A normative database of A-scan data using the Heidelberg Spectralis Spectral Domain Optical Coherence Tomography machine

Purpose To develop the first normative database of macular and circumpapillary scans with reference values at the level of the A-scan using the Heidelberg Spectralis Optical Coherence Tomography (OCT) machine. Methods This study is a retrospective cross sectional analysis of macular and circumpapillary OCT scans of healthy individuals. All participants had a full ophthalmic examination, including best corrected visual acuity, intraocular pressure, biomicroscopy, posterior segment examination and OCT scan. The volume and thickness of each of the nine Early Treatment Diabetic Retinopathy zones at the macula were analysed for the total retinal thickness, retinal nerve fibre layer (RNFL), ganglion cell layer (GCL) and inner plexiform layer (IPL). The thickness of the circumpapillary RNFL was analysed at the disc. Associations between age, gender, refractive error and OCT measurements were explored. De-identified A-scans were extracted from the OCT machine as separate tab-separated text file and made available according to the data sharing statement. Results Two-hundred eyes from 146 participants were included of which 69 (47%) were female. The mean age (SD) was 48.52 (17.52). Participants were evenly distributed across four age groups and represented nine broad ethnic groups in proportions comparable to the local distribution. All the macular scans were 20° x 20° (5.9 mm x 5.9 mm), with a total scan density between 12,800 and 49,152 A-scans. The peripapillary scans were all 12° (3.5 mm), at a scan density of 768 A-scans. The mean retinal, GCL and IPL volumes were significantly greater in males than females. Mean peripapillary RNFL thickness did not differ significantly between males and females. Age and total retinal volume (r = –0.2561, P = 0.0003), GCL volume (–0.2911, P < 0.0001) and IPL volume (–0.3194, P < 0.0001) were negatively correlated. The IPL had the strongest three significant negatively associated segments; superior inner IPL (r = –0.3444, P < 0.0001), nasal outer IPL (r = –0.3217, P < 0.0001) and inferior inner IPL (r = –0.3179, P < 0.0001). The temporal inner macular RNFL showed a statistically significant positive correlation (r = 0.1929, P = 0.0062) with age. The only significant association between age and thickness at the peripapillary disc scan was the superior temporal sector (r = –0.1910, P = 0.0067). All retinal layers were negatively correlated for refractive error, except for the central RNFL which was positively correlated (r = 0.1426, P = 0.044). Conclusion This study provides a normative database of macular and circumpapillary scans with reference values at the level of the A-scan using the Heidelberg Spectralis Optical Coherence Tomography (OCT) machine.


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Purpose 29 Develop the first normative database of macular and circumpapillary scans with 30 reference values at the level of the A-scan using the Heidelberg Spectralis Optical Coherence 31 Tomography (OCT) machine. 32 33

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This study is a retrospective cross sectional analysis of macular and circumpapillary OCT 35 scans of healthy individuals. All participants had a full ophthalmic examination, including 36 best corrected visual acuity, intraocular pressure, biomicroscopy, posterior segment 37 examination and OCT scan. The volume and thickness of each of the nine Early Treatment 38 Diabetic Retinopathy zones at the macula were analysed for the total retinal thickness, retinal 39 nerve fibre layer (RNFL), ganglion cell layer (GCL) and inner plexiform layer (IPL). The 40 thickness of the circumpapillary RNFL was analysed at the disc. De-identified A-scans were 41 extracted from the OCT machine as separate tab-separated text file and made available 42 according to the data sharing statement. 43

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Two-hundred eyes from 144 participants were included of which 98 (49%) were female. The 45 mean age (SD) was 48.52 (17.52). Participants were evenly distributed across four age 46 groups and represented nine broad ethnic groups in proportions comparable to the local 47 distribution. All the macular scans were 20° x 20° (5.9 mm x 5.9 mm), with a total scan 48 density between 12,800 and 49,152 A-scans. The peripapillary scans were all 12° (3.5 mm), 49 at a scan density of 768 A-scans. The mean retinal, GCL and IPL volumes were significantly 50 greater in males than females. Age and total retinal volume (r = -0.2561), GCL volume (-51 0.2911) and IPL volume (-0.3194) were negatively correlated. No significant correlation was 52 found between the RNFL and age. 53

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This study provides a normative database of macular and circumpapillary scans with 55 reference values at the level of the A-scan using the Heidelberg Spectralis Optical Coherence 56 Tomography (OCT) machine. 57 Introduction 58 Optical coherence tomography (OCT) is a non-invasive imaging technology that uses low 59 coherence interferometry to create two-dimensional cross-sectional imaging of biological 60 systems. [1] In ophthalmic practice, OCT is used to image and measure the retinal architecture 61 and changes that occur in disease states. Diseases, such as glaucoma and compressive optic 62 neuropathy, manifest distinct changes on OCT scans, particularly on the inner retinal layers. 63 Important OCT measurements for both diseases include the circumpapillary retinal nerve 64 fibre layer (RNFL), macular RNFL and the macular ganglion cell layer (GCL OCT and the Heidelberg Eye Explorer version 6.7.13.0 (Heidelberg Engineering, Heidelberg, 118 Germany). All scans were completed by experienced medical imaging personnel at The RMH 119 medical imaging department; they were performed in a dark room as per the standard hospital 120 protocol. Only the well-centred scans (>15dB quality) were included in the analysis. The 121 number of dioptres focus spherical was recorded for each scan as a proxy for the refractive 122 error. The scans were quality controlled for the accurate segmentation of each macular retinal 123 inner layer and peripapillary scan, and an experienced grader manually corrected any 124 aberrations. 125 The macular scans were divided into 1 mm, 3 mm and 6 mm rings on the macular ETDRS 126 map. The inner ring was defined as the central thickness, and the middle and outer rings were 127 divided into four zones designated as the superior, nasal, inferior and temporal zones. The 128 average thickness in each of the nine zones, the macular thickness and the full 360° 129 peripapillary scans were included in the final analysis. 130

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. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) were included in the study (Table 2). There were significant differences in the proportion of 157 broad ethnic categories compared to the census population proportions in four out of the nine 158 groups. 159 Distribution of macular and circumpapillary measurements 170 The mean (SD) total retinal volume was 8.67 mm 3 (0.38) (range: 7.65-9.58). The

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The multivariate regression analysis controlling for age and ethnicity (Table 3) showed that 184 the retinal and GCL volumes were significantly less for females. The total RT was 185 significantly lower in females in all sectors except for the superior outer sector. The same 186 was true for the central, nasal inner, temporal inner, inferior inner macular RNFL, GCL and 187 IPL thicknesses. The GCL and IPL also showed that females had significantly lower superior 188 inner sectors. There were no significant differences found at the peripapillary RNFL between 189 males and females (Table 4). 190 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)  peripapillary RNFL thicknesses were grouped by age (Table 10). 202    is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint    is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted February 19, 2021.  is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted February 19, 2021.
Linear regression analysis showed a significant negative correlation between the total retinal 213 volume and age (r = -0.2561), GCL volume and age (-0.2911) and IPL volume and age (-214 0.3194). There was no significant correlation found between the RNFL and age. Figs 3 and 4 215 demonstrate trend lines for layer measurements against age. Table 11 demonstrates the 216 regression analysis of segmental retinal thickness (RT) values against age. The strongest 217 three significant negative associations were found in the superior inner IPL (r = -0.3444), 218 nasal outer IPL (r = -0.3217) and inferior inner IPL (r = -0.3179) segments. The only 219 significant positively correlated segment was the temporal inner RNFL (r = 0.1929). The only 220 significant association between age and thickness at the peripapillary disc scan was the 221 superior temporal sector (r = -0.1910) (Table 12). 222   Table 11. Regression analysis of layer thickness (µm) against age (years) and p-value for 228 each macular segment 229   19] This study is consistent with these findings; however, the negative correlation found in 296 the temporal inner and inferior inner segments was found not to be statistically significant. 297 Similar to other studies, the central area had almost no association (r = 0.00899, p = 0.9008). 298 This study identified that the GCL and IPL thickness and volume for all the sectors 299 (excluding the centre for the IPL) decreased with age. This was in keeping with findings from 300 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted February 19, 2021. ; https://doi.org/10.1101/2021.02.16.21251860 doi: medRxiv preprint previous studies. [12,17] This finding represents a normal process of ageing with loss of 301 RNFLs over time, which has been reported to be between 0.3% and 0.6% of neurons lost per 302 year.
[20] This is important for differentiating losses due to age-related processes from those 303 caused by disease processes, such as glaucoma or compressive optic neuropathy. 304 A statistically significant positive correlation was found between increasing age and temporal 305 inner RNFL thickness (r = 0.1929, p = 0.0062). Similarly, Nieves-Moreno et al. found a 306 positive correlation between temporal inner RNFL and age (r = 0.256, p = <0.001). 11 No 307 other significant correlations were found between RNFL volume or thickness and age in this 308 study. Given that the temporal inner is the thinnest RNFL sector, this study postulated that it 309 would be proportionally the most affected by an increasing thickness observed in the internal 310 limiting membrane with age and, therefore, correlate positively with age. Males were found 311 to have a significantly higher RT, RNFL, GCL and IPL thickness than females. This was 312 most evident in the inner layers, which is similar to the OCT results reported in other 313 studies.
[12,17] 314 The Limitations of this study include its retrospective design, which led to missing variables 315 that may have affected the OCT measurements, including the axial length and refraction. This 316 study provides normal baseline data for the comparison of various macular diseases. These 317 data will also be used to monitor patients with glaucoma and compressive optic neuropathy at 318 The RMH. 319 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted February 19, 2021. ;