Craig Blackwell, MD

Santa Cruz, CA
Diplomate: American Board of Ophthalmology
Fellow: American Academy of Ophthalmology

Welcome to the Website of Craig Blackwell, MD

An Ophthalmology Practice in Santa Cruz, CA

The Retina

The retina is a layer of nerve tissue lining the inside of the eye that receives light and makes a picture, like film in a camera.

The illustration shows the retina as the orange-colored layer covering almost the entire inside of the back of the eye. When we look into the living eye we see through the retina, which is actually clear, to the orange color of the pigment layer.

The retina is composed of several types of cells organized in layers. The outermost layer is the Pigment Epithelium (RPE), a layer of cells that support the metabolism of the photoreceptors, the rods and cones.

Rods and Cones

The Rods and Cones are the sensory cells within the retina that receive the photons of light and generate a nerve impulse.
Cones are responsible for color vision. There are three types of cones, each sensitive to a particular color, blue, green or red, but they take relatively more light to activate. Cones predominate in the center of the retina so you perceive color most acutely in your central vision.
Rods have no color preference, and take only a single photon to activate. Rods predominate in the peripheral retina giving side vision and vision in low light conditions. For instance, if you are looking at stars in the night sky you will see the dim ones slightly better if you look just a little off center.

The nerve impulse generated by the photoreceptors is carried by an intermediate set of cells, (Bipolar and several types of horizontal cells, which provide basic signal processing) to the Ganglion cells from which it is sent along the axon on its journey back toward the brain.

Photoreceptor -> Bipolar Cell -> Ganglion Cell -> Visual Cortex

The Macula

This is a view of the central retina looking in through a dilated pupil.
The Macula is the center part of the retina used to see moderate detail. The Fovea is the very center where the finest detail is seen, like reading and recognizing faces.
The vessels on the surface of the retina supply the inner layers. Usually your brain ignores their presence, unless highlighted by a bright light.

The most common problems with the retina are detachment, diabetic retinopathy and macular degeneration.