To employ optical coherence tomography (OCT) to analyze the morphologic changes in the inner retina in different categories of age-related macular degeneration (AMD).
Observational cross-sectional study.
Single-center study. Inclusion criteria were age over 50, diagnosis of Age-Related Eye Disease Study (AREDS) category 2 and 3, naïve neovascular AMD, and atrophic AMD. Healthy patients of similar age acted as a control group. Primary outcome measures were the changes in ganglion cell complex (GCC) and retinal nerve fiber layer (RNFL). Secondary outcomes included modifications of rim area and cup-to-disc ratio.
One hundred and thirty eyes of 130 patients were recruited: 26 eyes for AREDS category 2, 26 for AREDS category 3, 26 for neovascular AMD, 26 with atrophic AMD, and 26 controls. Mean peripapillary RNFL thickness was significantly lower in neovascular AMD, compared to controls ( P = .004); peripapillary RNFL did not significantly vary among AREDS category 2 and 3 and atrophic AMD groups, compared to controls. Mean GCC thickness was higher in the control group, becoming progressively thinner up to neovascular and atrophic AMD groups ( P < .0001). Rim area was significantly thinner in the neovascular AMD group compared with controls ( P = .047); cup-to-disc ratio was higher in the neovascular AMD group compared with the control group ( P = .047).
This study demonstrates that eyes with neovascular AMD display reduced RNFL and GCC thickness. RNFL is partially spared in atrophic advanced AMD. The identification of alteration in RNFL and GCC thickness may reveal useful for future therapeutic implications.
Age-related macular degeneration (AMD) is the leading cause of visual loss among the elderly in industrialized countries. AMD development and progression depends on the complex interaction of genetic, metabolic, and environmental factors that affect different structures of the macular region.
Many studies have focused on AMD abnormalities involving the outer retinal layers and the choroidal structures. On the other hand, there is scant information regarding the condition of the inner retina in the different stages of the disease. Some authors have hypothesized that AMD might also affect the 3 innermost retinal layers, referred to collectively as the ganglion cell complex (GCC)—the inner plexiform layer (IPL), which contains the retinal ganglion cell dendrites; the ganglion cell layer (GCL), which is composed of ganglion cell bodies; and the retinal nerve fiber layer (RNFL), where the ganglion axons are located.
The aim of the present study was to employ spectral-domain optical coherence tomography (SD OCT) to analyze the morphologic changes in the GCC and RNFL layers in different categories of AMD.
This observational, cross-sectional study prospectively recruited consecutive series of patients affected by AMD who were referred to the Ophthalmology Department of San Raffaele Hospital in Milan. Written informed consent to participation in this research was obtained from all subjects. The protocol was approved by the Institutional Review Board of San Raffaele Hospital and the procedures adhered to the tenets of the Declaration of Helsinki.
Inclusion criteria were age over 50, diagnosis of Age-Related Eye Disease Study (AREDS) categories 2 or 3 AMD, and AREDS category 4 both naïve neovascular and atrophic AMD.
Exclusion criteria were any other disorder able to confound the results; a history of eye surgery, including anti–vascular endothelial growth factor (anti-VEGF) injections and laser photocoagulation; or photodynamic therapy at any time. Moreover, particular care was taken to rule out patients affected by ocular hypertension and glaucoma by checking their history and intraocular pressure.
Healthy patients of similar age acted as a control group.
Each patient underwent an ophthalmologic examination that included measurement of best-corrected visual acuity (BCVA) on standard ETDRS charts, intraocular pressure, and biomicroscopy. One study eye per patient was selected and independently classified according to the AREDS criteria by 2 retinal specialists in 2 separate sessions (M.G., M.V.C.). Uncertain cases were judged by a third retinal specialist (F.B.). Category 2 included eyes with multiple small drusen (63–124 μm in diameter) or a few medium-sized drusen and RPE abnormalities. Eyes placed in category 3 had either many medium-sized drusen, at least 1 large druse (≥125 μm in diameter), or geographic atrophy not involving the center of the fovea. Eyes with neovascular AMD had naïve CNV in 1 eye and eyes with dry AMD had geographic atrophy (GA) in at least 1 eye. Each eye underwent a complete SD OCT examination (Cirrus HD; Carl Zeiss Meditec Inc, Jena, Germany) in order to assess the retina, registering central retinal thickness, RNFL, GCC, and choroid thickness.
Patients included in the neovascular AMD group, which was affected by naïve CNV, underwent fluorescein angiography (FA) (Heidelberg Retinal Angiograph 2; Heidelberg Engineering, Heidelberg, Germany) to identify the exact type of CNV, as well as indocyanine green angiography (ICGA), if deemed necessary. A classification into classic, occult, or mixed CNV and retinal angiomatous proliferation was carried out independently by 2 retinal specialists (M.B.P., N.C.), based on the type of CNV, as revealed by fundus examination, FA, or ICGA. Uncertain cases were judged by a third retinal specialist (F.B.).
In all patients included in the atrophic AMD group, the diagnosis of GA was based on the identification of patches of at least 250 μm in longest linear dimension of partial or complete depigmentation, showing sharply demarcated borders, visible underlying choroidal vessels, or excavated or punched-out appearance.
The scan pattern used to measure central macular thickness (CMT) and GCC thickness was the Cirrus HD-OCT Macular Cube 512 × 128 scan. Each image had 5 μm axial and 10 μm transverse resolutions in tissue and consisted of a 512 × 128 volume cube (128 horizontal examination lines of 512 A-scans each). The scanning area measured 6 mm × 6 mm.
The choroidal measurement was performed by a Cirrus high-definition 1-line raster, which is a 6 mm line consisting of 4096 A-scans and 20 B-scans averaged together without tracking. The subfoveal choroidal thickness (SCT), defined as the vertical distance between the hyperreflective line of the Bruch membrane and the chorioscleral interface, was manually measured using the enhanced depth imaging technique, as reported previously. Choroidal thickness was measured at 500 μm, 1000 μm, and 1500 μm intervals on horizontal and vertical line scans centered on the fovea. RNFL was measured using the Optic Disc Cube mode, consisting of a raster of 200 B-scans covering a 6 mm 2 area centered on the optic disc. This technology provides RNFL thickness maps with 17 parameters: average thickness, 4 quadrants (superior, inferior, nasal, and temporal), and 12 clock-hour measurements. The Macular Cube 512 × 128 protocol was used to obtain CMT and GCC measurements.
Primary outcome measures of the present study were the morphologic changes on OCT in GCC and RNFL layers in different categories of AMD. Secondary outcomes included modifications of the rim area and the cup-to-disc ratio in AMD patients.
Statistical analyses were performed using the Statistical Package for Social Sciences (version 17.0; SPSS Inc, Chicago, Illinois, USA). Comparisons of mean BCVA (converted to the logarithm of the minimal angle of resolution [logMAR]), CMT, RNFL, and GCC between the 5 groups were performed using Student t test and analysis of variance. The chosen level of statistical significance was P < .05.
Altogether, 132 patients were originally considered for the study, but 2 patients were excluded as they were found to be affected by open-angle glaucoma. Only 130 eyes of 130 patients were therefore included in the final study: 26 with AREDS category 2, 26 with AREDS category 3, 26 with neovascular AMD, 26 with atrophic advanced AMD, and 26 controls. Complete data regarding the patients and controls are listed in Table 1 . All neovascular AMD eyes were affected by treatment-naïve neovascular AMD and included 12 occult CNV (46.2%), 9 classic CNV (34.6%), 3 mixed CNV (11.5%), and 2 retinal angiomatous proliferation (7.6%).
|Control||AREDS Category 2||AREDS Category 3||Neovascular AMD||Atrophic AMD||Total|
|Age (y) (mean ± SD)||71.6 ± 6.3||74.6 ± 6.6||72.6 ± 7.7||77.5 ± 8||78 ± 10.8||74.5 ± 7.9|
|• Male, n (%)||12 (46.2%)||11 (42.3%)||4 (15.4%)||10 (38.5%)||16 (61.5%)||53 (40.7%)|
|• Female, n (%)||14 (53.8%)||15 (57.7%)||22 (84.6%)||16 (61.5%)||10 (38.5%)||77 (59.3%)|
|BCVA (logMAR ± SD)||0.0 ± 0.0||0.1 ± 0.0||0.1 ± 0.1||0.5 ± 0.2||0.7 ± 0.4||0.2 ± 0.2|
Mean CMT showed a significant increase in the advanced AMD neovascular category (351.4 ± 103 μm) and a significant decrease in the atrophic category (183.9 ± 47 μm), compared with AREDS categories 2 and 3 groups (254.8 ± 35 μm in category 2 and 254.11 ± 24 μm in category 3) and controls (262 ± 103 μm) ( P < .001).
Peripapillary RNFL thickness and mean GCC thickness data are reported in Table 2 . In detail, only in neovascular AMD was mean peripapillary RNFL thickness lower, with a statistically significant difference with respect to controls ( P = .004), but it did not vary significantly among AREDS categories 2 and 3 groups in comparison with healthy eyes ( Table 2 ). Peripapillary RNFL in advanced atrophic AMD patients did not differ significantly from control eyes ( P = .676). Mean GCC thickness, automatically measured as the sum of GCL and IPL, was higher in control subjects, becoming progressively thinner in the neovascular AMD and dry AMD groups, with a statistically significant difference in all groups compared to controls ( Table 2 ).
|Control||AREDS Category 2||AREDS Category 3||Neovascular AMD||Atrophic AMD|
|Average RNFL (mean ± SD) (μm)||88.1 ± 9.7||85.2 ± 9.5||85.5 ± 11.2||79.4 ± 11.2||86.6 ± 11.6|
|P ( t test)||.285 a||.512 a||.004 a||.676 a|
|Average GCC (mean ± SD) (μm)||79.9 ± 5.5||71.7 ± 17.2||74.2 ± 11.5||53.6 ± 16.9||50.4 ± 17.9|
|P ( t test)||.025 a||.049 a||<.0001 a||<.0001 a|
The rim area showed a statistically significant reduction in neovascular AMD subjects compared with controls ( P = .047) ( Table 3 ), whereas no significant reduction was seen in atrophic AMD subjects compared with controls ( P = .328). The cup-to-disc ratio showed a statistically significant increase in neovascular AMD subjects compared with controls ( P = .047) ( Table 3 ). No difference was found between the atrophic AMD group and controls as regards the cup-to-disc ratio ( P = .400). In addition, RNFL thickness and rim area were found to be positively correlated in eyes in the neovascular AMD group (r = 0.486, r 2 = 0.236; P = .005), while RNFL and cup-to-disc ratio were negatively correlated (r = −0.351, r 2 = 0.123; P = .039). No correlation was found between the RNFL or GCC layers and visual acuity.
|Control||Neovascular AMD||Atrophic AMD|
|Average rim area (mean ± SD) (mm 2 )||1.5 ± 0.3||1.4 ± 0.3||1.4 ± 0.3|
|P ( t test)||.047 a||.328 a|
|Average cup-to-disc ratio (mean ± SD)||0.4 ± 0.2||0.5 ± 0.2||0.4 ± 0.2|
|P ( t test)||.047 a||.400 a|