CYCLOPS

Light therapy for diabetic macular edema (DME)Compared to other cells, rods consume a great deal of

oxygen when dark-adapted, but this can be reduced bykeeping them light-adapted. British scientists have shown,in a proof of principle study, that asking patients withDME to sleep with light-emitting diode masks that kepttheir rods light-adapted, reduced the DME as measured byocular coherence tomography.1 This was also associatedwith positive changes in acuity, contrast sensitivity andmicroperimetric thresholds. The improvements cameabout because reduction in photoreceptor oxygen con-sumption prevents the hypoxia that could stimulate vascu-lar endothelial growth factor (VEGF) upregulation andsubsequent neovascularization. An accompanying edito-rial even suggests this form of light therapy might be usefulfor preventing or treating wet age-related macular degen-eration (AMD).2

Synthetic photoreceptors genetically engineeredNerve cells communicate across synapses with special-

ized receptor molecules. Scientists have taken a receptormolecule normally activated by acetylcholine and inserteda ligand that is light-sensitive.3 Violet light activated thereceptor, taking us closer to the day when hybrid photore-ceptors can be used to restore sight by making neurons thatnormally do not respond to light become photosensitive.

Retinal pigment epithelial (RPE) cells made intomultipotent stem cells

Adult multipotent human stem cells have been found inRPE cells. They can be activated to grow into neural andmesenchymal cells.4 Besides the obvious promise of thisdiscovery for replacement therapies, it also accounts forsome human ocular pathology, including proliferative vit-reoretinopathy. See also the discussion by P. Coffey.5

Gene therapy rescues photoreceptor blindness indogs

Recent success in the treatment of Leber’s congenitalamaurosis hinged on gene therapy that corrected errorsarising in the retinal pigment epithelium. Unfortunately,the vast majority of blinding retinal conditions result fromphotoreceptor damage, requiring a therapy that targetsthese mutant photoreceptors. A dog model of retinitis pig-mentosa cured by gene therapy has just been described.6

The authors feel that their findings will lead to “a path fortranslation to human treatment” of human X-linked reti-nitis pigmentosa.

Avoiding collisions with homonymous visual fielddefects (HVFDs)

German investigators examined the abilities of 30 pa-

tients with HVFDs to avoid collisions in a virtual reality

traffic display.7 Not surprisingly, they had more difficultyavoiding simulated collisions with vehicles that ap-proached from their blind side, compared to visually-nor-mal controls. The surprising finding was the range of per-formance in the patient group, with some performing atnear-normal levels. The conclusion drawn is that predict-ing performance from static visual field data alone is inad-equate because some learn to compensate for the field losswith eye and head movements.

Crowding in amblyopia can be reduced by perceptuallearning

Practice can lead to improvement in a variety of percep-tual tasks, a not-surprising manifestation of what is as-sumed to be cortical visual plasticity. In amblyopes, suchperceptual learning has been shown in the past to improvevisual acuity and contrast sensitivity. What has not beenclear is whether the improvement is associated with a re-duction in the effects of crowding where a letter sur-rounded by others becomes more difficult to identify.United Kingdom investigators have just shown that per-ceptual learning reduced the negative effects of crowding,adding to the benefits this approach provides for improv-ing vision in amblyopic adults and children.8

REFERENCES

1. Arden GB, Jyothi S, Hogg CH, Lee YF, Sivaprasad S. Regression of earlydiabetic macular oedema is associated with prevention of dark adaptation.Eye (Lond). 2011;25:1546-54.

2. Heckenlively JR. New concept: treating nonproliferative diabetic retinop-athy with light adaptation of rods during sleep. Eye (Lond). 2011;25:1533-4.

3. Tochitsky I, Banghart MR, Mourot A, et al. Optochemical control ofgenetically engineered neuronal nicotinic acetylcholine receptors. NatChem. 2012;4:105-11.

4. Salero E, Blenkinsop TA, Corneo B, et al. Adult human RPE can beactivated into a multipotent stem cell that produces mesenchymal deriv-atives. Cell Stem Cell. 2012;10:88-95.

5. Coffey P. Untapping the potential of human retinal pigmented epithelialcells. Cell Stem Cell. 2012;10:1-2.

6. Beltran WA, Cideciyan AV, Lewin AS, et al. Gene therapy rescues pho-toreceptor blindness in dogs and paves the way for treating human X-linked retinitis pigmentosa. Proc Natl Acad Sci U S A. 2012;109:2132-7.

7. Papageorgiou E, Hardiess G, Ackermann H, et al. Collision avoidance inpersons with homonymous visual field defects under virtual reality con-ditions. Vision Res. 2012;52:20-30.

8. Hussain Z, Webb BS, Astle AT, McGraw PV. Perceptual learning reducescrowding in amblyopia and in the normal periphery. J Neurosci. 2012;32:474-80.

Cyclops provides a singular view of the basic science literature onvision and is a sampling of what’s new and interesting. The au-thor, Martin J. Steinbach, PhD, welcomes your feedback and

suggestions, which can be sent to mjs@yorku.ca.

CAN J OPHTHALMOL—VOL. 47, NO. 3, JUNE 2012 201