Alejandro Cerviño

Prevalence of corneal astigmatism before cataract surgery.

PURPOSE: To analyze the prevalence and presentation patterns of corneal astigmatism in cataract surgery candidates. SETTING: University of Valencia, Valencia, Spain. METHODS: Refractive and keratometric values were measured before surgery in patients having cataract extraction. Descriptive statistics of refractive and keratometric cylinder data were analyzed and correlated by age ranges. RESULTS: Refractive and keratometric data from 4540 eyes of 2415 patients (mean age 60.59 years ± 9.87 [SD]; range 32 to 87 years) differed significantly when the patients were divided into 10‐year subsets. There was a trend toward less negative corneal astigmatism values, except the steepest corneal radius and the J45 vector component, in older groups (Kruskal‐Wallis, P<.01). In 13.2% of eyes, no corneal astigmatism was present; in 64.4%, corneal astigmatism was between 0.25 and 1.25 diopters (D) and in 22.2%, it was 1.50 D or higher. CONCLUSIONS: Corneal astigmatism less than 1.25 D was present in most cataract surgery candidates; it was higher in about 22%, with slight differences between the various age ranges. This information is useful for intraocular lens (IOL) manufacturers to evaluate which age ranges concentrate the parameters most frequently needed in sphere and cylinder powers and for surgeons to evaluate which IOLs provide the most effective power range.

Central and peripheral corneal thickness measurement with Orbscan II and topographical ultrasound pachymetry

Purpose: To compare thickness measurements of the central 6.0 mm of the cornea obtained with the Orbscan® II topography system and topographical ultrasound pachymetry. Setting: School of Optometry, University of Santiago de Compostela, Galicia, Spain. Methods: In 24 right eyes, pachymetric measurements were taken at the center and 1.2 mm and 3.0 mm on the superior and inferior hemimeridians. A 1‐sample t test was applied to assess the significance of the relationship between Orbscan II and ultrasound methods. The relationship between the 2 was assessed by analyzing regression and plotting the differences against the mean corneal thickness. Orbscan II data were analyzed in 3 ways: (1) without the application of an acoustic equivalent correction factor; (2) with a correction factor of 0.92, as recommended by the manufacturer; (3) with correction using the equations derived in this study. The data were systematically compared with those of ultrasound pachymetry. Results: Before the correction factor was applied, the Orbscan II overestimated the corneal thickness at all locations, with the mean difference (48.15 &mgr;m ± 33.74 [SD]) significantly different from zero (P < .001). Differences increased toward the periphery, and the reliability of Orbscan II readings seemed to decrease with thicker corneas. After the acoustic equivalent was applied, the differences were significantly less; however, this effect did not seem clinically significant as large differences remained. When specific corrective equations were applied for each corneal location, the level of agreement between Orbscan II and ultrasound pachymetry improved substantially; the mean (–0.11 ± 15.22 &mgr;m) was not statistically different from zero (P > .05). Conclusions: The acoustic equivalent correction factor proposed by the manufacturer to obtain corneal thickness measurements with the Orbscan II compared to those from ultrasound pachymetry was not valid for all corneal topography positions. Orbscan II measurements agreed better with those of ultrasound pachymetry when equations for the central and each peripheral location across the topography were applied.

Analysis of the possible benefits of aspheric intraocular lenses: Review of the literature

We reviewed recently published studies that analyzed the visual and optical quality in eyes with different spherical and aspheric intraocular lenses (IOLs). Recent studies focused on visual quality metrics, such as visual acuity and contrast sensitivity, under photopic and mesopic lighting conditions and optical metrics, such as wavefront aberrations, especially spherical aberration. The results in this review were used in an attempt to understand whether there is a visual and/or optical benefit of implanting aspheric IOLs over implanting spherical IOLs.

Apodized diffractive versus refractive multifocal intraocular lenses : Optical and visual evaluation

PURPOSE: To evaluate the optical and visual performance after implantation of refractive or apodized diffractive multifocal intraocular lenses (IOLs). SETTING: Military Health Service Institute, Warsaw, Poland. METHODS: Uncorrected distance visual acuity, best distance‐corrected visual acuity, best distance‐corrected near visual acuity, distance contrast sensitivity under photopic conditions (CSV‐1000), residual refractive error, and wavefront aberrations (LADARWave Hartmann‐Shack wavefront analyzer) were measured in 23 patients who had bilateral implantation of the AcrySof ReSTOR SN60D3 IOL and 23 patients who had bilateral implantation of the ReZoom IOL…. RESULTS: At the 6‐month postoperative visit, the mean photopic uncorrected distance acuity was 0.03 ± 0.05 (SD) in the ReSTOR group and 0.02 ± 0.06 logMAR in the ReZoom group (both approximately 20/20) (P = .569). In all patients, the mean photopic best distance‐corrected acuity was 0.00 logMAR (approximately 20/20) and the mean photopic best distance‐corrected near acuity at 35 cm was 0.10 logMAR. The photopic contrast sensitivity was within the standard normal range in both IOL groups. The difference in photopic contrast sensitivity between groups was statistically significant (P<.001). Higher‐order aberrations, in particular coma and spherical aberrations, were significantly higher in the ReZoom group (all P<.001). CONCLUSIONS: AcrySof ReSTOR SN60D3 and ReZoom IOLs provided good visual performance at distance and near under photopic conditions. Optical quality measures were significantly worse in patients with ReZoom IOLs.

Short-Term Changes in Light Distortion in Orthokeratology Subjects

Purpose. Quantifying adaptation to light distortion of subjects undergoing orthokeratology (OK) for myopia during the first month of treatment. Methods. Twenty-nine healthy volunteers (age: 22.34 ± 8.08 years) with mean spherical equivalent refractive error −2.10 ± 0.93D were evaluated at baseline and days 1, 7, 15, and 30 of OK treatment. Light distortion was determined using an experimental prototype. Corneal aberrations were derived from corneal topography for different pupil sizes. Contrast sensitivity function (CSF) was analyzed for frequencies of 1.50, 2.12, 3.00, 4.24, 6.00, 8.49, 12.00, 16.97, and 24.00 cpd under photopic conditions. Results. Average monocular values of all light distortion parameters measured increased significantly on day 1, returning to baseline after 1 week (P < 0.05 in all cases). Spherical-like aberration stabilized on day 7 for all pupil diameters, while coma-like for smaller pupils only. CSF was significantly reduced on day 1 for all spatial frequencies except for 1.5 cpd, returning to baseline afterwards. Significant correlation was found between light distortion and contrast sensitivity for middle and high frequencies (P < 0.05) after 15 days. Conclusion. Despite consistently increased levels of corneal aberrations, light distortion tends to return to baseline after one week of treatment, suggesting that neural adaptation is capable of overcoming optical quality degradation.

Performance of the compensation comparison method for retinal straylight measurement: effect of patient’s age on repeatability

Aim: The assessment of repeatability and reproducibility of retinal straylight measurements with the C-Quant straylight meter (Oculus AG, Germany) and the effect of patient’s age on the instrument performance are tested with a series of experiments. Methods: First, 20 eyes from 20 subjects (mean age 26.9 (SD 2.7) years, mean refractive error −1.34 (2.72) D) were examined with the C-Quant straylightmeter, taking 10 consecutive readings. Five subjects were also examined on five consecutive days to assess reproducibility. Additionally, repeated measures of straylight from 84 subjects of ages ranging from 19 to 86 years (mean (SD): 42.4 (24.0) years) were retrospectively analysed to assess the effect of patient’s age on repeatability. Results: The results failed to show significant differences between the readings taken within the same session (mean (0.07), p>0.05) or between sessions (mean (0.05), p>0.05). Variability of intrasession measurements was not significant for subjects of different age (p = 0.094). Conclusion: It may be concluded that the C-Quant straylightmeter is repeatable and reliable for the assessment of retinal straylight in human eyes. Age of the patient does not decrease repeatability, even though they feel more insecure about their ability to perform the test.

The Tear Film and the Optical Quality of the Eye

The stability of the tear film plays an important role in the optical quality of the eye. Various methods have been developed to quantify the contribution of the tear film to optical quality, including the double-pass optical method, Hartmann-Shack wavefront sensing, videokeratoscopy, retroillumination analysis, and interferometry. In addition to assessing the effect of tear film irregularities, these methods can aid in the diagnosis of dry-eye related conditions and the monitoring of therapy. This review describes the methodologies used to assess the relationship between the tear film and optical quality of the eye and summarizes the most important findings obtained with these methods with regard to the healthy human eye, the dry eye, and the effect of artificial tear instillation.

Accuracy and precision of EyeSys and Orbscan systems on calibrated spherical test surfaces.

Background: It is important to know how well the surface topography can be measured with current devices for corneal topographic analysis. There are several applications that need an accurate and precise method to measure corneal shape and variations, such as the effect of contact lens wear and the different refractive surgery techniques. Purpose: The aim of this study is to compare the accuracy and reproducibility of the measurement of the central curvature on calibrated steel balls using the EyeSys videokeratoscope and the Orbscan corneal topography system. Methods: The videokeratoscope (EyeSys Corneal Analysis System 2000, version 3.1) and the Orbscan corneal topography system (Orbscan II version 3.0) were used by four trained investigators to measure a series of five uniform and calibrated test surfaces with known radius of curvature ranging from 6.13 to 9.00 mm. Result: No statistically significant difference was found between the videokeratoscope and Orbscan systems in relation to accuracy or precision. The 95% confidence limits showed a close agreement between both instruments. The mean bias was less than ± 0.05 mm for both devices. The precision of the instruments was found to be similar. Conclusion: The EyeSys seems to measure more accurately, but the accuracy of the Orbscan was also acceptable, suggesting that both instruments are accurate and precise enough for research and clinical purposes. However, further studies of accuracy and repeatability of topographical measurements on human eyes generated by different topographers are necessary.

Retinal straylight and complaint scores 18 months after implantation of the AcrySof monofocal and ReSTOR diffractive intraocular lenses.

PURPOSE To evaluate retinal straylight and patient complaint scores 18 months after implantation with the AcrySof ReSTOR diffractive multifocal intraocular lens (IOL) (Alcon Laboratories Inc). METHODS Retinal straylight was measured with the C-Quant (Oculus Optikgeräte GmbH) system in 40 eyes implanted with the AcrySof ReSTOR IOL (SA60D3) and in 40 eyes implanted with the AcrySof SA60AT monofocal IOL. Complaint scores were assessed by a questionnaire in both groups of patients at three different lighting conditions--day light, dimmed light, and at night. RESULTS Seventy-five percent of eyes (30/40) of the ReSTOR group and 80% of eyes (32/40) of the SA60AT control group showed a retinal straylight value within or better than the normal range. No statistically significant differences between groups were found (P = .790). Patients of the ReSTOR group showed significantly more complaint scores at all assessed lighting conditions: increasing factors were 1.53, 2.02, and 2.66, for day light, dimmed light, and night, respectively (P < .0001). Comparing the amount of straylight, the multifocal group had 20% more straylight, albeit not significant at the 1% level. CONCLUSIONS The AcrySof ReSTOR IOL showed similar retinal straylight values compared to the monofocal IOL. Subjectively, patients with the diffractive IOL claimed significantly more glare for all light conditions, especially at night.

Retinal straylight in patients with monofocal and multifocal intraocular lenses

PURPOSE: To determine the differences in retinal straylight perceived by patients with monofocal intraocular lenses (IOLs) and patients with multifocal IOLs. SETTING: Vissum‐Instituto de Oftalmológico de Alicante, Alicante, Spain. METHODS: In this prospective study, contrast sensitivity and retinal straylight were measured prospectively 6 months postoperatively in 67 eyes of 40 patients with a monofocal or multifocal IOL. In the monofocal group, a ThinOptX IOL (ThinOptX, Inc.) was implanted in 12 eyes and an Acri.Smart 48 S IOL (Acri.Tec) in 20 eyes. In the multifocal IOL group, a ReZoom IOL (Advanced Medical Optics) was implanted in 13 eyes and a ReSTOR IOL (Alcon Laboratories) in 22 eyes. RESULTS: All measured values were similar between the monofocal and multifocal groups. Contrast sensitivity correlated significantly with the retinal straylight value (r = 0.258; P = .026) and the mean residual spherical equivalent. There was no statistically significant relationship between IOL type and the retinal straylight value (P = .089). Adjusted mean scores suggest that straylight values in the monofocal group were slightly higher than in the multifocal group. In the monofocal group, retinal straylight values were significantly correlated with pupil size (r = −0.377; P = .033). In the multifocal group, a correlation was found between retinal straylight values and contrast sensitivity (r = 0.397; P = .024). After controlling for age differences, there were no significant differences in retinal straylight between IOLs (P = .069). CONCLUSIONS: No significant differences in straylight values were found between multifocal IOLs and monofocal IOLs. Pupil miosis during retinal straylight measurement and neural adaptation after multifocal IOL implantation may overcome differences between IOLs.