all study subjects were recruited in a consecutive manner from our glaucoma clinic ; the patients were examined between february and april 2010 at the asan medical center , seoul , korea . on initial evaluation
, all subjects underwent a complete ophthalmologic examination including the recording of medical , ocular , and family histories ; visual acuity ( va ) testing ; a humphrey field analyzer ( hfa ) swedish interactive threshold algorithm 24 - 2 full threshold test ( carl zeiss meditec ) ; multiple intraocular pressure measurements using goldmann applanation tonometry ; stereoscopic optic nerve photography ; and cirrus oct .
all participants had previously experienced several instances of hfa testing . to minimize any learning effect ,
only the final hfa test results were used for analysis in the current study . for inclusion , all participants had to meet the following criteria : best - corrected visual acuity ( bcva ) of 20 / 30 or better , with a spherical equivalent within 5 diopters ( d ) and cylinder correction within + 3 d ; presence of a normal anterior chamber and open angle on slit - lamp and gonioscopic examination ; and reliable hfa test results with a false - positive error < 15% , a false - negative error < 15% , and a fixation loss < 20% . any patient with any ophthalmic disease that could result in hfa defects or with a history of diabetes mellitus was excluded .
all participants had glaucomatous optic discs , as confirmed and agreed upon by two glaucoma experts ( krs and jhn ) , and when glaucomatous visual field ( vf ) defects meeting at least two of the following criteria were present : 1 ) a cluster of three points with a probability of less than 5% on a pattern deviation map in at least one hemifield , including at least one point with a probability of less than 1% , or a cluster of two points with a probability of less than 1% ; 2 ) glaucoma hemifield test results outside normal limits ; and 3 ) a pattern standard deviation less than 5% .
cataract severity was graded as 0 , 1 , or 2 according to the extent of nuclear , cortical , and subcapsular opacity .
all procedures conformed to the declaration of helsinki and the study was approved by the institutional review board of the asan medical center at the university of ulsan , seoul , korea .
3.0.0.50 ) uses spectral - domain technology ; an optic disc cube is obtained from a three - dimensional dataset composed of 200 a - scans derived from 200 b - scans that cover a 6  6 mm area centered on the optic disc .
after creation of an rnfl thickness map from the cube dataset , the software automatically determines the center of the disc and then extracts a circumpapillary circle ( 1.73 mm in radius ) from the dataset to perform rnfl thickness measurements .
maculae were scanned using the macular cube mode ; the data were obtained from a three - dimensional dataset composed of 512 a - scans derived from 128 b - scans that cover a 6  6 mm area centered on the fovea .
the ss values of macular and optic disc mode images were compared using the paired t - test .
the relationship between macular and optic disc mode image ss was assessed by pearson correlation analysis .
clinical characteristics were compared between high- and low - ss patients imaged in each mode , using the mann - whitney u - test .
individual factors were subjected to univariate logistic regression analysis and subsequently were included in the multivariate analysis in a backward stepwise manner if the p - value was less than 0.20 .
all p - values were two - sided , and p < 0.05 was considered significant . all statistical analyses were performed using spss ver . 15.0 ( spss inc . ,
3.0.0.50 ) uses spectral - domain technology ; an optic disc cube is obtained from a three - dimensional dataset composed of 200 a - scans derived from 200 b - scans that cover a 6  6 mm area centered on the optic disc .
after creation of an rnfl thickness map from the cube dataset , the software automatically determines the center of the disc and then extracts a circumpapillary circle ( 1.73 mm in radius ) from the dataset to perform rnfl thickness measurements .
maculae were scanned using the macular cube mode ; the data were obtained from a three - dimensional dataset composed of 512 a - scans derived from 128 b - scans that cover a 6  6 mm area centered on the fovea .
the ss values of macular and optic disc mode images were compared using the paired t - test .
the relationship between macular and optic disc mode image ss was assessed by pearson correlation analysis .
clinical characteristics were compared between high- and low - ss patients imaged in each mode , using the mann - whitney u - test .
individual factors were subjected to univariate logistic regression analysis and subsequently were included in the multivariate analysis in a backward stepwise manner if the p - value was less than 0.20 .
all p - values were two - sided , and p < 0.05 was considered significant .
ninety - two eyes of 92 patients ( male 32 and female 60 ) were enrolled .
the mean age of the study participants was 54.0  13.8 years and the average md value yielded by vf testing was -6.7  6.7 db ( table 1 ) .
ss was significantly higher in images obtained by the macular cube mode compared to the optic disc cube mode ( 7.8  1.3 vs. 6.9  1.1 , respectively ; p = 0.001 ) .
a comparison of the ss values yielded by the two modes showed a statistically significant positive correlation with mode ( r = 0.581 , p < 0.001 ) ( fig .
, 31 images were classified as being of low ss ( ss < 7 ) , whereas 61 were of high ss ( ss 7 ) .
however , when the macular cube mode was employed , 16 and 76 eyes were classified into the low- and high - ss groups , respectively .
more patients were classified as high - ss subjects when the macular cube mode was employed compared to those so designated when the optic disc cube mode was used ( 82.6% vs. 66.3% , respectively ; p = 0.002 ) .
age and va differed significantly between the high- and low - ss groups when either the optic disc or macular cube mode was employed ( optic disc mode : age , p = 0.027 , va , p = 0.012 ; macular cube mode : age , p = 0.046 , va , p = 0.014 ) . with use of either mode ,
patients in the high - ss group were younger and had better va than those in the low - ss group .
however , the extent of cataracts and the vf md did not significantly differ between groups ( tables 2 and 3 ) . upon univariate logistic regression analysis ,
the extent of cataracts was associated with ss when the optic disc cube mode was used . however , no significant factor emerged upon multivariate analysis ( table 4 ) . in the macular cube mode ,
no analyzed factor was associated with ss upon either univariate or multivariate analysis ( table 5 ) .
oct is now recognized as an important diagnostic tool for providing quantitative data on rnfl and macular thicknesses .
a critical feature of oct imaging used in glaucoma diagnosis is the reliability of test results .
cheung et al . emphasized the importance of a high ss when rnfl is measured using oct .
also , it has been suggested that an ss value of over 7 is essential to guarantee reproducibility of results from the stratus oct . in the present study , we investigated factors associated with image ss obtained by cirrus oct .
moreno - montanes et al . reported that cirrus oct afforded a higher ss than did stratus oct .
although simple ss comparisons between different oct instruments is not appropriate , because oct versions might vary in their approaches toward image processing and data analysis , it remains possible that cirrus oct may provide higher - quality imaging when image acquisition is performed under the same conditions using different instruments .
this is because cirrus oct uses a line - scanning ophthalmoscope fitted with a 750-nm superluminescent diode as a light source , which facilitates image alignment . in the present study ,
images obtained in the optic cube mode were of lower ss compared to those obtained employing the macular cube mode .
the macula is aligned along the visual axis , whereas the optic disc is located in a position nasal to this axis .
thus , macular images can be obtained by central fixation , whereas optic disc image acquisition requires eccentric fixation .
it follows that if the two structures are tested under the same conditions , it would be easier to retain central fixation , rather than defer to eccentric fixation , during image acquisition .
moreover , if the direction of disc attachment with respect to the orbit is unusual , as may be observed with a tilted disc , this can lead to a reduction in ss because reflectance is inconsistent .
subjects in the high - ss group , evaluated by either oct mode , were younger and had better va .
imaging data obtained using the stratus oct are known to be influenced by the presence of cataracts .
the results of the present work indicate that the extent of cataracts did not differ between the high- and low - ss patient groups .
in addition , the patients of the present study were relatively young , with a mean age of 54 years , and most cataracts ( 90.2% ) were mild , being of grade 0 or 1 .
however , logistic regression analysis showed that the extent of cataracts was significantly associated with ss when the optic disc cube mode was employed , and this suggests that scan quality may vary with cataract density when the cirrus oct is used , as is the case when the stratus oct is employed .
meanwhile no meaningful between - group difference was noted when the macular cube mode was used .
pupil size can affect both the reproducibility and the quality of images obtained by oct . to exclude any confounding effects of pupil size
, we obtained cirrus oct images after pupil dilation in all patients , as mentioned above .
all images were obtained by a single experienced examiner ; this may not reflect the real clinical situation .
however , we found that it was more difficult to obtain high - quality images when the optic disc cube mode was employed , compared to the macular cube mode used under similar conditions .
further , we found that age , va , and extent of cataracts seemed to affect acquisition of high - ss images by the cirrus oct .
further work with a larger number of patients is needed to verify the effects of the extent and type of cataracts on image quality , and the impact of ss on glaucoma diagnosis .
 purposethe aim of this study was to investigate factors associated with the signal strengths ( ss , image quality scores ) of optic disc and macular images obtained using cirrus spectral domain optical coherence tomography ( oct).methodsninety - two glaucomatous eyes were imaged using the cirrus oct macular and optic disc cube modes after pupil dilation . 
 the influences of patient age , spherical equivalent , cataract presence , and cataract and glaucoma severity ( visual field mean deviation ) , on the ss of images obtained using the two cube modes were compared between patients whose images showed high ss ( ss 7 ) and low ss ( ss < 7).resultsthe signal strength was significantly higher in images obtained using the macular cube compared to the optic disc cube mode ( 7.8  1.3 vs. 6.9  1.1 , respectively ; p = 0.001 ) . 
 age and visual acuity of patients differed significantly between the high- and low - ss groups when data acquired using the optic disc ( p = 0.027 and 0.012 , respectively ) and macular cube modes ( p = 0.046 and 0.014 , respectively ) were analyzed . 
 when the optic disc cube mode was employed , the extent of cataracts was significantly related to ss , whereas when the macular cube mode was used , none of the factors analyzed was significantly associated with ss.conclusionsage , visual acuity , and the extent of cataracts were significantly associated with images of higher ss when the cirrus oct optic disc cube mode was employed . 
Materials and Methods
Optical coherence tomography imaging
Analysis
Results
Discussion