Choroidal vascular analysis in myopic eyes: evidence of foveal medium vessel layer thinning.

PURPOSE: To analyse morphologic features of the choroid in Non-pathological myopic eyes using spectral-domain (SD) optical coherence tomography (OCT). METHODS: Retrospective analysis of enhanced depth SD-OCT images of Non-pathological myopic eyes in comparison with age-matched healthy controls was performed. Choroidal thickness (CT) and large choroidal vessel thickness (LCVT) were measured at the fovea, 750 µm nasally from fovea (N750) and 750 µm temporally (T750) from fovea. Medium choroidal vessel thickness (MCVT) was calculated by subtracting LCVT from CT. Choriocapillaris was encompassed by MCVT, given its reduced thickness. Linear regression analysis evaluated the relationship between age and axial with CT, LCVT and MCVT. RESULTS: The study group comprised 42 eyes of 31 patients (mean age 46.13 ± 15.63; 15 females). Control group included 57 eyes of 34 patients (mean age of 42.3 ± 15.29; 24 females). Mean axial length in myopic eyes and control group was 26.57 ± 1.27 and 23.59 ± 0.99 mm respectively. Myopic eyes showed significant thinning of MCVT and CT at all locations (p < 0.0001) compared to controls, unlike LCVT (p > 0.05). With each decade, thinning of up to 37 µm in CT was noted along with thinning of LCVT (up to 22.6 µm) and MCVT (up to 25 µm). Each mm increase in axial length caused 38.2 µm thinning of choroid along with LCVT (<10 µm), however, MCVT showed more notable thinning (>30 µm). CONCLUSION: Significant thinning of MCVT was noted in non-pathological myopic eyes in comparison to healthy subjects. It appears that MCVT has stronger relationship with age and axial length.

Prevalence and Distribution of Segmentation Errors in Macular Ganglion Cell Analysis of Healthy Eyes Using Cirrus HD-OCT.

PURPOSE: To determine the frequency of different types of spectral domain optical coherence tomography (SD-OCT) scan artifacts and errors in ganglion cell algorithm (GCA) in healthy eyes. METHODS: Infrared image, color-coded map and each of the 128 horizontal b-scans acquired in the macular ganglion cell-inner plexiform layer scans using the Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA) macular cube 512 × 128 protocol in 30 healthy normal eyes were evaluated. The frequency and pattern of each artifact was determined. Deviation of the segmentation line was classified into mild (less than 10 microns), moderate (10-50 microns) and severe (more than 50 microns). Each deviation, if present, was noted as upward or downward deviation. Each artifact was further described as per location on the scan and zones in the total scan area. RESULTS: A total of 1029 (26.8%) out of total 3840 scans had scan errors. The most common scan error was segmentation error (100%), followed by degraded images (6.70%), blink artifacts (0.09%) and out of register artifacts (3.3%). Misidentification of the inner retinal layers was most frequent (62%). Upward Deviation of the segmentation line (47.91%) and severe deviation (40.3%) were more often noted. Artifacts were mostly located in the central scan area (16.8%). The average number of scans with artifacts per eye was 34.3% and was not related to signal strength on Spearman correlation (p = 0.36). CONCLUSIONS: This study reveals that image artifacts and scan errors in SD-OCT GCA analysis are common and frequently involve segmentation errors. These errors may affect inner retinal thickness measurements in a clinically significant manner. Careful review of scans for artifacts is important when using this feature of SD-OCT device.

Structure-Function Relationship in Glaucoma Using Ganglion Cell-Inner Plexiform Layer Thickness Measurements.

PURPOSE: To evaluate the structure-function relationship between ganglion cell-inner plexiform layer (GCIPL) thickness at the macula and 10-2 standard automated perimetry (SAP) in glaucoma and to evaluate the relationship using a recently proposed linear model. METHODS: In a cross-sectional analysis, structure-function relationship was determined in 50 glaucomatous eyes (40 patients, mean deviation: -15.4 ± 7.5 dB) and 21 control eyes (13 subjects, mean deviation: -3.4 ± 3.0 dB), which had undergone 10-2 SAP and GCIPL imaging on the same day. Functional loss was derived from total deviation numerical values on 10-2 SAP and calculated on both a linear (reciprocal of Lambert) and a decibel scale after accounting for the retinal ganglion cell displacement at the macula. Strength of relationship was reported as coefficient of determination (R2) of the linear regression models fitted to the data separately for different sectors. The relationship was also evaluated using a linear model. RESULTS: The R2 for the associations between GCIPL thickness sectors and the corresponding sector SAP total deviation values ranged from 0.19 (for superonasal GCIPL sector) to 0.60 (for average GCIPL thickness) when functional loss was calculated on the decibel scale and 0.16 (for superonasal sector) to 0.54 (for inferior sector) on the linear scale. All associations were statistically significant (P < 0.05). The linear model fitted the data reasonably well. CONCLUSIONS: Significant structure-function associations were found between GCIPL thickness measurements at the macula and the functional loss measured on 10-2 SAP in glaucoma. Best fit was found for the inferior and average GCIPL sector thickness. The linear model was useful to study the structure-function relationship.

Comparing the Structure-Function Relationship at the Macula With Standard Automated Perimetry and Microperimetry.

PURPOSE: To compare the structure-function relationship between ganglion cell-inner plexiform layer (GCIPL) thickness measurements using spectral-domain optical coherence tomography (SDOCT) and visual sensitivities measured using standard automated perimetry (SAP) and microperimetry (MP) at the macula in glaucoma. METHODS: In a prospective study, 45 control eyes (29 subjects) and 60 glaucoma eyes (45 patients) underwent visual sensitivity estimation at the macula (central 10°) by SAP and MP, and GCIPL thickness measurement at the macula by SDOCT. Structure-function relationships between GCILP thickness and visual sensitivity loss with SAP and MP at various macular sectors were assessed using the Hood and Kardon model. To compare structure-function relationship with SAP and MP, we calculated the number of data points falling outside the 5th and the 95th percentile values of the Hood and Kardon model with each of the perimeters. RESULTS: The number of points falling outside the 5th and 95th percentile values of the Hood and Kardon model ranged from 28 (superior sector) to 48 (inferonasal sector) with SAP and 33 (superior sector) to 49 (inferonasal sector) with MP. The difference in the number of points falling outside the 5th and 95th percentile values with SAP and MP was statistically insignificant (P > 0.05, χ(2) test) for all the sectors. CONCLUSIONS: Visual sensitivity measurements of both SAP and MP demonstrated a similar relationship with the GCIPL measurements of SDOCT at the macula in glaucoma.