Sphero-cylindrical error for oblique gaze as a function of the position of the centre of rotation of the eye.

PURPOSE: New designs of ophthalmic lenses customised for particular wearing conditions (e.g., vertex distance or wrap tilt angle) have emerged during the last few years. However, there is limited information about the extent of any improvement in visual quality of these products. The aim of this work was to determine whether customisation according to the centre of rotation of the eye (CRE) improves visual quality for oblique gaze in monofocal spherical lenses. METHODS: Conventional spherical lenses were designed by numerical ray tracing with back vertex powers (BVP) ranging from +8 to -8 dioptres (D) and base curves from 0 to 8 D. The wavefront error at oblique gaze (40°) was computed for each design with CRE positions from 20 to 35 mm. Sphero-cylindrical (SC) error was calculated using wavefront Zernike coefficients, considering only monochromatic aberrations. Visual acuity in logMAR was estimated following the Raasch empirical regression model. RESULTS: SC error and visual acuity maps were calculated for each BVP as a function of base curves and CRE in a graded colour scale. From SC error maps maximum spherical and cylindrical errors (MSE and MCE) of 1.49 D and -1.24 D respectively were found for BVP from 0 to -2 D, 2.27 D and -1.90 D for BVP from -2 D to -4 D, 2.59 D and -2.20 D for lenses from -4 D to -6 D and 2.63 D and -2.28 D for lenses from -6 D to -8 D. Concerning positive lenses, we obtained MSE and MCE of 0.37 D and -1.35 D respectively for lenses from 0 D to +2 D, 0.39 D and -2.23 D for lenses from +2 D to +4 D and 0.36 D and -2.73 D for lenses from +4 D to +6 D. Regarding visual acuity maps for 40° oblique gaze, significant loss of visual acuity (>0.30 logMAR, Snellen 6/12, 20/40, decimal 0.50) was found for BVP as low as -2 D. Clinically negligible high order aberration levels (equivalent spherical power <0.25 D) were found for all cases. CONCLUSIONS: We calculated SC error and visual acuity maps as a function of base curves and CRE position for a set of spherical lenses at oblique gaze. These maps could be useful as a clinical guide to select the best base as a function of CRE and BVP for each patient. It was found that negative lenses with low BVP provided high SC error when they were designed with low bases. However, high BVP negative lenses with low SC error were found for medium bases and low CRE or for low bases and high CRE positions. In the case of positive lenses, the dependence of SC error with CRE position was less noticeable. Finally, high order aberrations did not have a significant influence over visual quality.

Lower- and higher-order aberrations predicted by an optomechanical model of arcuate keratotomy for astigmatism.

PURPOSE: To develop a realistic model of the optomechanical behavior of the cornea after curved relaxing incisions to simulate the induced astigmatic change and predict the optical aberrations produced by the incisions. SETTING: ICMA Consejo Superior de Investigaciones Científicas and Universidad de Zaragoza, Zaragoza, Spain. METHODS: A 3-dimensional finite element model of the anterior hemisphere of the ocular surface was used. The corneal tissue was modeled as a quasi-incompressible, anisotropic hyperelastic constitutive behavior strongly dependent on the physiological collagen fibril distribution. Similar behaviors were assigned to the limbus and sclera. With this model, some corneal incisions were computer simulated after the Lindstrom nomogram. The resulting geometry of the biomechanical simulation was analyzed in the optical zone, and finite ray tracing was performed to compute refractive power and higher-order aberrations (HOAs). RESULTS: The finite-element simulation provided new geometry of the corneal surfaces, from which elevation topographies were obtained. The surgically induced astigmatism (SIA) of the simulated incisions according to the Lindstrom nomogram was computed by finite ray tracing. However, paraxial computations would yield slightly different results (undercorrection of astigmatism). In addition, arcuate incisions would induce significant amounts of HOAs. CONCLUSIONS: Finite-element models, together with finite ray-tracing computations, yielded realistic simulations of the biomechanical and optical changes induced by relaxing incisions. The model reproduced the SIA indicated by the Lindstrom nomogram for the simulated incisions and predicted a significant increase in optical aberrations induced by arcuate keratotomy.

Pendred syndrome in two Galician families: insights into clinical phenotypes through cellular, genetic, and molecular studies.

CONTEXT: We studied two families from Galicia (northwest Spain) with Pendred syndrome (PS) and unusual thyroid phenotypes. In family A, the proposita had a large goiter and hypothyroxinemia but normal TSH and free T3 (FT3). In family B, some affected members showed deafness but not goiter. OBJECTIVE: Our objective was to identify the mutations causing PS and molecular mechanisms underlying the thyroid phenotypes. INTERVENTIONS: Interventions included extraction of DNA and of thyroid tissue. PATIENTS: Propositi and 10 members of the two families participated in the study. MAIN OUTCOME MEASURES: Main outcome measures included SLC26A4 gene analysis, deiodinase activities in thyroid tissue, and c.416-1G-->A effects on SLC26A4 splicing. In addition, a primary PS thyrocyte culture, T-PS2, was obtained from propositus B and compared with another culture of normal human thyrocytes, NT, by Western blotting, confocal microscopy, and iodine uptake kinetics. RESULTS: Proposita A was heterozygous for c.578C-->T and c.279delT, presented with goiter, and had normal TSH and FT3 but low FT4 attributable to high type 1 and type 2 iodothyronine deiodinase activities in the goiter. Propositus B bore c.279delT and a novel mutation c.416-1G-->A; some deaf relatives were homozygous for c.416-1G-->A but did not present goiter. The c.279delT mutation was associated with identical haplotype in the two families. T-PS2 showed truncated pendrin retained intracellularly and high iodine uptake with low efflux leading to iodine retention. CONCLUSIONS: c.279delT is a founder mutation in Galicia. Proposita A adapted to poor organification by increasing deiodinase activities in the goiter, avoiding hypothyroidism. Lack of goiter in subjects homozygous for c.416-1G-->A was due to incomplete penetrance allowing synthesis of some wild-type pendrin. Intracellular iodine retention, as seen in T-PS2, could play a role in thyroid alterations in PS.

Adaptive model of the gradient index of the human lens. II. Optics of the accommodating aging lens.

A simple, parametric model of the gradient refractive index distribution (GRIN) of the human lens with conicoid surfaces able to adapt to individual distributions as well as to the changes of the lens shape and structure with age and accommodation is presented. The first part of this work was published in a companion paper [J. Opt. Soc. Am. A24, 2175 (2007)]. It included the development of the mathematical formulation of the adaptive model; the validation of its customization capability by fitting, sample by sample, a set of in vitro refractive index distributions of lenses of different ages, ranging from 7 to 82 years, from the recent literature; and an average model of the (in vitro) aging crystalline lens. Here we extrapolate that in vitro GRIN model by assuming that the same structural parameters are valid for the living lens. Then, recent data of the changes of the shape of the aging lens with accommodation from the literature are used to build an aging and accommodating lens model. This is straightforward since the GRIN model adapts automatically to the chosen external lens geometry. A strong coupling was found between the adaptive GRIN distributions and the conic constants affecting the refractive power. To account for the lens paradox and the reported changes in lens spherical aberration with age and accommodation, age- and accommodation-dependent functions for the anterior and posterior internal conic constants were derived through optimization.

Adaptive model of the gradient index of the human lens. I. Formulation and model of aging ex vivo lenses.

A simple, parametric adaptive model of the refractive index distribution of the ex vivo crystalline lens is presented. It assumes conicoid (or nonrevolution quadric in 3D) iso-indical surfaces, concentric with the external surfaces of the lens. The model uses a minimum number of internal structural parameters, while the shape of the iso-indical surfaces adapts automatically to the external geometry. In this way, it is able to adapt and fit individual distributions as well as adapt to the changes of the lens shape and structure with age and accommodation. The model is fit to experimental data for individual eyes spanning ages 7 to 82 years, where for each eye the crystalline lens dimensions and iso-indical index data are known. The analysis demonstrates that only one age-dependent structural parameter is needed to replicate the internal iso-indical index structure, given age-dependent models for the external surfaces. An age-dependent-parameter global model is derived and is shown to predict age-dependent changes in the ex vivo lens power and longitudinal spherical aberration with age.