Software-based evaluation of toric IOL orientation in a multicenter clinical study.

PURPOSE: To evaluate the rotational stability of a new one-piece hydrophobic acrylic toric intraocular lens (IOL) using a custom-developed software for analysis of slit-lamp photographs. METHODS: In a prospective, multicenter study, 174 eyes were implanted with the TECNIS Toric IOL (Abbott Medical Optics, Inc., Santa Ana, CA). A custom-developed software was used to analyze high-resolution slit-lamp photographs of 156 eyes taken at day 1 (baseline) and 1, 3, and 6 months postoperatively. The software uses iris and sclera landmarks to align the baseline image and later images for comparison. Validation of software was performed through repeated analyses of protractor images rotated from 0.1° to 10.0° and randomly selected photographs of 20 eyes. RESULTS: Software validation showed precision (repeatability plus reproducibility variation) of 0.02° using protractor images and 2.22° using slit-lamp photographs. Good quality slit-lamp images and clear landmarks were necessary for precise measurements. At 6 months, 94.2% of eyes had 5° or less change in IOL orientation versus baseline; only 2 eyes (1.4%) had axis shift greater than 30°. Most eyes were within 5° or less of rotation between 1 and 3 months (92.9%) and 3 and 6 months (94.1%). Mean absolute axis change (± standard deviation) from 1 day to 6 months was 2.70° ± 5.51°. CONCLUSIONS: The new custom software was precise and quick in analyzing slit-lamp photographs to determine postoperative toric IOL rotation.

Wavefront-guided PRK treatment of myopia using a refractive aberrometer.

PURPOSE: To evaluate the safety, effectiveness, and patient-reported outcomes of wavefront-guided photorefractive keratectomy (PRK) for the correction of myopic refractive errors with and without astigmatism. SETTING: U.S. multicenter study. DESIGN: Prospective, nonrandomized clinical investigation. METHODS: 334 eyes (167 patients) underwent wavefront-guided PRK with the STAR S4 IR Excimer Laser System. Patients had preoperative myopic refractive errors with sphere up to -8.00 diopters (D) and cylinder up to -4.00 D with a maximum spherical equivalent (SE) of -10.00 D. All eyes were targeted for emmetropia, and treatment plans were derived from the iDESIGN system wavefront measurements. RESULTS: At 6 months, the point of refractive stability, 99.4% of eyes achieved 20/20 or better uncorrected distance visual acuity (UDVA), 92% of eyes achieved 20/16 or better UDVA, 85.5% of eyes achieved manifest refraction SE (MRSE) within 0.50 D of target, mean SE was -0.06, and less than 1% of eyes lost more than 2 lines of corrected distance visual acuity. Glare and halos occurred with similar or lower frequencies at 6 months vs preoperative. Results from the National Eye Institute Refractive Error Quality of life questionnaire showed statistically significant improvements at 6 months vs preoperative across most measures of vision-related functioning and well-being. Approximately 98% of patients reported high satisfaction with their overall vision at 6 months. CONCLUSIONS: Wavefront-guided PRK with the iDESIGN aberrometer was safe, effective, and predictable for the correction of low to moderate myopia with and without astigmatism and led to high patient satisfaction.

MRI study of the changes in crystalline lens shape with accommodation and aging in humans.

Magnetic Resonance Imaging was used to study changes in the crystalline lens and ciliary body with accommodation and aging. Monocular images were obtained in 15 young (19-29 years) and 15 older (60-70 years) emmetropes when viewing at far (6 m) and at individual near points (14.5 to 20.9 cm) in the younger group. With accommodation, lens thickness increased (mean ± 95% CI: 0.33 ± 0.06 mm) by a similar magnitude to the decrease in anterior chamber depth (0.31 ± 0.07 mm) and equatorial diameter (0.32 ± 0.04 mm) with a decrease in the radius of curvature of the posterior lens surface (0.58 ± 0.30 mm). Anterior lens surface shape could not be determined due to the overlapping region with the iris. Ciliary ring diameter decreased (0.44 ± 0.17 mm) with no decrease in circumlental space or forward ciliary body movement. With aging, lens thickness increased (mean ± 95% CI: 0.97 ± 0.24 mm) similar in magnitude to the sum of the decrease in anterior chamber depth (0.45 ± 0.21 mm) and increase in anterior segment depth (0.52 ± 0.23 mm). Equatorial lens diameter increased (0.28 ± 0.23 mm) with no change in the posterior lens surface radius of curvature. Ciliary ring diameter decreased (0.57 ± 0.41 mm) with reduced circumlental space (0.43 ± 0.15 mm) and no forward ciliary body movement. Accommodative changes support the Helmholtz theory of accommodation including an increase in posterior lens surface curvature. Certain aspects of aging changes mimic accommodation.

The influence of oblique viewing on axial and peripheral refraction for emmetropes and myopes.

Refraction may be affected by the forces of lids and extraocular muscles when eye direction and head direction are not aligned (oblique viewing) which might potentially influence past findings on peripheral refraction of the eye. We investigated the effect of oblique viewing on axial and peripheral refraction. In a first experiment, cycloplegic axial refractions were determined when subjects' heads were positioned to look straight-ahead through an open-view autorefractor and when the heads were rotated to the right or left by 30 degrees with compensatory eye rotation (oblique viewing). Subjects were 16 young emmetropes (18-35 years), 22 young myopes (19-36 years) and 15 old emmetropes (45-60 years). In a second experiment, cycloplegic peripheral refraction measurements were taken out to +/-34 degrees horizontally from fixation while the subjects rotated their heads to match the peripheral refraction angles (eye in primary position with respect to the head) or the eyes were rotated with respect to the head (oblique viewing). Subjects were 10 emmetropes and 10 myopes. We did not find any significant changes in axial or peripheral refraction upon oblique viewing for any of the subject groups. In general for the range of horizontal angles used, it is not critical whether or not the eye is rotated with respect to the head during axial or peripheral refraction.

In vivo study of changes in refractive index distribution in the human crystalline lens with age and accommodation.

PURPOSE: Magnetic resonance imaging (MRI) was used to map the refractive index distribution in human eye lenses in vivo and to investigate changes with age and accommodation. METHODS: Whole-eye MR images were obtained for sagittal and transverse axial planes in one eye each of 15 young (19-29 years) and 15 older (60-70 years) subjects when viewing a far ( approximately 6 m) target and at individual near points in the young subjects. Refractive index maps of the crystalline lens were calculated by using a procedure previously validated in vitro. RESULTS: A central high refractive index plateau region and sharp decline in refractive index at the periphery were seen in all three groups. The peripheral decline was steepest in the older lenses and least steep in the young accommodated lenses. Average lens thickness increased (+0.27 mm; P < 0.05) and equatorial diameter decreased (-0.35 mm; P < 0.05) with accommodation. Axial thickness (+0.96 mm; P < 0.05) and equatorial diameter (+0.28 mm; P < 0.05) increased with age. The central index (1.409 +/- 0.008) did not differ between groups. The axial thickness of the central plateau increased with age (+0.83 mm; P < 0.05) but not significantly with accommodation. The equatorial diameter of the central plateau increased with age (+0.56 mm; P < 0.01) and decreased with accommodation (-0.43 mm; P < 0.05). CONCLUSIONS: The refractive index of the central plateau region does not change significantly with accommodation or ageing, but its size increases with age and the peripheral decline in refractive index becomes steeper in older lenses.

Age-related changes in optical and biometric characteristics of emmetropic eyes.

We measured optical and biometric parameters of emmetropic eyes as a function of age. There were approximately 20 subjects each in age groups 18-29, 30-39, 40-49, 50-59, and 60-69 years with similar male and female numbers. One eye was tested for each subject, having spherical equivalent in the range -0.88 D to +0.75 D and

New algorithm for toric intraocular lens power calculation considering the posterior corneal astigmatism.

PURPOSE: To assess the accuracy of toric intraocular lens (IOL) power calculations of a new algorithm that incorporates the effect of posterior corneal astigmatism (PCA). SETTING: Abbott Medical Optics, Inc., Groningen, the Netherlands. DESIGN: Retrospective case report. METHODS: In eyes implanted with toric IOLs, the exact vergence formula of the Tecnis toric calculator was used to predict refractive astigmatism from preoperative biometry, surgeon-estimated surgically induced astigmatism (SIA), and implanted IOL power, with and without including the new PCA algorithm. For each calculation method, the error in predicted refractive astigmatism was calculated as the vector difference between the prediction and the actual refraction. Calculations were also made using postoperative keratometry (K) values to eliminate the potential effect of incorrect SIA estimates. RESULTS: The study comprised 274 eyes. The PCA algorithm significantly reduced the centroid error in predicted refractive astigmatism (P < .001). With the PCA algorithm, the centroid error reduced from 0.50 @ 1 to 0.19 @ 3 when using preoperative K values and from 0.30 @ 0 to 0.02 @ 84 when using postoperative K values. Patients who had anterior corneal against-the-rule, with-the-rule, and oblique astigmatism had improvement with the PCA algorithm. In addition, the PCA algorithm reduced the median absolute error in all groups (P < .001). CONCLUSIONS: The use of the new PCA algorithm decreased the error in the prediction of residual refractive astigmatism in eyes implanted with toric IOLs. Therefore, the new PCA algorithm, in combination with an exact vergence IOL power calculation formula, led to an increased predictability of toric IOL power.

Age related changes in the characteristics of the near pupil response.

Static and dynamic aspects of the near pupil response were studied in human subjects in the age range when accommodative amplitude steadily declines. Dynamic accommodative and pupillary responses to step stimuli were recorded in 66 subjects (ages: 14-45 years). Exponential fits to data provided amplitude, peak velocity and time constants. Accommodative amplitude decreased linearly with age (p < 0.05). Pupil constriction per diopter of accommodative response increased exponentially with age (p < 0.05). The amplitude of pupil constriction for a 2D stimulus decreased linearly with age (p < 0.05) and for a 5D stimulus did not change with age (p = 0.90). The latency of pupil constriction did not change with age (p = 0.65), while the mean peak velocity decreased linearly with age (p < 0.05). An increase in the amount of pupil constriction per diopter of accommodative response, but not per diopter of stimulus amplitude, suggests that the near effort per se does not increase with age. There is a slight reduction in the speed of near pupil response with age.

Age related changes in accommodative dynamics in humans.

Age related changes in the dynamics of accommodation (far to near focus) and disaccommodation (near to far focus) are reported in this study. Dynamic responses to step stimulus demands from 1D to 6D, in 1D steps, were recorded with a PowerRefractor in 66 subjects in the age range 14-45 years. The accommodative and disaccommodative responses were fit with exponential functions to calculate response amplitude, time constant and peak velocity. The latency of accommodation did not change and the latency of disaccommodation increased with age. For accommodation, time constant increased and peak velocity decreased with age. For disaccommodation, no change in time constant or peak velocity was found with age. The form of the peak velocity vs response amplitude relationship (main sequence) of accommodation changed with age. The differences in the dynamics of accommodation and disaccommodation with age are discussed with reference to the age related changes in the eye leading to presbyopia.

Influence of amplitude and starting point on accommodative dynamics in humans.

PURPOSE: The effects of amplitude and the starting point of an accommodative response on the dynamics of far-to-near (accommodation) and near-to-far (disaccommodation) focus were studied. METHODS: Step responses were recorded with a dynamic optometer in nine 22- to 30-year-old subjects, under three conditions: (1) Fixed far: accommodative demands from 1 to 6 D were created by placing the far target at 6 m and the near target at various proximal distances. (2) Fixed near: accommodative demands from 1 to 5 D were created by placing the near target at 16.7 cm and the far target at various distal positions. (3) Fixed amplitude: far and near target positions were changed to create an accommodative demand of 1.5 D from starting positions of 1 to 4.5 D in 0.5-D steps. Each recorded response was fitted with an exponential function to calculate response amplitude, peak velocity, time constant, and starting point. RESULTS: The relationship between starting point and amplitude of accommodation and disaccommodation was effectively manipulated in the three conditions. For accommodation and disaccommodation, peak velocity increased linearly with response starting point, whereas the peak velocity versus response amplitude relationship differed according to the condition. Similar amplitude responses were associated with a higher peak velocity and a smaller time constant at proximal starting points than at distal starting points. Low-amplitude responses were influenced by both starting point and amplitude. CONCLUSIONS: The dynamics of accommodation and disaccommodation are strongly influenced by the starting point, but less so by amplitude.

Dynamics of accommodative fatigue in rhesus monkeys and humans.

Changes in accommodative dynamics with repeated accommodation were studied in three anesthetized rhesus monkeys and two conscious humans. Maximum accommodation was centrally stimulated via the Edinger-Westphal nucleus in monkeys with a 4 s on, 4 s off paradigm (4 x 4) for 17 min, 4 x 1.5 for 27 min and 2 x 1 for 16 min. Humans accommodated repeatedly to visual targets (5 x 5; 5D and 2 x 2; 6D) for 30 min. In all cases, accommodation was sustained throughout. The anesthetized monkeys showed inter-individual variability in the extent of changes in accommodative dynamics over time while no systematic changes were detected in the human accommodative responses. Little accommodative fatigue was found compared to previous studies which have reported a complete loss of accommodation after 5 min of repeated stimulation in monkeys.

Lens Shape and Refractive Index Distribution in Type 1 Diabetes.

PURPOSE: To compare lens dimensions and refractive index distributions in type 1 diabetes and age-matched control groups. METHODS: There were 17 participants with type 1 diabetes, consisting of two subgroups (7 young [23 ± 4 years] and 10 older [54 ± 4 years] participants), with 23 controls (13 young, 24 ± 4 years; 10 older, 55 ± 4 years). For each participant, one eye was tested with relaxed accommodation. A 3T clinical magnetic resonance imaging scanner was used to image the eye, employing a multiple spin echo (MSE) sequence to determine lens dimensions and refractive index profiles along the equatorial and axial directions. RESULTS: The diabetes group had significantly smaller lens equatorial diameters and larger lens axial thicknesses than the control group (diameter mean ± 95% confidence interval [CI]: diabetes group 8.65 ± 0.26 mm, control group 9.42 ± 0.18 mm; axial thickness: diabetes group 4.33 ± 0.30 mm, control group 3.80 ± 0.14 mm). These differences were also significant within each age group. The older group had significantly greater axial thickness than the young group (older group 4.35 ± 0.26 mm, young group 3.70 ± 0.25 mm). Center refractive indices of diabetes and control groups were not significantly different. There were some statistically significant differences between the refractive index fitting parameters of young and older groups, but not between diabetes and control groups of the same age. CONCLUSIONS: Smaller lens diameters occurred in the diabetes groups than in the age-matched control groups. Differences in refractive index distribution between persons with and without diabetes are too small to have important effects on instruments measuring axial thickness.

Amplitude dependent accommodative dynamics in humans.

Dynamics of accommodation (far-to-near focus) and disaccommodation (near-to-far focus) are described as a function of response amplitude. Accommodative responses to step stimuli of various amplitudes presented in real space were measured in eight 20-30 year old subjects. Responses were fitted with exponential functions to determine amplitude, time constant and peak velocity. Despite the intersubject variability, the results show that time constants of accommodation and peak velocity of disaccommodation increase with amplitude in all subjects. The dynamics of accommodation and disaccommodation are dependent on amplitude, but have different properties in each case.

Evaluation of a satisfied bilateral scleral expansion band patient.

PURPOSE: To measure accommodation subjectively and objectively in a satisfied bilateral scleral expansion band patient. SETTING: University of Houston, College of Optometry, Houston, Texas, USA. METHODS: One bilateral scleral expansion patient (age 50 years), 9 age-matched normal presbyopic control subjects (age range 48 to 52 years), and 1 normal control subject (age 27 years) participated. The scleral expansion patient had a complete eye examination, corneal topography, and wavefront measurements 19 months postoperatively. Accommodation was measured subjectively with the push-up technique, minus to blur, and dioptric range of clear vision. Accommodation was determined objectively by measuring the accommodative responses to negative lenses and pilocarpine 6% with a Hartinger coincidence refractometer and to real targets with a dynamic infrared optometer. RESULTS: Distance and near acuity of 20/20 was achieved with +1.00 diopter (D) in the left eye, +0.50 D in the right eye, and a near add of +2.25 D. Corneal topography and ocular aberration measurements revealed no suggestion of optical multifocality. Subjective measurements resulted in accommodative amplitudes of 1.50 to 4.00 D, and objective measurements resulted in amplitudes of 0.25 to 1.33 D. The PowerRefractor showed an accommodative response of 0.50 D to stimuli of 1.00 to 4.00 D and strong pupillary constriction with accommodative effort compared with the control. CONCLUSIONS: No increase in accommodative amplitude above normal age-matched controls was found. Patient satisfaction may have come from the high expectations this patient had for a positive surgery outcome.

A population study on changes in wave aberrations with accommodation.

Wave aberrations were measured with a Shack-Hartmann wavefront sensor (SHWS) in the right eye of a large young adult population when accommodative demands of 0, 3, and 6 D were presented to the tested eye through a Badal system. Three SHWS images were recorded at each accommodative demand and wave aberrations were computed over a 5-mm pupil (through 6th order Zernike polynomials). The accommodative response was calculated from the Zernike defocus over the central 3-mm diameter zone. Among all individual Zernike terms, spherical aberration showed the greatest change with accommodation. The change of spherical aberration was always negative, and was proportional to the change in accommodative response. Coma and astigmatism also changed with accommodation, but the direction of the change was variable. Despite the large inter-subject variability, the population average of the root mean square for all aberrations (excluding defocus) remained constant for accommodative levels up to 3.0 D. Even though aberrations change with accommodation, the magnitude of the aberration change remains less than the magnitude of the uncorrected aberrations, even at high accommodative levels. Therefore, a typical eye will benefit over the entire accommodative range (0-6 D) if aberrations are corrected for distance viewing.

Methods to estimate the size and shape of the unaccommodated crystalline lens in vivo.

PURPOSE: The purpose of this article was to present methods capable of estimating the size and shape of the human eye lens without resorting to phakometry or magnetic resonance imaging (MRI). METHODS: Previously published biometry and phakometry data of 66 emmetropic eyes of 66 subjects (age range [18, 63] years, spherical equivalent range [-0.75, +0.75] D) were used to define multiple linear regressions for the radii of curvature and thickness of the lens, from which the lens refractive index could be derived. MRI biometry was also available for a subset of 30 subjects, from which regressions could be determined for the vertex radii of curvature, conic constants, equatorial diameter, volume, and surface area. All regressions were compared with the phakometry and MRI data; the radii of curvature regressions were also compared with a method proposed by Bennett and Royston et al. RESULTS: The regressions were in good agreement with the original measurements. This was especially the case for the regressions of lens thickness, volume, and surface area, which each had an R(2) > 0.6. The regression for the posterior radius of curvature had an R(2) < 0.2, making this regression unreliable. For all other regressions we found 0.25 < R(2) < 0.6. The Bennett-Royston method also produced a good estimation of the radii of curvature, provided its parameters were adjusted appropriately. CONCLUSIONS: The regressions presented in this article offer a valuable alternative in case no measured lens biometry values are available; however care must be taken for possible outliers.

Objective accommodation measurement with the Grand Seiko and Hartinger coincidence refractometer.

PURPOSE: Subjective push-up tests and dynamic retinoscopy are standard clinical accommodation tests. These are inadequate for assessing if accommodation can be restored in presbyopes. Commercially available clinical autorefractors offer potentially reliable methods for objective accommodation measurement. This study evaluated accuracy and reliability of the Grand Seiko WR-5100K autorefractor for objective accommodation measurement in young adults. METHODS: Twenty-two subjects, aged 21 to 30 years (mean 25.6 +/- 2.26) participated. Three methods were used to stimulate and measure accommodation: (1) subjective push-up test in free space, (2) a near target pushed-up on a near-point rod and the response measured with the WR-5100K and a Hartinger coincidence refractometer (HCR), and (3) a distant target viewed through increasing powered negative trial lenses and the response measured with the WR-5100K and the HCR. Trial lens calibration procedures were also used to test the accuracy of the instruments. RESULTS: Average maximum accommodative amplitude with the subjective push-up test was 7.74 D +/- 0.36 D (mean +/- SE). For a 5 D stimulus, accommodation of 4.68 D +/- 0.10 D (mean +/- SE) and 4.13 D +/- 0.09 D was measured with the WR-5100K and the HCR, respectively. With a distant target viewed through a -5.00 D trial lens, the WR-5100K measured 4.07 D +/- 0.09 D and the HCR measured 4.05 D +/- 0.09 D of accommodation. Maximum mean response measured with trial lens-induced accommodation was 5.67 D +/- 0.15 D with the WR-5100K and 5.77 D +/- 0.18 D with the HCR. CONCLUSIONS: The subjective push-up test overestimated accommodative amplitude relative to the objective measures. The WR-5100K showed good agreement in the responses measured for both pushed-up near targets and a distant target viewed through trial lenses with the HCR, a widely used laboratory instrument. The Grand Seiko WR-5100K, a commercially available instrument, has been demonstrated to be well suited for clinical, objective accommodation measurement using a population of normal young adults.

Simultaneous measurements of refraction and A-scan biometry during accommodation in humans.

PURPOSE: Accommodation is a dioptric change in power of the crystalline lens resulting from ciliary muscle contraction that leads to an increase in lens surface curvatures and thickness and changes in the position of lens surfaces. Previous studies have used A-scan ultrasound to measure changes in the position of lens surfaces with voluntary accommodation, but have not simultaneously measured the change in refraction. The goal of this study is to simultaneously measure and correlate refractive and biometric changes in the lens during voluntary accommodation in humans. METHODS: Refraction was measured off-axis in the right eye and biometry on-axis in the left eye simultaneously during voluntary accommodation in 22 human subjects between the ages of 21 and 30 years (mean +/- standard deviation: 25.8 +/- 2.3 years). Subjects viewed a distant target and four near targets spanning the full accommodative range available to evaluate refraction and lens surface position at each accommodative state. RESULTS: Maximum objectively measured accommodative amplitude of all subjects was 5.64 +/- 0.21 D (mean +/- standard error of mean). Biometric and refractive changes during accommodation were linearly correlated. The mean +/- standard error of mean decrease in anterior chamber depth was 0.051 +/- 0.008 mm/D, increase in lens thickness was 0.067 +/- 0.008 mm/D, and increase in anterior segment length was 0.017 +/- 0.005 mm/D during accommodation. There was a net anterior movement of the lens center of 0.017 +/- 0.005 mm/D. CONCLUSION: Anterior chamber depth, lens thickness, and anterior segment length change linearly with refraction during accommodation. Per-diopter changes in the lens were greater in the current study compared with previous studies in which only accommodative demand was measured, which overestimates the accommodative response.

Characteristics of pupil responses during far-to-near and near-to-far accommodation.

The static and dynamic aspects of the pupil response associated with various amplitudes of far-to-near (accommodation) and near-to-far (disaccommodation) focusing responses were evaluated in this study. Dynamic refractive and pupillary changes were measured simultaneously during focusing responses to targets at real distances in 12 young (23-26 years) emmetropic subjects. The targets were presented alternately at far (6 m) and at one of six near positions from 1 D (1 m) to 6 D (16.7 cm) in 1 D steps. The latency, magnitude and peak velocity of pupil changes associated with accommodation and disaccommodation responses were calculated. The latency of refractive changes was shorter than that of pupillary changes. In general, the pupil constricted with accommodation and started dilating while accommodation was still maintained, resulting in reduced pupil dilation with disaccommodation. The magnitude of the pupil response increased linearly with that of accommodation and disaccommodation. The amount of pupil change per dioptre of refractive change was invariant with various amplitudes of refractive change. The peak velocity of pupil constriction was greater than that of pupil dilation for corresponding amplitudes. The pupil response is more closely associated with accommodation than with disaccommodation.