Background To estimate and compare changes in the Bruch’s membrane opening—minimum rim width (BMO–MRW) and area in normal, ocular hypertensive and glaucoma eyes following acute elevations in intraocular pressure (IOP).
Methods The optic nerve heads (ONHs) of 104 subjects (31 normals, 20 ocular hypertension (OHT) and 53 with primary glaucoma) were imaged using Spectral-domain optical coherence tomography (OCT; Spectralis, Heidelberg Engineering, Germany). IOP was raised twice by applying a force (0.64 n then 0.9 n) to the anterior sclera using an ophthalmo-dynamometer. After each IOP increment, IOP was held constant, measured with a Tonopen (AVIA applanation tonometer, Reichert, Depew, New York, USA), and ONH was rescanned with OCT. In each OCT volume, BMO–MRW and area were calculated and at each IOP increment.
Results The baseline MRW was significantly smaller in glaucoma subjects (174.3±54.3 µm) compared with normal (287.4±42.2 µm, p<0.001) and OHT subjects (255.4±45.3 µm, p<0.001). MRW of glaucoma subjects was significantly thinner at the first and second IOP elevations than that at baseline (both p<0.01), but no significant change was noted in normal and OHT subjects. There was no significant change of BMO area at acute IOP elevations from baseline in all diagnoses (all p>0.05).
Conclusion Acute IOP elevation leads to compression of the nerve fibre layers of neuroretinal rim in glaucoma subjects only without changing ONH size. This suggests that the neural and connective tissues at ONH level in glaucoma subjects are more susceptible to acute IOP episodes than OHT or normal controls.
- Intraocular pressure
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Contributors SS collected, cleaned and analysed the data, drafted and revised the paper. TAT contributed to the design and initiation of the project, designed data collection tools, monitored data collection, drafted and revised the paper. MB and EA contributed to the analysis and interpretation of data and revised the draft paper. SGT, ZL and DM contributed to the interpretation of data and revised the draft paper. NGS contributed to the analysis and interpretation of data for the work and revised the draft paper. TA and MJAG contributed to the design and initiation of the project, designed data collection tools, monitored data collection, contributed to the interpretation of data, drafted and revised the paper.
Funding This study was supported by the National University Singapore Young Investigator Award (MG; NUSYIA_FY13_P03; R-397-000-174-133) and the Singapore Ministry of Health’s National Medical Research Council under its Singapore Translational Research Investigator Award (NMRC/STAR/0023/2014). The sponsor or funding organisation had no role in the design or conduct of this research. NGS was supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Moorfields Eye Hospital National Health Service Foundation Trust and University College of London Institute of Ophthalmology.
Disclaimer The views expressed here are those of the author(s) and not necessarily those of the National Health Service, the National Institute for Health Research or the UK Department of Health.
Competing interests None declared.
Ethics approval SingHealth Centralized Institutional Review Board.
Provenance and peer review Not commissioned; externally peer reviewed.
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