Optometry and Vision Sciences - Research Publications
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ItemOscillopsia and the Influence of Stress and Motivation in Fusion Maldevelopment Nystagmus Syndrome(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2013-03)PURPOSE: We examined factors influencing perceptual stability in observers with fusion maldevelopment nystagmus syndrome (FMNS). In addition, we also investigated the effect of visual demand, task-related physiologic stress, and motivation on the nystagmus waveform. METHODS: Perception of oscillopsia during daily activities was assessed via a questionnaire. Perception of oscillopsia in the laboratory was assessed using central and peripheral (10°) light emitting diodes (LEDs) in front of a background display of random, fixed-contrast shapes. Task-induced stress was achieved via a time restricted acuity task with or without concurrent mental arithmetic challenge, and motivation varied using a reward-penalty paradigm. The experiments have been previously described elsewhere. RESULTS: Six out of nine subjects reported experiencing oscillopsia in certain daily activities. in the laboratory, the percentages of trials with perceptions of motion of the led and background were as follows: neither, 60% to 70%; background only, 20% to 30%; both, 5% to 15%, and LED only, 5% to 15%. Over all trials, six of nine experienced oscillopsia for both the low- and high-contrast image respectively (i.e., three subjects never experienced oscillopsia). The background was frequently seen moving for both images regardless of contrast and/or condition. Trials with and without oscillopsia did not differ when comparing foveation. In the second experiment, task-related physiologic stress and motivation were reflected in an increase in heart rate; nystagmus waveform intensity increased and foveation decreased. The magnitude of changes in heart rate was uncorrelated with changes in waveform parameters for all experiments, however. CONCLUSIONS: Preliminary results suggest that the FMNS group does perceive spatially inhomogeneous oscillopsia, similar to infantile nystagmus syndrome (INS), in certain visual environments. In investigating the effect of stress and motivation on FMNS, a new, if tentative, finding suggests that task-induced stress and/or motivation may have a negative impact on the nystagmus. Taken together, our findings provide an insight into the particular environments and tasks that are likely to present particular challenges to persons with FMNS.
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ItemHypertensive retinopathy: comparing the Keith-Wagener-Barker to a simplified classification(LIPPINCOTT WILLIAMS & WILKINS, 2013-05)PURPOSE: This study assessed the interobserver and intraobserver grading reliability of the Keith-Wagener-Barker (KWB) system to the proposed Mitchell-Wong 'simplified' three-grade classification for hypertensive retinopathy. METHODS: Digital retinal images of normal and hypertensive human fundii (n = 50 per group) were randomly graded by an optometrist and an ophthalmologist using the two systems. Interobserver agreement was compared to a 'gold standard' research grader. Intraobserver agreement was assessed through a repeat grading after 6 months. Cohen's kappa coefficients were used to assess the degree of agreement. RESULTS: Both clinicians demonstrated a good level of agreement with the KWB and simplified classification compared with a 'gold standard' grader; there was no significant difference in the level of agreement for either of the two classification methods for either observer. The simplified classification was found to be equally as efficacious as the KWB system with respect to interobserver and intraobserver agreement for both practitioners. CONCLUSION: These findings indicate that the simplified classification of hypertensive retinopathy is both reliable and repeatable. The advantage of the simplified method over the KWB system in correlating retinal microvascular signs to incident cardiovascular risk supports its adoption in clinical practice.
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ItemHow Useful Is Population Data for Informing Visual Field Progression Rate Estimation?(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2013-03)PURPOSE: Bayesian estimators allow the frequency of visual field progression rates in the population (the prior distribution) to constrain rate estimates for individuals. We examined the benefits of a prior distribution accounting for one of progression's major risk factors--whether intraocular pressure is treated--to gauge the maximum benefit expected from developing priors for other glaucoma risk factors. METHODS: Our prior distribution was derived from published data from either treated (matched-prior condition) or untreated (unmatched-prior condition) glaucoma patients. We simulated MD values (6-monthly) with true underlying progression rates drawn from the same distribution as the prior for the matched-prior condition. We estimated rates through linear regression, and determined the likelihood of obtaining this estimate as a function of a range of true underlying progression rates (the likelihood function). The maximum likelihood estimate of rate was the most likely value of the posterior distribution (the product of the prior distribution and likelihood function). RESULTS: For short (4) visual field series, the matched-prior condition, unmatched-prior condition, and linear regression gave median errors (estimated minus true rate) of 0.02, 0.20, and 0.00 dB/y, respectively. Positive predictive values for determining rapidly progressing (<-1 dB/y) rates were 0.46, 0.42, and 0.38, with negative predictive values of 0.93, 0.94, and 0.95. For more extended series the magnitude of the differences between techniques decreased, although the order was unchanged. CONCLUSIONS: Performance shifts in bayesian estimators of visual field progression are modest even when prior distributions do not reflect large risk factors, such as IOP treatment.
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ItemSusceptibility of Streptozotocin-Induced Diabetic Rat Retinal Function and Ocular Blood Flow to Acute Intraocular Pressure Challenge(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2013-03)PURPOSE: To consider the hypothesis that streptozotocin (STZ)-induced hyperglycemia renders rat retinal function and ocular blood flow more susceptible to acute IOP challenge. METHODS: Retinal function (electroretinogram [ERG]) was measured during acute IOP challenge (10100 mm Hg, increments of 5 mm Hg, 3 minutes per step, vitreal cannulation) in adult Long-Evans rats (6 weeks old; citrate: n = 6, STZ: n = 10) 4 weeks after citrate buffer or STZ (65 mg/kg, blood glucose >15 mM) injection. At each IOP, dim and bright flash (-4.56, -1.72 log cd x s x m(-2)) ERG responses were recorded to measure inner retinal and ON-bipolar cell function, respectively. Ocular blood flow (laser Doppler flowmetry; citrate: n = 6, STZ: n = 10) was also measured during acute IOP challenge. Retinas were isolated for quantitative PCR analysis of nitric oxide synthase mRNA expression (endothelial, eNos; inducible, iNos; neuronal, nNos). RESULTS: STZ-induced diabetes increased the susceptibility of inner retinal (IOP at 50% response, 60.1, CI: 57.0-62.0 mm Hg versus citrate: 67.5, CI: 62.1-72.4 mm Hg) and ON-bipolar cell function (STZ: 60.3, CI: 58.0-62.8 mm Hg versus citrate: 65.1, CI: 61.9-68.6 mm Hg) and ocular blood flow (43.9, CI: 40.8-46.8 versus citrate: 53.4, CI: 50.7-56.1 mm Hg) to IOP challenge. Citrate eyes showed elevated eNos mRNA (+49.7%) after IOP stress, an effect not found in STZ-diabetic eyes (-5.7%, P < 0.03). No difference was observed for iNos or nNos (P > 0.05) following IOP elevation. CONCLUSIONS: STZ-induced diabetes increased functional susceptibility during acute IOP challenge. This functional vulnerability is associated with a reduced capacity for diabetic eyes to upregulate eNos expression and to autoregulate blood flow in response to stress.
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ItemIncreased Susceptibility to Injury in Older Eyes(LIPPINCOTT WILLIAMS & WILKINS, 2013-03)PURPOSE: To determine whether there is an age-dependent susceptibility in retinal function in response to repeated anterior chamber cannulation with or without intraocular pressure (IOP) elevation. METHODS: Baseline electroretinograms were measured in 3- and 18-month-old Sprague-Dawley rats (n = 16 each group). Following baseline assessment, eyes were randomly assigned to undergo a 60-min anterior chamber cannulation with IOP either left at baseline (sham, 15 mm Hg) or elevated to 60 mm Hg. This was repeated three additional times, with each episode separated by 1 week. At weeks 1 to 3, dark-adapted retinal function was assessed immediately before cannulation, with final functional assessment at week 4. RESULTS: Both sham and IOP elevated eyes of older rats showed retinal dysfunction, which became more pronounced with the number of repeated insults. This effect was largest for responses arising from the inner retina. Repeated insult in younger eyes did not produce a change in amplitude but an increase in the sensitivity to light of photoreceptoral and bipolar cell components of the electroretinogram. CONCLUSIONS: Repeated trauma, not IOP, produces permanent retinal dysfunction in older eyes. Younger eyes appear to be able to withstand this type of injury by upregulating sensitivity of outer and middle retinal responses to maintain normal inner retinal function.
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ItemElectroretinography in streptozotocin diabetic rats following acute intraocular pressure elevation(SPRINGER, 2013-02)BACKGROUND: We consider whether pre-existing streptozotocin induced hyperglycemia in rats affects the ability of the eye to cope with a single episode of acute intraocular pressure (IOP) elevation. METHODS: Electroretinogram (ERG) responses were measured (-6.08 to 1.92 log cd.s.m(-2)) in anaesthetized (60:5 mg/kg ketamine:xylazine) dark-adapted (>12 h) adult Sprague-Dawley rats 1 week after a single acute IOP elevation to 70 mmHg for 60 min. This was undertaken in rats treated 11 weeks earlier with streptozotocin (STZ, n = 12, 50 mg/kg at 6 weeks of age) or citrate buffer (n = 12). ERG responses were analyzed to derive an index of photoreceptor (a-wave), ON-bipolar (b-wave), amacrine (oscillatory potentials) and inner retinal (positive scotopic threshold response, pSTR) function. RESULTS: One week following acute IOP elevation there was a significant reduction of the ganglion cell pSTR (-35 ± 11 %, P = 0.0161) in STZ-injected animals. In contrast the pSTR in citrate-injected animals was not significant changed (+16 ± 14 %). The negative component of the STR was unaffected by IOP elevation in either citrate or STZ-treated groups. Photoreceptoral (a-wave, citrate-control +4 ± 3 %, STZ +4 ± 5 %) and ON-bipolar cell (b-wave, control +4 ± 3 %, STZ +4 ± 5 %) mediated responses were not significantly affected by IOP elevation in either citrate- or STZ-injected rats. Finally, oscillatory potentials (citrate-control +8 ± 23 %, STZ +1 ± 17 %) were not reduced 1 week after IOP challenge. CONCLUSIONS: The ganglion cell dominated pSTR was reduced following a single episode of IOP elevation in STZ diabetic, but not control rats. These data indicate that hyperglycemia renders the inner retina more susceptible to IOP elevation.