Trial Distinguishes Risks Associated With Corneal Central Thickness

Thicker central corneas, combined with demographic factors such as age and sex can help clinicians distinguish a patient’s risk for glaucoma from ocular hypertension, according to a study published in the British Journal of Ophthalmology. 

Patients with elevated intraocular pressures (IOP) who are men in younger age groups, and who have thicker central corneas, tend to be diagnosed with primary open angle glaucoma (POAG), while those with elevated IOPs and thicker corneas without other risk factors tend to develop ocular hypertension (OHT), the study says.

Researchers assessed 1105 eyes with POAG and 271 eyes with OHT in 771 patients older than 18 years in this secondary study to report baseline IOP characteristics and diurnal fluctuation in participants of the LiGHT trial (ClinicalTrials.gov Identifier: NCT03395535). They performed baseline IOP measurements, a complete ophthalmic eye examination, biomicroscopy, gonioscopy, and applanation tonometry on all participants. 

The mean age of POAG patients was 49.76±17.19 years and 58% were men (n=364) compared with a mean age of 38.81±14.69 years and 48.3% men (n=72) in the OHT cohort. Mean IOP was 20.4±5.4 mm Hg for eyes with POAG compared with 24.4±3.2 mm Hg for eyes with OHT. OHT eyes had a statistically significant higher IOP and thicker central corneas than POAG (P <.001). Pearson correlation analysis revealed that higher IOP was significantly associated with thicker central corneas and younger age in the OHT group (all P <.05).  However, younger age, male sex, thicker central corneas, and lower spherical equivalent were all associated with increasing IOP in the POAG group (all P <.01).

“The results in our study have confirmed a positive relationship between IOP and [central corneal thickness], which has been documented consistently in the literature. Our data revealed that an increase of 10 μm in [central corneal thickness] was associated with an increase of 0.21 mm Hg in OHT and 0.25 mm Hg in POAG,” the researchers explain.

A secondary finding reveals diurnal variations in IOP among both groups. In a majority of eyes, IOP hit a peak around 8:00 am (POAG: 51.3%, 18.7±5.1 mm Hg, OHT: 56.4%, 23.3±3.3 mm Hg) and receded to a low around 2:30 pm (POAG: 31.7%, 17.3±4.5 mm Hg, OHT: 42.8%, 20.9±2.9 mm Hg). 

Investigators highlight the importance of understanding associations with IOP and its diurnal variations. “IOP is an important indicator in the development and progression of glaucoma, thus fully understanding risk factors of elevated IOP and IOP fluctuation is of great significance.” 

Study limitations include possible confounding due to a failure to measure ambulatory blood pressure and axial length.

Reference

Yang Y, Zhang X, Chen Z, et al. Intraocular pressure and diurnal fluctuation of open- angle glaucoma and ocular hypertension: a baseline report from the LiGHT China trial cohort. Br J Ophthalmol. Published online January 27, 2022. doi:10.1136/bjophthalmol-2021-320128