Abstract:
ABSTRACT
Background: Due to the substantial increase in the projected number of glaucoma cases within
the next several decades, glaucoma is a significant public health issue. The main objective of this
study was joint modeling of longitudinal intraocular pressure change and time to blindness of
glaucoma patients at Felege Hiwot Referral Hospital, Bahir dar, Ethiopia.
Method: A retrospective cohort study design was conducted from 328 randomly selected
glaucoma patients in ophthalmology clinic at FHRH under the follow-up period from January
2014 up to December 2018. The analysis consists of exploratory data analysis and fitting three
different models namely; a linear mixed effects model for the longitudinal data, a semiparametric
survival model for the time-to-event data and a joint modeling of the two responses
linked by shared random effects.
Result: The use of a joint analysis compared to separate models shows a reduction in the
standard errors which indicates that more adequate and efficient inferences can be made by
using joint model estimates. The overall performance of both the separate and joint models in
terms of model parsimony and goodness of fit, the joint model was performed better based on its
lower AIC, BIC and based on a significant likelihood ratio test as well. The estimated
association parameter (α) in the joint model is 0.0160 and statistically significant (p - value
=0.0349). This indicated that there is strong evidence of association between the effects of the
longitudinal intraocular pressure to the risk of blindness. The result indicated that the higher
value of intraocular pressure was associated with the higher risk of blindness. For a unit
increased in age, the average IOP of the patients was significantly increased by 0.0726 mmHg
(p-value < 0.0001) keeping all variables constant.
Conclusion: The predictor age, blood pressure, type of medication and cup-disk ratio were
significantly associated with the two responses of glaucoma patients. Health professionals give
more attention for patients who have blood pressure and cup-disk ratio greater than 0.7 during
the follow-up time to reduce intraocular pressure and to minimize the risk of blindness of
glaucoma patients.
Keywords: Intraocular pressure, time to blindness, linear mixed model, joint model, Cox
proportional hazard model