Maddalena De Bernardo

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.

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 &mgr;m, after anesthesia, it was 547.76 ± 36.56 &mgr;m (p = 0.86). In the fellow eyes, the first mean CCT was 548.82 ± 35.2 &mgr;m and the second was 547.55 ± 35.9 &mgr;m (p = 0.82). The mean CTP before anesthesia was 543.99 ± 35.23 &mgr;m, after it was 544.89 ± 36.3 &mgr;m (p = 0.88). In the fellow eyes, the first mean CTP was 544.15 ± 35.35 &mgr;m and the second was 542.81 ± 36 &mgr;m (p = 0.81). Before topical anesthesia, the mean CV was 60.55 ± 3.84 mm3, after it was 60.66 ± 3.97 mm3 (p = 0.86). In the fellow eyes, the first mean CV was 60.93 ± 3.87 mm3 and the second was 60.73 ± 4 mm3 (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.

Prevalence of corneal astigmatism before cataract surgery in Caucasian patients.

Purpose To analyze and quantify the pattern of corneal astigmatism in patients awaiting cataract surgery to provide information for cataract surgeons and intraocular lens (IOL) manufacturers and to establish the demand for toric IOLs in a hospital. Methods This cross-sectional retrospective study evaluated keratometric (K) values measured by partial coherence interferometry (IOLMaster) in cataract surgery candidates, who were then analyzed and correlated by age and axial length (AL) ranges. Results The study evaluated the K values in 757 eyes of 380 patients with a mean age of 71.9 ± 10.2 years (range 33–96 years). The mean corneal astigmatism was 1.02 ± 0.69 D (range 0.06–4.57 D). It was 1 D or higher in 316 (41.74%) eyes. The mean AL was 23.56 ± 1.35 mm (range 20.53–31.86 mm). Conclusions Our study shows that roughly 50% of the eyes have more than 1 D of astigmatism. The results can help hospitals plan and analyze the amount and costs of using toric IOLs in patients with corneal astigmatism.

Long-term results of corneal collagen crosslinking for progressive keratoconus

PURPOSE To evaluate long-term keratoconus stability after corneal crosslinking (CXL) with riboflavin. METHODS In this prospective study, 57 eyes of 55 patients with progressive keratoconus, consecutively treated with ultraviolet A (UVA) - riboflavin CXL, were examined with the corneal topographer Pentacam, the biometer IOLMaster and the analyzer of corneal biomechanics Ocular Response Analyzer before and during a 24 months follow-up after CXL. RESULTS Twenty-four months after CXL, there was a significant improvement in best corrected visual acuity (BCVA) (P<0.01), a significant decrease in corneal thinnest point (CTP), keratometry readings at the keratoconus apex (K max), and corneal volume (CV) (P<0.01), and a significant increase in axial eye length (AL) (P=0.01). No significant changes in anterior chamber volume (ACV) and depth (ACD), (P=0.8), corneal hysteresis (CH) (P=0.16) and corneal resistance factor (CRF) (P=0.06) were found. However, in the subgroup of patients with decreased K max readings 24 months after treatment, both CH and CRF showed a significant reduction (P<0.01). CONCLUSION In the first month after the procedure, CXL induces a reduction in corneal volume. During the 24 months follow-up the cornea tends to recover its original volume with a persistence of the CXL efficacy.

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

PurposeTo 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. MethodsOne 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. ResultsThe 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. ConclusionsOur 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.

Trans epithelial corneal collagen crosslinking for progressive keratoconus: 6 months follow up.

PURPOSE To evaluate keratoconus biomechanical changes after transepithelial corneal collagen cross linking (TE CXL) using riboflavin and ultraviolet A (UVA). SETTING Second University of Naples, Naples, Italy. DESIGN Prospective non comparative case series study. METHODS Patients with progressive keratoconus were examined, before and during a 6 months follow up after TE CXL, with a Pentacam, an Ocular Response Analyzer and an IOLMaster. Best corrected visual acuity (BCVA), refraction, corneal thinnest point (CTP), keratometry readings at the keratoconus apex (Kmax), axial eye length (AL), corneal volume (CV) anterior chamber volume (ACV), anterior chamber depth (ACD), corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated. RESULTS Thirty-six eyes of 36 patients with progressive keratoconus were analyzed. Six months after treatment there was a significant improvement in BCVA (p<0.01), no significant changes in refraction (p=0.57), CTP (p=0.07), Kmax (p=0.88), AL (p=0.07), CV (p=0.38), ACV (p=0.07), ACD (p=0.7), CH (p=0.1) and CRF (p=0.3). CONCLUSIONS According to our results TE CXL stabilizes most of the patients with progressive keratoconus, without affecting in negative way the corneal elasticity.

Relationship Between Corneal Hysteresis and Corneal Resistance Factor with Other Ocular Parameters

Abstract Purpose: To evaluate the relationship between corneal hysteresis (CH) and corneal resistance factor (CRF) with age, central corneal thickness (CCT), corneal curvature (KM), corneal volume (CV), and refractive error in naïve eyes. Methods: 105 healthy subjects (58 male and 47 female) were included in this study. The ages ranged from 19 to 82 years (mean 43.1 ± 15.4 years) and refraction between −11 D and +6 D (mean −0.79 ± 2.95 D). CH and CRF obtained with the Ocular Response Analyzer (ORA) were correlated with age, refractive error, Goldmann Applanation Tonometry (GAT), and with CCT, KM, CV obtained with the Pentacam, and with Corneal-Compensated Intraocular Pressure (IOPcc) and Goldmann-correlated intraocular pressure measurement (IOPg) obtained with ORA. A multivariable mixed effect model was used to evaluate associations among these parameters. Results: CH ranged from 6.9 to 14.6 mmHg (mean 10.26 ± 1.49 mmHg); CRF ranged from 5.8 to 17 mmHg (mean 10.38 ± 1.64 mmHg). Multivariate analysis showed a statistically significant correlation between CH with CCT (p < 0.001), and KM (p < 0.001), and between CRF with CCT (p < 0.001) and GAT (p < 0.001). Conclusions: Our findings support the hypothesis that CH and CRF are related to the corneal shape and thickness, and show a decrease of CH with age.

Pentacam vs SP3000P specular microscopy in measuring corneal thickness.

PURPOSE To compare corneal thickness (CT) measurements obtained with SP3000P specular microscope and Pentacam in eyes screened to undergo refractive surgery (RS). METHODS In this prospective study, a non-randomized consecutive series of 73 healthy eyes (age range: 14-78 years; mean=38.4±14.9) underwent CT measurement with both Oculus Pentacam and Topcon SP3000P specular microscope to assess their suitability to undergo corneal RS. RESULTS CT measurements with SP3000P ranged from 451 to 609 μs (mean 523.1±34.4 μs). The measurements obtained with Pentacam ranged at the corneal apex from 477 to 672 μs (mean 558.9±38.9 μs), at the pupil center from 477 to 672 μs (mean 557.9±38.9 μs) and at the thinnest point from 474 to 669 μs (mean 551.1±39.4 μs). CT measurements showed a good correlation but a statistically significant difference at the pupil center (mean -34.9±14.6 μs, R(2)=0.860, p<0.001), at the apex (mean -35.9±14.9 μs, R(2)=0.856, p<0.001) and at the thinnest point (mean -32±14.8 μs, R(2)=0.862, p<0.001). The calculated regression formulas were: y=0.816x+66.94 for the apex, y=0.819x+66.07 for the pupil center and y=0.810x+73.13 for the thinnest point; where y is the CT measured with the SP3000P and x is the measurement obtained with the Oculus Pentacam. CONCLUSIONS Our results suggest that SP3000P measures thinner corneas compared to the Pentacam and that the correcting factor we identified should be applied to make comparisons between these two devices.

IOL power calculation after corneal refractive surgery.

Purpose. To describe the different formulas that try to overcome the problem of calculating the intraocular lens (IOL) power in patients that underwent corneal refractive surgery (CRS). Methods. A Pubmed literature search review of all published articles, on keyword associated with IOL power calculation and corneal refractive surgery, as well as the reference lists of retrieved articles, was performed. Results. A total of 33 peer reviewed articles dealing with methods that try to overcome the problem of calculating the IOL power in patients that underwent CRS were found. According to the information needed to try to overcome this problem, the methods were divided in two main categories: 18 methods were based on the knowledge of the patient clinical history and 15 methods that do not require such knowledge. The first group was further divided into five subgroups based on the parameters needed to make such calculation. Conclusion. In the light of our findings, to avoid postoperative nasty surprises, we suggest using only those methods that have shown good results in a large number of patients, possibly by averaging the results obtained with these methods.

Coronal Axis Measurement of the Optic Nerve Sheath Diameter: Letters to the Editor

To the Editor: We read with great interest the article by Amini et al comparing the traditional visual axis technique to an infraorbital coronal axis technique for assessing the optic nerve sheath diameter using a highfrequency linear array transducer, with the purpose of overcoming the variability of the true optic nerve sheath diameter cutoff value for detecting elevated intracranial pressure. We would like to congratulate the authors for their interesting and nice paper, but we would like to make some comments on this article, as we believe there are some points that need to be clarified. The real problem in the variability of the cutoff is not the visual axis technique, but the result of using a B scan. This kind of measurement can be influenced by the so-called blooming effect. Although this effect may be less important when dealing with large lesions, it can be misleading when we expect that a difference of less than 0.5 mm can make a difference, as in the case of differential diagnosis of optic nerve lesions. In these cases, measurements with the so-called standardized A Scan can be much more precise, even if it requires some skill and is a little bit more difficult to perform. Moreover, an increase in the optic nerve diameter is not typical of an intracranial hypertension, because an optic neuritis or an optic nerve glioma can show a similar picture. The only way to ensure that the optic nerve increase is caused by an intracranial hypertension is to perform the so-called 30-degree test. This test that has been around since the late 1970s by Karl Ossoinig starts with a measurement of the arachnoidal diameter in straight gaze. Then the maximal arachnoidal diameter is remeasured in maximal abduction of the eye (30-degree gaze): A decrease of the maximal arachnoidal diameter greater than 5% from the initial straight gaze measurement proves subarachnoidal fluid and differentiates this fluid distension of the optic nerve from either (1) solid thickening of the sheaths (eg, in Graves orbitopathy, optic nerve sheaths meningiomas, or leukemic infiltration of the optic nerve) or (2) swelling of the pial and arachnoidal sheaths with engorged vessels in cases of severe orbital congestions (eg, in arteriovenus fistulas or in acute orbital inflammation).