Montserrat Arjona

Optical quality of foldable monofocal intraocular lenses before and after injection: Comparative evaluation using a double-pass system

PURPOSE: To use the double‐pass technique to evaluate the in vitro optical quality of foldable monofocal intraocular lenses (IOLs) used to correct aphakia. SETTING: Universitat Politècnica de Catalunya, Terrassa, and Instituto de Microcirugía Ocular de Barcelona, Barcelona, Spain; Universidad Nacional de Tucumán, Tucumán, Argentina. METHODS: This study assessed the in vitro optical quality of 7 IOLs before and after injection in an artificial eye that was attached to a double‐pass system (Optical Quality Analysis System [OQAS]). The procedure imitated the conventional in vivo technique used to assess the optical quality of eyes with an IOL. The following parameters were evaluated: point‐spread function, modulation transfer function (MTF), MTF cutoff frequency, Strehl ratio, and OQAS values. RESULTS: The in vitro optical quality of most IOLs was as good after injection as before injection. In 1 IOL, the post‐injection optical quality was statistically significantly different but the optical quality remained high. CONCLUSIONS: Results indicate that after an IOL is placed in the eye, its optical performance will be good, providing good visual quality. The eye cell model attached to the double‐pass system was useful and effective for fully characterizing the optical quality of IOLs and evaluating variations resulting from the injection process.

Intra- and intersession repeatability of a double-pass instrument.

Purpose. To evaluate the intra- and intersession repeatability of the optical quality parameters provided by the Optical Quality Analysis System (OQAS), which is based on the double-pass technique. Methods. We performed optical quality measurements using the OQAS on 20 eyes of 10 healthy subjects who had best spectacle-corrected visual acuity of 20/20 or better. Measurements were performed by the same examiner in three different sessions that were separated by 10-min intervals. The subjects eye was realigned at the beginning of each session. During each session, three consecutive measurements were taken without realignment. The following optical quality parameters were analyzed: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl2D ratio, the OQAS values (OV) at contrasts of 100%, 20%, and 9%, and the objective scatter index (OSI). Results. The mean coefficients of repeatability obtained for the first session were 4.51 (MTFcutoff), 0.049 (Strehl2D ratio), 0.15 (OV 100%), 0.21 (OV 20%), 0.28 (OV 9%), and 0.11 (OSI), which were similar to those found in the second and third sessions. The confidence limits in the Bland and Altman charts when the intrasession repeatability was assessed (in a comparison of the first and second measurements of the first session) ranged from −3.16 to 3.94 (MTFcutoff), −0.060 to 0.069 (Strehl2D ratio), −0.12 to 0.18 (OV 100%), −0.20 to 0.23 (OV 20%), −0.29 to 0.27 (OV 9%), and −0.12 to 0.13 (OSI). The same limits when the intersession repeatability was assessed (in a comparison of the first and second sessions) ranged from −5.30 to 5.49 (MTFcutoff), −0.054 to 0.050 (Strehl2D ratio), −0.17 to 0.17 (OV 100%), −0.22 to 0.19 (OV 20%), −0.26 to 0.29 (OV 9%), and −0.12 to 0.13 (OSI). Conclusions. Our findings showed that OQAS is a clinical instrument with a good intra- and intersession repeatability and that the realignment of the eye does not introduce any additional variability in the measurements.

Optical performance in eyes wearing two multifocal contact lens designs

The optical performance of eyes wearing soft multifocal contact lenses was studied using the double‐pass technique. Retinal image quality was measured in a group of six eyes wearing two different designs of multifocal lenses: an aspheric design and a spheric multicurve design. Measurements were performed for far, intermediate and near vision conditions and with two different pupil diameters: 3 and 5 mm. The results show that the best optical performance is obtained for far vision conditions when no lens is worn. For near vision conditions, the optical performance when the lens is worn is, in general, better than when no lens is worn. When the lens is worn, the optical performance for far and intermediate vision conditions is similar for the aspherical design, but it decreases for near vision conditions. For the spherical multicurve design, the optical performance obtained for far vision conditions is similar to that obtained for intermediate vision conditions for low values of object vergence, but decreases when the object vergence is high and therefore also for near vision. In general, the differences in optical performance are greater for small pupil diameters (3 vs 5 mm). The general trends of the results obtained by computing the modulation transfer function of the contact lens–eye system can also be shown qualitatively by means of double‐pass images or quantitatively by computing the Imax/Imed of the image.

Effect of laser in situ keratomileusis on vision analyzed using preoperative optical quality

PURPOSE: To evaluate the effect on vision of laser in situ keratomileusis (LASIK) based on preoperative optical quality. SETTING: Universitat Politècnica de Catalunya, Terrassa, and Barcelona Institute of Ocular Microsurgery, Barcelona, Spain. DESIGN: Comparative case series. METHODS: The relative change in optical quality and visual acuity were evaluated in eyes that had LASIK for myopia. The optical quality was assessed before and 3 months after surgery using parameters provided by a double‐pass system. Patients were classified into 4 groups by preoperative optical quality: low (Group 1), moderate (Group 2), high (Group 3), and very high (Group 4). RESULTS: The study evaluated 25 patients (50 eyes). The optical quality parameters improved postoperatively in Group 1 and Group 2, with the improvement ranging from 15% to 21% and from 13% to 17%, respectively. The preoperative and postoperative optical quality in Group 3 was similar. The optical quality in Group 4 worsened significantly by percentages ranging from −20% to −26%. Although visual acuity had the same trend, there were no statistically significant changes. CONCLUSION: The changes in optical quality after LASIK surgery depended on the patient’s preoperative optical quality; visual acuity showed the same trend, although no change was significant. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Optical quality after myopic photorefractive keratectomy and laser in situ keratomileusis: Comparison using a double-pass system

PURPOSE: To use a double‐pass system to compare the optical quality after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for mild to moderate myopia. SETTING: Universitat Politècnica de Catalunya, Terrassa, Barcelona Institute of Ocular Microsurgery, Barcelona, Spain. DESIGN: Comparative case series. METHODS: Optical quality was assessed with a clinical double‐pass system preoperatively and 3 months after PRK or LASIK. The modulation transfer function (MTF), retinal image quality parameters (MTF cutoff frequency, Strehl ratio), and intraocular scattering (objective scatter index [OSI]) were calculated. RESULTS: This study evaluated 34 eyes that had PRK and 55 eyes that had LASIK. Both PRK and LASIK had a statistically significant impact on retinal image quality, although no significant differences between the techniques were observed. The MTF at 30 cycles per degree decreased by a factor of 1.50 in the PRK group and by a factor of 1.32 in the LASIK group. The MTF cutoff frequency decreased by a factor of 1.04 in the PRK group and by a factor of 1.06 in the LASIK group. The Strehl ratio decreased by a factor of 1.10 and 1.07, respectively. Photorefractive keratectomy and LASIK increased the objective scatter index by factors of 1.48 and 1.57, respectively. Significant correlations between the preoperative refraction and the OSI were found. CONCLUSIONS: Retinal image quality was similarly reduced with PRK and LASIK, with no significant differences between the 2 methods. Some PRK patients had a residual refractive error that might have been related to corneal‐wound healing still present 3 months postoperatively. Financial Disclosure: Dr. Arjona is an investor in and Drs. Güell and Pujol are investors in and consultants to Visiometrics S.L., Terrassa, Spain. None of the other authors has a financial or proprietary interest in any material or method mentioned.

Influence of amount and changes in axis of astigmatism on retinal image quality

We measured retinal image quality in astigmatic eyes, using the double-pass technique. We analyzed the influence of the amount of astigmatism and changes in axis of astigmatism on the eyes optical performance. Different amounts of astigmatism were obtained by variation of the cylindrical power of a lens situated in front of the eye, between 0.25-diopter (D) overcorrection and 1-D undercorrection at intervals of 0.25 D. Changes in the axis of astigmatism were obtained by rotation of the lens, which neutralizes the astigmatism in an angle of +/- 10 degrees at 5 degrees intervals. The results show the decrease in retinal image quality and the increase in the degree of image astigmatism obtained when the amount of astigmatism increases or the angle between the lens and the eye axis is other than zero. In general, the largest variations correspond to when the astigmatism changes from 0 to 0.25 D or when the axis changes from 0 degree to +/- 5 degrees. The reduction in optical performance is smaller in living eyes than in an eye model or in an artificial eye. The aberrations present in the living eye reduce the relative loss of retinal image quality introduced by astigmatism.

Grading nuclear, cortical and posterior subcapsular cataracts using an objective scatter index measured with a double-pass system

Purpose To evaluate objectively intraocular scattering in eyes with nuclear, cortical and posterior subcapsular cataracts by means of an objective scatter index (OSI) obtained from double-pass images. To compare the results with those obtained using clinical conventional procedures. Methods In this prospective, observational, cross-sectional, non-consecutive case series study, 188 eyes with cataracts of 136 patients were analysed (123 eyes had nuclear, 41 eyes had cortical and 24 eyes had posterior subcapsular cataracts). The control group consisted of 117 eyes of 68 healthy patients. Patient examination included subjective refraction, best spectacle-corrected visual acuity (BSCVA), cataract grade using the lens opacities classification system III (LOCS III) and OSI. Results We found a decrease in the BSCVA and an increase in the OSI with increasing cataract grade. Statistically significant differences were observed when the OSI of eyes without cataracts and those with different LOCS III were compared. The comparison between the OSI and LOCS III reported good percentages of agreement regarding the number of eyes classified in equivalent levels: 72.4% (nuclear cataracts), 86.6% (cortical cataracts) and 84.3% (posterior subcapsular cataracts). A non-linear regression model was applied between OSI and BSCVA, which resulted in the following multiple correlation coefficients: r=0.878 (nuclear), r=0.843 (cortical) and r=0.844 (posterior subcapsular). Conclusions The results of the study showed that OSI is a useful parameter for evaluating large amounts of intraocular scattering that can be used, in combination with other conventional procedures, as a valuable tool in clinical practice to grade cataracts objectively.

Curvature sensor for ocular wavefront measurement

We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eyes measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes.

Optimized algorithm for the spatial nonuniformity correction of an imaging system based on a charge-coupled device color camera

We present an optimized linear algorithm for the spatial nonuniformity correction of a CCD color cameras imaging system and the experimental methodology developed for its implementation. We assess the influence of the algorithms variables on the quality of the correction, that is, the dark image, the base correction image, and the reference level, and the range of application of the correction using a uniform radiance field provided by an integrator cube. The best spatial nonuniformity correction is achieved by having a nonzero dark image, by using an image with a mean digital level placed in the linear response range of the camera as the base correction image and taking the mean digital level of the image as the reference digital level. The response of the CCD color cameras imaging system to the uniform radiance field shows a high level of spatial uniformity after the optimized algorithm has been applied, which also allows us to achieve a high-quality spatial nonuniformity correction of captured images under different exposure conditions.

Multispectral system for reflectance reconstruction in the near-infrared region

We analyze the performance of a multispectral system that works in the near- infrared (NIR) region of the electromagnetic spectrum (NIR: 800-1000 nm). The system, which uses a CCD camera as a sensor with five acquisition channels, is capable of reconstructing the NIR spectral reflectance curves for a wide range of samples with a high degree of accuracy. We carried out a study of the sources of error in the experimental system, developed a luminance adaptation model to remove the dependence of the captured images on the exposure time of the camera and the f-number of the objective lens, and performed reconstructions of the spectral reflectances of a set of 80 samples. We achieved the best results by using a 12-bit camera, considering a different luminance adaptation transform for each channel, and by using the pseudoinverse reconstruction method. Under these conditions, the system provided mean percentages of reconstruction higher than 99.8% and root-mean-square-error values lower than 0.17, and is therefore suitable for use as a spectrophotometric instrument.