this retrospective study was performed at the l. v. prasad eye institute in india from september 2012 to january 2013 .
prior approval from the institutional review board of the institute was obtained , and informed consent was obtained from each study subject for the diagnostic procedures .
fifty - one eyes ( 26 patients ) with a diagnosis of some form of macular dystrophy other than retinitis pigmentosa were included in this study .
all participants underwent a comprehensive ophthalmic examination including best - corrected visual acuity ( bcva ) testing using early treatment diabetic retinopathy study charts , slit - lamp biomicroscopy , intraocular pressure measurement using goldmann applanation tonometer and dilated fundoscopic examination .
all patients underwent electroretinography and electrooculogram for diagnosis of dystrophy as per physician 's discretion .
exclusion criteria included optic atrophy , visually significant cataract , high myopia or hyperopia ( > 6 or + 3 diopters of refractive error ) , poor image quality , any other associated retinal pathology , or history of any intraocular surgery .
control group included age - matched healthy subjects with no ocular disease and without high refractive power ( more than  6d or + 3d ) , which included 251 subjects ( 467 eyes ) , ranging from 5 to 80 years ( unpublished data ) .
the sd - oct scans were obtained using cirrus high - definition ( hd)-oct ( carl zeiss meditec , inc . ,
dublin , ca , usa ) after dilatation of the pupil with 1% tropicamide and 10% phenylephrine eye drops .
the scan used for imaging in this study is hd 1-line raster with edi which is a 6-mm line consisting of 4096 a - scans , an imaging speed of 27,000 a - scans per second , an axial resolution of 5 microns , and a transverse resolution of 15 microns in tissue and averages 20 frames ( b - scans ) .
edi , which automatically sets the choroid closer to the zero - delay line and thus theoretically provides better visualization of the choroidescleral interface , was used for all scans .
scans with a signal strength of more than or equal to 6 were used for analysis . using the cirrus linear measurement tool , a single observer measured ct perpendicularly from the outer portion of the hyperreflective line corresponding to the rpe , to the inner surface of the sclera at 500 microns intervals temporal and nasal from the fovea , up to 3000 microns as published in the literature .
we also evaluated choroidal contour to note if any area of focal thinning was noted , especially in the areas of outer retinal thinning .
as both eyes of 25 subjects were included for analysis , the correlation between the two eyes of the same subject was adjusted using generalized estimating equations ( gee ) during the calculation of summary descriptive parameters .
multivariate models adjusted using gee methods were fit to assess the effects of age , gender , and macular thickness on the ct measurements .
statistical analyses were performed using medcalc for windows , version 12.5 ( medcalc software , ostend , belgium ) . the alpha level ( type i error )
all the graphs were performed made using graphpad prism ( graphpad software , version 6.00 for windows , la jolla california , usa , www.graphpad.com ) .
the sd - oct scans were obtained using cirrus high - definition ( hd)-oct ( carl zeiss meditec , inc . ,
dublin , ca , usa ) after dilatation of the pupil with 1% tropicamide and 10% phenylephrine eye drops .
the scan used for imaging in this study is hd 1-line raster with edi which is a 6-mm line consisting of 4096 a - scans , an imaging speed of 27,000 a - scans per second , an axial resolution of 5 microns , and a transverse resolution of 15 microns in tissue and averages 20 frames ( b - scans ) .
edi , which automatically sets the choroid closer to the zero - delay line and thus theoretically provides better visualization of the choroidescleral interface , was used for all scans .
scans with a signal strength of more than or equal to 6 were used for analysis .
using the cirrus linear measurement tool , a single observer measured ct perpendicularly from the outer portion of the hyperreflective line corresponding to the rpe , to the inner surface of the sclera at 500 microns intervals temporal and nasal from the fovea , up to 3000 microns as published in the literature .
we also evaluated choroidal contour to note if any area of focal thinning was noted , especially in the areas of outer retinal thinning .
using the cirrus linear measurement tool , a single observer measured ct perpendicularly from the outer portion of the hyperreflective line corresponding to the rpe , to the inner surface of the sclera at 500 microns intervals temporal and nasal from the fovea , up to 3000 microns as published in the literature .
we also evaluated choroidal contour to note if any area of focal thinning was noted , especially in the areas of outer retinal thinning .
as both eyes of 25 subjects were included for analysis , the correlation between the two eyes of the same subject was adjusted using generalized estimating equations ( gee ) during the calculation of summary descriptive parameters .
multivariate models adjusted using gee methods were fit to assess the effects of age , gender , and macular thickness on the ct measurements .
statistical analyses were performed using medcalc for windows , version 12.5 ( medcalc software , ostend , belgium ) . the alpha level ( type i error )
all the graphs were performed made using graphpad prism ( graphpad software , version 6.00 for windows , la jolla california , usa , www.graphpad.com ) .
present study included 51 eyes of 26 subjects with inherited retinal disease other than rp .
mean age of the study group was 28.49  16.7 years , with 20 males and 6 females .
mean bcva was 0.59  0.33 logmar ( snellen equivalent 20/70 ) , ranging from 0 to 1.1 ( snellen equivalent 20/2020/250 ) ) . mean spherical equivalent was 1.2d  0.75d .
mean subfoveal ct and central macular thickness ( cmt ) among study subjects was 266.33  76 microns and 122.39  77 microns respectively .
1 . ct profile at different points from fovea in study subjects composite image showing color photograph ( a and b ) , and autofluorescence ( c and d ) and spectral domain optical coherence tomography ( e and f ) with choroidal thickness measurements in a case of stargardt 's disease age - matched control groups included 466 eyes of 233 eyes subjects with mean age of 25.9  18.11 years ( range : 580 years ) .
mean spherical equivalent in control group was  0.22d  0.9 d. all patients were phakic .
mean subfoveal ct and cmt was 297.66  48 microns and 204.4  32.2 microns respectively . on regression analysis , no significant correlation was found between subfoveal ct and any other variable such as age ( p = 0.9 ) , gender ( p = 0.5 ) , cmt ( p = 0.1 ) , spherical equivalent ( p = 0.3 ) , and bcva ( p = 0.6 ) .
while comparing with age - matched healthy subjects decade - wise , no significant statistical difference was noted ( p > 0.05 ) among all age groups [ table 2 ] .
clinical and oct characteristics of study subjects we did not find any areas of focal choroidal thinning at the areas of outer retinal damage irrespective of the type of dystrophy .
our study reports ct distribution at different locations in hereditary retinal diseases in indian population .
age , gender , spherical equivalent has been shown to be related to ct in normal population ; however , we did not find any significant correlation between subfoveal ct and any other variables among eyes with inherited retinal diseases .
there was no significant difference between study group and age - matched healthy subjects , among all age groups .
there is only one study by yeoh et al . , which reports changes in choroidal structures in eyes with inherited retinal diseases .
they reported focal areas of mild to moderate choroidal thinning on edi oct in 5 patients , which corresponded with the clinically visible areas of discrete outer retinal , rpe and choriocapillaris atrophy . in our study
, we did not notice any focal thinning , and change in contour of choroid in relation to outer retinal structure damage . as reported by yeoh et al . , we also noticed a choroidal thinning in eyes with bietti 's crystalline dystrophy and best disease .
yeoh et al . , reported 3 of 6 eyes with stargardt 's having thinning of choroid ; however , in our study , we did not notice any significant choroidal thinning in eyes with stargardt 's disease . while the histopathological studies have demonstrated the degeneration of choriocapillaris , loss of photoreceptors , and rpe in the region of atrophy in eyes with various dystrophies , we did not find any choroidal thinning in areas of retinal thinning , specifically outer retinal thinning in our study subjects .
due to limited resolution of presently available sd - oct devices , measurement of choriocapillaris thickness is not possible . as there was no choroidal thinning noted in areas of outer retinal damage , further improvement in resolution or angiographic studies
. limitations of our study include retrospective nature ; small sample size and unavailability of genetic analysis for our subjects , however , clinical diagnosis as supported by investigations when required .
no statistically significant difference compared to age - matched controls could be due to small sample size ; however , our study provides an outline for future studies .
our study reports quantitative changes in ct in various common inherited retinal diseases seen in indian populations . to validate changes in choroid , a longitudinal study with larger sample size
further understanding of individual layers of choroid may provide more insight into inherited retinal diseases , which may help to plan therapeutic interventions and follow - up .
 purpose : to evaluate changes in choroidal thickness ( ct ) in inherited retinal diseases and its relationship with age , spherical equivalent , visual acuity , and macular thickness.methods:retrospective analysis of 51 eyes with features of retinal dystrophy of 26 subjects , who underwent enhanced depth imaging using spectral domain ( sd ) optical coherence tomography ( oct ) , were included . 
 the ct measurements were made at the fovea and at 5 points with an interval of 500 microns in both directions , nasal and temporal from the fovea and were compared with age - matched healthy subjects . 
 step - wise regression was used to find the relationship between age , spherical equivalent , best - corrected visual acuity ( bcva ) , central macular thickness ( cmt ) , and subfoveal ct.results:disease distribution was as follows : stargardt 's disease 18 eyes ( 9 subjects ) ; best disease 5 eyes ( 3 subjects ) ; cone - rod dystrophy 26 eyes ( 13 subjects ) ; and bietti 's crystalline dystrophy 2 eyes ( 1 subject ) . 
 mean subfoveal ct was 266.33  76 microns . on regression analysis , no significant correlation was found between subfoveal ct and any other variable such as age ( p = 0.9 ) , gender ( p = 0.5 ) , cmt ( p = 0.1 ) , spherical equivalent ( p = 0.3 ) and bcva ( p = 0.6 ) . 
 while comparing with age - matched healthy subjects , no significant statistical difference was noted ( p < 0.05 ) among all age groups.conclusion:our study reports quantitative changes in ct in various common inherited retinal diseases seen in indian populations . to validate changes in choroid , a longitudinal study with larger sample size 
 is warranted . 
Methods
Choroidal imaging
Image analysis
Choroidal thickness measurement
Statistical analysis
Results
Discussion
Conclusion