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 Vitreous


The eye is an inflated hollow structure like a basketball. The large space behind the iris and lens is filled with a clear jelly-like material called Vitreous. If you dissected a cow’s eye in high school biology you will remember the gooey stuff that blobbed out, like egg-white in consistency.
The vitreous gel forms a cohesive body that is firmly attached to the inside front of the eye and at patches on the surface of the retina. Whether it serves any useful function is debatable. For various reasons it can be surgically removed and replaced with saline with no loss of function in the eye.
Looking into the living eye with the microscope we see thin strings and gossamer veils suspended in a clear liquid. As the eye moves the gel shifts, looking very much like the kelp forest swaying with the action of the waves.

Flashes and Floaters

In youth the gel is optically quite clear. Over time opacities gradually accumulate in the vitreous which cast shadows we see as “floaters.”
Besides accumulation of the floaters the body of vitreous gradually shrinks which causes it to pull on the places inside the eye where it is attached. As the gel pulls on the retina it triggers a nerve impulse which you see as a brief flash of light. For most people the attachment of the vitreous to the retina is not particularly strong and the vitreous pulls free. You may notice a few new floaters, which are a nuisance, but no harm done.

Retinal Tear

In a small percentage of people the gel is firmly attached to the retina and when it pulls it causes a tear in the retina. If the tear includes a blood vessel then strings of blood create heavy dark shadows in your vision. If only the retina tears there is usually pigment released that looks like a lot of new black spots in the vision.
Once there is a tear in the retina then the liquid portion of the vitreous, shown by the blue arrow, can get through the hole and create a separation of the retina from the wall of the eye, referred to as a detachment. The area of detachment starts small and gradually increases in size, usually over a few days. As the detachment grows the retina loses function and vision is lost in that area, so it looks like a gray curtain or window-shade blocking part of vision.

If a retinal tear is caught early then it is a simple thing to repair it with a laser. More specifically, the laser spots are placed to surround the tear. As the laser light is absorbed by the pigment layer it creates a burn that acts like a spot-weld.
If the tear is not treated early, then as time goes by the area of detachment spreads and an increasingly complicated procedure is required to repair it. If the area of detachment is small then laser treatment can still be done followed by injection of an air bubble. With proper head position the air bubble can hold the retina in place while the laser spots take hold. Once the area of detachment has reached significant size then full retinal surgery is required, with removal of vitreous, drainage of fluid and sometimes placement of an encircling band around the eye.

Recommendation. If you see the sudden appearance of new floaters there is no way for you to tell if there has been a retinal tear and it is worthwhile having the retina checked.