Emily Wiecek

Spatial-frequency dependent binocular imbalance in amblyopia

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p < 0.01). Good test-retest reliability of the method was demonstrated by the Bland-Altman plot. Our findings suggest that spatial-frequency dependent binocular imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy.

Novel quantitative assessment of metamorphopsia in maculopathy.

PURPOSE Patients with macular disease often report experiencing metamorphopsia (visual distortion). Although typically measured with Amsler charts, more quantitative assessments of perceived distortion are desirable to effectively monitor the presence, progression, and remediation of visual impairment. METHODS Participants with binocular (n = 33) and monocular (n = 50) maculopathy across seven disease groups, and control participants (n = 10) with no identifiable retinal disease completed a modified Amsler grid assessment (presented on a computer screen with eye tracking to ensure fixation compliance) and two novel assessments to measure metamorphopsia in the central 5° of visual field. A total of 81% (67/83) of participants completed a hyperacuity task where they aligned eight dots in the shape of a square, and 64% (32/50) of participants with monocular distortion completed a spatial alignment task using dichoptic stimuli. Ten controls completed all tasks. RESULTS Horizontal and vertical distortion magnitudes were calculated for each of the three assessments. Distortion magnitudes were significantly higher in patients than controls in all assessments. There was no significant difference in magnitude of distortion across different macular diseases. There were no significant correlations between overall magnitude of distortion among any of the three measures and no significant correlations in localized measures of distortion. CONCLUSIONS Three alternative quantifications of monocular spatial distortion in the central visual field generated uncorrelated estimates of visual distortion. It is therefore unlikely that metamorphopsia is caused solely by retinal displacement, but instead involves additional top-down information, knowledge about the scene, and perhaps, cortical reorganization.

Metamorphopsia and letter recognition.

Acuity is the most commonly used measure of visual function, and reductions in acuity are associated with most eye diseases. Metamorphopsia--a perceived distortion of visual space--is another common symptom of visual impairment and is currently assessed qualitatively using Amsler (1953) charts. In order to quantify the impact of metamorphopsia on acuity, we measured the effect of physical spatial distortion on letter recognition. Following earlier work showing that letter recognition is tuned to specific spatial frequency (SF) channels, we hypothesized that the effect of distortion might depend on the spatial scale of visual distortion just as it depends on the spatial scale of masking noise. Six normally sighted observers completed a 26 alternate forced choice (AFC) Sloan letter identification task at five different viewing distances, and the letters underwent different levels of spatial distortion. Distortion was controlled using spatially band-pass filtered noise that spatially remapped pixel locations. Noise was varied over five spatial frequencies and five magnitudes. Performance was modeled with logistic regression and worsened linearly with increasing distortion magnitude and decreasing letter size. We found that retinal SF affects distortion at midrange frequencies and can be explained with the tuning of a basic contrast sensitivity function, while object-centered distortion SF follows a similar pattern of letter object recognition sensitivity and is tuned to approximately three cycles per letter (CPL). The interaction between letter size and distortion makes acuity an unreliable outcome for metamorphopsia assessment.

A statistical analysis of metamorphopsia in 7106 amsler grids.

Metamorphopsia (visual distortion) is experienced by patients with macular disease, and is a A-II symptom in the Preferred Practice Patterns for patient history, diagnosis, treatment intervention, and follow-up.1 The Amsler grid is used to detect the presence of metamorphopsia in the clinic and at home. Patients fixate the grid centrally and note any lines that appear distorted or missing. In spite of its clinical significance, the prevalence, variation, and progression of metamorphopsia have not previously been reported. This study estimates the prevalence and magnitude of metamorphopsia in retinal clinic patients and provides statistical data to assist in the management of macular disease.

Metamorphopsia and interocular suppression in monocular and binocular maculopathy.

–1.0 D OD and –0.25 D OS. Her IOP was 14 mmHg OD and 15 mmHg OS. Ophthalmoscopy revealed bilateral neuroretinal rim narrowing at the optic disc margin, inferior retinal nerve fibre layer (RNFL) defect and peripapillary retinoschisis without a posterior vitreous detachment in the right eye with normal open anterior chamber angle (Fig. 1). Fluorescein angiography showed no leakage or any signs of an optic disc pit. Optical coherence tomography (OCT, OCT3-STRATUS, Carl Zeiss Meditec) revealed peripapillary retinoschisis and retinal detachment. Humphrey field analyzer (HumphreyZeiss System) showed a superior Bjerrum scotoma corresponding to the inferior RNFL defect in both eyes. She was followed without any treatment because of her good vision. The headaches and periorbital pain disappeared after 1 month. She noticed that the paracentral scotoma had moved gradually towards the central visual field, and the peripapillary retinoschisis turned to macular retinoschisis at 15 months but she maintained good vision of 20/20. The macular retinoschisis completely resolved after 3 years without any recurrence for 2 years. Vision was maintained at 20/20 without a central scotoma. The IOP remained within the normal range without any topical medication and no progression of the visual field defect was detected. Spectral domain OCT (Cirrus-HD-OCT, Carl Zeiss Meditec) showed a resolution of the macular retinoschisis with partially detachment of the posterior vitreous cortex. The optic disc cup was deeper corresponding to the resolution of the peripapillary retinoschisis and schisis within the optic disc. Kahook et al. (2007) described two cases of peripapillary retinoschisis associated with increased IOP and angle-closure glaucoma. An acute elevation of the IOP can lead to structural defects in the optic nerve head and peripapillary retinoschisis as seen in cases of optic disc pit maculopathy. Zumbro et al. (2007) reported that vitreous surgery can resolve a retinoschisis associated with an enlarged optic disc cup. They reported that vitreous traction may have played a role in the development of the macular retinoschisis and foveal detachment. Zhao & Li (2011) described a case of macular retinoschisis that developed in an eye with normal tension glaucoma. They also suggested that vitreous traction was the cause of the retinoschisis near the RNFL defect, and the foveal detachment developed by the seeping of fluid through the intraretinal spaces. The IOP was normal as in our patient, and vitreous traction probably caused the peripapillary and macular retinoschisis that resolved spontaneously when the posterior vitreous cortex was partially detached. Hwang et al. (2014) described a case of peripapillary retinoschisis within the retinal nerve fibre, ganglion cell and inner plexiform layers detected in the OCT images of 19 glaucomatous eyes. However, none of the eyes developed macular retinoschisis, and the peripapillary retinoschisis resolved without any treatment. Our patient developed symptomatic peripapillary retinoschisis and retinal detachment which expanded to macular retinoschisis. Thus, peripapillary retinoschisis associated with glaucomatous optic neuropathy can progress to macular retinoschisis which can resolve spontaneously by a partial vitreous detachment.

Word and Sentence Level Spatial Information In Reading

Reading is considered an inefficient activity that requires independent detection of individual letters without integrating word or sentence information. We studied the use of word- and sentence-shape information using word discrimination and reading tasks with spatially distorted text in 18 naïve observers. Threshold durations were measured as a function of the wavelength and magnitude of spatial distortion applied to text for word/non-word classification of 4 and 8 letter words, and true/false classification of 4-word sentences. Spatial distortion slowed word recognition and reading. Unlike the uni-modal tuning functions observed in noise masking studies, we find multi-modal tuning functions that correspond to maximal impairment at around 2 cycles per letter, 2 cycles per word and 2 cycles per line of text. These data imply that information at these word- and sentence-length dependent scales are important for word recognition and reading, This finding is consistent with the robustness of reading letter-substituted text, proof-reading errors and the ineffectiveness of letter-based assistive reading methods. Meeting abstract presented at VSS 2015.