Evaluation of corneal biomechanical parameters after simultaneous phacoemulsification with intraocular lens implantation and limbal relaxing incisions.

PURPOSE: To determine whether alterations in architecture cause corneal biomechanical changes after simultaneous cataract surgery and limbal relaxing incisions (LRIs). SETTING: Department of Ophthalmology, Kitasato University, Kanagawa, Japan. DESIGN: Observational case series. METHODS: This study longitudinally assessed corneal hysteresis (CH) and the corneal resistance factor (CRF) using the Ocular Response Analyzer in eyes having cataract surgery with LRIs. The relationship between these biomechanical parameters and central corneal thickness (CCT), measured using an ultrasound pachymeter, was also assessed. RESULTS: The mean CH was 10.0 mm Hg ± 1.2 (SD) preoperatively, 9.0 ± 1.6 mm Hg 1 day postoperatively, 9.7 ± 1.4 mm Hg at 1 week, 9.6 ± 1.4 mm Hg at 1 month, and 10.2 ± 1.3 mm Hg at 3 months. The mean CRF was 10.0 ± 1.5 mm Hg, 8.9 ± 1.6 mm Hg, 9.5 ± 1.5 mm Hg, 9.5 ± 1.4 mm Hg, and 9.5 ± 1.4 mm Hg, respectively. There were significant differences between preoperative and 1-day postoperative measurements (P=.005, CH; P=.004, CRF). The CH and CRF were significantly correlated with CCT (r = 0.33, P=.04 and r = 0.40, P=.01, respectively) 3 months postoperatively. CONCLUSIONS: The CH and CRF values decreased 1 day after simultaneous cataract surgery with LRIs but soon recovered to preoperative levels, suggesting there were no significant changes in corneal biomechanical factors after 1 day. Corneal thickness may play a role in biomechanical factors even in such eyes.

Modulation transfer function of intraocular collamer lens with a central artificial hole.

BACKGROUND: A modified implantable collamer lens (ICL) with a central hole (diameter 0.36 mm), "Hole-ICL", was created to improve aqueous humour circulation. The aim of this study is to investigate the effects of ICL power and the relationship between pupil size and modulation-transfer functions (MTFs) in a Hole-ICL in vitro. METHODS: The ICL and intraocular lens (IOL) studied were the Collamer ICL (Model ICM, STAAR Surginal) and the monofocal IOL AF-1 (VA-60BBR, HOYA). The ICLs' powers were -20.0 diopters (D), -10.0 D, -5.0 D, +3.0 D, and +10.0 D. A modified ICL with a central hole (diameter 0.36 mm), "Hole-ICL", was created. The monofocal IOL, which was used as an artificial crystalline lens, was +30.0 D in power, and it was 13.0 mm in length with an optic diameter of 6.0 mm. The line-spread function (LSF) was recorded with the OPAL Vector System (Image Science Ltd.), and a model eye (Menicon Co.) was used that consisted of a wet cell. A conventional ICL or Hole-ICL was placed in the posterior chamber of the model eye. The MTF was calculated from the LSF using fast Fourier transform techniques. Furthermore, we investigated the relationship between pupil size and the MTF of the ICL for -5.0 D. The sizes of the effective aperture were 2.0, 3.0, 4.0, and 5.0 mm. RESULTS: The in-focus contrasts of the conventional ICL at 100 cyc/mm for a 3.0-mm effective aperture were 37%, 40%, 39%, 38%, and 39% for -20.0 D, -10.0 D, -5.0 D, +3.0 D, and +10.0 D respectively. The in-focus contrasts of the Hole-ICL at 100 cyc/mm for a 3.0-mm effective aperture were 37%, 40%, 39%, 38%, and 38% for -20.0 D, -10.0 D, -5.0 D, +3.0 D, and +10.0 D respectively. The results for a 2.0-mm effective diameter showed that the in-focus MTF in the Hole-ICL was lower than in the conventional ICL, although the difference was small. CONCLUSION: These results suggest that differences in MTF between the Hole-ICL and the conventional ICL for various ICL powers and effective pupil diameters were small and clinically negligible.

Time course of corneal biomechanical parameters after phacoemulsification with intraocular lens implantation.

PURPOSE: To assess the time course of corneal biomechanical parameters after phacoemulsification with intraocular lens implantation. METHODS: We examined 54 eyes of 33 consecutive patients undergoing cataract surgery. We quantitatively assessed the values of corneal biomechanics characterized by corneal hysteresis (CH) and corneal resistance factor (CRF) using an Ocular Response Analyzer before and 1 day, 1 week, 1 month, and 3 months after surgery. We also investigated the relationship between these biomechanical parameters and central corneal thickness 3 months after surgery. RESULTS: The CH was 9.7 ± 1.1 (mean ± SD) mm Hg preoperatively, and 9.0 ± 1.4, 9.7 ± 1.1, 9.7 ± 1.1, and 9.7 ± 1.3 mm Hg 1 day, 1 week, 1 month, and 3 months postoperatively, respectively. The CRF was 9.5 ± 1.1 mm Hg preoperatively, and 8.8 ± 1.2, 9.2 ± 1.3, 9.1 ± 0.9, and 9.2 ± 1.2 mm Hg 1 day, 1 week, 1 month, and 3 months postoperatively, respectively. Multiple comparisons demonstrated significant differences between measurements made before and 1 day after surgery (P = 0.01 for CH and CRF, Dunnett test). Both CH and CRF were significantly correlated with central corneal thickness (Pearson correlation coefficient r = 0.29; P = 0.03 for CH and r = 0.42; P = 0.002 for CRF). CONCLUSIONS: Both CH and CRF decreased briefly at 1 day after cataract surgery but soon recovered to the preoperative levels, suggesting that cataract surgery does not induce a significant change in corneal biomechanics, except for 1 day postoperatively. The corneal thickness may play some role in corneal biomechanics even in postcataract eyes.

Effect of aging on corneal biomechanical parameters using the ocular response analyzer.

PURPOSE: To assess the effect of aging on corneal biomechanical parameters in a normal population. METHODS: We prospectively examined 204 normal eyes of 204 healthy Japanese volunteers (68 men, 136 women; mean age 46.7+/-19.4 years [range: 19 to 89 years]). Corneal hysteresis, corneal resistance factor, corneal-compensated intraocular pressure (IOP(cc)), and Goldmann-correlated intraocular pressure (IOP(G)) were qualitatively assessed using a Reichert Ocular Response Analyzer. Central corneal thickness was measured using an ultrasound pachymeter. This measurement was performed 3 times, and the mean value obtained was used for statistical analysis. The relationships between patient age and corneal biomechanical parameters, or age and intraocular pressure (IOP), were investigated. RESULTS: Mean corneal hysteresis and corneal resistance factor were 10.1+/-1.5 mmHg and 10.1+/-1.6 mmHg, respectively. Mean central corneal thickness was 539.1+/-30.9 microm. A weak, but significant, negative correlation was found between age and corneal hysteresis (Pearson's correlation coefficient r=-0.17, P=.02) and corneal resistance factor (r=-0.18 P=.01). On the other hand, no significant correlation was found between age and central corneal thickness (r=-0.06, P=.41), age and IOP(cc) (r=-0.02, P=.82), or age and IOP(G) (r=-0.11, P=.11). CONCLUSIONS: Corneal biomechanical parameters are significantly decreased by aging without significant changes in central corneal thickness or IOP, suggesting that age-related structural changes resulting from collagen cross-linking may lead to a reduction of corneal biomechanical variables independent of central corneal thickness or IOP.

Comparison of the changes in corneal biomechanical properties after photorefractive keratectomy and laser in situ keratomileusis.

PURPOSE: To compare the postoperative biomechanical properties of the cornea after photorefractive keratectomy (PRK) and after laser in situ keratomileusis (LASIK) in eyes with myopia. METHODS: We retrospectively examined 27 eyes of 16 patients undergoing PRK and 31 eyes of 16 patients undergoing LASIK for the correction of myopia. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with Ocular Response Analyzer before and 3 months after surgery. We also investigated the relationship between these biomechanical changes and the amount of myopic correction. RESULTS: The CH was decreased significantly from 10.8 +/- 1.3 (mean +/- SD) mmHg to 9.2 +/- 1.6 mmHg after PRK (P < 0.001), and from 10.8 +/- 1.4 mmHg to 8.6 +/- 0.9 mmHg after LASIK (P < 0.001). The CRF was also decreased significantly, from 10.3 +/- 1.5 mmHg to 8.4 +/- 1.8 mmHg after PRK (P < 0.001), and from 10.3 +/- 1.5 mmHg to 7.7 +/- 1.3 mmHg after LASIK (P < 0.001). The amount of decrease in CH and CRF was significantly larger after LASIK than after PRK (P = 0.04). There was a significant correlation between the amount of myopic correction and changes in biomechanical properties after PRK (r = -0.61, P < 0.01 for CH, r = -0.41, P < 0.05 for CRF) and LASIK (r = -0.37, P < 0.05 for CH, r = -0.45, P < 0.05 for CRF). CONCLUSIONS: Both PRK and LASIK can affect the biomechanical strength of the cornea depending on the amount of myopic correction. The amount of biomechanical changes is larger after LASIK than after PRK. From a biomechanical viewpoint, PRK may be a less invasive surgical approach for the correction of myopia than LASIK.

Time course of corneal biomechanical parameters after laser in situ keratomileusis.

PURPOSE: To assess the time course of corneal biomechanics after laser in situ keratomileusis (LASIK). METHODS: We examined 36 eyes of 20 consecutive patients undergoing LASIK for low to moderate myopia. We quantitatively assessed the values of corneal biomechanics characterized by corneal hysteresis (CH) and corneal resistance factor (CRF) using an Ocular Response Analyzer (Reichert Ophthalmic Instruments) before and 1 week, 1, 3, and 6 months after surgery. We carried out this measurement 3 times, and the average value was used for statistical analysis. RESULTS: The CH was 10.6 +/- 1.7 (mean +/- SD) mm Hg preoperatively, and 8.6 +/- 1.2, 9.0 +/- 1.7, 9.0 +/- 1.4, and 8.9 +/- 1.5 mm Hg 1 week, 1, 3, and 6 months postoperatively, respectively. The CRF was 10.0 +/- 1.7 mm Hg preoperatively, and 7.3 +/- 1.5, 7.6 +/- 2.0, 7.8 +/- 1.6, and 7.7 +/- 1.6 mm Hg 1 week, 1, 3, and 6 months postoperatively, respectively. The variances of the data were statistically significant (p < 0.001 for both CH and CRF). Multiple comparisons demonstrated significant differences between measurements made before surgery and at all postoperative times (at 1 week and 1, 3, and 6 months; p < 0.001 for CH and CRF, Fisher's least significant difference test). CONCLUSIONS: Over the study period, the largest changes in corneal biomechanical parameters occurred within 1 week after surgery, and these then became nearly stable. No progressive deterioration of the corneal biomechanics was observed at any time during the 6-month follow-up period.