Brillouin Scanning in Cataractous Eyes

Brillouin microscopy (BM), based on Brillouin light scattering theory, has become established in clinical ophthalmology for examining retinal properties, corneal diseases, and age-related lens changes. These BM-derived metrics can portray the intrinsic characteristics of the biosystem, such as the hydration state or the content and anisotropy of corneal collagen fibers, while remaining unaffected by factors such as intraocular pressure and central corneal thickness. In vivo, BM has been shown to characterize the depth-dependent or gradient viscoelastic properties of ocular lenses. Some studies have used this technique to show that the lens nucleus thickens with age, while the thickness of the lens cortex remains constant. Laboratory studies have also shown an increase in the stiffness of the lens nucleus, while later clinical Brillouin measurement studies have shown that the nucleus is clearly distinct from the softer cortex.

Although data on age-related lenticular changes already exist, the in vivo lenticular biomechanics of cataract lenses derived from Brillouin still need to be comprehensively investigated. This is relevant in that the correlation of Brillouin-derived cataract lens mechanics with the Lens Opacity Classification System (LOCS III) and/or the phacoemulsification energy required for cataract surgery may provide useful information about whether the technique could provide valuable insights into lens nuclear stiffening. Very hard or soft nuclei remain one of the major risk factors for the complications occuring during cataract surgery. In the former case, a significantly higher amount of energy is required during phacoemulsification, which can lead to simultaneous damage to the corneal endothelium and prolonged surgical recovery. In the latter case, intraoperative fragmentation of the cell nucleus poses a challenge.

Currently, the type, degree, and (representative) hardness of the cataract lens are assessed preoperatively using a slit lamp examination with the LOCS III system. The degree of lens opacity provides information about how phacoemulsification should be performed, which viscoelastic device should be selected, and what experience the surgeon needs to perform the operation. However, the slit lamp assessment method is susceptible to subjective variability between observers. Given the unique characteristics of assessing the biomechanical properties of the lens in vivo and the short scan time, BM could be used as a novel complementary objective method for surgical decision-making.