Effect of oxybuprocaine eye drops on corneal volume and thickness measurements.

PURPOSE: To investigate the effect of oxybuprocaine eye drops on corneal volume (CV) and corneal thickness measurements. METHODS: Central corneal thickness (CCT), corneal thinnest point (CTP), and CV of 78 eyes of 78 healthy volunteers were measured with Pentacam, before and 5 min after the administration of oxybuprocaine eye drops. The fellow non-anesthetized eyes were used as control. RESULTS: Before topical anesthesia, the mean CCT was 546.76 ± 35.3 µm, after anesthesia, it was 547.76 ± 36.56 µm (p = 0.86). In the fellow eyes, the first mean CCT was 548.82 ± 35.2 µm and the second was 547.55 ± 35.9 µm (p = 0.82). The mean CTP before anesthesia was 543.99 ± 35.23 µm, after it was 544.89 ± 36.3 µm (p = 0.88). In the fellow eyes, the first mean CTP was 544.15 ± 35.35 µm and the second was 542.81 ± 36 µm (p = 0.81). Before topical anesthesia, the mean CV was 60.55 ± 3.84 mm, after it was 60.66 ± 3.97 mm (p = 0.86). In the fellow eyes, the first mean CV was 60.93 ± 3.87 mm and the second was 60.73 ± 4 mm (p = 0.75). CONCLUSIONS: Oxybuprocaine eye drops do not appear to induce a significant corneal swelling and do not affect the measurements when comparing CCT measured with optical or ultrasound devices.

Reliability of the IOLMaster in measuring corneal power changes after hyperopic photorefractive keratectomy.

PURPOSE: To test the accuracy of the IOLMaster (Carl Zeiss Meditec) in detecting corneal power changes after hyperopic photorefractive keratectomy (PRK). METHODS: Forty-five consecutive eyes that underwent hyperopic PRK with the SCHWIND ESIRIS excimer laser, ranging from +0.75 to +7.00 diopters (D) (mean: +3.84±1.56 D), were analyzed. Data included pre- and postoperative (1, 3, and 6 months) fogging refraction and automated keratometry (K). Statistical analysis was performed to determine the correlation between the changes in refraction at the corneal plane and the changes in keratometry. RESULTS: The mean difference between the changes in refraction and the measured corneal changes was +0.27±1.19 D (range: -1.91 to +4.28 D) (P=.18) at 1 month; +0.56±0.97 D (range: -1.00 to +2.96 D) (P=.006) at 3 months; and +0.67±0.80 D (range: -0.73 to +2.31 D) (P=.00002) at 6 months. Based on these results, we suggest using the regression formula found at 6-month follow-up (y=0.8074 x + 0.092) to better calculate the effective corneal power. Comparison between the data obtained with IOLMaster measurements and equivalent K readings from the Holladay report obtained with the Pentacam (Oculus Optikgeräte GmbH) shows good agreement (R(2)=0.9). CONCLUSIONS: Automated keratometry provided by the IOLMaster underestimates the effective refractive changes after hyperopic PRK, and a correcting factor is needed to calculate the corneal power in these cases.

Corneal thickness and endothelial cell characteristics in patients with myotonic dystrophy.

PURPOSE: To compare the characteristics of the endothelial cells of patients with myotonic dystrophy and those of normal subjects to determine if thicker corneas in patients with myotonic dystrophy are the result of their having abnormal endothelial cells leading to corneal edema. DESIGN: Prospective, comparative case series. PARTICIPANTS: Fifty-two eyes of patients with myotonic dystrophy and 52 eyes of normal age- and gender-matched subjects. METHODS: Central corneal thickness (CCT) and endothelial cell counts and shape were measured with an SP 3000P specular microscope (Topcon, Tokyo, Japan) in patients with myotonic dystrophy and were compared with those of age- and gender-matched healthy subjects. MAIN OUTCOME MEASURES: Central corneal thickness, endothelial cell counts, pleomorphism, and coefficient of variation (CoV). RESULTS: In patients with myotonic dystrophy, the mean+/-standard deviation CCT measurement was 533+/-38 microm; the mean+/-standard deviation cell count was 2601+/-365 cell/mm(2); and the mean+/-standard deviation CoV was 23.3+/-4.4 (P<0.001). The mean+/-standard deviation pleomorphism was 64.4+/-8.4%. In healthy subjects, the mean+/-standard deviation CCT measurement was 514+/-27 microm (P = 0.002); the mean+/-standard deviation cell count was 2649+/-363 cell/mm(2) (P = 0.48); the mean+/-standard deviation CoV was 27.6+/-5.5 (P<0.001); and the mean+/-standard deviation pleomorphism was 61.1+/-8.6% (P = 0.04). CONCLUSIONS: Thicker corneas found in patients with myotonic dystrophy are not related to endothelial number or appearance as assessed in this study.

Corneal parameters and difference between goldmann applanation tonometry and dynamic contour tonometry in normal eyes.

PURPOSE: To compare the difference between 2 methods of measuring the intraocular pressure (IOP), namely, Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) and to study the relationship with the corneal parameters in patients with no glaucoma signs. METHODS: One hundred and eighteen eyes of 118 healthy subjects from 20 to 77 years of age underwent IOP measurements with DCT and GAT, central corneal thickness, and corneal volume measurements with Pentacam Scheimpflug camera. Pentacam examination has been performed first, then DCT and, after 10 minutes, GAT measurements. RESULTS: The measurements with GAT ranged between 11 and 22 mm Hg (m=15.49+/-2.43 mm Hg), the measurements with DCT ranged between 10.5 and 25.1 mm Hg (m=17.59+/-2.9 mm Hg). DCT showed a statistically significant (P<0.0001) higher IOP measurement compared with GAT. A relation between differences in IOP with central corneal thickness and corneal volume was found, whereas no relation was found with corneal radius and age. CONCLUSIONS: Our results show a discrete correlation between GAT and DCT measurements, but DCT showed slightly higher values of IOP. If DCT should be considered the gold standard, higher values of IOP could still be considered normal. These 2 devices cannot to be used interchangeably.

Comparison of central corneal thickness measured with Orbscan and Pentacam.

PURPOSE: To compare central corneal thickness measurements obtained with Orbscan II using the acoustic equivalent correction factor (CF) and Pentacam in eyes screened for refractive surgery. METHODS: Central corneal thickness in 91 eyes of 51 volunteers with a spherical equivalent refraction ranging from -17.00 to +5.50 diopters (D) (mean: -3.75+/-4.19 D) was measured with both Orbscan II (CF) and Pentacam prior to refractive surgery. RESULTS: Central comeal thickness measurements ranged from 438 to 610 microm with Orbscan II (CF) and from 472 to 634 microm with Pentacam. The differences between Pentacam and Orbscan II (CF) measurements ranged from -43 to +52 microm (mean: -13.98+/-14.79 microm); these differences were statistically significant (P<.0001). No correlation was found between the difference in central corneal thickness and refractive error. CONCLUSIONS: These results suggest measurements obtained with the Orbscan II (CF) are thinner than those obtained with the Pentacam. Further studies are needed to determine which instrument is more accurate in measuring central corneal thickness.