ORCID Profile
0000-0002-9892-2964
Current Organisation
The University of Auckland
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Publisher: Wiley
Date: 05-12-2019
DOI: 10.1111/OPO.12656
Abstract: 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. Experiment 1: The gmfERG responses (direct, DC, and induced, IC, litudes 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. Experiment 1: DC and IC response litudes 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 litudes 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 litude, p = 0.39 DC latency, p = 0.10 IC litude, p = 0.51 IC latency, p = 0.64). 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.
Publisher: Springer Science and Business Media LLC
Date: 27-10-2020
DOI: 10.1038/S41598-020-75342-9
Abstract: 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.
Publisher: Springer Science and Business Media LLC
Date: 23-11-2017
DOI: 10.1038/S41598-017-16320-6
Abstract: 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, litude 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.
Publisher: Wiley
Date: 15-05-2023
DOI: 10.1111/OPO.13163
Abstract: 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 litudes 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. 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 litudes 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). We observed significant differences in the gmfERG responses between the single‐vision and dual‐focus contact lenses. Overall, DC litudes peaked between zero and +2.00D secondary power, while IC litudes were maximal between +2.00D and +4.00D. Compared with the single‐vision control, the greatest increase in DC and IC litudes 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. 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 litudes 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.
Publisher: Informa UK Limited
Date: 11-2007
DOI: 10.1111/J.1444-0938.2007.00179.X
Abstract: This report describes the short- and long-term ocular signs and symptoms of a patient with an orbital blow-out fracture and discusses the differential diagnosis of vertical diplopia. A blow-out fracture occurs when blunt trauma is applied either directly to the eyeball itself or the orbital rim and usually results in a fracture of the orbital floor with consequential excavation and entrapment of orbital contents in the fracture. Vertical diplopia is a common presenting symptom for a blow-out fracture of the orbit but careful considerations should be given to other potential conditions leading to such diplopia. A patient is presented who suffered a blow-out fracture almost a decade earlier, secondary to blunt trauma to the globe. The clinical findings are provided immediately after the trauma, post-surgery and during a recent ocular examination.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2016
DOI: 10.1097/OPX.0000000000000957
Abstract: A number of optical methods for slowing myopia progression have been tested and are now available. However, data on real-world use in clinical use is scarce. Here, we present a review of the clinical outcomes for patients attending a specialist myopia control clinic at The University of Auckland Optometry School, NZ. We report a comparative case series of 110 patients (aged 4–33 years, mean: 12.13 ± 4.58 years, 62% female) who attended the clinic between 2010 and 2014. Fifty-six were prescribed orthokeratology, 32 dual focus soft contact lenses, and 22 received advice only. Initial myopia, vitreous and axial eye length, previous myopia progression, age, number of myopic parents, and gender were not significantly different between orthokeratology and dual focus soft contact lens groups. Mean follow-up time for the orthokeratology and dual focus lens groups was the same (orthokeratology: 1.30 ± 0.88 years dual focus lens: 1.33 ± 0.80 years (p = 0.989)). There was a significant reduction in the annualized myopia progression in both groups (orthokeratology: −1.17 ± 0.55 to −0.09 ± 017 D/yr, p 0.001 dual focus soft contact lens: −1.15 ± 0.46 to −0.10 ± 0.23 D/yr, p 0.001). There was no difference between orthokeratology and dual focus lens treatment efficacy (p = 0.763), nor in axial or vitreous chamber length changes after treatment (p = 0.184). One adverse event was reported over the 4-year period. Both orthokeratology and dual focus soft contact lenses are effective strategies for targeting myopia progression in the clinic. We saw no significant difference in the efficacy of the two methods in this regard, and so we believe there are very few barriers for any contact lens practitioner to be actively promoting myopia control treatment to at-risk patients.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 13-01-2017
Abstract: The purpose of this study was to determine the relative roles of the sympathetic (SNS) and parasympathetic nervous system (PNS) in pupillary hippus. 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 s ling 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. 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. 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.
Publisher: Elsevier BV
Date: 09-2015
DOI: 10.1016/J.CUB.2015.07.073
Abstract: 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.
No related grants have been discovered for Philip Turnbull.