 Without 11-cis-retinal, the rod photoreceptor cells no longer produce all-trans-retinol and production of A2E is halted.The isomerisation of all-trans-retinol to 11-cis-retinol also plays a key role in the pathogenesis of diabetic macular edema (DME), but by a different outcome of the same mechanism.One of the consequences of diabetes is damage to blood vessels; damaged vessels are less able to carry oxygen, thus inhibiting one of the most important biological processes within the eye.