Vision in fishes layers of other neurons before it reaches them. The retina contains rod cells and cone cells. Within the retina, rod cells provide high visual sensitivity (at the cost of acuity), being used in low light conditions. Cone cells provide higher spatial and temporal resolution than rods can, and allow for the possibility of colour vision by comparing absorbances across different types of cones which are more sensitive to different wavelengths. The ratio of rods to cones depends on the ecology of the fish species concerned, "e.g.", those mainly active during the day in clear waters will have more cones than
Gene therapy of the human retina Thus overall, subretinal AAV is 5-10 times more efficient than delivery using the intravitreal route. One important factor in gene delivery is developing altered cell tropisms to narrow or broaden rAAV-mediated gene delivery and to increase its efficiency in tissues. Specific properties like capsid conformation, cell targeting strategies can determine which cell types are affected and also the efficiency of the gene transfer process. Different kinds of modification can be undertaken. For example, modification by chemical, immunological or genetic changes that enables the AAV2 capsid to interact with specific cell surface molecules. Initial studies with AAV in the retina have