Age-Related Macular Degeneration Diagnosis
Eye doctors use a variety of methods used to diagnose AMD.
This method is used to diagnose non-neovascular AMD. To perform ophthalmoscopy, the doctor dilates the pupils with eyedrops and uses an ophthalmoscopean instrument with a light at the endto magnify and examine the back of the eye. The slit lamp biomicroscope also is commonly used with an examining lens to detect early and intermediate AMD.
Non-neovascular AMD is diagnosed when the doctor sees drusen or other pigment changes in the macula. A diagnosis of neovascular AMD is suspected when an individual experiences new symptoms and ophthalmoscopy shows fluid, blood, lipid (fat) deposits, or elevation of the RPE in the area of the macula.
The diagnosis of AMD is confirmed by another test, known as fluorescein angiography. This test enables the doctor to examine the blood vessels in the eye. It is important that fluorescein angiography be performed and interpreted promptly, because neovascular AMD can progress within a matter of days.
This test involves an injection of a dye called fluorescein into a vein in your arm. After the dye circulates and reaches the blood vessels of the eye, a camera with a blue filter takes photographs of the retina. The blue light in the flash stimulates the fluorescein to emit a yellow-green light, which allows the doctor to see the fluorescein in the blood vessels of the retina and choroid, as well as any of the dye that may have leaked from damaged vessels. In rare cases, fluorescein angiography can cause a life-threatening allergic reaction.
There is a small chance of nausea, vomiting, a skin rash, or itching. If the dye leaks out of a vein during injection, a burning sensation or yellow stain may result. In most cases, however, fluorescein angiography, which is essential to diagnose neovascular AMD and to identify the sites of neovascularization, does not cause any problems.
A newer test, indocyanine green angiography, which uses a similar procedure but a different dye, may be used if fluorescein angiography does not adequately highlight the abnormal vessels. In some cases, the green dye can provide a clear image despite barriers such as bleeding or changes in pigmentation.
People with cataracts may need to have them removed before a diagnosis can be made or treatment of AMD is begun, since the cataracts can obstruct the view of the back of the eye. In some cases, removal of the cataracts improves vision.
Ocular coherence tomography
Also called optical coherence tomography, OCT is a recent advance in imaging technology that is becoming increasingly popular. The test is similar to ultrasound except that it measures the reflection of infrared light rather than sound. The noninvasive, high-resolution technique creates cross-sectional images, which make it easier for doctors to see the anatomy of the back of the eyeprimarily the retina and the optic nerveand quantify the effects of damage to the nerve fibers of the retina.
OCT is very helpful in identifying and measuring fluid in and below the retina in people with wet (neovascular AMD) or diabetic retinopathy. Doctors are also using OCT to help individualize treatment regimens for people with wet AMD.