Transcript No Slide Title

Choroidal thickness measurement in myopic eyes by
enhanced depth optical coherence tomography
Vesta CK Chan, Mary Ho, David TL Liu,
Alvin L Young, Dennis SC Lam
Department of Ophthalmology & Visual Sciences,
Prince of Wales Hospital, Hong Kong SAR
Introduction
The axial elongation of the globe in pathological myopia leads to stretching of retinal tissue and reduced retinal function.
Choroid is important to maintain retinal function as it supplies nutrients to retinal pigment epithelial cells and the outer retina.
Compromised choroidal circulation may account for the retinal dysfunction and vision loss in high myopic. Direct choroidal
layer visualization and measurement could be obtained through enhanced depth imaging spectral domain optical coherence
tomography (OCT). This study aims at delineating cause for loss in vision in high myopic eyes without attributable myopic
macular changes.
Design
To measure choroidal thickness in myopic eyes using enhanced depth imaging in a cross-sectional study.
Methods
Fifty-six consecutive patients with spherical equivalent refractive error of at least 6 diopters were evaluated using enhanced
depth imaging optical coherence tomography images that were obtained by positioning the spectral-domain optical coherence
tomography (OCT) device close enough to the eye to acquire an enhanced signal of the choroidal layer. The choroidal depth was
measured as the distance between the outer reflective retinal pigment epithelium layer and the inner sclera border.
Measurements were made at horizontal fashion across the fovea at 500µm intervals of sections. Choroidal thickness (CT) were
measured at the subfoveal region, 3mm temporal to fovea and 3 mm nasal to fovea respectively in a horizontal fashion.
Results
Mean age of the 56 patients was 50.4 years ( +/- 2.03 years standard deviation SD; interquatile range IQR: 42 years to 62 years) ,
and the mean refractive error was – 8.7 D (IQR; -6.1D to -11D) . The mean subfoveal CT was 118µm ( +/- 68μm ) and was
correlated negatively with age (P=0.032) and refractive error (P= 0.011). Regression analysis suggested that subfoveal CT
decreased by 11.9µm per each decades of life and by 6.205µm for each diopter of myopia. The subfoveal choroidal thickness was
inversely correlated with logarithm of the minimum angle of resolution visual acuity (P= 0.008) and visual acuity improved by
0.02 (log MAR) by 10µm increase in choroidal thickness.
Conclusion
Choroidal thickness decreases with age and severity of myopia. Visual acuity drops in line with decreasing subfoveal choroidal
thickness. Reduction in choroidal thickness is related to aging and severity of myopia, while visual acuity depends on subfoveal
choroidal thickness. Our study supports the theory that choroidal abnormality may play a key role in pathogenesis of myopic
degeneration. The axial elongation of the globe in pathological myopia leads to stretching of retinal tissue and reduced retinal
function. Choroid is important to maintain retinal function as it supplies nutrients to retinal pigment epithelial cells and the
outer retina. Compromised choroidal circulation may account for the retinal dysfunction and vision loss in high myopic. Direct
choroidal layer visualization and measurement could be obtained through enhanced depth imaging spectral domain optical
coherence tomography (OCT).
Figure 1:
Figure illustration of obtaining choroidal thickness of myopic eyes.
The choroid is seen in cross-section on OCT scan. Fig 1A: Showing
a sample scan from a 28-year-old male with 6-diopter of myopia,
the choroidal thickness was measured vertically from the outer
border of retinal pigment epithelium to the outer border of
choroid (bounded by two lines). Fig 1B: An OCT scan of a 67year-old male with reduced choroidal thickness with increasing
age.
The Association Between the Visual Acuity in logMAR with the
Subfoveal Thickness. Univariate Linear Mixed Model:
(dependent variable: log MAR, independent variable: choroidal
thickness)
Myopic Coefficient Standard T
patient >/
Error
6 diopters
Figure 2: Scatterplot showing negative correlation
between subfoveal choroidal thickness with severity
of myopia. (CT: choroidal thickness, D: diopter)
References
P value
log MAR -0.002
0.000623 -2.317 0.038
Intercept 0.4866
0.0972
5.006 0.000
(log MAR:log minimum angle of resolution)
The visual acuity in logMAR was fitted with fixed
coefficients (fixed effects) on subfoveal thickness, with
random intercepts (random effects) at the subject level to
adjust correlation between fellow eyes.
Lam CS, Goldschmidt E, Edwards MH. Prevalence of myopia in local and international schools in Hong Kong. Optom Vis Sci
2004;81:317-22.
Curtin BJ, Karlin DB. Axial length measurements and fundus changes of the myopic eye. Am J Ophthalmol 1971;71:42-53.
Povazay B, Hermann B, Unterhuber A, et al. Three-dimensional optical coherence tomography at 1050 nm versus 800 nm in
retinal pathologies: enhanced performance and choroidal penetration in cataract patients. J Biomed Opt 2007;12:041211.
Fujiwara T, Imamura Y, Margolis R, et al. Enhanced depth imaging optical coherence tomography of the choroid in highly
myopic eyes. Am J Ophthalmol 2009;148:445-50.