Sir,

We read with interest the article ‘Fellow eye effect of unilateral intravitreal bevacizumab injection in eyes with diabetic macular edema’.1 The authors report improvement in the non-injected eye of patients that received unilateral bevacizumab for diabetic macular oedema. A previous study also reported a significant difference in the mean macular thickness of the fellow eye treated with unilateral intravitreal bevacizumab for diabetic macular oedema, but no difference in the fellow eye of those receiving unilateral ranibizumab.2

We report a case of a significant improvement in macular thickness of the non-injected eye of a patient receiving unilateral ranibizumab for diabetic macular oedema. To our knowledge, this effect has not previously been reported.

An 81-year-old man with type II diabetes was referred with bilateral diabetic macular oedema. Best-corrected visual acuity was 6/30 in each eye. Baseline OCT scans showed a right central retinal thickness (CRT) of 607 μm and left CRT of 798 μm (Figures 1 and 2). Fundus fluorescein angiography demonstrated leaking microaneurysms close to the fovea. The patient elected to initially have ranibizumab therapy only in the right eye. No treatment was performed to the left eye, and there was no significant change to his diabetic medications or glycaemic control. Following three loading phase injections to the right eye, follow-up OCT scanning demonstrated a significant improvement in the macular oedema in both eyes, with the CRT measuring 185 and 157 μm, respectively (Figures 3 and 4). Unfortunately, there was no significant corresponding improvement in vision, representing likely underlying macular ischaemia.

Figure 1
figure 1

Pretreatment OCT of right eye showing diabetic macular oedema.

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Figure 2
figure 2

OCT of left eye showing diabetic macular oedema.

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Figure 3
figure 3

OCT of the right eye demonstrating improved macular oedema following three loading ranibizumab injections.

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Figure 4
figure 4

OCT of the left (non-injected) eye showing improved macular oedema following three loading injections to the right eye.

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There have been previous case reports of two patients achieving a beneficial effect in both eyes from the unilateral injection of ranibizumab for uveitis-related macular oedema,3 and a case of bilateral beneficial effect of both unilateral ranibizumab and bevacizumab in a patient with branch retinal vein occlusion.4

Our case suggests that unilateral ranibizumab can have an effect on the fellow non-injected eye in a patient with diabetic macular oedema. This is contrary to previous reports, which indicate that such an effect is only seen with bevacizumab. We suggest clinicians be aware of this possible effect to determine whether there are further similar cases.