What Should Not Be Missed When Reading an OCT in a Patient with AMD
By: Marco Nassisi, MD, and Michael Ip, MD
Patients with intermediate age-related macular degeneration (AMD) have a 27% risk of progressing to advanced AMD within five years, and the risk increases to 43% if choroidal neovascularization (CNV) and/or atrophy are present in the fellow eye.1 It is important to identify individuals with a significant risk of AMD progression in order to provide optimal patient counseling and monitoring.
Before optical coherence tomography (OCT) was widely available, the presence of large drusen and retinal pigment epithelial changes on clinical examination were two risk factors used for determining risk of progression to advanced AMD.2 The introduction of OCT technology considerably improved the assessment of patients with AMD, allowing an in vivo visualization of the retinal structure almost comparable to a histological examination.
Modern Fourier domain (FD) OCT technology offers to the clinician two types of scans. The B-scan is a cross-sectional image of the retina that displays all the retinal layers thanks to their different reflectivities. The acquisition of a series of consecutive B-scans in the macular area allows a tridimensional reconstruction of the macula, providing a virtual macular brick through which multiple shifting sections in the coronal plane result in the C-scan (or en face) images (Figure 1).
Figure 1. B-scans (top) and C-scans (bottom) of a healthy eye. The C-scans are generated automatically by pooling multiple consecutive B-scans and represent coronal sections of the retina passing through different layers. In this figure, each section is represented with dotted magenta lines on the B-scans: superficial layer (A), mid-retinal layer (B), ellipsoid zone (C) and choroid (D).
Over the last 20 years, research has elucidated OCT-based features that can help clinicians in assessing the risk of AMD progression: higher drusen volume, intraretinal hyperreflective foci (HRF), heterogeneous internal reflectivity (hIR) within drusenoid lesions, and reticular pseudodrusen are OCT-based features that have been reported to be risk factors for progression to advanced AMD. Drusen volume, as well as a map of each lesion, can be generated automatically by some OCT devices.
A threshold of 0.03 mm3 in the central 3.00 mm2 of the macula has been suggested for predicting progression to advanced AMD; the risk may be four times higher compared to patients with lower drusen volumes.3 However, this parameter alone is an inadequate prognostic feature since drusen may grow or collapse and, for example, a “sudden” reduction in drusen volume may precede the development of advanced AMD.
Intraretinal HRF correspond to areas of hyperpigmentation in color fundus photographs and may represent retinal pigment epithelial cells that have migrated into the retina (Figure 2).4,5 Their presence and quantity are significant predictors for the development of geographic atrophy.5,6 Moreover, HRF have been associated with retinal angiomatous proliferation (type 3 neovascularization).7
Figure 2. Intraretinal hyperreflective foci on a drusen lesion.
The hIR of a drusenoid lesion can be easily observed in a C-scan using a section passing through the lesion itself (Figure 3). Areas of hIR may represent a softening of the internal structure of the drusen and may represent the first step before drusen collapse and the development of atrophy.8
Figure 3. C-Scan (A) and B-Scan (B) of a patient with large central confluent drusen. The C-scan represents a coronal section passing through the center of the drusenoid lesions. In both images, it is possible to observe hyporeflectivity inside the drusenoid lesion (white square).
Finally, reticular pseudodrusen may be detected easily with B-scan and/or C-scan and their presence (independent of their number and pattern) is a consistent risk factor for progression to both atrophy and CNV6,9 (Figure 4).
Figure 4. C-Scan (A) and B-Scan (B) of a patient with reticular pseudodrusen (white arrows). The C-scan represents a coronal section passing through the inner segment/outer segment layer. In the C-scan (A), the pattern of distribution of the reticular pseudodrusen is clearly visible.
Recently, a very simple scoring system based on these characteristics has been proposed in order to stratify patients with early AMD into four categories of risk to progression to advanced AMD.6 Each feature is worth one point toward the score, for a maximum of eight points (four per eye). The higher the score, the higher the category, and the higher the risk of developing advanced AMD. In the study, the risks of progression to late AMD within one year of follow-up were 0%, 14.3%, 47.5% and 73.3% for category I, II, III and IV, respectively.6
In conclusion, careful evaluation of OCT imaging in patients with early or intermediate AMD provides important prognostic information, which will help to optimize patient counseling and follow-up.
1. 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 Oct;119:1417-1436.
2. Davis MD, Gangnon RE, Lee LY, et al; Age-Related Eye Disease Study Research Group. The Age-Related Eye Disease Study severity scale for age-related macular degeneration: AREDS Report No. 17. Arch Ophthalmol. 2005 Nov;123:1484-1498.
3. Abdelfattah NS, Zhang H, Boyer DS, et al. Drusen Volume as a Predictor of Disease Progression in Patients With Late Age-Related Macular Degeneration in the Fellow Eye. Invest Ophthalmol Vis Sci. 2016;57:1839-1846.
4. Folgar FA, Chow JH, Farsiu S, et al. Spatial correlation between hyperpigmentary changes on color fundus photography and hyperreflective foci on SDOCT in intermediate AMD. Invest Ophthalmol Vis Sci. 2012 Jul 9;53:4626-4633.
5. Christenbury JG, Folgar FA, O’Connell RV, et al; Age-related Eye Disease Study 2 Ancillary Spectral Domain Optical Coherence Tomography Study Group. Progression of intermediate age-related macular degeneration with proliferation and inner retinal migration of hyperreflective foci. Ophthalmology. 2013 May;120:1038-1045.
6. Lei J, Balasubramanian S, Abdelfattah NS, Nittala MG, Sadda SR. Proposal of a simple optical coherence tomography-based scoring system for progression of age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol. 2017 Aug;255:1551-1558.
7. Nagiel A, Sarraf D, Sadda SR. Type 3 neovascularization: evolution, association with pigment epithelial detachment, and treatment response as revealed by spectral domain optical coherence tomography. Retina. 2015 Apr;35:638-647.
8. Ouyang Y, Heussen FM, Hariri A, Keane PA, Sadda SR. Optical coherence tomography-based observation of the natural history of drusenoid lesion in eyes with dry age-related macular degeneration. Ophthalmology. 2013 Dec;120:2656-2665.
9. Finger RP, Chong E, McGuinness MD, et al. Reticular Pseudodrusen and Their Association with Age-Related Macular Degeneration: The Melbourne Collaborative Cohort Study. Ophthalmology. 2016 Mar;123:599-608.
About our author(s):
Marco Nassisi, MD is a Clinical Research Fellow at Doheny Eye Institute, Los Angeles. He specializes in retinal imaging.
Michael S. Ip, MD, is Professor of Ophthalmology at the David Geffen School of Medicine at the University of California - Los Angeles, and a member of the Doheny Eye Institute.