Preoperative, intraoperative, and postoperative assessment of corneal biomechanics in refractive surgery.

PURPOSE OF REVIEW: To review current and emerging methods and utilities of preoperative, intraoperative, and postoperative measurements of corneal biomechanics and their effects on refractive surgery decision-making. RECENT FINDINGS: Several recent clinical and preclinical studies have demonstrated the utility of corneal biomechanical analysis in refractive surgery. These studies focus on both screening surgical candidates for keratoconic disease as well as intraoperative and postoperative monitoring. The measurement of spatially resolved biomechanics is beginning to be studied in humans. SUMMARY: Clinically available screening methods combining corneal biomechanics with topographic and tomographic data provide increased utility when screening for keratoconic disorder. Spatially resolved measurement of corneal biomechanics holds great potential for preoperative, intraoperative, and postoperative evaluation of refractive surgery candidates as well as for more individualized procedures in the future.

The Relationship Between Corneal Biomechanics and Intraocular Pressure Dynamics in Patients Undergoing Intravitreal Injection.

PRECIS: A higher "corneal resistance factor" (CRF) was associated with greater intraocular pressure (IOP) elevation after intravitreal injection of bevacizumab. Both higher "corneal hysteresis" (CH) and CRF were associated with more rapid IOP recovery postinjection. PURPOSE: The purpose of this study was to evaluate the relationship between measurable corneal biomechanical properties and acute IOP elevation after rapid intraocular volume expansion from the routine intravitreal injection. MATERIALS AND METHODS: A total of 100 patients necessitating unilateral intravitreal injection with 0.05 mL of bevacizumab for retinal pathology were analyzed before injection with Goldmann Applanation Tonometry to measure IOP, Ocular Response Analyzer (ORA) to measure corneal biomechanical properties, and optical biometry to calculate globe measurements. IOP and ORA were measured again within 5 minutes of the injection and then IOP measurements were taken every 10 minutes until the IOP was ≤150% of the preinjection IOP. Linear regression and logistic regression were used to test variables associated with acute IOP increase. A Cox proportional hazard model accounting for preinjection IOP and postinjection IOP was used to test the effect of CH or CRF on the time required to return to 150% of baseline IOP. RESULTS: Higher CRF was associated with greater immediate postinjection IOP (P=0.026) elevation. A preinjection IOP>15.5 mm Hg moderately predicted postinjection IOP≥35 mm Hg (area under the receiver operating characteristics curve=0.74). A preinjection IOP>18.5 mm Hg combined with CH poorly predicted postinjection IOP>50 mm Hg (area under the receiver operating characteristics curve=0.67). A higher CH [hazard ratio (HR)=1.24; 95% confidence interval (CI)=1.08-1.42; P=0.002] and preinjection IOP (HR=1.16; 95% CI=1.09-1.22; P<0.001), along with a lower immediate postinjection IOP (HR=0.93; 95% CI=0.90-0.95; P<0.001), were each independently associated with quicker IOP recovery postinjection. Similar results were seen in the Cox model examining CRF and IOP recovery. CONCLUSIONS: Higher CRF and preinjection IOP were independently associated with greater postinjection IOP elevations. ORA metrics did not greatly strengthen the prediction of patients who would have postinjection IOP>50 mm Hg. Higher CH and CRF were associated with faster IOP recovery after intravitreal injection, demonstrating the dynamic relationship between ocular biomechanical properties and aqueous outflow pathways.

Transepithelial Corneal Crosslinking Using a Novel Ultraviolet Light-Emitting Contact Lens Device: A Pilot Study.

Purpose: To evaluate the feasibility of a novel, on-eye UVA light-emitting contact lens device driven by fiber optics for the corneal crosslinking (CXL) of patients with keratoconus. Methods: In nine corneal transplant candidates with advanced keratoconus a scleral contact lens reservoir containing 0.007% benzalkonium chloride preserved with 0.25% riboflavin-monophosphate was placed on the eye for 30 minutes. The reservoir lens was removed and replaced with the CXLens UVA light-emitting contact lens. A 375-nm UVA light at 4 mW/cm2 intensity was delivered for 30 minutes for a dose of 7.2 J/cm2. A one-sided paired t-test was used to evaluate mean differences in maximum keratometry, thinnest corneal thickness, and endothelial cell density between screening and 6 months after CXL. A two-sided paired t-test was used to evaluate differences in best-corrected distance visual acuity between screening and 6 months after CXL. Results: All patients received the treatment as per protocol and adhered to follow-up testing. At 6 months after CXL, treated eyes had an average -1.0 ± 1.6 diopters decrease in the maximum keratometry (P = 0.049), a nonsignificant 2.3 ± 7.5 letter improvement in best-corrected distance visual acuity (P = 0.19), a nonsignificant -17 ± 14 µm decrease in thinnest corneal thickness (P < 0.01), and a nonsignificant -86 ± 266 cells/mm2 decrease in endothelial cell density (P = 0.20). Conclusions: Our pilot study demonstrated the feasibility of the novel CXL device for the treatment of keratoconus and indicates the device is ready for larger scale studies with longer follow-up periods. Translational Relevance: The novel CXLens on-eye UVA light-emitting contact lens device offers the potential for efficient, high-throughput transepithelial corneal CXL.