Purpose: To study microperimetric macular sensitivity in diabetic macular oedema (DMO) in relation to lesion characteristics obtained by optical coherence tomography (OCT), colour fundus photography, and fluorescein angiography (FA).

Methods: The study comprised 20 eyes in 15 patients with nonproliferative diabetic retinopathy and recently diagnosed untreated DMO. Investigations included microperimetry, fluorescein angiography, colour fundus photography, and OCT. All measures and gradings were made for each of the nine fields of an early treatment diabetic retinopathy study macula template. Statistical analysis was made using Spearman’s nonparametric test including field and mean values within fields. Comparisons were made within the study population and with a normative microperimetry database.

Results: Subnormal microperimetric sensitivity was associated with cystoid macular oedema, both in foveal petaloid (r = -0.50, p = 0.02) and extrafoveal honeycomb patterns (r = -0.8, p < 0.0001) and with outer nuclear layer cysts (r = -0. 5, p = 0.024), inner nuclear layer cysts (r = -0.31, p = 0.03), and hard exudate (r = -0.38, p = 0.0026). There was no detectable effect of focal noncystoid oedema (r = -0.16, p = 0. 48), diffuse noncystoid oedema (r = -0.14, p = 0.55), capillary nonperfusion (r = -0.33, p = 0.15), intraretinal haemorrhage (r = -0.15, p = 0.53), or serous retinal detachment (r = -0.11, p = 0.63). Foveal thickening was associated with locally reduced sensitivity (r = -0.54, p = 0.01). Foveal sensitivity was positively correlated to the visual acuity, with a correlation of 0.44 and a borderline significance (p = 0.0509).

Conclusions: Macular hard exudates and cystoid oedema were associated with locally reduced sensitivity. Thus, the lesions associated with reduced sensitivity for a white-on-white stimulus were such lesions that cause light to be blocked or scattered before it reaches the photoreceptors, suggesting that optical effects are a major cause of sensitivity loss.