Does a Relationship Exist Between Posterior Vitreous Detachment, Macular Thickness and Foveal Avascular Zone Dimensions in Myopic Eyes? 2

Background: The posterior vitreous detachment (PVD) is a separation of the posterior 19 vitreous cortex from the internal limiting membrane of the retina. The PVD induces 20 several potentially serious pathologic events at the vitreoretinal interface. The aim of 21 the study is to determine if relationships exist between PVD, macular thickness (MT) 22 and the foveal avascular zone (FAZ) in myopic eyes. 23 Methods: This is a retrospective case study of 63 myopic subjects who underwent 24 comprehensive eye examination including the optical coherence tomography 25 angiography (OCTA) between January 1 and Jun 30, 2019. The spherical equivalent 26 (SE) was calculated using the manifest refraction. The myopia grouping was based on 27 a severity scale, namely mild, moderate, high and very high using standard refractive 28 error classifications. The PVD classification was based on optical coherence 29 tomography (OCT) images. The status of the PVD and MT were evaluated with Macular 30 Cube 200 × 200 images and the FAZ was imaged with an OCTA, Angioplex. The MT and 31 FAZ dimensions were calculated using a custom algorithm. 32 Results: A total of 114 myopic eyes subjects had median (range) age of 26.00 (22.00 - 33 28.00) years. Of this cohort, females comprised 62.3 % of the dataset, and the right 34 eyes were 50.00 %. In this population, 10 eyes had no PVD in any quadrant, and 73 35 eyes had incomplete PVD in all four quadrants. The inferior quadrant had the 36 maximum number of PVD cases and the nasal quadrant had the least number of cases. 37 High myopic eyes exhibited significantly increased low foveal volume (p = 0.000). The 38 inferior part of para- and perimacular area showed a significant thinning in very high myopic eyes (p = <0.05). A statistically significant alteration of FAZ circularity index found in very high myopic eyes (p = 0.002). Conclusion: In high and very high myopic eyes, an increasing trend of partial PVD is 42 seen. The most commonly involved location was the inferior quadrant. A significant 43 alteration in foveal volume and circularity index of the FAZ is seen in high and very 44 high myopic eyes.


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Background 49 Liquefaction of the vitreous gel which is attached to the internal limiting membrane of the 50 retina [1][2][3] or spontaneous posterior vitreous detachment (PVD) from the retina is considered 51 to be a part of normal aging process [1,4]. The onset of PVD is usually reported around the

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Foveal retinoschisis and posterior staphyloma are also reported in high myopia [4]. Bond- 4 Taylor et al. [12] reported the PVD prevalence in normal individuals was 24 % among subjects 66 aged between 50-59 and increases to 89 % in the 9 th decade of life.

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However, in high myopes, the onset of PVD has been reported to occur much earlier than non-68 myopic or low-moderate myopic eyes [4,13]. For example, Akiba

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However, in the peri-macular area, the nasal quadrant alone showed significant loss of vessel 182 density. Table 4 shows the correlation between myopia (SE) verses macular thickness and 183 macular vessel density different ETDRS quadrants. A significant negative correlation was 184 found between myopia and foveal thickness. However, a weak positive correlation was seen 185 with inferior para-macular region and overall peri-macular thickness.

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However, Lim et al. [28] showed that the average macular retinal thickness did not 207 significantly vary between various degrees of myopia. The possible reason for discrepancies 208 in the association of myopia severity and foveal thickness could be due to the fact that these 209 13 studies did not take into account the influence of PVD. We found that there was a reduction 210 in macular volume with degree of myopia. This result is similar to that of Hwang et al. [29] 211 who found that macular volume was lower in very-high myopia. This could be due to 212 progressive thinning of the para-and peri-foveal thickness with increasing myopia. Zhao et 213 al. [16] reported that the para-and peri-foveal thickness were negatively correlated with the 214 axial length and positively associated with the SE. Since the current study was retrospective, we had very few cases with axial length data. The 236 best way to classify myopia should be based on the corneal-axial ratio or at least by axial 237 length. Sampson et al. [20] reported that the FAZ area is affected by its axial magnification 238 during the image acquisition. This can be rectified by correcting for image magnification 239 induced by the axial length variation [34]. In cases of high myopia (SE -6.00 to -10.00D) or very 240 high myopia (SE >-10.00 D) of our sample, none of the cases had a corneal curvature >44.00D.

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Likewise, no eyes had cataractous changes and all the subjects had axial myopia. The second 242 shortcoming was the low sample size of the various myopic sub-groups. We hope to further 243 expand on the datasets as well as pathological conditions in future research.

Conclusions 245
In summary, we report characteristic retinal changes in high and very high myopic eyes.

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An increasing trend of partial PVD is seen in eyes classified as having high and very high 247 myopia. An asymmetric PVD in location was observed and the most commonly involved