The 'colour-shading effect' describes the phenomenon whereby chromatic variations affect the magnitude of perceived shape-from-shading in luminance patterns. A previous study showed that in mixed colour-plus-luminance sine-wave plaids, impressions of depth in the luminance component were enhanced by non-aligned chromatic components, and suppressed by aligned chromatic components [Nature Neuroscience 6 (2003) 641-644]. Here we examine the chromatic determinants of these effects. Colour contrast was defined along the cardinal axes of colour space in order to isolate the L-M and S-(L+M) post-receptoral chromatic mechanisms. We found no difference in the potency of L-M-only and S-(L+M)-only gratings, either for enhancing or suppressing perceived depth. Moreover, the magnitude of depth-suppression was no different for any combination of depth-enhancing and depth-suppressing cardinal directions. Finally we tested whether the visual system carried the assumption that natural shading is tinged with blue, by measuring perceived depth in a colour-plus-luminance grating that was made to appear either bright-yellow/dark-blue or bright-blue/dark-yellow. However there was no difference in the magnitude of depth-suppression between conditions, suggesting that the visual system does not make any assumption about the colour of natural shading. Taken together, the results suggest that while the colour-shading effect is highly sensitive to colour contrast, it is agnostic with respect to colour direction.

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Purpose: To report the clinical course of a patient presenting with stellate nonhereditary idiopathic foveomacular retinoschisis (SNIFR) in response to topical Dorzolamide treatment. Methods: Case report, with multimodal imaging findings, including spectral domain optical coherence tomography and fluorescein angiography. Topical Dorzolamide Hydrochloride 2% drops were used three times per day in the affected eye. Results: We identified a 27-years-old male patient who presented with 1-week history of decreased vision in his left eye. Spectral domain optical coherence tomography of the affected eye showed macular splitting of the inner plexiform layer and outer plexiform layer involving the fovea with no other evidence of a hereditary or acquired predisposing condition. The patient was started on the topical treatment for 6 months with visual improvement from 20/40 to 20/30 in the left eye, after which the decision to stop topical dorzolamide therapy was made. On 3 months of follow-up, visual acuity decreased back to 20/40 in the left eye with an increase in retinal thickening on spectral domain optical coherence tomography. Topical dorzolamide was restarted three times per day in the left eye. At 1-year point after restarting treatment, visual acuity was 20/20 in the left eye, with resolved inner plexiform layer and outer plexiform layer splitting on spectral domain optical coherence tomography in the left eye. Conclusion: Stellate nonhereditary idiopathic foveomacular retinoschisis can be a devastating problem causing decrease in vision. To the best of our knowledge, this is the first case in the literature to report the complete resolution of SNIFR in response to topical dorzolamide hydrochloride 2% therapy. Further prospective studies are vital to better elucidate our understanding of this new disease identity.

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