**Purpose**:
We previously reported that the retinal deformation due to myopia was represented by the peripapillary retinal arteries angle (PRAA). In this study, we investigated the relationship between the PRAA and biomechanical properties measured with Corvis ST (CST) tonometry.

**Methods**:
Thirty-four normative eyes of 34 subjects who underwent CST measurement were enrolled. The PRAA was calculated from a fundus photograph. Variables related to the PRAA were identified from age, axial length, spherical equivalent refractive error, and 10 CST parameters using model selection with the second-order bias-corrected Akaike information criterion index.

**Results**:
The PRAA was best described with axial length (coefficient = −5.66, *P* < 0.0001), maximum deflection amplitude (mm; coefficient = 130.5, *P* = 0.0004), and deflection amplitude ratio (DA ratio) 2 mm (coefficient = −25.8, *P* = 0.0032), where mm was the amount of the maximum corneal apex movement and DA ratio 2 mm was the ratio between the deformation amplitudes at the apex and 2 mm away from the apex. The optimal model was significantly better than the model only with axial length (*P* = 0.0014, analysis of variance).

**Conclusions**:
The PRAA was significantly better described with the CST parameters compared to the axial length model only; eyes with small PRAA (larger myopic retinal deformation) showed narrow and shallow maximum corneal deflection.

**Translational Relevance**:
The Corvis ST parameters, which represents corneal biomechanical characteristics, were associated with myopic retinal deformation.

^{1}because the global prevalence of myopia has increased rapidly in the past 50 years, especially in east and southeast Asia.

^{1–4}The Tajimi study has revealed that the incidence of myopia in the Japanese population was the highest in the world, with an incidence of 41.8% for myopia <−0.5 diopters (D) and 5.5% for myopia <−6.0 D in individuals 40 years old.

^{5}Myopia also is considered to be related to various ophthalmologic diseases, such as cataract,

^{6}glaucoma,

^{7}choroidal neovascularization,

^{8}and retinal detachment.

^{9}

^{10}In particular, previous studies showed that the retina was mechanically stretched around the papillomacular bundle in myopic eyes, and this retinal deformation was represented by the circumpapillary retinal nerve fiber layer (cpRNFL) peak angles and also peripapillary retinal arteries angle (PRAA).

^{11–13}Of note, the correlation between AL and the cpRNFL peak angle or PRAA was merely moderate (

*r*= −0.49 or −0.38, respectively), which implies there is a wide variety in the magnitudes of retinal deformation even in eyes with an identical AL value.

^{11,14}However, the cpRNFL thickness can be affected by various ocular conditions, such as age

^{15}and glaucoma.

^{11}PRAA and cpRNFL peaks angle were very closely associated with the correlation coefficient value of 0.92 in young healthy subjects,

^{11}and PRAA is not affected by the aforementioned issues. Moreover, PRAA can be identified very easily in a fundus photograph. Hence, PRAA may be superior to cpRNFL peaks angle in the universal usefulness in estimating the retinal deformation due to myopia.

^{16}However, CST currently uses a newer software (version 1.13b1361), which yields a much larger number of raw parameters (previously 12 and currently 29 parameters). Moreover, the current CST software displays six summary parameters calculated from the 29 raw parameters, which enables us to analyze corneal elasticity and stiffness. This is very important clinically, because raw CST parameters merely show the shape of the cornea at each timing, in contrast to the newly available summary parameters.

^{14}In short, optic disc color fundus photographs were obtained using either OCT (OCT-2000; Topcon) or a retinal camera (TRC-50DX; Topcon). ImageJ software (available in the public domain at https://imagej.nih.gov/ij/; National Institutes of Health, Bethesda, MD) was used to draw a 3.4-mm diameter peripapillary scan circle on the obtained fundus photographs. Then, PRAA was calculated from the points where the 3.4 mm-diameter peripapillary scan circle and the superotemporal/infratemporal major retinal arteries intersected (Fig. 1). Magnification effects of the camera were corrected using the Littmann's formula.

^{17}

^{18}CST monitors the corneal response to an air puff pulse during the inward and outward movements with a high-speed Scheimpflug camera, capturing 4330 frames per second. This imaging system allows us to investigate the dynamic inspection of the actual deformation process in vivo.

^{19}From the total of 36 corneal biomechanical properties measurable with the new version of CST, following our previous report, we used 10 summary CST parameters:

^{20}

- Ambrosio Relational Thickness horizontal (ARTh): The quotient and change of the corneal thickness.
^{21} - Integrated Radius: The integrated area under the radius of the inversed curvature during the concave phase.
^{21} - Stiffness parameter (SP-A1): The resulting pressure on the cornea divided by the deflection amplitude at the first applanation.
^{22} - Corneal biomechanical index (CBI): The combination of the summary parameters indicating the likelihood of subclinical keratoconus and corneal ectasia.
^{21} - Deflection amplitude ratio (DA ratio) 1 mm: The ratio of deflection amplitude (the corneal movement compensating the eye movement) at apex and at 1 or 2 mm.
- DA ratio 2 mm: The ratio of deflection amplitude (the corneal movement compensating the eye movement) at apex and at 2 mm.
- Whole eye movement (WEM; ms): The duration of the eye during the examination.
- WEM (mm): The total amount of the eye movement during the examination.
- Maximum Deflection amplitude (ms): The duration of the corneal movement compensating for WEM.
- Maximum Deflection amplitude (mm): The maximum amount of the corneal movement compensating for WEM.

^{13}patterns using the 13 candidate variables. The Akaike information criterion index (AIC)

^{23}is defined as follows:

*L*and

*K*represent the maximized likelihood function and asymptotic bias correction term. The AICc is a corrected version of the AIC,

^{24}which provides an accurate estimation even when the sample size is small,

^{25}defined as follows:

*n*stands for the sample size. The decrease in AICc indicates the improvement of the model.

^{26}The selected variables through the model selection were regarded as significant, because they provided us the objective measures for selecting among different models fitted to data considering the contributions and interactions between parameters.

^{27}The log-likelihood values of a paired model were compared using the analysis of variance (ANOVA) test.

*P*= 0.0015, and coefficient = 1.61 with

*P*= 0.0046, respectively).

*P*< 0.0001) × AL + 130.5 (SE = 32.8,

*P*= 0.0004) × Maximum deflection amplitude [mm] − 25.8 (SE = 8.05,

*P*= 0.0032) × DA ratio 2 mm (AICc = 265.1). The log-likelihood of the optimal model was significantly larger than that of the model only with AL (AICc = 274.7,

*P*= 0.0014, ANOVA).

^{20}We recently investigated the relationship between circumpapillary retinal nerve fiber layer (cpRNFL) peak angle and the older CST raw parameters (version 1.00r30) and cpRNFL peak angle was best described using AL and CST − measured A1 length, A1 time, and A2 time (cpRNFL peaks angle = −901.1 + 132.7 × A1 length + 27.8 × A1 time + 31.0 × A2 time − 3.4 × axial length).

^{16,28}The newer CST parameters were developed mainly to represent the elasticity and stiffness of the cornea. Our study suggested PRAA was better represented using the newer CST parameters of the magnitude of maximum deflection amplitude and DA ratio 2 mm, which enabled us to directly interpret the obtained results.

^{29}examined the relationship between AL and CST maximum deflection amplitude, and suggested that greater maximum corneal deflection was observed in eyes with longer AL. They inferred this tendency was due to a low viscous damping property in eyes with longer AL, which agreed with the previous report that eyes with long AL had small corneal energy absorption.

^{16}However, of note, myopic retinal deformation cannot be fully explained only with AL and PRAA exceeded in its description, as we reported previously.

^{11}According to the current result, eyes with greater myopic retinal deformation (smaller PRAA) showed shallower maximum corneal deflection. The entire mechanism of this finding is unclear, but it may be because eyes with small PRAA suggest that retinal deformation is particularly large at the posterior pole of the eye and the shape of an eyeball is distorted. If enlargement of an eye occurs equally in the whole eye, PRAA would remain relatively large. This implies eyes with PRAA (and long AL) resist the deformation associated with the elongation of an eye, and such eyes may show shallow maximum corneal deflection. Furthermore, our results suggested that myopic retinal deformation was better analyzed using DA ratio 2 mm, in addition to maximum corneal deflection. As a result, it is suggested that large myopic retinal deformation is associated with long AL and small (narrow and shallow) maximum corneal deflection in the CST measurement.

**S. Asano**, None;

**R. Asaoka**, None;

**T. Yamashita**, None;

**S. Aoki**, None;

**M. Matsuura**, None;

**Y. Fujino**, None;

**H. Murata**, None;

**S. Nakakura**, None;

**Y. Nakao**, None;

**Y. Kiuchi**, None

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