Interface fluid syndrome after bioptics.

PURPOSE: To report an unusual case of interface fluid syndrome after refractive surgery. METHODS: A 37-year-old man with high myopia underwent a planned bioptics procedure including creation of a corneal flap using a mechanical microkeratome and concurrent anterior chamber phakic intraocular lens implantation; excimer laser ablation was not performed at this time. RESULTS: Postoperatively, the patient developed corneal edema and was referred to our department. Interface fluid syndrome was confirmed using optical coherence tomography; the mechanism was due to endothelial cell pump dysfunction. CONCLUSIONS: This is the first report to document interface fluid syndrome following a planned bioptics procedure.

Screening of forme fruste keratoconus with the ocular response analyzer.

PURPOSE: To evaluate the performance of the Ocular Response Analyzer (ORA) in the screening of forme fruste keratoconus (FFKc). METHODS: A retrospective comparative study was conducted involving 180 eyes. ORA preoperative data were analyzed for 125 normal control eyes (64 patients) undergoing laser in situ keratomileusis (LASIK) without corneal ectasia after 24 months of follow-up and 55 case eyes with unilateral keratoconus from a database (BCVA of 1.0, KISA index <60%). All eyes were matched in four groups of central corneal thickness (CCT): group 1, <500 microm; group 2, 500 to 539 microm; group 3, 540 to 579 microm; and group 4 >580 microm. Corneal hysteresis (CH), the corneal resistance factor (CRF), the air pressure curve, and the infrared signal were compared between FFKc and normal eyes in each group. RESULTS: The mean CH was 9.1 +/- 1.8 mm Hg for FFKc and 10.3 +/- 1.9 mm Hg for control eyes (P < 0.001), and the mean CRF was 9.2 +/- 1.8 and 11.1 +/- 2 mm Hg (P < 0.001), respectively. Sensitivity in each group was as follows: group 1, CH < 9.5 mm Hg (91%) and CRF < 9.5 mm Hg (81%); group 2, CH < 10.5 mm Hg (91%) and CRF < 10 mm Hg (87%); group 3, CH < 11.5 mm Hg (79%) and CRF < 11 mm Hg (74%); group 4 had two cases of FFKc, and the difference was not significant. Air pressure levels at inward and outward applanation and the maximum air pressure level were significantly lower and shorter in time in FFKc (P < 0.001), whereas the shape of the infrared signal was more variable. CONCLUSIONS: The ORA provides additional information in the screening of FFKc, with an accurate analysis of the corneal biomechanical properties according to CCT, air pressure, and infrared curves.

Biomechanical and morphological corneal response to placement of intrastromal corneal ring segments for keratoconus.

PURPOSE: To evaluate the biomechanical and morphological changes in keratoconic corneas after Intacs intrastromal corneal ring segment (ICRS) implantation. SETTING: Department of Ophthalmology, National Reference Center for Keratoconus, Bordeaux University, Bordeaux, France. METHODS: Keratoconic eyes were retrospectively analyzed after ICRS implantation; preoperative and 6-month postoperative evaluation were done using the Ocular Response Analyzer (ORA) and the Orbscan II topographer. Biomechanical parameters included corneal hysteresis (CH), the corneal resistance factor (CRF), and other parameters extracted from the signal curves. Morphological parameters included simulated keratometry and the cone location magnitude index from the axial map (aCLMI) and tangential map (tCLMI). Parameters were extracted using software designed to read and process topographic maps. RESULTS: There were no significant differences between preoperatively and postoperatively in mean CH (7.7 mm Hg +/- 1.4 [SD] versus 7.4 +/- 1.4 mm Hg) or mean CRF (6.6 +/- 1.8 mm Hg versus 6.1 +/- 1.4 mm Hg). Only 2 ORA signal parameters were significantly different. Topographic parameters with significant decreases were minimum central keratometry (K) (mean change -5.8 +/- 2.9 diopters [D]) (P<.001), minimum central K (mean change -5.8 +/- 2.3 D) (P<.001), mean aCLMI (9.6 +/- 2.7 preoperatively versus 7.7 +/- 2.5 postoperatively) (P<.009), and mean tCLMI (18.9 +/- 2.8 versus 12.9 +/- 4.4) (P<.002). The only significant correlation between biomechanical and topographic parameters was postoperative ORA infrared signal peak 1 and postoperative aCLMI. CONCLUSIONS: Intrastromal corneal ring implantation significantly decreased corneal curvature, with preoperative values predicting magnitude of change. However, it did not alter the viscoelastic biomechanical parameters of CH and CRF.

Correlations between corneal hysteresis, intraocular pressure, and corneal central pachymetry.

PURPOSE: To analyze the correlation between corneal hysteresis (CH) measured with the Ocular Response Analyzer (ORA, Reichert) and ultrasonic corneal central thickness (CCT US) and intraocular pressure measured with Goldmann applanation tonometry (IOP GA). SETTING: Bordeaux 2 University, Ophthalmology Department, Bordeaux, France. METHODS: This study comprised 498 eyes of 258 patients. Corneal hysteresis, corneal resistance factor (CRF), and IOP corneal-compensated (IOPcc) were provided by the ORA device; CCT US and IOP GA were also measured in each eye. The study population was divided into 5 groups: normal (n = 122), glaucoma (n = 159), keratoconus (n = 88), laser in situ keratomileusis (LASIK) (n = 78), and photorefractive keratectomy (n = 39). The Pearson correlation was used for statistical analysis. RESULTS: Corneal hysteresis was not strongly correlated with IOP or CCT US. The mean CH in the LASIK (8.87 mm Hg) and keratoconus (8.34 mm Hg) groups was lower than in the glaucoma (9.48 mm Hg) and normal (10.26 mm Hg) groups. The lower the CH, the lower its correlation with IOPcc and IOP GA. A CH higher than the CRF was significantly associated with the keratoconus and post-LASIK groups. CONCLUSIONS: Corneal hysteresis, a new corneal parameter, had a moderate dependence on IOP and CCT US. Weaker corneas could be screened with ORA parameters, and low CH could be considered a risk factor for underestimation of IOP. The CCT US should continue to be considered a useful parameter.

Biomechanical characteristics of the ectatic cornea.

The ocular response analyzer (ORA) (Reichert, Inc.) was used in the case of a middle-aged man who developed unilateral corneal ectasia after bilateral laser in situ keratomileusis (LASIK). The preoperative refraction was similar in the 2 eyes. Post-LASIK ectasia was central in the left eye; topography was oblate in the right eye. The ORA values consisted of the mean of 4 measurements. Corneal hysteresis and corneal resistance factor were almost equal in the ectatic eye and the nonectatic eye. However, significant between-eye differences in the morphology of the signals were noted, most prominently in the lower amplitude of the applanation peaks in the ectatic eye. The shape of the applanation signal yielded important information in addition to corneal hysteresis and corneal resistance factor.