PURPOSE

Characterize the relationship between intraocular pressure (IOP) as measured by standard and modified Goldmann prisms and the progressive loss of retinal nerve fiber layer (RNFL) in a cohort of glaucoma patients.

DESIGN

Retrospective cross-sectional cohort data analysis.

PARTICIPANTS

The study included all patients from a database of 1927 eyes, 966 patients with same visit sequential standard and modified Goldmann IOP measurements. From the database, 148 eyes, 75 patients met the inclusion criteria of a diagnosis of primary open angle glaucoma (POAG) with at least 5 sequential quality optical coherence tomographer (OCT) measurements.

METHODS

Sequential OCT images were obtained with the spectral domain Zeiss OCT5000. Participants were all diagnosed with POAG by untreated IOP ≥ 22, disk changes, and visual field (HVF) loss consistent with glaucomatous optic neuropathy (GON). Included were 575 Goldmann IOP measurements with standard and modified prisms affixed to the Goldmann applanation tonometer (GAT) armature. A modified prism includes a corneal conforming applanation surface minimizing the cornea's contribution to the IOP measurement. The study included a total of 940 OCT visits with an average of 6.3 visits per eye over an average of 4.9 years. Retinal nerve fiber layer (RNFL) loss rate was calculated by serial linear fit of average RNFL thickness measurements. Demographics as well as central corneal thickness (CCT) and corneal hysteresis (CH) data were also collected.

OUTCOME MEASURES

Pearson correlation coefficients and random coefficient models were used to evaluate the relationship between mean standard and modified IOP measurements and RNFL thickness measurements over time in POAG subjects. Secondary outcomes of CCT and CH correlation to RNFL were similarly analyzed.

RESULTS

For all 148 POAG eyes, the overall rate of RNFL loss for an average standard GAT IOP of 17.9 mmHg was 1.08 µm per year (p = 0.002). Each 1-mmHg increase in standard GAT IOP was associated with an additional RNFL loss of 0.047 µm per year (r = 0.153, p = 0.06). Each 1-mmHg increase in modified GAT IOP was associated with an additional RNFL loss of 0.084 µm per year (r = 0.289, p = 0.0005). A modified prism IOP measurement ≥ 22 mmHg indicates a 2.57 times greater probability of significant RNFL loss than a standard prism IOP measurement ≥ 22 mmHg, p < 0.0001.

CONCLUSIONS

Higher levels of GAT IOP during follow-up were related to higher rates of progressive RNFL loss detected by optic nerve OCT in treated POAG. A modified GAT prism surface demonstrates a significantly increased sensitivity, reliability and differentiation to progressive RNFL loss when compared to a standard GAT prism measured IOP. PRéCIS: A modified applanation surface prism with a corneal conforming shape used on a Goldmann tonometer appears to be a more sensitive and reliable indicator of progressive glaucomatous optic neuropathy as measured by retinal nerve fiber layer changes.