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Dr Laura Downie
BOptom PhD(Melb) PGCertOcTher FACO FAAO DipMus(Prac) AMusA
Lecturer and Clinical Leader,  Cornea and Contact Lenses, University of Melbourne

Retinal sensitivity is reduced in patients with obstructive sleep apnoea

Patients with obstructive sleep apnoea (OSA) have been shown to have reduced retinal sensitivity, as measured using standard automated perimetry (SAP), compared with age-matched, healthy control patients.

This study involved the prospective enrolment of OSA patients (n = 80) and age-matched controls (n = 111). Participants underwent at least one reliable SAP (Humphrey 24-2 SITA standard). Peripapillary retinal nerve fibre layer thickness (RNFL) was measured with spectral domain optical coherence tomography (SD-OCT). OSA patients were sub-classified into three groups based on the apnoea/hypopnoea index as having mild, moderate or severe OSA.

Mean visual acuity, central corneal thickness and RNFL thickness did not differ significantly between the OSA and control groups. The SAP mean deviation was higher in patients with OSA compared with controls (-0.23 ± 0.8 dB versus -1.74 ± 2.8 dB, p < 0.001). In patients with OSA, SAP threshold values were more depressed in the peripheral field. The apnoea/hypopnoea index was significantly correlated with the SAP indices (p < 0.001).

It is important for clinicians to be aware that OSA patients may have non-glaucomatous visual field abnormalities, which needs to be differentiated from glaucoma.

Invest Ophthalmol Vis Sci 2014; 55: 11: 7119-7125.

Motor vehicle collisions and central binocular visual field damage in primary open angle glaucoma patients

In this Japanese study, the number of self-reported motor vehicle collisions was found to not be related to the extent of central visual field abnormality in patients with primary open angle glaucoma (POAG).

POAG patients (n = 247) were surveyed about their motor vehicle collision history and driving habits. The relationship between motor vehicle collision history and 52 total deviation values of an integrated binocular visual field, better and worse visual acuities, age and gender were examined.

A total of 51 patients (20.6 per cent) reported a prior motor vehicle collision. There were significant differences between patients with and without a collision history for better visual acuities, a single total deviation value in the superior-right visual field and the average distance driven per week (p < 0.05). No significant relationship was evident between collision history and the mean visual field deviation. There was a significant positive relationship between collisions and the distance driven per week (p ?=? 0.005).

Taken together, these data suggest a complex relationship between visual function and driving tasks in POAG. Careful consideration should be taken with regard to attempting to predict a patient’s driving abilities from their central visual field findings.

PLoS One 2014; 9: 12: e115572.

Association between mitral valve prolapse and open-angle glaucoma

The presence of pre-existing mitral valve prolapse (MVP) has been found to be a significant predictor for the development of open-angle glaucoma.

This retrospective cohort study used a longitudinal health insurance database from the National Health Insurance program in Taiwan, consisting of more than one million individuals who were followed from 1996 to 2008. A total of 21,677 people had experienced MVP; 86,708 subjects without MVP were propensity-score matched and served as a comparison group.

The incidence of open-angle glaucoma in patients without MVP and those with a history of MVP was 10.2 and 16.1 per 10,000 person-years, respectively. The adjusted HR for open-angle glaucoma in the MVP group was 1.88 (95% CI: 1.58 to 2.23).

Heart 2014; ePub 11 December 2014.

Effectiveness of tele-glaucoma versus in-patient examination for glaucoma screening

Tele-glaucoma, involving the electronic examination of stereoscopic digital ocular images by an ocular specialist, has been shown to be an effective screening tool for glaucoma.

A systematic review and meta-analysis sought to both assess the usefulness of tele-glaucoma as a screening tool for glaucoma and to provide estimates of the diagnostic accuracy, diagnostic odds ratio and the relative percentage of glaucoma cases that were detected.

A total of 45 randomised controlled clinical trials were included. Meta-analysis showed that tele-glaucoma was relatively more specific (specificity: 0.790, 95% CI: 0.668 -0.876) and less sensitive (sensitivity: 0.832, 95% CI: 0.770 -0.881) than in-person patient examinations. It was reported that the relative odds of a positive screen test in glaucoma cases was 18.7 times more likely than a negative screen test in a non-glaucoma case.

This analysis demonstrates that tele-glaucoma can be used to screen for glaucoma. The findings suggest that more cases of glaucoma can be detected using this method than in-person examination.

PLoS One 2014; 9: 12: e113779.

Relationship between central corneal thickness and oxygen levels in the anterior chamber angle

An inverse correlation has been found between central corneal thickness and oxygen levels in the anterior chamber angle.

This prospective, cross-sectional study involved 124 patients undergoing cataract and/or glaucoma surgery. Prior to the surgical procedure, an oxygen sensor was used to measure anterior chamber oxygen levels at three locations: near the central corneal endothelium, in the mid-anterior chamber and in the anterior chamber angle. Multivariate regression analyses were used to assess for correlation between oxygen levels and central corneal thickness.

The only significant relationship found was a correlation was between central corneal thickness and oxygen in the anterior chamber angle.

It was concluded that this finding could provide insight into the reason why a relatively thinner cornea could increase glaucoma risk. The authors hypothesised that exposure of the outflow system to higher oxygen levels may increase the risk of oxidative damage within the trabecular meshwork.

Am J Ophthalmol 2014; ePub 26 November 2014.

NTG and optic nerve head torsion

Optic nerve head torsion has been found to be a feature of normal-tension glaucoma (NTG).

Using two-dimensional optical coherence tomography images, this study compared optic nerve head tilt and torsion in eyes with NTG (n = 78) and primary open angle glaucoma (POAG, n = 78); eyes were matched according to age and axial length. Comparisons between the groups were made for the extent of horizontal, vertical and maximum optic nerve head tilt and torsion. Further comparisons were undertaken based on myopic status and visual field deficit location.

The degree of vertical and horizontal tilt did not differ between NTG and POAG eyes. NTG eyes had significantly higher degrees of torsion than POAG eyes (p = 0.022) did with matched axial length. In addition, NTG eyes showed a significant difference in the degree of maximum tilt and torsion, and the direction of vertical tilt and torsion by the location of the visual field defect.

Taken together, these data suggest that NTG is more prominently associated with optic nerve head torsion compared with POAG in eyes of similar axial length.

Invest Ophthalmol Vis Sci 2014; Nov 25; 56: 1: 156-163.

Uveitis a potential confounding factor for retinal nerve fibre layer thickness measurements

The presence of uveitis has been reported to be a confounding factor that may limit the accurate assessment of retinal nerve fibre layer (RNFL) thickness, using optical coherence tomography (OCT).

A comparative, retrospective pilot study involved consecutive uveitis patients who had undergone OCT RNFL measurements in an ophthalmology clinic. Included in the study were uveitic eyes without glaucoma (n = 76) and uveitic eyes with established glaucoma (n = 135). Global and sectoral RNFL thickness measurements were taken.

In non-glaucomatous uveitic eyes with active inflammation (n = 19), mean global- and sectorial-RNFL measurements were thicker than the normative 95th percentile.

The mean global RNFL measurement in these eyes was also greater than in the non-glaucomatous uveitic eyes without active inflammation (n = 57). In uveitic eyes (both quiescent and active) with glaucoma, the mean global RNFL thickness was found to be significantly greater than in eyes with a similar stage (moderate) of non-uveitic glaucoma.

It was concluded that these findings raise concern about the value of OCT RNFL measurements for detecting and monitoring glaucoma in eyes with uveitis.

Ophthalmology 2014; ePub 4 November 2014.

Relationship between iris surface features and anterior chamber angle width

An association has been described between irises with more surface crypts and a lighter colour and a wider anterior chamber angle, in Asian eyes.

In this prospective, cross-sectional study, subjects (n = 600) were recruited from a large population-based study in Singapore. Digital slitlamp photographs were used to assess iris surface features (that is, the number and size of crypts, the number and circumferential extent of furrows and colour). Anterior chamber width was measured using optical coherence tomography images. Data from right eyes were used in analyses.

Included in the analyses were a total of 464 eyes, which had digital photographs of suitable quality for grading. Following adjustments for age, sex, ethnicity, pupil size and corneal arcus, it was found that a higher crypt grade was independently associated with a wider anterior chamber angle. Darker irises were associated with a narrower anterior chamber angle.

The authors concluded that these findings suggest that iris surface features may be a useful adjunctive measure to assess the risk of angle closure.

Invest Ophthalmol Vis Sci 2014; 55: 12: 8144-8148.

Swimming goggle wear is not associated with an increased prevalence of glaucoma

A recent Australian study has shown that frequent wearing of swimming goggles does not lead to an increased risk of glaucoma.

Regular swimmers (n = 231) and non-swimmers (n = 118) underwent comprehensive ocular examination, including the measurement of intraocular pressure, visual fields and retinal nerve fibre layer (RNFL) thickness using optical coherence tomography.

Based on intraocular pressure and visual fields, no new cases of glaucoma were detected in the participants who swam regularly. There were also no significant differences in RNFL thickness between swimmers and non-swimmers.

Br J Ophthalmol 2014; ePub 9 September 2014.

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