They may extend into the inner retina causing localized disorganization of the retinal layers.

10.4OCT in Geographic Atrophy

Geographic Atrophy (GA) is a frequent cause of severe visual loss in patients with AMD [24Ð26]. The atrophic process involves not only the retinal RPE but also the outer neurosensory retinal layer and the choriocapillaris [10, 12, 27]. In areas of geographic atrophy, SD-OCT scans show thinning and loss of the RPE (Fig. 10.9). Usually, BruchÕs membrane is visible as a straight line. The outer layers such as IS/OS interface and external limiting membrane are severely altered or even no longer visible. The outer nuclear layer may be absent in zones of geographic atrophy. The outer plexiform layer can come in direct contact to the RPE resulting in retinal thinning. However, the internal retinal layers remain generally relatively unaffected. Alterations in the junctional zone between normal retina and zones of geographic atrophy show migration of RPE cells and severe alterations of the outer retinal layers [10, 12].

10.5OCT in Exudative AMD

Exudative or neovascular AMD includes CNV and associated manifestations such as retinal pigment epithelium detachment, RPE tears, Þbrovascular scars, and vitreous hemorrhages. Visual symptoms include blurred or reduced vision, metamorphopsia, or scotoma. These symptoms are caused by subretinal ßuid, intraretinal ßuid, blood, or destruction of photoreceptors and the RPE by Þbrous or Þbrovascular tissue [28, 29].

The gold-standard for classiÞcation of the endovascular lesion in exudative AMD is ßuorescein angiography [30]. The neovascular complex can be categorized into classic and occult CNV. Occult CNV refers to two different hyperßuorescent patterns on ßuorescein angiography. The Þrst pattern is called a Þbrovascular pigment epithelium detachment, which appears as an irregular elevation of the RPE with stippled hyperßuorescence on late angiographic studies. The second pattern refers to late leakage of undetermined source visualized as speckled hyperßuorescence with pooling of dye in the subretinal space in late angiographic studies.

On OCT scans, the neovascular complex is usually visible as hyperreßective structure associated with intraor subretinal ßuid accumulation (Fig. 10.10). In occult CNV, the hyperreßective structure is located underneath the RPE whereas in classic or mixed CNV, the hyperreßective structure is anterior to the RPE complex (Fig. 10.11). Other features of the neovascular lesion like hard exudates or hemorrhages are visualized as hyperreßective structures.

10.6OCT for Follow-up After Treatment for Exudative AMD

Treatment of exudative AMD has been revolutionized with the introduction of intravitreal anti-VEGF therapy [31Ð 35]. Currently, the major questions related to anti-VEGF therapy for exudative AMD are treatment strategies as well as re-treatment and criteria. In general, re-treatment is recommended in eyes with active CNV. OCT imaging may help to identify these eyes. Although no prospective studies have been performed to prove the predictive value of OCT imaging for re-treatment decisions on exudative AMD, OCT

studies are widely used in clinical practice to guide re-treatment.

Several studies have used retinal thickness measurements from OCT scans to guide re-treatment [36, 37]. These studies have been based on OCT scans recorded with time-domain OCT systems. Thickness measurements in eyes with severely disturbed retinal layers are difÞcult to reproduce. Therefore, it has been suggested not to use retinal thickness measurements (Fig. 10.12) but the presence of intraor subretinal ßuid accumulation as re-treatment criteria (Fig. 10.13). In single OCT scans, small amounts of ßuid accumulation may be overseen; therefore, it is recommended to perform three-dimensional scan patterns covering a large proportion of the macula. These scans should be reviewed for the presence of intraor subretinal ßuid.

The presence of intraretinal accumulation may not represent active CNV but may be a feature of retinal degeneration in Þbrotic scars (Fig. 10.14).

Summary for Clinician

›The SD-OCT technology has improved the imaging technique for retinal diseases signiÞcantly. SD-OCT imaging is widely used for diagnosis and follow-up of patients with AMD. Especially, for the management of anti-VEGF therapy in exudative AMD the detections of intraor subretinal ßuid in SD-OCT scans is essential.

Fig. 10.12 Retinal thickness maps calculated from a volume SD-OCT scan using 49 line scans. The top retinal thickness map was recorded 4 weeks after intravitreal anti-VEGF therapy for

exudative AMD. The map below represents the retinal thickness shortly before the initial treatment. Note the reduction of the central retinal thickness from 502 to 425 mm