Table 2shows the results of multivariate analysis in an interval-censored model. Significant factors identified in the multivariate analysis included manifest spherical equivalent (β = −0.3570,
P = <0.0001), mean preoperative corneal curvature (β = −0.1807,
P = 0.0009), diameter of optic zone (β = −0.6593,
P = 0.0043), undercorrection (β = 0.5530,
P = 0.0396), and age (β = 0.0297,
P = 0.0734). The risks of myopia regression in the five periods (γ
1, γ
2, … , γ
5) are also shown in
Table 2 .
Using our interval-censored model,
Table 3shows the predicted probability of myopia regression in each period and cumulative probability up to a certain period using three selected eyes, representing groups with low, moderate, or high myopia. Taking the first case as an example, the score is calculated as:
\[\mathrm{intercept}{+}{\beta}_{1}\ {\times}\ \mathrm{MSE}{+}{\beta}_{2}{\times}\mathrm{Mean\ K}{+}{\beta}_{3}{\times}\mathrm{size_OZ}{+}{\beta}_{4}\ {\times}\mathrm{undercorrection}{+}{\beta}5{\times}\mathrm{age}{=}5.9856{+}({-}0.3570){\cdot}({-}13.625){+}({-}0.1807){\cdot}44.24{+}({-}0.6593){\cdot}5.5{+}0.5530{\cdot}0{+}0.0297{\cdot}23{=}{-}0.0875,\]
where β
1,β
2, … , β
5 are the coefficients for each period in
Table 2 . Calculation of
equation 1shows that the predicted probability (π
1) of myopia regression in the first period (from 1 week to 1 month after LASIK) is
\[{\pi}_{1}{=}1{-}\mathrm{exp}{\{}{-}{[}\mathrm{exp}({\gamma}_{1}{+}\mathrm{SCORE}){]}{\}}{=}0.6002,\]
where γ
1 is the regression coefficient of the first follow-up period
(Table 3) . The predicted probability of other periods (π
2, π
3, π
4, and
π5) for the same patient can be calculated in a similar manner. Therefore, the cumulative probability of myopia regression until period 5 is equivalent to
\[{\pi}(\mathrm{recurrence\ in\ period}\ 1)\ {+}{\pi}(\mathrm{recurrence\ in\ period\ 2\ and\ no\ recurrence\ in\ period\ 1})\ {+}{\ldots}{+}{\pi}(\mathrm{recurrence\ in\ period\ 5},\]
\[\mathrm{no\ recurrence\ in\ period\ 1,\ .\ .\ ,\ and\ period\ 4})\]
\[{=}{\pi}_{1}{+}{\pi}_{2}(1{-}{\pi}_{1}){+}{\pi}_{3}(1{-}{\pi}_{1})(1{-}{\pi}_{2})\]
\[{+}{\pi}_{4}(1{-}{\pi}_{1})(1{-}{\pi}_{2})(1{-}{\pi}_{3}){+}{\pi}_{5}(1{-}{\pi}_{1})(1{-}{\pi}_{2})\]
\[{\times}(1{-}{\pi}_{3})(1{-}{\pi}_{4}){=}1{-}{[}(1{-}{\pi}_{1})(1{-}{\pi}_{2}){\times}(1{-}{\pi}_{3})(1{-}{\pi}_{4})(1{-}{\pi}_{5}){]}{=}1{-}{[}(1{-}0.6002)(1{-}0.2975)\]
\[{\times}(1{-}0.5092)(1{-}0.3211)(1{-}0.3126){]}{=}0.9357.\]
(Table 3) . The eyes with a higher score had a greater probability of myopia regression. The predicted probabilities of average risk based on the mean of all eyes are also shown in
Table 3 .
Figure 3shows the cumulative probability up to a a certain period in the three groups. The risk of myopia regression increased rapidly within a month, slowed between 1 and 6 months, and became steady after 6 months, regardless of risk group. The risks of myopia regression up to 6 months after LASIK were 86%, 42%, and 2% for high, moderate, and low risks, respectively. The corresponding risk estimate for the average risk based on all eyes was 21%.