Factors associated with intraocular pressure before and during 9 years of treatment in the Collaborative Initial Glaucoma Treatment Study

Abstract

Purpose: To evaluate, both at initial glaucoma diagnosis and during treatment, the role of demographic and clinical factors on intraocular pressure (IOP).

Design: Cohort study of patients enrolled in a randomized clinical trial.

Participants: Six hundred seven patients with newly diagnosed open-angle glaucoma (OAG) were enrolled at 14 centers in the United States.

Methods: After randomization to initial surgery or medications, patients were followed at 6-month intervals. Intraocular pressure was measured by Goldmann applanation tonometry. Predictive factors for IOP at baseline and during follow-up were analyzed using linear mixed models.

Main outcome measure: Intraocular pressure at baseline and during follow-up.

Results: The mean baseline IOP was 27.5 mmHg (standard deviation, 5.6 mmHg). Predictive factors for higher baseline IOP included younger age (0.7 mmHg per 10 years), male gender (2.4 mmHg higher than females), pseudoexfoliative glaucoma (5.4 mmHg higher than primary OAG), and pupillary defect (2.2 mmHg higher than those without a defect). During 9 years of follow-up, both surgery and medications dramatically reduced IOP from baseline levels, but the extent of IOP reduction was consistently greater in the surgery group. Over follow-up years 2 through 9, mean IOP was 15.0 versus 17.2 mmHg for surgery versus medicine, respectively. Predictive associations with higher IOP during follow-up included higher baseline IOP (P<0.0001), worse baseline visual field (mean deviation; P<0.0001), and lower level of education (P = 0.0019). Treatment effect was modified by smoking status: nonsmokers treated surgically had lower IOP than smokers treated surgically (14.6 vs. 16.7 mmHg, respectively; P = 0.0013). Clinical center effects were significant (P<0.0001) in both the baseline and follow-up models.

Conclusions: In this large cohort of newly diagnosed glaucoma patients, predictors of pretreatment IOP and IOP measurements over 9 years of follow-up were identified. Our findings lend credence to the postulate that sociodemographic, economic, compliance, or other environmental influences play a role in IOP control during treatment.

Figure 1

Box plots of the range (maximum minus minimum) of the six baseline intraocular pressure (IOP) measures by increasing groups of baseline IOP values. [Note: The box extends from the 25^th to the 75^th percentiles; the bar across the box and the “+” sign indicate the median and mean, respectively. The whiskers extend to the nearest observation within 1.5 times the inter-quartile range, and the square symbols beyond the whiskers represent outlying observations.]

Figure 2

Intraocular pressure (IOP) mean values across time for the two treatment groups. Error bars indicate 95% confidence intervals.

Figure 3

Predicted intraocular pressure (IOP) values at five years, by smoking status, for each step of the treatment sequence (medicine→ALT→trabeculectomy or trabeculectomy→ALT→ medicine) in an “as treated” analysis. Error bars indicate 95% confidence intervals, and the number at the base of each bar is the sample size.