In 1987, John E. Dowling published his groundbreaking The Retina: An Approachable Part of the Brain, instantly becoming the benchmark/go-to for retinal anatomy, physiology, and function. Despite emphasis on human retina, the text afforded a broad insight to multiple classes of vertebrate retina, astutely identifying commonalities and differences governed by habitat and survival needs. In 2012, Dowling published a revised edition, including timely updates and two new chapters: “Color Vision” and “Retinal Degenerations, Electroretinography, and Genetics.”
How does one study a brain composed of 1012 neurons, each making 10,000 synaptic connections? The text proposes two methods: (1) study simpler nervous systems, exemplified by an illustrative description of lateral inhibition in horseshoe crab and the link to Mach bands, and (2) study well-characterized parts of the vertebrate brain, emphasizing that the retina, “pushed out into the eye during development,” is an accessible part of the brain, enabling detailed study of anatomy, physiology, and pharmacology of neural mechanisms likely to exist at higher, less accessible levels.
A brief account of retinal development and evolution is followed by chapters covering retinal anatomy and cellular classification and connectivity, including differences and common schemes of vertebrate retina synaptic organization. Chapters on neuron responses and function, retinal chemistry of neurotransmission and neuromodulation, and retinal visual adaptation include classic and updated findings such as recent work on light-sensitive melanopsin-containing ganglion cells and retinal effects of retinoic acid, dopamine, and cannabinoids. The new chapter on color vision is rich with illustrative material on cones, photopigments, color deficiency, evolution, and neural processing, including a recent report of normal color vision in adult color-deficient monkeys after gene therapy to replace the missing photopigment, suggesting that postreceptoral connections for trichromacy exist in dichromats. A new chapter on retinal degenerations and electroretinography covers vitamin A and night blindness, component analysis of electroretinography, and retinitis pigmentosa with animal models to prevent or slow retinitis pigmentosa progression, including light restriction, gene therapy, and mutation induction to clarify roles of gene products. A final chapter discusses how retinal mechanisms, such as electrical coupling and chemical neuromodulation, can be generalized to the brain.
The Retina: An Approachable Part of the Brain remains the consummate standard for understanding functional organization of the retina, highly recommended, in whole or part, for graduate and undergraduate students of neuroscience and psychology, as well as ophthalmology and optometry.
Jeff C. Rabin
San Antonio, TX