Biomedical subjects

John de Brabander

Publications and source records attributed to John de Brabander.

4 recordsLinked to original sources

PubMed2006

Evaluation of pupil dynamics after implantation of artisan phakic intraocular lenses.

PURPOSE: To compare pre- and postoperative horizontal and vertical pupil diameters after horizontal Artisan phakic intraocular lens (PIOL) (Ophtec BV, Groningen, The Netherlands) implantation for correction of myopia. METHODS: The pre- and postoperative scotopic pupil diameters measured by the Colvard pupillometer (Oasis Medical, Glendora, Calif) were compared in 71 eyes after Artisan PIOL implantation (Artisan Colvard group). Analysis of pupil shape (vertical vs horizontal diameter, V/H ratio) after horizontal Artisan PIOL implantation was performed with the Procyon pupillometer (Procyon Instruments Ltd, London, United Kingdom) in 121 eyes (Artisan Procyon group) under scotopic, mesopic-low, and mesopic-high conditions and compared to an age- and refraction-matched control group of 121 eyes of refractive surgery candidates (Procyon control group). RESULTS: After horizontal Artisan PIOL implantation, the mean horizontal pupil diameter decreased from 6.231 +/- 0.70 mm preoperatively to 5.34 +/- 0.68 mm postoperatively in the Artisan Colvard group (P < .01). The mean horizontal scotopic diameter was 5.60 +/- 0.66 mm, the mesopic-low diameter was 4.94 +/- 0.71 mm, and the mesopic-high diameter was 3.98 +/- 0.54 mm for the Artisan Procyon group. The mean horizontal scotopic diameter was 6.29 +/- 0.91 mm, the mesopic-low diameter was 5.40 +/- 0.96 mm, and the mesopic-high diameter was 4.16 +/- 0.80 mm in the Procyon control group. A significant increase was noted in V/H ratio under scotopic, mesopic-low, and mesopic-high conditions from 1.02, 1.02, and 1.01, respectively, in the Procyon control group to 1.17, 1.12, and 1.06, respectively, in the Artisan Procyon group (P < .01). CONCLUSIONS: Horizontal pupil size was significantly decreased after horizontal Artisan PIOL implantation and might be attributed to a mechanical restriction of the iris in the horizontal meridian.

Follow-Up Studies↗

PubMed2004

Effectiveness of multifocal intraocular lenses to correct presbyopia after cataract surgery: a randomized controlled trial.

PURPOSE: Although monofocal intraocular lenses (IOLs) are effective in improving vision after cataract surgery, the loss of accommodation is not restored by implantation of these IOLs. Because multifocal IOLs may improve uncorrected distance and near vision, we compared the clinical outcome and patient satisfaction after implantation of monofocal and multifocal IOLs. Sociodemographics, eagerness for spectacle independence (ESI), and neuroticism were tested as predictors of satisfaction. DESIGN: Randomized controlled trial. PARTICIPANTS: Cataract patients with no ocular comorbidity were operated from August 1999 to January 2001; 75 patients were implanted with monofocal IOLs, and 78 with multifocal IOLs. METHODS: Assessments were made preoperatively (t1), 3 months after first-eye surgery (t2), and 3 months after second-eye surgery (t3). Primary outcomes were obtained by ophthalmic tests, whereas secondary outcomes were examined by interviews. MAIN OUTCOME MEASURES: Primary outcomes consisted of near and distance visual acuity (VA). Secondary outcomes related to spectacle dependence, vision-related functioning, and patient satisfaction. RESULTS: At t3, multifocal IOLs showed significantly better uncorrected near VA than monofocal IOLs (P<0.01) and an increase in quality ratings of unaided near vision between t1 and t3 (on a scale of 1-5: 1.6 at t1 vs. 2.9 at t3, P<0.001). At t2 and t3, patients with multifocal IOLs were more likely to "never" or "only now and then" wear spectacles for near and distance than patients with monofocal IOLs (at t3, 42.7% multifocal vs. 21.6% monofocal for near [P = 0.002] and 75.0% multifocal vs. 46.2% monofocal for distance [P = 0.001]). On a 0- to 15-point scale, monofocal IOL patients showed fewer complaints from cataract symptoms, including halos and distorted vision, at t3 (1.2 monofocal vs. 2.1 multifocal [P = 0.002]). Satisfaction related to preoperative expectations was similar in the monofocal and multifocal groups. The perceived quality of corrected near vision had the strongest relationship with patient satisfaction (beta = 0.22; 95% confidence interval: 0.060-0.523). Sociodemographics, ESI, and neuroticism did not predict patient satisfaction. CONCLUSIONS: Overall, patient satisfaction did not differ between the groups of monofocal and multifocal IOLs. Independent of ESI or neuroticism scores, success of both IOLs depends on preoperative expectations and postoperative quality of aided near vision. This article contains additional online-only material available at .

Accommodation, Ocular↗

PubMed2003

Simulated optical performance of custom wavefront soft contact lenses for keratoconus.

PURPOSE: Outstanding improvements in vision can theoretically be expected using contact lenses that correct monochromatic aberrations of the eye. Imperfections in such correction inherent to contact lenses are lens flexure, translation, rotation, and tear layer effects. The effects of pupil size and accommodation on ocular aberration may cause further difficulties. The purpose of this study was to evaluate whether nonaxisymmetric soft contact lenses could efficiently compensate for higher-order aberrations induced by keratoconus and to what extent rotation and translation of the lens would degrade this perfect correction. METHODS: Height topography data of nine moderate to severe keratoconus corneas were obtained using the Maastricht Shape Topographer. Three-dimensional ray tracing was applied to each elevation topography to calculate aberrations in the form of a phase error mapping. The effect of a nonaxisymmetric soft contact lens tailored to the corneal aberrations was simulated by adding an opposite phase error mapping that would theoretically compensate all corneal-induced optical aberrations of the keratoconus eyes. Translation (0.25, 0.5, 0.75, and 1.0 mm) and rotation (2.5 degrees, 5.0 degrees, 7.5 degrees, and 10 degrees ) mismatches were introduced. The modulation transfer function (MTF) of each eye with each displaced correction and with various pupil sizes (3, 5, and 7 mm) was deduced from the residual phase error mapping. A single performance criterion (mtfA) was calculated as the area under the MTF over a limited spatial frequency range (5 to 15 periods per degree). Finally, the ratio (RmtfA) of corrected mtfA over uncorrected mtfA provided an estimate of the global enhancement in contrast sensitivity with the customized lens. RESULTS: The contrast improvement ratios RmtfA with perfectly located lenses were for an average pupil size of 4.5 mm between 6.5 and 200. For small translation errors (0.25 mm), RmtfA ranged between 2 and 7. The largest lens translation tested (1 mm) often resulted in poorer performance than without correction (RmtfA <1). More than threefold improvements were achieved with any of the angular errors experimented. RmtfA values showed significant variations for pupil diameters between 3 and 7 mm. CONCLUSIONS: Three-dimensional aberration-customized soft contact lenses may drastically improve visual performance in patients with keratoconus. However, such lenses should be well positioned on the cornea. In particular, translation errors should not exceed 0.5 mm. Angular errors appeared to be less critical. It is further questioned whether the visual system is able to adapt to variations in optical performance of the correction in situ due to lens positioning and pupil size.

Contact Lenses, Hydrophilic↗

PubMed2002

Optimising RGP lens fitting in normal eyes using 3D topographic data.

PURPOSE: To analyse, retrospectively, the effect of fitting characteristics on comfort of wear and the role that 3D topographic data can play in attaining an optimal lens fit with rigid gas permeable (RGP) contact lenses in normal eyes. METHODS: Included were 60 normal myopic eyes (1.00-5.00 D) with astigmatism limited to 2.00 D. Lenses were ordered empirically, based on traditional fitting rules. RESULTS: The initial fit based on traditional computation was accepted in 40% of the eyes. To achieve an acceptable fit, 15% of the eyes needed an adaptation of the back optic zone radius, in 28% switching from a multicurve to an aspheric lens design was indicated and in 17% a non-rotational symmetric lens design was favoured. The reason for changing the lens parameters could in 88% be attributed to mid-peripheral differences between corneal shape as found with 3D corneal topography. Average comfort of wear improved statistically significantly (chi(2), P<0.05) from 5.2 initially to 7.7 after 3 months in the group with optimal lens fits, while comfort slightly decreased (not significant) in the group with sub-optimal fits. Switching to a non-rotational symmetric lens design, when indicated, improved comfort significantly (chi(2), P<0.05) from 5.0 to 7.3. CONCLUSION: In normal eyes, the measurement of corneal shape, especially in the mid-peripheral regions, is of importance to optimise RGP lens fit. Optimised lens fits increases comfort of wear.

Journal Article↗