In the simple regression analyses, AL was influenced by CR, WTW, ACD, and LT. While similar findings were reported in previous studies, not all of these parameters were examined together. Furthermore, some previous single regression analyses differed in their use of multiple instruments.
The relationship between AL and CCT was investigated by Shimmyo et al. [5] (R2 = 0.00728) and Chen et al. [6] (R2 = 0.0028). However, similar to the current results, there were no significant correlations found between AL and CCT. Recent studies reported significant but low correlations between AL and CCT (Table 3). Therefore, it is believed that AL does not vary with changes in CCT.
Table 3
Correlation coefficients between AL and each parameter in previous studies. NR denotes data not reported. Values with "*" represent statistical significance.
Study name
|
Country
|
Year of Publication
|
CCT (㎛)
|
CR (㎜)
|
WTW (㎜)
|
ACD (㎜)
|
LT (㎜)
|
present study
|
Japan
|
-
|
0.12; P = 0.095
|
0.33; P༜0.001*
|
0.29; P༜0.001*
|
0.59; P༜0.001*
|
−0.30; P༜0.001*
|
Kim et al. [29]
|
Korea
|
2023
|
0.071; P < 0.001*
|
NR
|
0.285; P < 0.001*
|
0.503; P < 0.001*
|
−0.288; P < 0.001*
|
Miao et al. [28]
|
China
|
2022
|
0.15; P < 0.001*
|
NR
|
0.21; P < 0.001*
|
0.32; P < 0.001*
|
NR
|
Lei et al. [27]
|
China
|
2021
|
NR
|
NR
|
0.325; P < 0.01*
|
0.544; P < 0.01*
|
−0.212; P < 0.01*
|
Natung et al. [26]
|
India
|
2019
|
NR
|
NR
|
0.205; P = 0.000*
|
0.298; P = 0.000*
|
NR
|
Hashmani et al. [25]
|
Pakistan
|
2019
|
0.149; P = 0.030*
|
NR
|
NR
|
NR
|
NR
|
Muthu Krishnan et al. [24]
|
South India
|
2019
|
0.211; P = 0.008*
|
0.287; P = 0.000*
|
NR
|
NR
|
NR
|
Huang et al. [23]
|
western China
|
2018
|
NR
|
NR
|
NR
|
0.542; P < 0.01*
|
NR
|
Ferreira et al. [22]
|
Portugal
|
2017
|
NR
|
NR
|
0.454; P < 0.001*
|
0.571; P < 0.001*
|
−0.334; P < 0.001*
|
Chen et al. [21]
|
south China
|
2016
|
NR
|
NR
|
NR
|
0.652; P < 0.001*
|
NR
|
Fernández-Vigo et al. [20]
|
Spain
|
2016
|
NR
|
NR
|
NR
|
0.625; P < 0.001*
|
NR
|
Cui et al. [19]
|
southern China
|
2014
|
NR
|
NR
|
0.185; P < 0.01*
|
0.385; P < 0.01*
|
NR
|
Yin et al. [9]
|
China
|
2012
|
0.11; P < 0.001*
|
NR
|
0.06; P = 0.001*
|
0.34; P < 0.001*
|
−0.11; P < 0.001*
|
the Singapore Chinese Eye Study [18]
|
Singapore
|
2012
|
0.033; P = 0.278
|
NR
|
NR
|
NR
|
NR
|
the Singapore Indian Eye Study [17]
|
Singapore
|
2011
|
NR
|
0.48; P < 0.05*
|
NR
|
0.47; P < 0.01*
|
NR
|
Nangia et al. [10]
|
India
|
2010
|
0.09; P < 0.001*
|
NR
|
NR
|
0.19; P < 0.001*
|
0.03; P = 0.06
|
Hoffmann et al. [16]
|
Germany
|
2010
|
NR
|
NR
|
0.294; P < 0.001*
|
0.324; P < 0.001*
|
NR
|
Fotedar et al. [15]
|
Australia
|
2010
|
NR
|
NR
|
0.343; P < 0.0001*
|
0.424; P < 0.0001*
|
NR
|
Park et al. [7]
|
Korea
|
2010
|
−0.049; P < 0.511
|
NR
|
0.279; P < 0.001*
|
0.506; P < 0.001*
|
NR
|
Chen et al. [6]
|
Republic of China
|
2009
|
−0.053; P = 0.233
|
NR
|
NR
|
NR
|
NR
|
Praveen et al. [14]
|
India
|
2009
|
NR
|
NR
|
NR
|
NR
|
−0.01; P < 0.001*
|
Jivrajka et al. [8]
|
USA
|
2008
|
NR
|
NR
|
NR
|
0.423; P < 0.001*
|
−0.179; P < 0.001*
|
Oliveira et al. [13]
|
USA
|
2006
|
0.07; P = 0.4
|
NR
|
NR
|
NR
|
NR
|
Shimmyo et al. [5]
|
USA
|
2005
|
0.0853; F = 0.0049
|
NR
|
NR
|
NR
|
NR
|
Osuobeni et al. [12]
|
Saudi Arabia
|
1999
|
NR
|
NR
|
NR
|
0.56; P < 0.05*
|
−0.32; P < 0.05*
|
Carney et al. [11]
|
Australia
|
1997
|
NR
|
0.409; P = 0.0001*
|
NR
|
0.515; P = 0.0001*
|
−0.089; P = 0.3484
|
To the best of our knowledge, there have been no reports on the simple regression analysis of the relationship between AL and CR. However, multiple studies reported a significant positive correlation between the two (Table 3). As AL elongates, it is likely that the cornea becomes flatter due to the larger CR.
In relation to the relationship between AL and WTW, Park et al. [7] (R2 = 0.0786) reported similar findings to the present study. As AL increases, WTW also increases. Similarly, Jivrajka et al. [8] (R2 = 0.1792) reported a similar relationship between AL and ACD. As AL increases, ACD seems to increase as well. Previous studies showed significant positive correlations between AL and WTW, and between AL and ACD (Table 3).
The relationship between AL and LT was discussed in Jivrajka et al. [8] (R2 = 0.0321), which made a similar report. Previous studies pointed out several significant negative correlations between the two, suggesting that LT becomes thinner as AL increases.
Our multiple regression analysis revealed that CR, ACD, and LT were significant coefficients for predicting AL. Previous studies conducted multiple regression analyses with AL as the dependent variable, but the overlapping parameters with our study were different. Specifically, Yin et al. [9] included CCT, CR, ACD, and LT as parameters, Nangia et al. [10] included ACD and LT, and Park et al. [7] included ACD. The explanatory variables used in each study were different. However, all reports included ACD, suggesting that it is the parameter most closely related to AL. Additionally, some of these used multiple instruments to measure biometrics.
Since studies of Yin et al. [9] and Nangia et al. [10] did not mention R2, we did not know how well the regression equation could predict AL. Park et al. [7] obtained a much higher coefficient of determination with age, spherical equivalent of refractive error, corneal curvature (diopter), ACD, and retinal nerve fiber layer (RNFL) thickness as explanatory variables (R2 = 0.918). From this point of view, the ocular axis length cannot be predicted with a high probability using only the data obtained from OA-2000 as in our study.
We would like to share useful information in clinical practice from these results. CCT is not affected by AL. Since CCT cannot be predicted from the AL, it is necessary to consciously check the measured CCT value. Moreover, there is something that should be considered during cataract surgery for the long-axial eye. Since WTW increases as AL increases, it is difficult to give a guideline for the size of continuous curvilinear capsulorhexis (CCC) with WTW. To accurately determine the size of CCC, a CCC marker should be used. Since ACD deepens with AL elongation, it should be noted that the lens is in a deeper position in the long-axial eye. In addition, since the lens is thinner in the long-axial eye, we must be aware of posterior capsule rupture during cataract surgery.
This report is based on data derived from a single machine. It does not consider age, gender, stature, weight, refractive power, and social life circumstances (e.g., medical history, educational background, and frequency of reading books), as reported in previous reports [17], [30], [31]. Therefore, it is possible that good results were not obtained. Moreover, since our hospital is a medical institution that handles difficult cases, there may be a selection bias.
In summary, LT tended to be thinner as AL increased, while CR, WTW, and ACD tended to increase.