In Vivo 3-Dimensional Strain Mapping Confirms Large Optic Nerve Head Deformations Following Horizontal Eye Movements.
OBJECTIVE
To measure lamina cribrosa (LC) strains (deformations) following abduction and adduction in healthy subjects and to compare them with those resulting from a relatively high acute intraocular pressure (IOP) elevation.


METHODS
A total of 16 eyes from 8 healthy subjects were included. Among the 16 eyes, 11 had peripapillary atrophy (PPA). For each subject, both optic nerve heads (ONHs) were imaged using optical coherence tomography (OCT) at baseline (twice), in different gaze positions (adduction and abduction of 20°) and following an acute IOP elevation of approximately 20 mm Hg from baseline (via ophthalmodynamometry). Strains of LC for all loading scenarios were mapped using a three-dimensional tracking algorithm.


RESULTS
In all 16 eyes, LC strains induced by adduction and abduction were 5.83% ± 3.78% and 3.93% ± 2.57%, respectively, and both significantly higher than the control strains measured from the repeated baseline acquisitions (P < 0.01). Strains of LC in adduction were on average higher than those in abduction, but the difference was not statistically significant (P = 0.07). Strains of LC induced by IOP elevations (on average 21.13 ± 7.61 mm Hg) were 6.41% ± 3.21% and significantly higher than the control strains (P < 0.0005). Gaze-induced LC strains in the PPA group were on average larger than those in the non-PPA group; however, the relationship was not statistically significant.


CONCLUSIONS
Our results confirm that horizontal eye movements generate significant ONH strains, which is consistent with our previous estimations using finite element analysis. Further studies are needed to explore a possible link between ONH strains induced by eye movements and axonal loss in optic neuropathies.
Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore.
Xiaofei
X
Wang
Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore.
Meghna R
MR
Beotra
Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore 2Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
Tin Aung
TA
Tun
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 3Duke-NUS, Singapore.
Mani
M
Baskaran
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 3Duke-NUS, Singapore.
Shamira
S
Perera
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 3Duke-NUS, Singapore 4Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Tin
T
Aung
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 5NIHR Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom 6Discipline of Clinical Ophthalmology and Eye Health, University of Sydney, Sydney, New South Wales, Australia.
Nicholas G
NG
Strouthidis
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 3Duke-NUS, Singapore.
Dan
D
Milea
Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore 2Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
Michaël J A
MJ
Girard
D000328:Adult; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D020342:Finite Element Analysis; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure; D008297:Male; D009898:Optic Disk / Q000473:pathology* / Q000503:physiopathology; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000503:physiopathology; D041623:Tomography, Optical Coherence / Q000379:methods*; D055815:Young Adult