What is the role of optical coherence tomography (OCT) in the workup of choroidal neovascularization (CNV)?

Updated: Jan 07, 2019
  • Author: Lihteh Wu, MD; Chief Editor: Andrew A Dahl, MD, FACS  more...
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Answer

CNV causes thickening and fragmentation of the highly reflective RPE-choriocapillaris band. If the CNV is well defined, it is seen as a fusiform thickening of the RPE-choriocapillaris band. In contrast, poorly defined CNV is seen as a diffuse area of choroidal hyperreflectivity that blends into the normal contour of the normal RPE band. A normal boundary between the choriocapillaris and the RPE cannot be defined.

A subretinal hemorrhage is seen as a layer of moderate reflectivity that elevates the neurosensory retina and causes optical shadowing, resulting in a lower reflectivity of the underlying RPE and choroid. Serous, hemorrhagic, or fibrovascular RPE detachments reveal focal RPE elevations with shadowing of the structures beneath the elevated areas. Serous detachments are characterized by complete shadowing of the underlying structures. A hemorrhagic RPE detachment shows a moderately reflective layer beneath the detached RPE. Fibrovascular RPE detachments demonstrate moderate reflectivity throughout the entire sub-RPE space under the elevation.

Detachments of the neurosensory retina appear as elevations of a moderately reflective band above the RPE band. RPE tears can be seen as thick elevated areas of high reflectivity. The underlying choroid is completely shadowed, whereas the adjacent choroid reveals a hyperreflective image because of the absence of RPE. Retinal edema or thickness can be measured objectively by defining the anterior and posterior borders of the retina.

Rogers and coworkers have proposed an optical coherence tomography (OCT) classification scheme of CNV following photodynamic therapy (PDT). [1]

Stage I occurs shortly after PDT and lasts for about a week. It is characterized by an inflammatory reaction that causes an increase in intraretinal fluid in a circular fashion that corresponds with the treatment spot.

Stage II represents the restoration of a near-normal foveal contour with diminished subretinal fluid occurring 1-4 weeks after treatment.

Stage III represents reperfusion and involution of CNV. It typically occurs 4-12 weeks following treatment and is subdivided into 2 categories based on the ratio of subretinal fibrosis to fluid present. Stage IIIa contains a greater subretinal fluid to fibrosis ratio, indicating active CNV. Lesions in Stage IIIb have more prominent fibrosis with minimal intraretinal fluid, indicating inactive CNV.

Further involution of CNV may lead to cystoid macular edema, signifying Stage IV.

In Stage V, CNV and the subretinal fluid resolve, leading to fibrosis and retinal thinning.

Despite the many advantages of OCT, FA remains the imaging modality of choice in the management of CNV. Currently, OCT cannot replace FA in the management of CNV.

With the advent of anti-VEGF therapy, OCT plays a major role in the management of CNV. Most clinicians use the presence of fluid on the OCT scan as an indication of CNV activity and the need for further treatment.


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