Choroidal Neovascularization

Biology 103
2003 First Paper
On Serendip

Choroidal Neovascularization

HoKyung Choi

If you had to give up one of your five senses, which would it be? Would you give up your ability to see? A startling number of people lose their eyesight due to an eye disorder known as choroidal neovascularization. And soon I may be one of them. Although there is no known cure for this unfortunate disease, studies have been conducted to find the appropriate surgical treatment.

The outer portion of the 2.5 cm human eye is composed of three primary layers of tissue. The outermost layer is called the sclera, which acts as a protective coating. Within this layer the transparent cornea is present in the front area of the eyeball. Under the sclera is the choroid where the majority of blood vessels and the iris are located. The light-sensitive layer is known as the retina.

As mentioned, the choroid contains most of the eyeball's blood vessels. It is also the layer prone to bacterial and secondary infections. Choroidal neovascularization is a process in which new blood vessels grow in the choroid, through the Bruch membrane and invade the subretinal space. Because there is currently no medical treatment for this disease this abnormal growth can easily lead to the impairment of sight or complete loss of vision.

Three main diseases that cause choroidal neovascularization are age-related macular degeneration, myopia and ocular trauma. The Wisconsin Beaver Dam Study showed that 1.2% of 43-86 year old adults with age-related macular degeneration developed choroidal neovascularization. The study also proved that choroidal neovascularization was caused by myopia in 5-10% of myopes. Ocular trauma, another cause of choroidal neovascularization, is for reasons unknown found more often in males than females. More than 50 eye diseases have been linked to the formation of choroidal neovascularization. Even though most of these causes are idiopathic, among the known causes are related to degeneration, infections, choroidal tumors and or trauma. Among soft contact lens wearers choroidal neovascularization can be caused by the lack of oxygen to the eyeball. Unlike age-related macular degeneration, age is irrelevant to this cause.

Although no medical treatments have proven to be a cure for choroidal neovascularization, particular antiangiogenic substances such as thalidomide, angiostatic steroid, and metalloproteinase inhibitors are currently being tested. Through surgical testing, partial removal of choroidal neovascularization proved to be useless. Therefore the focus has been placed on photodynamic therapy, a procedure approved by the Food and Drug Administration.

In choroidal neovascularization patients, the fluid and blood along with the formation of new blood vessels form scar tissues which are trying to repair damages but are ultimately the cause of blindness. Photodynamic therapy is a treatment meant to stop the fluid as well as stunt further growth of the blood vessels among patients. Photodynamic therapy is performed in two phases. In the first phase Visudyne, a special dye that only attaches itself to abnormal blood vessels underneath the retina, is injected. Then a laser which does not damage the retina activates a compound which closes the anomalous blood vessels located in the eye. CNV has been seen to disappear 24 hours after the procedure. Unfortunately, CNV has also been seen to reappear 2-3 months later in almost all the patients and long-term benefits are still unknown. However, in a year-long Treatment of Age-related Macular Degeneration study of 609 patients16% of treated patients and 7% of placebo patients had visual improvement.

Another type of treatment that is being tested in a study called the Submacular Surgery Trials is an experimental procedure known as submacular surgery. This procedure is performed from the inside of the eye in order to work on the retinal tissues to remove and replace the vitreous fluid. The downside of this procedure is that in order to heal the patient must be face-down for several weeks after the fluid is replaced.

It is most unfortunate that there is still no effective medical treatments nor any completely successful surgical treatments because I was recently diagnosed with choroidal neovascularization in both of my eyes. Although the knowledge I have gained by researching this disease has been personally enlightening, the facts are frightening as well. But to remain optimistic, it is somewhat comforting to know that there are studies such as the Wisconsin Beaver Dam Study and the Submacular Surgery Trials working towards a cure.

References

1) Unified Medical Language System, Medical term dictionary
2) Submacular Surgery, Information about submacular sugery
3) The Royal College of Ophthalmologists, Information about photodynamic therapy
4) Barnes Retina Institute, Education website on photodynamic therapy
5) Ocular Photodynamic Therapy for Choroidal Neovascularization, Description of ocular photodynamic therapy
6) Eye (anatomy), Explanation and overview of the eyeball
7) eMedicine, Journal article on subretinal neovascular membranes
8) eMedicine, Journal article on choroidal neovascularization

Comments made prior to 2007

Hi! i'm Abie from the Philippines. I just saw your website when I was doing a research about choroidal neovascularization. My dad currently has this optical problem, and the doctor said that he has to undergo a certain operation called Vitrectomy. The problem is, during the operation, there is 2% chance that he'd get blind. I know that's it's just a very small chance but still, we are scared of the consequences of this operation. Is there anything that we can do to avoid that? What medicines can he take? I hope you can help me with this. Thanks! ... Abie, 4 April 2006