Varun Ranganathan, MC Optom

Clinical Optometrist

An OCULAR Interface Exclusive

Keywords: Glaucoma, corneal hysteresis, intraocular pressure, teleophthalmology, artificial intelligence in eyecare

Abstract: Primary open-angle glaucoma (POAG) remains a predominant cause of irreversible blindness globally. Elevated intraocular pressure (IOP) is widely acknowledged as a critical risk factor in the onset and advancement of POAG. Recent research has also identified modifications in corneal biomechanics as potential contributors to this condition.

Technological Advancements in Corneal Biomechanics Analysis: The advent of innovative diagnostic tools, notably the Ocular Response Analyzer (ORA) and the Corvis ST (CST), has revolutionised the assessment of corneal biomechanics. These devices provide insights into the initial biomechanical changes of the cornea in response to IOP fluctuations, thereby enhancing the precision in glaucoma detection and diagnosis.

Corneal hysteresis (CH) is a measure of how the viscoelasticity of cornea changes with an applied force, usually a jet of air, and the ability of the cornea to absorb and dissipate the energy is studied ⁽¹⁾. Low CH and associated optic nerve damage are considered as important biomarkers of glaucoma ⁽²⁾. With increasing age, our cornea becomes rigid and less elastic causing CH to decrease ⁽³⁾.

Ocular Response Analyzer (ORA): The ORA is the only device which offers in vivo quantification of corneal biomechanics and gives us a measure of CH and corneal resistance factor (CRF). As the pulse of air hits the cornea, both inward and outward displacement of cornea is measured ⁽⁴⁾.

Corvis ST (CST): The CST, a more recent innovation by Oculus, facilitates a comprehensive in vivo examination of corneal biomechanics. Employing a consistent air pulse, it captures the cornea’s dynamic response and uses an ultra-high-speed (UHS) Scheimpflug camera to acquire 4300 frames/s, covering 8.5 mm horizontally of a single slit, allowing a dynamic assessment of the induced deformation of the cornea ⁽⁵⁾.

Numerous studies have observed a diminished CH in various glaucoma types compared to normal eyes or those with ocular hypertension ^(6-7). Recent findings also link low CH values to optic nerve and visual field impairments in glaucoma. Intriguingly, the likelihood of glaucoma’s structural and functional progression seems more closely associated with CH than central corneal thickness (CCT) ⁽⁸⁾.

Application and Limitations: Both ORA and CST utilise an air jet/impulse for IOP and corneal mechanics assessment. However, their usage is confined to clinical settings, limiting accessibility. The recent pandemic has underscored the need for teleophthalmology advancements, driving the demand for novel, non-invasive technologies.

Future Directions in Glaucoma Monitoring: In the wake of these challenges, the development of innovative, minimally invasive technologies is imperative. Advancements in artificial intelligence (AI) offer promising avenues for non-intrusive monitoring of corneal shape alterations over time. One such emerging technology is spectacle-based biosensors, which could visualise corneal biomechanics and thereby continuously track glaucoma progression remotely. This approach aligns with the growing need for patient-centred, accessible ophthalmic care, particularly in telemedicine contexts.

Conclusion: The integration of cutting-edge devices like ORA and CST in clinical practice has marked a significant leap in understanding and managing glaucoma. However, the quest for more accessible, non-invasive, and AI-driven diagnostic tools remains critical, especially in the era of telemedicine and patient-centric healthcare approaches. The development of technologies like spectacle-based biosensors heralds a new era in glaucoma monitoring, potentially transforming patient outcomes and quality of life.

References:

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2. Susanna CN, Diniz-Filho A, Daga FB, et al. A prospective longitudinal study to investigate corneal hysteresis as a risk factor for predicting development of glaucoma. Am J Ophthalmol. 2018;187:148–152. doi: 10.1016/j.ajo.2017.12.018.
3. Murphy ML, Pokrovskaya O, Galligan M, O’Brien C. Corneal hysteresis in patients with glaucoma-like optic discs, ocular hypertension and glaucoma. BMC Ophthalmol. 2017;17(1):1. doi: 10.1186/s12886-016-0396-9.
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