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The authors presented the findings of a study that aimed to identify the maximum irradiance (power received by a surface per unit area) that can be tolerated by photophobic patients with infectious keratitis (IK). They recruited 30 patients (14 women and 16 men) and looked at 30 eyes suffering from IK (50% viral, 37% bacterial, 13% amoebic). They exposed the affected eyes to six different wavelengths of light of increasing intensity at 482, 650, 675, 700, 750 and 800nm with the patients being able to switch off the light when the discomfort became unbearable. A customised device was developed to quantify the highest irradiance tolerated. The order of the lights was randomised except for the last blue light due to its brightness and was used for comparison. The authors recorded the maximum exposure time and its associated irradiance. The eyes were exposed to lights for a total of 15 seconds. The authors compared irradiance data with exposure times using a non-parametric rank-sum test alongside a non-parametric U test to establish a difference according to keratitis severity. The results showed that the longer the wavelengths, the maximum cumulative irradiance tolerated increased significantly (p<0.001). More than half of all patients reached the maximum irradiance delivered by sources with wavelengths of 750 and 800nm, and the shorter wavelengths were stopped more quickly. This study shows that light sources of 750 and 800nm can be used in photophobic patients to obtain ophthalmic imaging due to their increased tolerance. A limitation of this study is the small sample size that may not be representative of the wider cohort.

Tolerance to light of patients suffering from infectious keratitis.
Courrier E, Lambert V, Renault D, et al.
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Kareem Waleed Alsaffarini

York Hospital, UK.

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