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Biomedical subjects

Jason Porter

Publications and source records attributed to Jason Porter.

10 recordsLinked to original sources
PubMed2006

Aberrations induced in wavefront-guided laser refractive surgery due to shifts between natural and dilated pupil center locations.

PURPOSE: To determine the aberrations induced in wavefront-guided laser refractive surgery due to shifts in pupil center location from when aberrations are measured preoperatively (over a dilated pupil) to when they are corrected surgically (over a natural pupil). SETTING: Center for Visual Science and Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: Shifts in pupil center were measured between dilated phenylephrine hydrochloride (Neo-Synephrine [2.5%]) and nonpharmacological mesopic conditions in 65 myopic eyes treated with wavefront-guided laser in situ keratomileusis (Technolas 217z, Bausch & Lomb). Each patient's preoperative and 6-month postoperative wave aberrations were measured over the dilated pupil. Aberrations theoretically induced by decentration of a wavefront-guided ablation were calculated and compared with those measured 6 months postoperatively (6.0 mm pupil). RESULTS: The mean magnitude of pupil center shift was 0.29 mm +/- 0.141 (SD) and usually occurred in the inferonasal direction as the pupil dilated. Depending on the magnitude of shift, the fraction of the higher-order postoperative root-mean-square wavefront error that could be due theoretically to pupil center decentrations was highly variable (mean 0.26 +/- 0.20 mm). There was little correlation between the calculated and 6-month postoperative wavefronts, most likely because pupil center decentrations are only 1 of several potential sources of postoperative aberrations. CONCLUSIONS: Measuring aberrations over a Neo-Synephrine-dilated pupil and treating them over an undilated pupil typically resulted in a shift of the wavefront-guided ablation in the superotemporal direction and an induction of higher-order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature on the eye will reduce the potential for inducing aberrations due to shifts in pupil center.

Adult↗
PubMed2006

Wavefront aberrations in eyes with Acrysof monofocal intraocular lenses.

PURPOSE: To characterize and measure the ocular aberrations in eyes implanted with monofocal intraocular lenses (IOLs) and to study any correlation between postoperative aberrations and surgical factors. METHODS: A Tscherning aberroscope was used to measure the wavefront aberrations of 62 eyes that had undergone phacoemulsification with the implantation of foldable monofocal Acrysof MA60BM IOLs (Alcon Laboratories Inc, Ft Worth, Tex). The Zernike coefficients, measured with a pupil diameter of 6 mm, were compared with those of a normal dataset of 82 eyes of healthy young myopes. RESULTS: Spherical aberration (Z(0)4) was the most predominant higher order aberration, with a mean value of 0.37 +/- 0.16 microm. A statistically significant linear relationship was noted between the magnitude of postoperative spherical aberration and the dioptric power of the IOL. The mean spherical aberration was 33 times more in the pseudophakic group than in normal young myopic eyes. The other major higher order aberrations were trefoil (Z(-3)3) with a mean of -0.13 +/- 0.22 microm and vertical coma (Z(-1)3) with a mean value of -0.11 +/- 0.23 microm. On average, the root-mean-square of higher order aberrations in pseudophakic eyes was 2.1 times that in a normal population of young myopic eyes. CONCLUSIONS: Eyes that undergo cataract surgery with monofocal IOL implantation suffer from significant higher order aberrations. The optical design of the IOL is most likely responsible for the increase in spherical aberration, the magnitude of which is a function of the dioptric power of the IOL.

Acrylic Resins↗
PubMed2005

Surgeon offsets and dynamic eye movements in laser refractive surgery.

PURPOSE: To determine the amount of static and dynamic pupil decentrations that occur during laser refractive surgery. SETTING: The Center of Visual Science and the Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: The surgeon's accuracy in aligning the pupil center with the laser center axis was measured when engaging the eye-tracker in 17 eyes receiving conventional laser in situ keratomileusis (LASIK) procedures (Technolas 217z; Bausch & Lomb). Eye movements were measured subsequently during the treatment in 10 eyes using a pupil camera operating at 50 Hz. Temporal power spectra were calculated from the eye movement measurements. RESULTS: The mean pupil misalignment by the surgeon at the beginning of the procedure was 206.1 microm +/- 80.99 (SD) (with respect to the laser center). The laser center was typically misaligned below (inferiorly) and to the left (nasally and temporally in left and right eyes, respectively) of the pupil [corrected] center. Small amounts of cyclotorsion were observed during the ablation (<2 degrees). The mean magnitude of dynamic pupil decentration from the laser center during treatment was 227.0 +/- 44.07 microm. The mean standard deviation of eye movements was 65.7 +/- 25.64 microm. Temporal power spectra calculated from the horizontal and vertical changes in eye position during the ablation were similar. Ninety-five percent of the total power of the eye movements was contained in temporal frequencies up to 1 Hz, on average, in both directions. CONCLUSIONS: Most eye movements during LASIK are slow drifts in fixation. An eye-tracker with a 1.4 Hz closed-loop bandwidth could compensate for most eye movements in conventional or customized ablations.

Calibration↗
PubMed2005

Higher-order aberrations in eyes with irregular corneas after laser refractive surgery.

PURPOSE: To investigate the distribution of the eye's higher-order aberrations in postoperative laser refractive surgery patients with visual complaints and highly irregular corneal shapes. DESIGN: Retrospective case-control study. PARTICIPANTS: Thirty-three symptomatic postoperative LASIK and/or photorefractive keratectomy eyes with subjective visual complaints not corrected by spectacles more than 6 months after surgery are compared with 46 normal preoperative and 46 asymptomatic successful postoperative conventional LASIK eyes. METHODS: Postoperative wave aberrations were measured for each patient using a Shack-Hartmann wavefront sensor (Zywave, Bausch & Lomb, Rochester, NY) over a 6-mm pupil. These measurements were averaged across patients with similar corneal topographic diagnoses (central islands, decentered ablations, a new group termed baby bowties, and irregularly irregular corneas). MAIN OUTCOME MEASURES: Higher-order aberrations and corneal topography. RESULTS: The average (+/-1 standard deviation) higher-order root-mean-square (rms) wavefront error values (third, fourth, and fifth orders) for the symptomatic patients was 1.31+/-0.58 microm. This was an average of 3.46 times greater than the average magnitude of normal preoperative eyes (mean rms, 0.38+/-0.14 microm), and an average of 2.3 times greater than the average magnitude of asymptomatic successful postoperative conventional LASIK eyes (mean rms, 0.58+/-0.21 microm) over a 6-mm pupil. Higher-order rms wavefront error increased with pupil size, roughly doubling for every millimeter of increasing pupil diameter. On average, eyes with central islands (n = 6) had the most vertical coma (Z3(-1); mean, -1.35+/-0.43 microm). Eyes with central islands and decentered ablations (n = 2) also had elevated amounts of spherical aberration (Z4(0); means of 0.83+/-0.11 microm and 0.69+/-0.29 microm, respectively) compared with successful postoperative LASIK eyes (mean of 0.42+/-0.20 microm). Eyes with a topographic central baby bowtie demonstrated the most secondary astigmatism (Z4(2) and Z4(-2); mean rms, 0.56+/-0.17 microm; n = 3), despite the lowest average higher-order rms (mean, 0.84+/-0.05 microm) among symptomatic topographic subgroups. Eyes with irregularly irregular corneas had a mean higher-order rms of 1.10+/-0.39 mum. CONCLUSIONS: Symptomatic postoperative laser refractive surgery patients with irregular corneas have higher-order aberrations that are 2.3 to 3.5 times greater than asymptomatic postoperative LASIK and normal preoperative eyes, respectively. The higher-order aberrations seem to correlate with corneal topography.

Adult↗
PubMed2005

Image metrics for predicting subjective image quality.

PURPOSE: Despite the proliferation of wavefront sensors to characterize the optical quality of individual eyes, there is not yet an accurate way to determine from a wave aberration how severely it will impact the patient's vision. Some of the most commonly used metrics, such as RMS wavefront error and the Strehl ratio, predict subjective image quality poorly. Our goal is to establish a better metric to predict subjective image quality from the wave aberration. METHODS: We describe three kinds of experiments designed to compare the effectiveness of different metrics in determining the subjective impact of the wave aberration. Subjects viewed a visual stimulus through a deformable mirror in an adaptive optics system that compensated for the subject's wave aberration. In the first experiment, we show that some Zernike modes such as spherical aberration and defocus interact strongly in determining subjective image quality. In the second experiment, the subject's wave aberration was replaced by the wave aberration corresponding to an individual Zernike mode. The subject then adjusted the coefficient of the Zernike mode to match the blur of a standard stimulus. In the third experiment, the subject viewed the same stimulus through the wave aberration of one of 59 different postoperative patients who had undergone LASIK and matched the blur by adjusting defocus. We then determined which among many image quality metrics best predicted these matching data. RESULTS: RMS wavefront error was a poor predictor of the data, as was the Strehl ratio. CONCLUSIONS: The neural sharpness metric best described the subjective sharpness of images viewed through the wave aberrations of real eyes. This metric can provide a single number that describes the subjective impact of each patient's wave aberration and will also increase the accuracy of refraction estimates from wavefront-based autorefractors and phoropters.

Humans↗
PubMed2004

Monochromatic ocular wavefront aberrations in the awake-behaving cat.

Measurement of wavefront aberrations in human eyes has become a reliable, quantitative way of assessing the optical impact of experimental and corrective ocular manipulations. Wavefront measures have also been performed in several other species, but never in cats, an animal model of choice for many ocular studies. Our goal in this study was to measure wavefront aberrations reliably in live, awake-behaving cats in a manner that is directly comparable to that used in human subjects. Six adult cats (felis cattus) were trained to fixate small targets on a computer screen. A compact Shack-Hartmann wavefront sensor was aligned with each animal's pupil center and line of sight during fixation. Wavefront images were then collected from which the cats' ocular aberrations were measured up to tenth order Zernike polynomials over a 6 mm pupil. Results show that cat and human ocular wave aberrations were very similar. Second order Zernike modes accounted for more than 90% of the total wave aberration. In agreement with our observation that cat ocular optics were comparable with those of humans, the half height width of both the cat and human higher order point spread function was about 0.95 degrees. These results form a solid basis for future wavefront sensing studies aiming to quantify the effects of ocular manipulations in experimental animals.

Animals↗
PubMed2003

Separate effects of the microkeratome incision and laser ablation on the eye's wave aberration.

PURPOSE: To study the optical changes induced by the microkeratome cut, the subsequent laser ablation, and the biomechanical healing response of the cornea in normal laser in situ keratomileusis (LASIK) eyes. DESIGN: Prospective randomized clinical trial. METHODS: A Hansatome microkeratome was used to cut a corneal flap in one eye (study eye) of 17 normal myopic patients and a subsequent laser ablation was performed 2 months after this initial microkeratome incision. Control eyes received conventional LASIK treatments at the latter time point. The wave aberration of both the study and contralateral control eyes were measured over a 6-mm pupil with a Shack-Hartmann wavefront sensor for all preoperative, postflap cut, and postablation visits. RESULTS: The eye's higher order aberrations had a small, but significant increase (P =.03) of approximately 30% 2 months after cutting a flap. No systematic changes were observed in nearly all Zernike coefficients from their preoperative levels at 2 months postflap cut. A significant difference between the study and control eyes was observed for one trefoil mode, Z(3)(3) (P =.04). CONCLUSIONS: There was a wide variation in the response of individual Zernike modes across patients after cutting a flap. The majority of spherical aberration induced by the LASIK procedure seems to be due to the laser ablation and not the microkeratome cut. In addition, the total and higher order root mean square of wavefront errors were nearly identical for both the study and control eyes 3-months after the laser ablation, indicating that a procedure in which the incision and the ablation are separated in time to better control aberrations does not compromise the outcome of a conventional LASIK treatment.

Adult↗
PubMed2002

Costs and consequences of comprehensive stillbirth assessment.

OBJECTIVE: The purpose of this study was to determine the consequences and costs of comprehensive stillbirth assessment. STUDY DESIGN: Through reconstruction, we determined what consequences arise from assessment in the first 1477 stillborn pregnancies that were referred to the Wisconsin Stillbirth Service Program. Economic costs of stillbirth assessment were derived from real-time studies of those who performed the analyses and the costs of materials that were consumed. RESULTS: When comprehensive, nonselective analysis is performed, new information that is relevant to recurrence risk estimation, prenatal diagnosis recommendation, or preconceptual, prenatal, perinatal, or neonatal treatment will arise in 51% of stillborn infants. The real cost of such assessment is approximately $1450 per assessment, or approximately $12 per cared-for pregnancy. CONCLUSION: Substantial relevant information can be learned from stillbirth assessment at a modest economic cost. Programs that can provide comprehensive stillbirth assessment services should become part of routine pregnancy care.

Cost-Benefit Analysis↗
PubMed2002

Calculated impact of higher-order monochromatic aberrations on retinal image quality in a population of human eyes.

We calculated the impact of higher-order aberrations on retinal image quality and the magnitude of the visual benefit expected from their correction in a large population of human eyes. Wave aberrations for both eyes of 109 normal subjects and 4 keratoconic patients were measured for 3-, 4-, and 5.7-mm pupils with a Shack-Hartmann sensor. Retinal image quality was estimated by means of the modulation transfer function (MTF) in white light. The visual benefit was calculated as the ratio of the MTF when the monochromatic higher-order aberrations are corrected to the MTF corresponding to the best correction of defocus and astigmatism. On average, the impact of the higher-order aberrations for a 5.7-mm pupil in normal eyes is similar to an equivalent defocus of approximately 0.3 D. The average visual benefit for normal eyes at 16 c/deg is approximately 2.5 for a 5.7-mm pupil and is negligible for small pupils (1.25 for a 3-mm pupil). The benefit varies greatly among eyes, with some normal eyes showing almost no benefit and others a benefit higher than 4 at 16 c/deg across a 5.7-mm pupil. The benefit for keratoconic eyes is much larger. The benefit at 16 c/deg is 12 and 3 for 5.7- and 3-mm pupils, respectively, averaged across four keratoconics. These theoretical benefits could be realized in normal viewing conditions but only under specific conditions.

Adult↗
PubMed2002

Calculated impact of higher-order monochromatic aberrations on retinal image quality in a population of human eyes.

We calculated the impact of higher-order aberrations on retinal image quality and the magnitude of the visual benefit expected from their correction in a large population of human eyes. Wave aberrations for both eyes of 109 normal subjects and 4 keratoconic patients were measured for 3-, 4-, and 5.7-mm pupils with a Shack-Hartmann sensor. Retinal image quality was estimated by means of the modulation transfer function (MTF) in white light. The visual benefit was calculated as the ratio of the MTF when the monochromatic higher-order aberrations are corrected to the MTF corresponding to the best correction of defocus and astigmatism. On average, the impact of the higher-order aberrations for a 5.7-mm pupil in normal eyes is similar to an equivalent defocus of approximately 0.3 D. The average visual benefit for normal eyes at 16 c/deg is approximately 2.5 for a 5.7-mm pupil and is negligible for small pupils (1.25 for a 3-mm pupil). The benefit varies greatly among eyes, with some normal eyes showing almost no benefit and others a benefit higher than 4 at 16 c/deg across a 5.7-mm pupil. The benefit for keratoconic eyes is much larger. The benefit at 16 c/deg is 12 and 3 for 5.7- and 3-mm pupils, respectively, averaged across four keratoconics. These theoretical benefits could be realized in normal viewing conditions but only under specific conditions.

Adult↗