Dual-focus contact lenses for myopia control modify central retinal electrophysiology in humans.

INTRODUCTION: Dual-focus contact lenses create two focal planes, one providing a clear retinal image while the other imposes myopic defocus on the retina to slow myopia progression. This study used global-flash multifocal electroretinogram (gmfERG) response amplitudes to compare central versus peripheral retinal responses under dual-focus conditions and to assess the optimal degree of myopic defocus compared with a single-vision control lens. METHODS: Twenty participants each underwent three gmfERG trials, wearing a spectacle correction over dual-focus contact lenses with plano central power and peripheral secondary focal powers of either +2.00D, +4.00D or a plano single-vision lens. We compared amplitudes and latencies of the gmfERG direct and induced components (DC and IC) within participants, between the three different contact lens powers and at different retinal eccentricities (gmfERG ring). RESULTS: We observed significant differences in the gmfERG responses between the single-vision and dual-focus contact lenses. Overall, DC amplitudes peaked between zero and +2.00D secondary power, while IC amplitudes were maximal between +2.00D and +4.00D. Compared with the single-vision control, the greatest increase in DC and IC amplitudes while wearing dual-focus lenses occurred within the central 10° of the retina. There was no interaction effect between gmfERG ring (eccentricity) and secondary power, and no difference in the latency of the gmfERG responses between different powers. CONCLUSION: We found that dual-focus contact lenses with a +2.00D secondary power are close to that expected to induce the greatest increase in gmfERG responses relative to a single-vision lens. Dual-focus lenses produced the highest DC and IC response amplitudes relative to a single-vision lens in the central 10° of the retina. This suggests that dual-focus contact lenses slow myopia progression by modifying central rather than peripheral retinal activity.

Diagnosis of colour vision deficits using eye movements.

We set out to develop a simple objective test of functional colour vision based on eye movements made in response to moving patterns. We exploit the finding that while the motion of a colour-defined stimulus can be cancelled by adding a low-contrast luminance-defined stimulus moving in the opposite direction, the "equivalent luminance contrast" required for such cancellation is reduced when colour vision is abnormal. We used a consumer-grade infrared eye-tracker to measure eye movements made in response to coloured patterns drifting at different speeds. An automated analysis of these movements estimated individuals' red-green equiluminant point and their equivalent luminance contrast. We tested 34 participants: 23 colour vision normal controls, 9 deuteranomalous and 2 protanomalous individuals. We obtained reliable estimates of strength of directed eye movements (i.e. combined optokinetic and voluntary tracking) for stimuli moving at 16 deg/s and could use these data to classify participants' colour vision status with a sensitivity rate of 90.9% and a specificity rate of 91.3%. We conclude that an objective test of functional colour vision combining a motion-nulling technique with an automated analysis of eye movements can diagnose and assess the severity of protanopia and deuteranopia. The test places minimal demands on patients (who simply view a series of moving patterns for less than 90 s), requires modest operator expertise, and can be run on affordable hardware.

The effect of cellphone position on driving and gaze behaviour.

Legislation frequently restricts the use of cellphones while driving. Despite this, many people continue to interact with cellphones covertly while driving, typically by concealing their device in their lap. This strategy leads to frequent diversion of the drivers' gaze from the road ahead, potentially reducing their driving performance. To evaluate the influence of cellphone use on driving, 30 participants took part in three randomly ordered 7-min virtual reality driving simulations. In each condition, drivers were presented with either (a) no cellphone, (b) a cellphone fixed to the windscreen, or (c) a cellphone positioned at lap level. Their task was to maintain road position and observe speed limits while answering maths problems (delivered intermittently via 'text message') and searching for external target objects. Outcome measures included speed, lane position standard deviation (LPSD), and fixation behaviour, which were compared between trials. In trials where a cellphone was present, participants shifted fixation more frequently, drove approximately 6 km/h faster, exhibited a lower LPSD and spent more time in the correct lane on the road (compared to the no-cellphone condition; all p < 0.001). Cellphone position influenced eye gaze behaviour, with drivers looking at the cellphone less frequently, and the speedometer more frequently. when the cellphone was in their lap compared to when the cellphone was positioned on the windscreen. Our results are consistent with participants driving more cautiously-checking speed and lane position more frequently-when they have a cellphone in the lap. Real-world driving data would be useful to determine whether this change in driving behaviour we observed is sufficient to offset the increased risk introduced by spending less time looking at the road ahead.

The effect of refractive error on optokinetic nystagmus.

Subjective refraction is the gold-standard for prescribing refractive correction, but its accuracy is limited by patient's subjective judgment about their clarity of vision. We asked if an involuntary eye movement, optokinetic nystagmus (OKN), could serve as an objective measure of visual-clarity, specifically measuring the dependence of OKN-elicited by drifting spatial-frequency filtered noise-on mean spherical equivalent (MSE) refractive error. In Experiment 1 we quantified OKN score-a measure of consistency with stimulus-direction-for participants with different MSEs. Estimates of MSE based on OKN scores correlate well with estimates of MSE made using autorefraction (r = 0.878, p < 0.001, Bland-Altman analysis: mean difference of 0.00D (95% limits of agreement: - 0.85 to + 0.85D). In Experiment 2, we quantified the relationship between OKN gain (ratio of tracking eye-movement velocity to stimulus velocity) and MSEs (- 2.00, - 1.00, - 0.50, 0.00 and + 1.00D) induced with contact lenses for each participant. The mean difference between measures of MSE based on autorefraction or on OKN gain was + 0.05D (- 0.90 to + 1.01D), and the correlation of these measures across participants was r = 0.976, p < 0.001. Results indicate that MSE attenuates OKN gain so that OKN can be used as an objective proxy for patient response to select the best corrective lens.

Additive effect of atropine eye drops and short-term retinal defocus on choroidal thickness in children with myopia.

Atropine eye drops and myopic retinal defocus each slow progression of myopia (short-sight). They also cause thickening of the choroid, and it has been suggested that the thickening is a precursor for reduced eye growth and slowed myopia progression. We investigated whether choroidal thickening due to optical defocus would add to thickening due to atropine when both were applied simultaneously. Addition would suggest that combining the two clinical treatments may improve efficacy of myopia control. We studied 20 children receiving 0.3% atropine daily for myopia control, over a period of 6 months. We imposed short periods of retinal defocus (1 h of myopic or hyperopic defocus (± 2.00D)) both before, and after 1 week and 3 and 6 months of atropine treatment. Prior to atropine, myopic or hyperopic defocus caused significantly thicker or thinner choroids respectively (± 12 µm, p < 0.001). After one week of atropine alone, thickness had increased (+ 21 µm; SD 17 µm; p < 0.001), and it increased further (by + 13 µm; SD 6 µm; p < 0.001) when exposed to myopic defocus. Atropine abolished choroidal thinning in response to hyperopic defocus. These effects remained the same after 3 and 6 months of atropine treatment. Our results show that additive effects of atropine and optical defocus are present at the level of the choroid, and suggest that combining optical and pharmaceutical treatments is likely to enhance efficacy of clinical myopia control.

The Effect of Simulated Visual Field Loss on Optokinetic Nystagmus.

Purpose: Assessment of functional vision across the visual field is hampered by a reliance on patients' subjective judgement of the presence of a stimulus, and the accompanying demands (time and attention) this places on them. As a first step toward determining whether an objective measure of an involuntary eye movement (optokinetic nystagmus [OKN]) could provide an objective measure of field loss, we determined how various measures of OKN depend on the extent of simulated visual field loss (SVFL). Methods: We used infrared eye-tracking to measure the eye movements of 16 healthy participants viewing horizontally translating 2-dimensional noise patterns over trials of varying contrasts and different levels of SVFL. We quantified the strength of OKN by estimating the velocity of tracking eye movements compared to the stimulus (OKN gain). These measurements were made using an open-loop SVFL paradigm, where a varying amount of gaze-contingent peripheral stimuli was occluded. Results: Full-field stimulation led to an average OKN gain of 0.92 ± 0.15. This value fell steadily with increasing SVFL to a value of 0.38 ± 0.20 when the periphery was not stimulated at all (i.e., the stimulus was a 5-deg. diameter foveal patch). We note considerable individual variation in OKN gain in all conditions. Conclusions: Measuring the extent of visual field loss using an objective measure of OKN gain is feasible. Translational Relevance: Simulated visual field loss reduces optokinetic nystagmus, but further refinement of this technique would be required to overcome individual differences and to pick up clinically relevant field defects.

Global-flash mfERG responses to local differences in spherical and astigmatic defocus across the human retina.

PURPOSE: Emmetropisation is essentially a visually guided, within-eye process. We investigated differences in global-flash multifocal electroretinogram (gmfERG) responses to naturally occurring differences in spherical and astigmatic defocus across the retina, which might provide a basis for guiding eye growth. METHODS: Experiment 1: The gmfERG responses (direct, DC, and induced, IC, amplitudes and latencies) recorded simultaneously from six retinal areas (15° eccentricity, spaced at 60°, areas 3.2°2 ) were correlated with the uncorrected retinal defocus measured at the six corresponding retinal locations in 20 adults with foveal refractive errors (-4.75 to +1.25D). No correcting lenses were used to avoid introduction of lens-induced aberrations and magnification. Experiment 2 investigated the effect of superimposing astigmatic defocus (+2.00/-4.00D Jackson Cross Cylinder presented at four orientations) on gmfERG responses. RESULTS: Experiment 1: DC and IC response amplitudes were greater in retinal regions naturally exposed to more hyperopic spherical defocus (DC: rho = 0.26, p = 0.005; IC: rho = 0.29, p = 0.001), but response latencies were unaffected by sign or magnitude of spherical defocus (DC: p = 0.34; IC: p = 0.40). Response amplitudes and latencies were unaffected by astigmatic defocus. Experiment 2: Rotating the JCC axis to four different orientations had no effect on the gmfERG responses (DC amplitude, p = 0.39; DC latency, p = 0.10; IC amplitude, p = 0.51; IC latency, p = 0.64). CONCLUSION: The gmfERG responses from discrete retinal areas varied with the sign and magnitude of local spherical defocus, but we found no evidence that retinal responses were affected by astigmatic defocus. Therefore, local astigmatism is unlikely to provide cues for controlling eye growth, whereas differences in response to spherical defocus between different retinal regions could potentially provide cues for controlling eye growth in emmetropisation.

Effect of virtual reality headset wear on the tear film: A randomised crossover study.

PURPOSE: To compare the effects of virtual reality headset wear and conventional desktop computer display use on ocular surface and tear film parameters. METHODS: Twenty computer operators were enrolled in a prospective, investigator-masked, randomised crossover study. On separate days, participants were randomised to 40 min of continuous virtual reality headset wear or conventional desktop computer display use. Outer eyelid and corneal temperatures, tear film lipid layer grade, and non-invasive tear film breakup time were measured at baseline and immediately following the 40-minute exposure period. RESULTS: Virtual reality headset wear resulted in increases in outer eyelid (mean difference +0.5 ±â€¯0.6 °C; p < 0.001) and corneal temperatures (mean difference, +0.4 ±â€¯0.6 °C; p = 0.004), relative to conventional desktop computer display use. These increases were associated with significant improvements in tear film lipid layer grade (median difference, +1 grade; interquartile range, 0 to +2 grades; p < 0.001) and non-invasive tear film breakup time (mean difference, +7.2 ±â€¯12.4 s; p = 0.02). CONCLUSIONS: Clinically significant improvements in lipid layer thickness and tear film stability were observed with virtual reality headset wear, despite producing only modest increases in ocular temperatures relative to conventional desktop computer display use. These findings would suggest that virtual reality headset wear demonstrates potential for dry eye relief for computer operators in the modern workplace environment.

Randomised trial of the clinical utility of an eyelid massage device for the management of meibomian gland dysfunction.

PURPOSE: To compare the single application and two week treatment effects of device-applied (Eyepeace) and manually-applied eyelid massage techniques, as an adjunct to warm compress therapy, on ocular surface and tear film parameters. METHODS: Twenty participants (11 females, 9 males; mean age, 27 ±â€¯11 years) with dry eye symptoms were recruited in a two week, investigator-masked, randomised, contralateral-eye trial. Following 10 min of warm compress therapy application (MGDRx EyeBag®) on both eyes, eyelid massage therapy was applied to one eye (randomised) by device, and to the fellow eye by manual eyelid massage, once daily for 14 days. Ocular surface and tear film measurements were conducted at baseline, and 15 min post-application by a clinician, then again after 14 days of self-administered daily treatment at home. RESULTS: Baseline clinical measurements did not differ between the treatment groups (all p > 0.05). Following two weeks of treatment, tear film lipid layer grade improved significantly with device massage (p = 0.008), and was marginally greater than manual massage by less than 1 grade (p = 0.03). Although immediate post-treatment improvements in tear film stability were observed in both groups (both p < 0.05), no significant long-term cumulative effects or inter-treatment differences in stability measures were detected (all p > 0.05). Visual acuity, tear meniscus height, conjunctival hyperaemia, ocular surface staining, and meibomian gland dropout did not change during the treatment period (all p > 0.05). CONCLUSIONS: Two weeks of treatment with the eyelid massage device, as an adjunct to warm compress therapy, effected marginally greater improvements in tear film lipid layer thickness than the conventional manual technique, which were statistically but not clinically significant. Future parallel group trials with longer treatment periods and a greater range of disease severity are required.

The Effect of Atropine on Human Global Flash mfERG Responses to Retinal Defocus.

Purpose: To investigate the action of atropine on global flash multifocal electroretinogram (gmfERG) responses to retinal defocus. Method: gmfERG recordings were made monocularly in 19 healthy adults under three lens-imposed defocus conditions (2 diopters myopic, 2 diopters hyperopic, and no defocus) before and 24 hours after instillation of 1 drop of 0.1% atropine. Signals reflecting activity from the outer and inner retina (direct [DC] and induced [IC] components respectively) were analyzed. Responses were grouped into either a central (0°-6°) or peripheral (6°-24°) retinal zone. The gmfERG responses were compared relative to the no defocus, no atropine condition. Results: Within the central zone, atropine had no effect on the amplitudes and peak times of DC or IC responses to defocus. For IC responses in the peripheral zone, there was a significant interaction effect of atropine and defocus (F2,36 = 6.050, P = 0.011) with greater post-atropine amplitudes under myopic defocus (mean increase = 15.5%, 95% confidence interval [CI] = 5.6%-25.4%, P = 0.004). Atropine also had a significant main effect of increasing IC peak times (F1,18 = 9.722, P = 0.006). For DC responses, atropine had a significant main effect of increasing DC amplitudes (F1,18 = 7.821, P = 0.012) and peak times (F1,18 = 15.406, P = 0.001) regardless of sign of defocus. Conclusions: Our results imply that atropine acts in the inner layers of the peripheral retina to affect neuronal responses to myopic defocus, raising the possibility that atropine may potentiate the effects of myopic defocus in inhibiting eye growth.

Repeatability of Arterial Spin Labeling MRI in Measuring Blood Perfusion in the Human Eye.

BACKGROUND: Quantifying blood perfusion in ocular tissues is challenging, partly because the majority of the blood is carried by the choroid, which is difficult to visualize because it is located between the retina and sclera. PURPOSE/HYPOTHESIS: To evaluate the intra- and interday repeatability of MRI measures of chorio-retinal blood perfusion. STUDY TYPE: Prospective, cross-sectional, observational study. POPULATION: Twenty young healthy adults (six male, age: 25 ± 5 years) scanned twice within a single session repeated at the same time of day on 2 days. FIELD STRENGTH/SEQUENCE: Arterial spin labeling (ASL) MRI at 3.0T using pseudocontinuous ASL (PCASL) labeling scheme and a 3D turbo-gradient-spin-echo (TGSE) acquisition, including axial T2 -weighted structural images using a 2D turbo-spin-echo (TSE) sequence. ASSESSMENTS: Region-of-interest analysis for assessment of chorio-retinal blood perfusion. STATISTICAL TESTS: Intra- and interday repeatability of measures analyzed using intraclass correlation coefficients (ICC), Pearson's correlation analysis, paired t-tests, and Bland-Altman plots. RESULTS: The mean chorio-retinal perfusion was 77.86 (standard deviation [SD] = 29.80) ml/100ml/min. Perfusion measurements correlated strongly within a single session (r = 0.95, 95% confidence interval [CI] [0.880-0.980], P < 0.001) and between the two sessions based on a single run (r = 0.80 [0.582-0.913], P < 0.001), and two runs (r = 0.80 [0.479-0.918], P < 0.001). There were mean differences of 2.69 [16.85 to -22.23] ml/100ml/min for intraday measures, -7.44 [27.45 to -42.32] ml/100ml/min for single-run interday measures, and 5.73 [28.71 to -40.17] ml/100ml/min for two-run interday measures, but none were significant (all P > 0.05). DATA CONCLUSION: Quantitative ASL-MRI measurements of chorio-retinal blood perfusion showed high intra- and interday repeatability. The ASL-MRI technique provides reliable measures of chorio-retinal perfusion in vivo. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;49:966-974.

Comparing the in vitro effects of MGO™ Manuka honey and tea tree oil on ocular Demodex viability.

PURPOSE: To compare the in vitro antiparasitic effects of MGO™ Manuka honey and tea tree oil against ocular Demodex. METHODS: Fifty-two viable Demodex mites were acquired from the epilated eyelashes of 9 participants with blepharitis and symptomatic dry eye. Viable mites were randomised to one of five treatment groups: cyclodextrin-complexed and uncomplexed Manuka Honey, 100% and 50% tea tree oil, and no treatment. Following treatment application, mite viability was assessed for 240 min, based on limb and body movement and/or the development of a crenated/translucent appearance. Kaplan-Meier survival analysis was then performed. RESULTS: The log-rank test demonstrated a significant treatment effect on the survival distribution of Demodex mites (p < 0.001). Bonferroni-corrected post-hoc pairwise analysis showed that all treatments except for uncomplexed honey effected lower survival probabilities than the untreated group (all p < 0.001). Among the four treatments, survival probabilities were lowest with 100% tea tree oil (all p < 0.001), and highest with uncomplexed honey (all p ≤ 0.001). No difference was observed between complexed honey and 50% tea tree oil (p = 0.81). CONCLUSIONS: The in vitro efficacy of cyclodextrin-complexed Manuka honey was comparable with 50% tea tree oil, an established treatment for ocular Demodex. The findings support future clinical trials investigating the therapeutic effects of complexed honey in demodectic blepharitis patients.

Comparison of treatment effect across varying severities of meibomian gland dropout.

PURPOSE: Better understanding of the pathophysiology of meibomian gland dysfunction (MGD) has provided the opportunity to develop treatments which could be tailored for specific presentations of MGD. This study sought to directly compare treatment effectiveness for three current therapies across differing levels of MG dropout. METHODS: Subjects (n=81), grouped by infrared meibography dropout proportions, into either no (control), mild, or pronounced MG dropout, were randomised to receive treatment with a latent heat device (n=25), liposomal spray (n=28), or heated warm compress (n=28). A battery of tear film measures was performed, pre- and post-application of treatment, and compared by treatment type and MG severity. RESULTS: Symptoms correlated with MG dropout proportions (r=0.618, p<0.001). Following treatment, non-invasive tear breakup time improved (p=0.010), independent of treatment type (p=0.131). The improvement was significant only in the pronounced MGD group (+4.32 ±1.15s, p=0.008), however, following treatment, the mild group was no longer distinct from the control group (p=0.843). Lipid layer grade (LLG) also improved following treatment (p<0.009), but again was not specific to treatment type (p=0.349). All three severity groups showed an improvement in LLG, with 49.3% of participants showing an improvement of at least one grade, and none showing decreased LLG. CONCLUSIONS: Increased LLG across all three treatment groups suggests that all methods increase meibum outflow to the tear film, resulting in a thicker lipid layer after treatment. These results suggest that all three treatments are effective in improving tear film quality, independent of MGD severity based either on symptoms or based on gland dropout.

Ocular effects of virtual reality headset wear in young adults.

Virtual Reality (VR) headsets create immersion by displaying images on screens placed very close to the eyes, which are viewed through high powered lenses. Here we investigate whether this viewing arrangement alters the binocular status of the eyes, and whether it is likely to provide a stimulus for myopia development. We compared binocular status after 40-minute trials in indoor and outdoor environments, in both real and virtual worlds. We also measured the change in thickness of the ocular choroid, to assess the likely presence of signals for ocular growth and myopia development. We found that changes in binocular posture at distance and near, gaze stability, amplitude of accommodation and stereopsis were not different after exposure to each of the 4 environments. Thus, we found no evidence that the VR optical arrangement had an adverse effect on the binocular status of the eyes in the short term. Choroidal thickness did not change after either real world trial, but there was a significant thickening (≈10 microns) after each VR trial (p < 0.001). The choroidal thickening which we observed suggest that a VR headset may not be a myopiagenic stimulus, despite the very close viewing distances involved.

Origins of Pupillary Hippus in the Autonomic Nervous System.

Purpose: The purpose of this study was to determine the relative roles of the sympathetic (SNS) and parasympathetic nervous system (PNS) in pupillary hippus. Methods: We used a paired-eye control study design with three cohorts receiving either 1.0% tropicamide (PNS antagonist) in light (TL), 1.0% tropicamide in dark (TD), or 10% phenylephrine (SNS) in light (PL), n = 12 in each. Each subject received one drop to the randomly determined treatment eye, while the other eye served as control. Bilateral measures of pupil size and dynamics were made over 2.6 seconds using an infrared eye-tracker sampling at 500 Hz. Measures were taken at baseline, then every 5 minutes for 40 minutes. Hippus, analyzed in both time and frequency domains, was compared between eyes and cohorts. Results: Pupillary hippus with a distinct dominant frequency was present in all measures at baseline (mean: 0.62 Hz, SD: 0.213 Hz), and that frequency did not change in any group (P = 0.971). Hippus magnitude (treatment eye relative to control eye) decreased in the TL (-72.8 ± 4.7%, P < 0.0001) and TD (-71.3 ± 2.6%, P < 0.0001) groups, but did not change in the PL (+5.4 ± 13.7%, P = 0.173) group, despite PL pupils dilating to a proportion similar to TD. Conclusions: Pupillary hippus can be extinguished by antagonizing the PNS, whereas agonizing the SNS dilates the pupil without affecting hippus. This suggests that hippus originates from central PNS activity, and not from SNS activity, or oscillations in the balance between PNS and SNS at the pupil.

Ocular surface microbiome in meibomian gland dysfunction.

BACKGROUND: To investigate the ocular microbiome in meibomian gland dysfunction in Auckland, New Zealand. DESIGN: Prospective, cross-sectional, observational, university-based study. PARTICIPANTS: Participants resident in New Zealand for ≥2 years (n = 157) were classified as normal (n = 66), mild (n = 41) or moderate-to-severe meibomian gland dysfunction (n = 50). Contact lens wear and anterior blepharitis status were recorded, as well as symptoms and clinical features. METHODS: Bacteria collected from lid margin swabs, before and after gland expression, were isolated and identified by conventional microbiological culture techniques. Aerobic isolates were identified in all 157 participants, and both aerobic and anaerobic bacteria isolated in a subset of 87 subjects. MAIN OUTCOME MEASURES: Bacterial incidence according to meibomian gland dysfunction status RESULTS: Symptoms, bulbar hyperaemia, conjunctival staining, lipid layer grade and tear film stability, but not corneal staining, showed moderate association with meibomian gland dysfunction severity. Participants with and without meibomian gland dysfunction showed a similar microbiome, unaffected by gland expression. Anterior blepharitis, a common co-morbidity, was not an independent predictor of the microbiome. Sterile cultures were more common in contact lens wearers than non-wearers. The incidence of Staphylococcus aureus was higher than anticipated across all severity groups, and that of coagulase-negative Staphylococcus, Corynebacterium and streptococci was lower. CONCLUSIONS: Modest differences in relative proportions of bacteria compared with other studies support climatic variations in the ocular surface microbiome. Similarity in microbiome profile, irrespective of meibomian gland dysfunction severity, anterior blepharitis presence or contact lens wear, suggests potential for commonality in treatment.

Similar contrast sensitivity functions measured using psychophysics and optokinetic nystagmus.

Although the contrast sensitivity function (CSF) is a particularly useful way of characterising functional vision, its measurement relies on observers making reliable perceptual reports. Such procedures can be challenging when testing children. Here we describe a system for measuring the CSF using an automated analysis of optokinetic nystagmus (OKN); an involuntary oscillatory eye movement made in response to drifting stimuli, here spatial-frequency (SF) band-pass noise. Quantifying the strength of OKN in the stimulus direction allows us to estimate contrast sensitivity across a range of SFs. We compared the CSFs of 30 observers with normal vision measured using both OKN and perceptual report. The approaches yield near-identical CSFs (mean R = 0.95) that capture subtle intra-observer variations in visual acuity and contrast sensitivity (both R = 0.84, p < 0.0001). Trial-by-trial analysis reveals high correlation between OKN and perceptual report, a signature of a common neural mechanism for determining stimulus direction. We also observe conditions where OKN and report are significantly decorrelated as a result of a minority of observers experiencing direction-reversals that are not reflected by OKN. We conclude that there are a wide range of stimulus conditions for which OKN can provide a valid alternative means of measuring of the CSF.

Visually guided eye growth in the squid.

Eyes with refractive error have reduced visual acuity and are rarely found in the wild. Vertebrate eyes possess a visually guided emmetropisation process within the retina which detects the sign of defocus, and regulates eye growth to align the retina at the focal plane of the eye's optical components to avoid the development of refractive error, such as myopia, an increasing problem in humans. However, the vertebrate retina is complex, and it is not known which of the many classes of retinal neurons are involved. We investigated whether the camera-type eye of an invertebrate, the squid, displays visually guided emmetropisation, despite squid eyes having a simple photoreceptor-only retina. We exploited inherent longitudinal chromatic aberration (LCA) to create disparate focal lengths within squid eyes. We found that squid raised under orange light had proportionately longer eyes and more myopic refractions than those raised under blue light, and when switched between wavelengths, eye size and refractive status changed appropriately within a few days. This demonstrates that squid eye growth is visually guided, and suggests that the complex retina seen in vertebrates may not be required for emmetropisation.

Prospective trial of intense pulsed light for the treatment of meibomian gland dysfunction.

PURPOSE: To evaluate the effect of intense pulsed light (IPL) applied to the periocular area for meibomian gland dysfunction (MGD) in a prospective, double-masked, placebo-controlled, paired-eye study. METHODS: Twenty-eight participants underwent IPL treatment, with homogeneously sequenced light pulses delivered to one eye and placebo treatment to the partner control eye at 1, 15, and 45 days following baseline (BL) evaluation. Lipid layer grade (LLG), noninvasive tear break-up time (NIBUT), tear evaporation rate (TER), tear meniscus height (TMH), and subjective symptom score using visual analogue scales (VAS) were compared with BL and control values at each visit. RESULTS: Lipid layer grade improved significantly from BL to Day (D) 45 in the treated eye (P < 0.001), but not the control eye (P = 0.714), with 82% of treated eyes improving by at least one LLG. Noninvasive tear break-up time also improved significantly from BL to D45 in the treated (P < 0.001) but not in the control eye (P = 0.056) and was significantly longer than in the treated eye at D45 (14.1 ± 9.8 seconds versus 8.6 ± 8.2 seconds, P < 0.001). The tear evaporation rate was not different in the treated eye compared with the control eye at any visit. Tear meniscus height did not change from BL in either eye (P > 0.05). Visual analog scale symptom scores improved from BL in the treated (P = 0.015), but not the control eye (P = 0.245), with 86% of participants noting reduced symptoms in the treated eye by D45. CONCLUSIONS: Intense pulsed light with multiple sculpted pulses shows therapeutic potential for MGD, improving tear film quality and reducing symptoms of dry eye. ( https://www.anzctr.org.au number, ACTRN12614000162617.).