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Rachel Hiscox, Christine Purslow, Rachel North, Ian Ketchell, Katharine Evans; Dark Adaptation and the effect of Oxygen Inhalation in Cystic Fibrosis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3016.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has shown impaired measures of dark adaptation in cystic fibrosis (CF), with the cause generally attributed to concomitant vitamin A deficiency. However, other factors including CF-related diabetes (CFRD) may influence these results. Impaired dark adaptation in Type 1 and 2 diabetics improves upon oxygen inhalation and has therefore been attributed to retinal hypoxia. The purpose of this preliminary study was to evaluate the effect of oxygen inhalation on dark adaptation in CF, to determine the underlying cause of impairment.
Dark adaptation was assessed in 9 CF (5 CFRD, 4 non-CFRD) and 9 age, gender and ethnicity-matched controls using a custom made computerised dark adaptometer to present an 11° achromatic stimulus centred on the fovea. All CF subjects were vitamin A sufficient. Following pupil dilation, a Maxwellian view optical system was used to administer an 82% cone and 75% rod photopigment bleach. Subsequently, threshold was monitored for 25 minutes whilst the patient inhaled either medical air or 100% oxygen (selected at random) through a 60% venti mask. This procedure was repeated for the second gas following a 15 minute wash out period. Threshold recovery parameters were modelled and the cone time constant of recovery (τ), final cone and final rod thresholds determined. Relationships were evaluated using paired and unpaired T-tests as appropriate.
Final rod threshold was significantly elevated in CF subjects compared to controls when inhaling medical air, -4.54 and -4.64 log cd/m2 respectively (p=0.03). Oxygen inhalation had no significant effect on any parameter for controls. Oxygen inhalation in CF subjects caused a significant decrease in final rod threshold compared to medical air, -4.66 and -4.54 log cd/m2 respectively (p=0.04). When analysed according to CFRD status, the CFRD group was found to have a significantly elevated final rod threshold compared to the non-CFRD group when inhaling medical air, -4.47 and -4.64 log cd/m2 respectively (p=0.03). This difference was not present when inhaling oxygen.
This study has shown final rod threshold to be significantly elevated in CF, particularly in those with CFRD, with recovery to normal levels upon inhalation of oxygen. For the first time, this observation suggests that CFRD subjects experience impaired dark adaptation secondary to retinal hypoxia, indicating similarities to Type 1 and 2 diabetics.
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