Poster Session: Experimental assessment of scleral anisotropy using multi-meridian air-coupled ultrasonic optical coherence elastography.

Scleral biomechanics plays a key role in the understanding of myopia progression. In this study, we characterized the elastic properties of sclera using an air-coupled ultrasonic (ACUS) optical coherence elastography (OCE) system. New Zealand rabbit eyes (n=7) were measured (<24hr postmortem) in four scleral locations: superior/inferior temporal (ST, IT), and superior/inferior nasal (SN, IN) maintaining an intraocular pressure of 15 mmHg. Elastic waves were induced in the sclera, and wave propagation velocity and shear modulus were measured along two directions: circumferential (superior-inferior) and meridional (nasal-temporal). Wave velocity in scleral tissue ranged from 6 to 24 m/s and shear modulus from 11 to 150 kPa. Velocity was significantly higher (p<.001) in the circumferential vs. meridional directions in the following locations: ST:15.83±2.85 vs 9.43±1.68 m/s, IT:15.00±3.98 vs 8.93±1.53 m/s; SN:16.79±4.30 vs 9.27±1.47 m/s; and IN:13.92±3.85 vs 8.57±1.46 m/s. The average shear modulus in the circumferential was also significantly higher (p<.001) than in the meridional direction for all locations: 65.37±6.04 vs 22.55±1.36 kPa. These results show that the rabbit sclera is mechanically anisotropic with higher rigidity in the circumferential direction compared to the meridional direction. ACUS-OCE is a promising non-invasive method to quantify the biomechanical changes in scleral tissue for future studies involving myopia treatments.

Poster Session: Estimation of scleral biomechanical properties from air-puff-coupled optical coherence tomography.

Progression of myopia is usually accompanied by axial overgrowth of the eyeball, which affects scleral biomechanics (BM). To study scleral biomechanics, we propose the use of air-puff deformation swept-source OCT imaging. Air-puff deformation imaging was performed at different sites of ex vivo porcine (n=5) and rabbit (n=3) eyes, (<24hr postmortem): Nasal/temporal equatorial and posterior sclera (NE, NP, TE, TP), superior (S) and inferior (I) sclera, and cornea (C). Intraocular pressure was kept at 15mmHg. Deformation data were used as input to inverse finite element model (FEM) algorithms to reconstruct BM properties. Experimental deformation amplitudes showed dependence on the animal model, with porcine scleras exhibiting greater inter-site variation (displacement of S, I was up to four times greater than that of N, T), while rabbit scleras exhibited at most 40% of displacement differences between all sites. Both models showed significant (p<.001) differences in the temporal deformation profile between sclera and (C), but similarities in all scleral locations, suggesting that the scleral temporal profile is independent of scleral thickness variations. The FEM estimated an elastic modulus of 1.84 ± 0.30 MPa (I) to 6.04 ± 2.11 MPa (TE) for the porcine sclera. The use of scleral air-puff imaging is promising for noninvasive investigation of structural changes in the sclera associated with myopia and for monitoring possible modulation of scleral stiffness with myopia treatment.

Estimation of scleral mechanical properties from air-puff optical coherence tomography.

We introduce a method to estimate the biomechanical properties of the porcine sclera in intact eye globes ex vivo, using optical coherence tomography that is coupled with an air-puff excitation source, and inverse optimization techniques based on finite element modeling. Air-puff induced tissue deformation was determined at seven different locations on the ocular globe, and the maximum apex deformation, the deformation velocity, and the arc-length during deformation were quantified. In the sclera, the experimental maximum deformation amplitude and the corresponding arc length were dependent on the location of air-puff excitation. The normalized temporal deformation profile of the sclera was distinct from that in the cornea, but similar in all tested scleral locations, suggesting that this profile is independent of variations in scleral thickness. Inverse optimization techniques showed that the estimated scleral elastic modulus ranged from 1.84 ± 0.30 MPa (equatorial inferior) to 6.04 ± 2.11 MPa (equatorial temporal). The use of scleral air-puff imaging holds promise for non-invasively investigating the structural changes in the sclera associated with myopia and glaucoma, and for monitoring potential modulation of scleral stiffness in disease or treatment.

Evaluation of the optical performance for aspheric intraocular lenses in relation with tilt and decenter errors.

PURPOSE: To evaluate and compare the effect of misalignment and tilt on the optical performance of different aspheric intraocular lens (IOL) designs. METHODS: Three aspheric IOLs with a different quantity of spherical aberration (SA) have been designed and the effect of IOL misalignment and tilt on the imaging quality of an eye model has been numerically assessed using a commercial optical design software. The prototypes have been manufactured by lathe turning and tested in vitro using the same optical bench (PMTF, Lambda-X) that complies with International Organization for Standardization standard 11979-2 requirements. Image quality was evaluated from the modulation transfer functions (MTFs), through-focus modulation transfer functions (TF-MTFs), root mean square (RMS) values of defocus, astigmatism and coma, and images of the United States Air Force (USAF) target were taken. A comparison with the optical performance of spherical IOLs has also been performed. RESULTS: Intraocular lens misalignment and tilt increased wavefront aberrations; the effect of misalignment on root mean square (RMS) astigmatism and coma was positively correlated with the spherical aberration of the IOL. Aberration-free IOLs showed the highest MTF for all misalignment values and for IOLs with negative SA correction the MTF decays below 0.43 when they are decentered 0.50 mm. CONCLUSIONS: Aspherical IOLs are more sensitive than spherical IOLs to misalignment or tilt, depending on their SA correction. The optical degradation caused by IOL misalignment had a greater effect on IOL designs with a higher amount of negative spherical aberration. In contrast, the effect of tilt on the optical performance was less sensitive to the IOL design.