Receiver operator characteristics (ROC) analysis applies the logistic
model to individual subject data and plots the sensitivity and 1 − specificity for classifying subjects as myopic or not across
the range of values for the model. The ROC curve associated with this
baseline model is presented in
Figure 6A . At the point of maximum discrimination, these features were only
moderately successful in distinguishing the myope from the nonmyope,
displaying good sensitivity but poor specificity (0.83 and 0.40,
respectively;
Table 4 , model A). The addition of relative peripheral refraction to
the baseline logistic model was a significant improvement
(χ
2 = 90.5,
df = 1,
P < 0.0001). The ROC curve associated with that
model is presented in
Figure 6B . The addition of relative peripheral
refraction decreased the sensitivity but increased the specificity
compared with the baseline model (0.71 and 0.79, respectively;
Table 4 ,
model B). The addition of vitreous chamber depth to the baseline
logistic model was also a significant improvement
(χ
2 = 235.8,
df = 1,
P < 0.0001). The ROC curve associated with that
model is presented in
Figure 6C . Vitreous chamber depth added to the
sensitivity and the specificity of the baseline model (0.88 and 0.94
respectively;
Table 4 , model C). Despite the association between
vitreous chamber depth and peripheral refraction
(Table 3) , the best
model included the baseline components and both vitreous chamber depth
and relative peripheral refraction (comparing full model to baseline
plus vitreous chamber depth model yields χ
2 = 26.0,
df = 1,
P < 0.0001; comparing full
model to baseline plus relative peripheral refraction model yieldsχ
2 = 171.2,
df = 1,
P < 0.0001). The ROC curve associated with that
model is presented in
Figure 6D . Sensitivity and specificity were the
highest with both vitreous chamber depth and relative peripheral
refraction in the model (0.97 and 0.91 respectively;
Table 4 , model D).
An enlarged vitreous chamber depth appeared to be the strongest
characteristic of the myopic eye, but both shape (prolate) and size
(elongated) were needed to best characterize the myopic eye.