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Jasleen Kaur Jolly, Charles L Cottriall, Markus Groppe, Robert E MacLaren; Characterisation of Scotopic Vision in Patients with Choroideremia Utilising full-field stimulus threshold (FST). Invest. Ophthalmol. Vis. Sci. 2016;57(12):621. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Loss of night vision is an early symptom of choroideremia and other retinal degenerations that primarily affects the rod photoreceptor. The full-field stimulus threshold (FST) is an established measure of absolute scotopic thresholds (in dB) and is a summed response across the retina. FST was therefore used to assess scotopic thresholds in a large cohort of patients with choroideremia.
FST measurements were made using the Espion 2 (Diagnosys LLC, Cambridge, UK). In order to characterise scotopic function in choroideremia, patients (n=56) attending screening appointments for the gene therapy trial (NCT01461213) underwent FST testing, following 45 minutes dark adaptation. Additionally a cohort of normal age-matched controls (n=34) and female choroideremia carriers (n=10) were also assessed with FST. All comparative statistics were conducted on the right eye only (tested first).
The FST threshold values (mean ± SEM) in the patient group were -21.2 ± 2.0dB, choroideremia carrier group -43.9 ± 2.4dB, and control group -51.8 ± 0.7dB. All three groups were significantly different to each other (Kruskal-Wallis ANOVA, p<0.0001 for all points). Males and females in the control group were compared. There was no effect of gender (unpaired t-test, p=0.85). The correlation between age and threshold was plotted. This shows a trend towards a decrease in sensitivity (represented by an increase in the value of the FST) of 0.13 dB per year in the control group (r=0.40, p=0.02), but a higher rate 0.5 dB change per year in the patient group (r=0.56, p<0.0001).
Scotopic vision, as assessed with the FST, declines with age and is further reduced in choroideremia patients and. Female carriers also have impairment. FST is able to detect reduced rod function in choroideremia and since it includes the peripheral retina, it is complementary to existing measurements made such as visual acuity and microperimetry.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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