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Ammar Mohamed Yusuf Al-Sayegh, Ambreen Tariq, Aman Kirmani, Samantha Mann, Christopher J Hammond, Omar Abdul Rahman Mahroo; Assessing pan-retinal cone function following ranibizumab treatment for diabetic macular edema by recording the photopic electroretinogram. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1763.
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AntiVEGF agents have shown to be effective in treating diabetic macular edema (DME). VEGF also has a maintenance role in the normal retina, so there are theoretical concerns about possible adverse ocular effects of inhibition. One study showed that switching off VEGF expression in the adult mouse retina led to marked cone photoreceptor dysfunction (Kurihara et al, J Clin Invest 2012). We explored whether patients receiving intravitreal ranibizumab for DME might have detectable changes in cone function after their first dose or after three loading doses by recording the photopic electroretinogram (ERG) at baseline and before each subsequent dose.
Patients, who had no previous antiVEGF treatment, and who were due to receive a course of ranibizumab treatment (three injections approximately 4-6 weeks apart) for DME in one eye were enrolled. Photopic 30 Hz flicker and flash full-field ERGs (corresponding to the ISCEV standard photopic protocol) were recorded from both eyes prior to their first treatment and at each subsequent visit prior to treatment. Response parameters (amplitudes and implicit times for flicker ERG and for flash a-waves and b-waves) post-treatment were compared to baseline (paired t test).
Post-treatment ERGs were available for 13 patients 4-6 weeks following their first injection. For these patients, post-treatment ERG parameters were no more than 10% different from baseline in the treated eye, and were no more than 20% different from baseline in the untreated eye. In the treated eye, none of the comparisons were statistically significant; in the untreated eye there was a significant increase in 30 Hz flicker amplitude (mean increase 15%, p = 0.026). For 6 patients, post-treatment ERGs were available 4-6 weeks following their third injection. Post-treatment ERG parameters for these patients were no more than 10% different from baseline for both treated and untreated eyes, and none of the comparisons here reached statistical significance.
In this exploratory study, no significant change in global cone function, as assessed from photopic ERG responses, was detectable in the treated eyes of patients, and changes appeared to be no greater than those seen in the untreated eyes.
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