Common tests to order for evaluation of patients with AMD

BySharon Fekrat, MD, FACS

Ophthalmologists have a variety of tests to evaluate patients with AMD. The more commonly used tests are color fundus photography, optical coherence tomography (OCT), red-free fundus photographs and intravenous fluorescein angiography (Table 1).

Table 1: What potential tests are more commonly used to evaluate an eye with AMD?

AMD staging

The stage of AMD often determines the tests ordered by an ophthalmologist:

Early AMD is characterized by small drusen, less than 63 µm.
Intermediate AMD is characterized by larger drusen, with at least one greater than 125 µm, or noncentral geographic atrophy.
Advanced AMD is characterized by geographic atrophy at the center of the macula and choroidal neovascularization (CNV).¹

Color fundus photography and OCT

Sharon Fekrat, MD, FACS

Ophthalmologists use color fundus photographs to document the state of AMD when first evaluating a patient and when evaluating progression from visit to visit. Those patients with early or intermediate AMD often want to know if more drusen has developed or if areas of geographic atrophy have developed or progressed when compared to the previous visit. Determination of such progression is facilitated by comparing color fundus photographs.

Color fundus photographs are also helpful in neovascular or wet AMD. Ophthalmologists can document, with or without treatment, the development or resolution of subretinal hemorrhage and increasing fibrosis, which may explain a change in visual acuity (Figure 1).

In addition to color fundus photographs, ophthalmologists can use OCT. OCT is a noninvasive, noncontact transpupillary form of imaging. It is similar to B-scan ultrasonography except light rather than sound is used to get a higher resolution of about 10 microns. Regular use of OCT can decrease the need for fundus contact lens examination. OCT is an optical cross-section. Three things to look for using OCT in an eye with macular degeneration are:

Subretinal fluid
Macular edema
Pigment epithelial detachments

Eyes with neovascular AMD can develop a rip in their retinal pigment epithelium (RPE) with or without AMD treatment. OCT scans can help ophthalmologists identify this finding as well.

Spectral domain optical coherence tomography (SDOCT) is a test gaining popularity among retinal specialists. It is a higher speed test at 40,000 scans per second and delivers, at 5µm a higher resolution than standard OCT. SDOCT includes software that allows multiple ways to manipulate images.

Figure 1: CNV with subretinal hemorrage and fibrosis

Red-free fundus photography and fluorescein angiography

Red-free fundus photography is an older test that can help identify hemorrhage. For example, if an ophthalmologist is attempting to identify small dots of hemorrhage in an eye with nonneovascular AMD, then a red-free fundus photograph may facilitate the detection of blood when it is not as apparent ophthalmoscopically. (Figure 2).

Intravenous fluorescein angiography is generally obtained when there is evidence from examination or from OCT that suggests the presence of CNV. In fluorescein angiography, a fluorescein dye is injected intravenously and the fundus is photographed using special filters.

With the advent of VEGF inhibitor treatments such as ranibizumab and bevacizumab, fluorescein angiography are often obtained at the baseline examination and less commonly during follow-up. Fluorescein angiography has been largely supplanted by OCT during the follow-up period after the initiation of anti-VEGF treatment. Ophthalmologists are still interested in the angiographic pattern of CNV at baseline and whether it is predominantly classic, minimally classic, and occult; however, this rarely decides the treatment regimen in 2008. The angiogram also helps determine where the CNV is in relation to the foveal center (extrafoveal, juxtafoveal or subfoveal) and how large the CNV is. Fluorescein angiography can also be helpful in evaluating the response to treatment in some eyes.

Figure 2: Red free fundus photograph assists with identification of heme

Other tests

There are many tests to evaluate eyes with AMD that are less commonly used, such as indocyanine green angiography (ICG), fundus autofluorescence and microperimetry.

ICG is typically used to look for CNV through subretinal hemorrhage. It is used in eyes with polypoidal choroidal vasculopathy and in the presence of large or small serous pigment epithelial detachments. With ICG, minimal leakage through the choriocapillaris fenestration results n better imaging of the choroidal vessels and lesions.

Fundus autofluorescence, which uses the confocal scanning laser ophthalmoscope, can identify areas of geographic atrophy due to an absence of fluorophores residing in the lipofuscin granules in the RPE.

Finally, microperimetry can map the scotoma resulting from the CNV by providing point-to-point correspondence between fundus image and perimetric results.

Conclusion

Multiple tests are available to document and characterize the progression of AMD. A combination of these tests determined by the stage of AMD can guide ophthalmologists in the effective treatment of these eyes.

References

Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 2001; 119:1417-1436.