Purpose:
To determine if adjusting baseline IOP for corneal thickness increases the predictive accuracy of the prediction model for the development of POAG.
Methods:
The prediction model for the development of POAG from the Ocular Hypertension Treatment Study and the European Glaucoma Prevention Trial includes baseline age, IOP, pattern standard deviation, cup/disc ratio and central corneal thickness (CCT)1 . We ran the same Cox proportional hazards model changing only whether IOP was/was not adjusted for CCT. Separate Cox proportional hazards model was run for each of five published correction algorithms (below), with/without CCT and the C-index was calculated.
Results:
In the models that included IOP adjusted for CCT, the C-indices ranged from 0.763 to 0.770, no better than the original prediction model (0.774). IOP, whether adjusted for CCT or not, was highly significant in all models. When CCT was added to models in which IOP was adjusted for CCT, CCT still made a statistically significant improvement. Conclusions: The calculation of individual risk for the development of POAG is simpler and equally accurate using IOP and CCT as measured, rather than applying an algorithm to correct IOP for CCT.
References:
1. Gordon MO et. al.,Ophthalmology 2007; 114:10-19.2. Ehlers N, et. al.. Acta Ophthalmol (Copenh) 1975;53:34-433. Whitacre MM,et. al. Am J Ophthalmol 1993;115:592-596.4. Orssengo GJ et. al. Bull Math Biol. 1999;61: 551-572.5. Doughty MJ et. al., Surv Ophthalmol. 2000; 44:367-408.6. Kohlhaas M, et. al., Arch Ophthalmol. 2006;124:471-476
Clinical Trial:
www.clinicaltrials.gov NCT00000125
Keywords: clinical (human) or epidemiologic studies: risk factor assessment • intraocular pressure • clinical (human) or epidemiologic studies: biostatistics/epidemiology methodology