Modern Analysis of Corneal Biomechanics

Abstract

The measurement of corneal biomechanics has gained significant importance recently. Over the past two decades, three devices capable of quantifying biomechanical properties have become commercially available: two non-contact tonometers (ORA and Corvis ST) that record changes in corneal shape induced by an air-puff, and a third device (BOSS) that quantifies rigidity by analysing the frequency shift of light scattered within the corneal tissue, in accordance with Brillouin scattering. Due to its unique technology, the BOSS can also quantify the rigidity of the crystalline lens. Data from ORA and Corvis ST have been employed to train supervised machine learning models for the detection of keratoconus and primary open-angle glaucoma. Various learners and strategies were used to identify the most effective model. Subsequently, another model was developed to differentiate between healthy eyes, primary open-angle glaucoma, normal-tension glaucoma, and ocular hypertension. After fine-tuning, this model was tested to determine if keratoconus (without glaucoma) could confound the labelling. Several experiments with the BOSS were conducted, including assessments of repeatability, correlations with measurements from ORA, Corvis ST, and OCT, and investigations into changes in corneal biomechanics related to age and refractive error. The thesis concludes with incidental findings on variations in crystalline lens thickness along the same meridian. The main findings are as follows: • It is possible to detect keratoconus and glaucoma using corneal biomechanical data and supervised machine learning algorithms. • Corneal biomechanics data from patients with keratoconus may confound the classification in a model designed to detect glaucoma. • The repeatability of the BOSS is high for lens modulus, but it is quite low for cornealmodulus. Other lens parameters show even lower repeatability. • BOSS measurements do not correlate with any measurement from ORA or Corvis ST, the machines do measure different corneal features. • The most notable change in ocular biomechanics due to age is the reduction in the Brillouin modulus (rigidity) of the crystalline lens, which is contrary to expectations. • Myopic eyes generally exhibit weaker biomechanics compared to emmetropic eyes. • Peripheral crystalline lens thickness varies across different meridians (considering the same eccentricity).