**Purpose**:
To quantitatively assess the posterior pole shape change in highly myopic eyes and to investigate the factors determining the speed of shape change.

**Methods**:
Local curvature of the Bruch's membrane on the optical coherence tomography image was measured at intervals of 1 μm, and the mean curvature and curvature variance were calculated for 1094 eyes with an axial length of ≥26 mm. Speed of shape change was calculated using two points of mean curvature and curvature variance, and compared according to age, sex, axial length, and baseline eye shape.

**Results**:
The posterior pole shape of females changed significantly greater than males (*P* < 0.01). Protruding change through the mean curvature was the greatest in the eyes with an axial length of ≥28 mm and <29 mm, while undulating change through the curvature variance became greater with axial length elongation in the eyes with an axial length of <29 mm and showed similar change in the eyes with an axial length of ≥29 mm. The eyes with a flatter shape at baseline tended to show a slow shape change, whereas those with moderate shape deformation at baseline showed faster shape change.

**Conclusions**:
Quantitative evaluation of posterior pole eye shape clearly demonstrated significant time-dependent protruding and undulating changes in highly myopic eyes. Sex, axial length, and baseline posterior pole eye shape significantly affected speed of the posterior pole shape change. Our findings will facilitate risk assessment of staphyloma-associated complications in highly myopic eyes through measurement of speed of the posterior pole shape change.

^{1–5}Because high myopia is associated with various ocular complications leading to severe visual impairment, more patients may be at risk of low vision or blindness in the near future. Many of these complications develop in association with posterior staphyloma in highly myopic eyes.

^{6–15}Studies on posterior staphyloma or posterior pole eye shape are needed to understand the mechanisms by which vision-threatening complications develop in high myopia, and preventive measures need to be identified. However, studies on staphyloma progression are limited, and time-course change of the posterior pole shape in highly myopic eyes has not been thoroughly investigated.

^{16–18}Quantitative evaluation of the posterior pole shape revealed that the eyes with myopic choroidal neovascularization (mCNV), myopic traction maculopathy, and chorioretinal atrophy had a unique characteristic shape; and the eyes with staphyloma and those without staphyloma could be clearly distinguished through quantitative measures of the curvature of OCT images.

^{16}In addition, quantitative analysis of OCT images could predict the occurrence of myopic traction maculopathy in highly myopic eyes.

^{17}Furthermore, quantitative evaluation of the posterior pole through OCT imaging was useful for epidemiologic cohort studies on staphyloma.

^{18}In the present study, we evaluated speed of the posterior pole shape change at two time points of OCT examination in highly myopic eyes, and investigated its association with sex, age, axial length, and baseline posterior pole shape.

^{16–18}The mean absolute curvature and variance of absolute curvature were calculated for each eye to evaluate the protruding shape change and undulating shape change, respectively (Fig. 1). The speed of the mean curvature change was calculated as the difference between the mean curvatures at the last and the first examinations, divided by the examination interval. The speed of the curvature variance change was calculated as the difference between variances of curvature at the last and the first examinations, divided by the examination interval.

*t*-test. Moreover, the speed was compared among six age groups: age of <40 years, -(40); ≥40 and <50, 40-(50); ≥50 and <60, 50-(60); ≥60 and <70, 60-(70); ≥70 and <80, 70-(80); and ≥80, 80-; and five axial length groups: eyes with axial length of ≥26 mm and <27 mm, 26-(27); ≥27 mm and <28 mm, 27-(28); ≥28 mm and <29 mm, 28-(29); ≥29 mm and <30 mm, 29-(30); and ≥30 mm, 30-, using ANOVA and Tukey's test. In addition, the speed was compared among five groups of mean curvature at the first examination: <7.5 × 10

^{−5}μm

^{−1}(-[7.5]), ≥7.5 × 10

^{−5}μm

^{−1}and <10.0 × 10

^{−5}μm

^{−1}(7.5-[10]), ≥10.0 × 10

^{−5}μm

^{−1}and <12.5 × 10

^{−5}μm

^{−1}(10-[12.5]), ≥12.5 × 10

^{−5}μm

^{−1}and <15.0 × 10

^{−5}μm

^{−1}(12.5-[15]), and ≥15.0 × 10

^{−5}μm

^{−1}(15-); and five groups of curvature variance at the first examination: <2.5 × 10

^{−9}μm

^{−2}(-[2.5]), ≥2.5 × 10

^{−9}μm

^{−2}and <5.0 × 10

^{−9}μm

^{−2}(2.5-[5]), ≥5.0 × 10

^{−9}μm

^{−2}and <7.5 × 10

^{−9}μm

^{−2}(5-[7.5]), ≥7.5 × 10

^{−9}μm

^{−2}and <10.0 × 10

^{−9}μm

^{−2}(7.5-[10]), and ≥10.0 × 10

^{−9}μm

^{−2}(10-), using ANOVA and Tukey's test. All statistical analyses were performed using Statistical Package for the Social Sciences (SPSS, version 24.0; IBM, New York, NY, USA). A

*P*value of <0.05 was considered as statistically significant.

^{−6}(μm

^{−1}/y), and mean speed of the curvature variance change or the undulating change was 1.73 × 10

^{−10}(μm

^{−2}/y). Speeds of both the mean curvature change (Fig. 4A) and curvature variance change (Fig. 4B) were significantly higher in females than males (Table 2,

*P*= 9.97 × 10

^{−3}and 7.26 × 10

^{−4}, respectively).

*F*

_{degree of freedom between groups, degree of freedom within groups}=

*F*

_{4,1089}= 4.704,

*P*= 9.12 × 10

^{−4}), with gradual increase from the eyes with axial length of ≥26 mm and <27 mm to the eyes with axial length of ≥28 mm and <29 mm (Fig. 4C,

*P*= 6.62 × 10

^{−4}), and subsequent decrease in the eyes with axial length of ≥30 mm (

*P*= 2.44 × 10

^{−2}). In contrast to speed of the mean curvature change, speed of the curvature variance change gradually increased from the eyes with axial length of ≥26 mm and <27 mm to the eyes with axial length of ≥28 mm and <29 mm (Fig. 4D,

*P*= 1.12 × 10

^{−2}), and then maintained the high speed up to axial length of ≥30 mm (

*P*= 5.38 × 10

^{−3}).

*F*

_{5,1088}= 2.472,

*P*= 3.08 × 10

^{−2}). It increased gradually with age until the age of 80, and then decreased (Fig. 4E). However, the Tukey's test did not detect statistically significant difference in speed, in any age group. The speed of the curvature variance change also increased gradually until the age of 80 (Fig. 4F), but the increase was not statistically significant.

^{−5}μm

^{−1}to the eyes with greater curvature of ≥12.5 × 10

^{−5}μm

^{−1}and <15.0 × 10

^{−5}μm

^{−1}(Fig. 4G,

*P*= 1.37 × 10

^{−6}). However, the eyes with greater curvature of ≥15.0 × 10

^{−5}μm

^{−1}showed a slower speed of the curvature change. In contrast to the mean curvature, speed of the curvature variance change gradually increased from the flatter eyes with initial mean curvature of <7.5 × 10

^{−5}μm

^{−1}to the eyes with greater curvature of ≥10.0 × 10

^{−5}μm

^{−1}and <12.5 × 10

^{−5}μm

^{−1}(Fig. 4H,

*P*= 3.58 × 10

^{−3}), and then maintained the high speed until the greater curvature was ≥15.0 × 10

^{−5}μm

^{−1}(

*P*= 5.02 × 10

^{−3}).

^{−9}μm

^{−2}and <5.0 × 10

^{−9}μm

^{−2}, and ≥5.0 × 10

^{−9}μm

^{−2}and <7.5 × 10

^{−9}μm

^{−2}(Fig. 4I,

*P*= 2.21 × 10

^{−5}and 2.50 × 10

^{−3}, respectively). The eyes with greater curvature variance at initial examination did not show notably high speed. Speed of the curvature variance change showed a similar pattern (Fig. 4J). It was significantly higher in the eyes with initial curvature variance of ≥2.5 × 10

^{−9}μm

^{−2}and <5.0 × 10

^{−9}μm

^{−2}, and ≥5.0 × 10

^{−9}μm

^{−2}and <7.5 × 10

^{−9}μm

^{−2}, than in the eyes with initial curvature variance of <2.5 × 10

^{−9}μm

^{−2}(

*P*= 1.47 × 10

^{−4}and 3.61 × 10

^{−3}, respectively) and ≥10.0 × 10

^{−9}μm

^{−2}(

*P*= 4.44 × 10

^{−4}and 3.28 × 10

^{−3}, respectively).

^{16,19}Quantitative evaluation of speed of the eye shape change at the posterior pole has potential to predict occurrence of vision-threatening complications in highly myopic eyes, and would be useful in understanding the factors that affect speed of the eye shape change at the posterior pole and, thus, in developing preventive methods for such complications.

^{−5}μm

^{−1}would suggest that the maximum mean curvature for the most highly myopic eyes is approximately 15.0 × 10

^{−5}μm

^{−1}; whereas, the finding of low speed of the curvature variance change in the eyes with baseline curvature variance of >10.0 × 10

^{−9}μm

^{−1}would suggest that the maximum curvature variance for the most highly myopic eyes is approximately 10.0 × 10

^{−9}μm

^{−1}.

^{−8}μm

^{−1}per year in male subjects with axial length of ≥26 mm and <27 mm and age of <40 years (

*n*= 9) to 4.64 × 10

^{−6}μm

^{−1}per year in female subjects with axial length of ≥28 mm and <29 mm and age of ≥70 and <80 years (

*n*= 40). In our previous study, we demonstrated that each complication of highly myopic eyes was characterized by the unique posterior pole shape.

^{16}Moreover, the mean curvature was (8.61 ± 4.2) × 10

^{−5}μm

^{−1}in highly myopic eyes without complications, (11.27 ± 3.01) × 10

^{−5}μm

^{−1}in the eyes with myopic choroidal neovascularization (mCNV), and (14.39 ± 3.17) × 10

^{−5}μm

^{−1}in the eyes with retinoschisis. Based on the differences in the characteristic mean curvatures, we could establish that eyes without complications would develop mCNV in 5.7 years, or retinoschisis in 12.5 years, at the highest speed of 4.64 × 10

^{−6}μm

^{−1}per year. Further longitudinal studies investigating the association between the eye shape at the posterior pole and development of vision-threatening complications are needed to allow accurate risk assessment of complications in highly myopic eyes. For example, mCNV develops in the eyes with moderate values of the mean curvature and curvature variance,

^{16}which suggests that the risk of developing mCNV would increase to some level and decrease thereafter as the curvature values increase. By estimating the rate of staphyloma progression, we can predict when the eye will be at high risk of developing mCNV and when at low risk of developing mCNV.

^{20}and refractive error could affect the accuracy of the analysis of the curvature through OCT.

^{21}Because we analyzed the local curvature, the results of the analysis should be more precise than those through analyzing the whole OCT image. Analysis of curvature variance may have other weakness. For example, the curvature variance is calculated as 0 in the eyes with the posterior pole shape shown in Figures 2A and 2B, although the mean curvature is quite different. To overcome such weakness, both mean and variance values should be evaluated simultaneously.

**T. Wakazono**, None;

**K. Yamashiro**, None;

**M. Miyake**, None;

**M. Hata**, None,

**M. Miyata**, None;

**A. Uji**, Canon (R);

**H. Nakanishi**, Tomey Corporation (F, R);

**A. Oishi**, None;

**H. Tamura**, None;

**S. Ooto**, Nidek (R);

**A. Tsujikawa**, Canon (F), Tomey Corporation (F), and Nidek (R)

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