The choroid plays a vital role in the pathophysiology of many diseases affecting the retina. Increasingly more studies now show that choroidal abnormalities such as vascular hyperpermeability, vascular loss, and thinning are found to be critical to the onset and progression of retinal diseases.
8 Recent advancements in SD-OCT now provide two ways for determining choroidal thickness: high-penetration OCT using a long-wavelength light source of 1060 nm
8,12,13 and the EDI technique developed earlier (Spectralis OCT; Heidelberg Engineering).
8,14 –16 Compared with conventional OCT using an 850-nm source,
17 long-wavelength OCT with a 1060-nm source has a higher penetration and, consequently, increased sensitivity, for the posterior choroid and the sclera, allowing visualization of the chorioscleral interface in eyes. The EDI system developed on SD-OCT also provides more details of the microarchitecture of the posterior choroid. Both methods facilitate an understanding of the choroidal abnormalities underlying various chorioretinal diseases. Ikuno et al.
18 had compared the agreement among these two modalities and showed that the results of choroidal thickness were well correlated.
Several studies have recently characterized normal choroidal thickness in normal subjects. Ikuno and colleagues
8 have shown an approximate SFCT of 354 μm in 43 Japanese subjects with a mean age of 39.4 years using a 1060-nm–based light source. At 3 mm to the fovea, the superior, temporal, inferior, and nasal choroid values were 364, 337, 345, and 227 μm, respectively. Margolis and Spaide
7 investigated SFCT in 30 normal subjects (mean age, 50.4 years) by an EDI technique and found that the choroid was thickest underneath the fovea (287 μm), and thickness decreased rapidly nasally, so that it averaged only 145 μm at 3 mm nasal to the fovea. The mean SFCT in the study by Spaide et al.
9 was 318 μm in right eyes and 335 μm in left eyes in 17 volunteers (mean age, 33.4 years) using an EDI system. Our present study showed that choroidal thickness in 210 healthy subjects with a mean age of 49.73 years was 261.93 ± 88.42 μm subfoveally; 224.21 ± 77.94 μm, 3 mm temporally; and 142.92 ± 69.70 μm, 3 mm nasally; these values were very similar to values reported by Margolis and Spaide
7 using an EDI system. The values in our study were somewhat thinner than those reported previously by Spaide and Ikuno. However, the differences may result from differences in the measuring software or the OCT light source, differences in ethnicity (although Margolis and Spaide
7 and Spaide et al.
9 did not specify their ethnic groups), or differences in patient profiles such as age, RE, or axial length. Notably, the other published studies all used a sample size < 50, whereas our study recruited 210 healthy volunteers.
Ikuno and colleagues
8 investigated the relation of SFCT and RE, and found there was a borderline significant positive correlation between them (
P = 0.086; y = 9.3x + 373.4;
R 2 = 0.046), which suggested that SFCT decreased by 9.3 μm for each diopter increase of myopia. In our study, no correlation between SFCT with RE was noted when the entire group of subjects was considered (
r = 0.026,
P = 0.596). The possible reason is that mean age of 43 subjects included in Ikuno's study is 39.4 years old, much younger than ours (49.73 years old). However, a significant positive correlation with RE was found in the subgroup younger than 60 years of age (
r = 0.307,
P < 0.001), but not correlated with SFCT in individuals older than 60 years of age (
r = 0.074,
P = 0.385). SFCT decreased by 10.87 μm for each diopter increase of myopia, which is quite similar to that reported by Ikuno and colleagues.
8
In previous studies, increasing age was shown to be significantly correlated with decreasing choroidal thickness. Regression analysis suggested an approximate decrease in thickness of 15.6 μm every 10 years by Margolis and Spaide
7 and 14 μm by Ikuno and colleagues.
8 Since our present study used a larger sample size (210 volunteers) with wider age ranges (from 20 to 85 years) for accurate analysis, we were able to subgroup volunteers by their ages. Statistical analysis showed that the SFCT in subjects younger than 60 years of age in four subgroups was very similar, as 293.51, 287.87, 299.69, and 297.24 μm in subjects 20–29, 30–39, 40–49, and 50–59 years of age, respectively. In the Combined Group that included 140 volunteers younger than 60 years of age, SFCT was 294.63 ± 75.90 μm, whereas in the Combined Group that included 70 subjects older than 60 years of age, SFCT was 196.52 ± 74.42 μm, or much thinner than that in the younger group. Stepwise regression analysis confirmed that age was not a significant factor of choroidal thickness in the population younger than 60 years of age. Thus, we suggested that age was the factor most associated with SFCT
only in people older than 60 years of age, but not in relatively younger people (younger than 60 years of age).
In our study, we showed a negative correlation between thickness and age in normal subjects older than 60 years of age, which suggested that progressive choroidal thinning occurs over time only in older people. This is a very different finding from that reported in previous studies. The microvascular loss in elderly people may decrease the ability of the choroid to supply proper levels of oxygen and other metabolites to the RPE and outer retina, thus at least partially explaining the mechanisms of age-related macular degeneration. The other factors that affect choroidal thickness remain unknown, so determining them is a high-priority task in future studies.
Supported by the Fundamental Research Funds of State Key Laboratory of Ophthalmology and Guangdong Provincial Natural Science Grants 10151008901000055 and 2011B031700045.