Due to the substantial increase in the number of glaucoma cases within the next several decades, glaucoma is a significant public health issue. The main objective of this study was to investigate determinants for the variation of intraocular pressure and time to blindness of glaucoma patients under treatment at Felege Hiwot Referral Hospital, Bahir Dar, Ethiopia.
Materials and Method
A retrospective cohort study design was conducted on 328 randomly selected glaucoma patients in ophthalmology clinic at the hospital under the follow-up period from January 2014 up to December 2018. A linear mixed effects model for intraocular data, a semi-parametric survival model for the time-to-blindness data and joint modeling of the two responses were used for data analysis.
The comparison of joint and separate models revealed that joint model was more adequate and efficient inferences because of its smaller standard errors in parameter estimations. This was also approved using AIC, BIC and based on a significant likelihood ratio test as well. The estimated association parameter (α) in the joint model was 0.0160 and statistically significant (p - value = 0.0349). This indicated that there was strong evidence for positive association between the effects of intraocular pressure and the risk of blindness. The result indicated that the higher value of intraocular pressure was associated with the higher risk of blindness. As age increased by one year, the average IOP of the patients was also increased by 0.0726 mmHg (p-value < 0.0001) keeping all variables constant.
The predictors; age, blood pressure, type of medication and cup-disk ratio were significantly associated with the two responses of glaucoma patients. Health professionals should give more attention for patients who have blood pressure and cup-disk ratio greater than 0.7 during the follow-up time to reduce the risk of blindness of glaucoma patients.