - total CSF area using all tests except the Cadwell test; - area of frequency bands (within 1-16 cycles per degree) using Vistech, Pelli-Robson, and the Arden tests; - maximum spatial frequency for tests with a fixed contrast using the LH and Regan tests.

qCSF in clinical application: efficient characterization and classification of contrast sensitivity functions in amblyopia

PURPOSE

The qCSF method is a novel procedure for rapid measurement of spatial contrast sensitivity functions (CSFs). It combines Bayesian adaptive inference with a trial-to-trial information gain strategy, to directly estimate four parameters defining the observer's CSF. In the present study, the suitability of the qCSF method for clinical application was examined.

METHODS

The qCSF method was applied to rapidly assess spatial CSFs in 10 normal and 8 amblyopic participants. The qCSF was evaluated for accuracy, precision, test-retest reliability, suitability of CSF model assumptions, and accuracy of amblyopia screening.

RESULTS

qCSF estimates obtained with as few as 50 trials matched those obtained with 300 Ψ trials. The precision of qCSF estimates obtained with 120 and 130 trials, in normal subjects and amblyopes, matched the precision of 300 Ψ trials. For both groups and both methods, test-retest sensitivity estimates were well matched (all R > 0.94). The qCSF model assumptions were valid for 8 of 10 normal participants and all amblyopic participants. Measures of the area under log CSF (AULCSF) and the cutoff spatial frequency (cutSF) were lower in the amblyopia group; these differences were captured within 50 qCSF trials. Amblyopia was detected at an approximately 80% correct rate in 50 trials, when a logistic regression model was used with AULCSF and cutSF as predictors.

CONCLUSIONS

The qCSF method is sufficiently rapid, accurate, and precise in measuring CSFs in normal and amblyopic persons. It has great potential for clinical practice.

Treated amblyopes remain deficient in spatial vision: a contrast sensitivity and external noise study

To evaluate residual spatial vision deficits in treated amblyopia, we recruited five clinically treated amblyopes (mean age=10.6 years). Contrast sensitivity functions (CSF) in both the previously amblyopic eyes (pAE; visual acuity=0.944+/-0.019 MAR) and fellow eyes (pFE; visual acuity=0.936+/-0.021 MAR) were measured using a standard psychophysical procedure for all the subjects. The results indicated that the treated amblyopes remained deficient in spatial vision, especially at high spatial frequencies, although their Snellen visual acuity had become normal in the pAEs. To identify the mechanisms underlying spatial vision deficits of treated amblyopes, threshold vs external noise contrast (TvC) functions--the signal contrast necessary for the subject to maintain a threshold performance level in varying amounts of external noise ("TV snow")--were measured in both eyes of four of the subjects in a sine-wave grating detection task at several spatial frequencies. Two mechanisms of amblyopia were identified: increased internal noise at low to medium spatial frequencies, and both increased internal noise and increased impact of external noise at high spatial frequencies. We suggest that, in addition to visual acuity, other tests of spatial vision (e.g., CSF, TvC) should be used to assess treatment outcomes of amblyopia therapies. Training in intermediate and high spatial frequencies may be necessary to fully recover spatial vision in amblyopia in addition to the occlusion therapy.

Disruption and reacquisition of binocular vision in childhood and in adulthood

PURPOSE OF REVIEW

This article reviews the most recent studies that address the loss of and restoration of binocular vision in childhood and adulthood and summarizes recent changes in treatment approaches.

RECENT FINDINGS

Studies during the last two years support the idea of continued plasticity of the binocular visual system throughout life. Children and adults with strabismus onset following binocular vision maturation are susceptibility to a permanent disruption of stereopsis and sensory fusion. Plasticity of the binocular visual system, however, also means continued restorability of function. Despite a rather short critical time interval for restoration of normal function (three months in children and 12 months in adults), peripheral or extramacular binocular visual function can be restored in most patients whose onset of disruption follows binocular maturation.

SUMMARY

Stereoacuity loss can occur in the visually mature patient who develops strabismus later in life and delay of treatment can be deleterious to the restoration of normal macular binocular vision. However, despite any delay of treatment, most patients with strabismus acquired following binocular vision maturation will manifest some stereoacuity or sensory fusion following eye realignment. These findings suggest all patients with strabismus need to have their eyes aligned, either surgically or optically, to maximize their binocular vision outcome.

Contrast sensitivity function of sound eye after occlusion therapy in the amblyopic children

To verify the changes of mesopic and photopic contrast sensitivity function of sound eye whose visual acuity was kept the same after occlusion therapy in the amblyopic children. Fourteen sound eyes of amblyopic children (mean; 7.67 years; S.D., 1.50 years) who kept their visual acuity the same after the occlusion therapy were tested. The children had 6 hours of part-time patch therapy for 3 months prior to this examination. Among 14 amblyopic children, 8 were anisometric and 6 were strabismic amblyopes. Using the visual capacity analyzer which measures the minimal contrast level at from low to high spatial frequencies, the contrast sensitivity of sound eye was measured, under both photopic and mesopic condition, before and after 3 months of occlusion therapy. Comparing the contrast sensitivity of sound eye after the occlusion therapy to that before the occlusion, there was no statistical difference in photopic condition. When it comes to mesopic condition, the contrast sensitivity decreased at the intermediate spatial frequency level (3-13 c.p.d, p=0.028) after the occlusion therapy. The occlusion caused statistically significant decrease in mesopic contrast sensitivity, when the visual acuity was not changed after the occlusion therapy. It may indicate that mesopic contrast sensitivity can be considered as a useful tool for early detection of hidden occlusion amblyopia.

Contrast sensitivity function in children: normalized notation for the assessment and diagnosis of diseases

The purpose of this article is to describe a normalized notation for the assessment of the contrast sensitivity in children. This notation is obtained dividing the log contrast sensitivity value found in a patient by the corresponding normative contrast sensitivity data. The ratio obtained describes the contrast sensitivity of a patient facilitating its understanding, assessment and consequently effective communications. This article shows the normalized notation developed for children aged from 3 to 7 years old. An evaluation of the contrast sensitivity in healthy and amblyopic patients has been shown in order to explain the procedure to follow. The use of normalized notation in clinical procedures will provide to the clinician a better understanding of the results and the changes over time as well by comparison in the assessment of an ocular disease.

The contrast sensitivity function and childhood amblyopia

We measured contrast sensitivity function and visual acuity in both eyes of strabismic and anisometropic amblyopic patients. There was a linear relationship between contrast sensitivity function and visual acuity in the amblyopic eye. As visual acuity decreased, the contrast sensitivity function decreased along the contrast sensitivity axis, and peak sensitivity shifted to lower spatial frequencies. After patching therapy, when visual acuity reached 20/20 in each eye, suggesting that the amblyopia was cured, there continued to be statistically significant difference in the contrast sensitivity functions between the eyes. The contrast sensitivity function from the previously amblyopic eye was depressed compared to the nonamblyopic eye. A comparison between patients with strabismic and anisometropic amblyopia showed that, when matched for visual acuity, the contrast sensitivity functions were similar for both the nonamblyopic and amblyopic eyes. However, a large difference was found between the amblyopic and nonamblyopic eyes of each group.

Contrast sensitivity in amblyopia. II. Changes during pleoptic treatment

Contrast sensitivity at spatial frequencies 1-19 c/deg was measured in 56 children (mean age 10 years), who had received pleoptic treatment. Measurements were done at the beginning and at the end of a pleoptic treatment period as well as at follow-up using vertical gratings. A deficiency was observed in contrast sensitivity of amblyopic eyes at all spatial frequencies, but it was most notable at high spatial frequencies. Both types of CSF presented by Hess & Howell (1977) were found in all groups of amblyopia. A statistically significant improvement in the mean value of contrast sensitivity of the amblyopic eyes was observed at all spatial frequencies during the pleoptic treatment, although in 12 cases fixation and vision did not improve. Correlation with the improvement in visual acuity was poor. In several cases a change was observed in only one of the two parameters in question. Regarding the better eye, there were some signs of 'hidden occlusion amblyopia': in a few cases contrast sensitivity of the dominant eye deteriorated during the treatment period without a changes in visual acuity only to risk back to the previous level at the follow-up.

Contrast sensitivity in amblyopia. I. Changes during CAM treatment

Contrast sensitivity of 29 children (mean age 8 years) was measured at the beginning, at the end, and during the follow-up of CAM treatment. The deficiency in contrast sensitivity of amblyopic eyes was most notable at high spatial frequencies, but in some cases it also occurred at intermediate and low spatial frequencies. Individually no distinct association was noticed between various CSF-types and different groups of amblyopia, but on average in anisometropia the deficiency at low spatial frequencies was more pronounced than in purely strabismic cases. During treatment contrast sensitivity improved significantly, most notable at high frequencies. Correlation between visual acuity and contrast sensitivity was poor. During follow-up visual acuity deteriorated in most cases, but contrast sensitivity remained on the level where it was at the end of the treatment. Our modification of measuring contrast sensitivity was tested in two samples of normal subjects. Between 1-11 c/deg contrast sensitivity was statistically significantly better in the adults (n = 25) than in the children (n = 20).

The objective assessment of contrast sensitivity function by electrophysiological means

In recent years it has been shown that it is of considerable clinical value to determine the visual contrast sensitivity function of the patient. This can reveal the wider effects of pathology on the visual system where visual acuity may or may not be affected. There is a comprehensive literature on subjective approaches of obtaining this function in the clinical environment but very little on alternative objective methods. This paper describes the latter approach, which exploits electrophysiological techniques using the visual evoked cortical potential (VECP) to checkerboard onset-offset stimulation. Its application in a variety of disorders of the visual system is described. The importance of selecting the most appropriate stimulus parameters is discussed, and the relative advantages and disadvantages as compared with psychophysical methods are appraised.

Effects of amblyopia therapy on contrast sensitivity as reflected in the visuogram

A quantitative evaluation of the Cambridge amblyopia treatment on contrast sensitivity was performed for 2 groups, one comprising 11 children with strabismic amblyopia (S) and another of 10 children with combined strabismic and anisometropic amblyopia (S & A). Contrast sensitivity deficits were expressed in dB CSL (Contrast Seeing Level) in relation to normal sensitivity of the same age group and represented in the form of visuograms. Mean contrast sensitivity losses in dB CSL were estimated within the low, medium and high spatial frequency ranges, as well as over the total frequency band. On an average S & A amblyopia was found to affect contrast sensitivity of all spatial frequencies, while S amblyopia affected mainly the higher frequency band, but to a smaller extent. After therapy average contrast sensitivity improved for both S and S & A groups, and reached the same, subnormal levels. The relation between highest resolvable spatial frequency (according to our method) and Snellen acuity was different for the 2 amblyopia groups. No correlation was found between improvements in contrast sensitivity and Snellen acuity, which is why both parameters should be estimated.

Recent advances in the management of amblyopia

Methods of detection and treatment of amblyopia as a developmental visual defect are reviewed. Traditional occlusion therapy is compared with recent therapy techniques using square-wave grating patterns as stimuli to increase visual sensitivity. Both methods can help manage amblyopia particularly during stages of early visual development. It is found that the grating pattern stimuli are not in themselves therapeutic, but rather it is probably occlusion in combination with demanding visual tasks which help reduce amblyopia.