Abstract
BackgroundTo better understand the role of corneal properties and intraocular pressure (IOP) in the evaluation of primary open-angle glaucoma (POAG); and to determine the feasibility of identifying glaucomatous optic neuropathy (GON) using IOP corrected and uncorrected for corneal biomechanics.MethodsRecords from 1,875 eyes of consecutively evaluated new patients were reviewed. Eyes were excluded if central corneal thickness (CCT) or Ocular Response Analyzer (ORA) measurements were unavailable. Presence or absence of GON was determined based on morphology of the optic disc, rim and retinal nerve fiber layer at the time of clinical examination, fundus photography and Heidelberg Retinal Tomography. Goldmann-applanation tonometry (GAT) in the untreated state was recorded and Goldmann-correlated (IOPg) and corneal-compensated IOP (IOPcc) were obtained using the ORA. Glaucomatous eyes were classified as normal or high-tension (NTG, HTG) using the conventional cutoff of 21 mm Hg. One eligible eye was randomly selected from each patient for inclusion.ResultsA total of 357 normal, 155 HTG and 102 NTG eyes were included. Among NTG eyes, IOPcc was greater than GAT (19.8 and 14.4 mm Hg; p < 0.001) and the difference between IOPcc and GAT was greatest for this subgroup of patients with NTG (p ≤ 0.01). The maximum combined sensitivity and specificity for detection of GON occurred at 20.9 mm Hg for GAT (59%, 90%) and 18.4 mm Hg for IOPcc (85%, 85%) and the area under the curve was greater for IOPcc (0.93 vs. 0.78; p < 0.001).ConclusionsIOPcc may account for measurement error induced by corneal biomechanics. Compared to GAT, IOPcc may be a superior test in the evaluation of glaucoma but is unlikely to represent an effective diagnostic test.
Highlights
To better understand the role of corneal properties and intraocular pressure (IOP) in the evaluation of primary open-angle glaucoma (POAG); and to determine the feasibility of identifying glaucomatous optic neuropathy (GON) using IOP corrected and uncorrected for corneal biomechanics
Using Receiver operating characteristic (ROC) curves we found that the areas under the curve (AUC) for the IOPcc (0.93) was greater than for Goldmann applanation tonometry (GAT) (0.78), indicating that compared to GAT, IOPcc may represent a superior test in the evaluation of glaucoma
Since IOPcc was greater than GAT in majority of normal tension glaucoma (NTG) eyes (92%) in this study, segregating NTG and high-tension glaucoma (HTG) using a GAT threshold of 21 mm Hg may not be optimal
Summary
To better understand the role of corneal properties and intraocular pressure (IOP) in the evaluation of primary open-angle glaucoma (POAG); and to determine the feasibility of identifying glaucomatous optic neuropathy (GON) using IOP corrected and uncorrected for corneal biomechanics. IOP as measured by Goldmann applanation tonometry (GAT) does not correlate well with glaucomatous optic neuropathy (GON) as there are Notwithstanding, data from clinical trials support a role for IOP reduction in patients with ocular hypertension, early or advanced primary open-angle glaucoma (POAG), and NTG [7,8,9,10,11]. As IOP remains the only modifiable risk factor for eyes with GON and IOP reduction remains the mainstay of treatment, greater accuracy and less confounding in IOP measurement should have value in the management of most glaucomas [7,8,9,10,11] It is not entirely clear whether the inconsistent association between IOP and glaucoma is related to shortcomings of office based IOP measurement, or whether IOP-independent risk factors are responsible for the pathological process in some glaucomas. Recent studies have shown that GAT calibration error is common [15]
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