Biomedical subjects

Patricia Schimchak

Publications and source records attributed to Patricia Schimchak.

3 recordsLinked to original sources

PubMed2006

Evidence for delayed presbyopia after photorefractive keratectomy for myopia.

PURPOSE: To evaluate uncorrected near visual acuity (NVA), accommodation, corneal aberrations, and the optical quality of the retinal image in presbyopic eyes after photorefractive keratectomy (PRK). DESIGN: Nonrandomized comparative retrospective study. PARTICIPANTS: Ten post-PRK patients and 10 normal patients. METHODS: Twenty eyes (10 right and 10 left after PRK for myopia, minimum of 10 years after the operation; group A) were compared with 20 eyes (10 right and 10 left age- and gender-matched normal controls; group B). All subjects were over 40 years of age. MAIN OUTCOME MEASURES: With best distance correction, NVA was measured at 40 cm (Jaeger, J series), and the range of accommodation (diopters [D]) was measured subjectively (negative relative amplitude and positive relative amplitude). The modulation transfer function (MTF) and corneal aberrations such as comalike, spherical (SAs), and higher order (HOAs) were measured with a Hartmann-Shack aberrometer. From the MTF curves, the spatial frequencies corresponding to contrast values of 0.1 and 0.5 were noted. RESULTS: Mean ages (+/- standard deviations [SDs]) were 46.3 years (4.7) for group A and 47.6 years (4.9) for group B (P>0.05). Near acuity was J1 or better in 12 of 20 post-PRK and 4 of 20 control eyes. Mean accommodations (+/- SDs) were 3.2 D (1.14) for right group A eyes and 2.1 D (0.94) for right group B eyes (P = 0.0152), and 3.4 D (0.99) for left A eyes and 2.3 D (1.02) for left B eyes (P = 0.0168). Total HOA indexes (+/- SDs) were 1.449 (0.409) for right group A eyes and 0.824 (0.241) for right group B eyes (P = 0.008), and 1.464 (0.388) for left A eyes and 1.067 (0.542) for left B eyes (P = 0.0752). Pooling the data from post-PRK and control eyes, a significant correlation was found between near acuity and SA (right eyes, r = -0.535, P = 0.015; left eyes, r = -0.493, P = 0.027). Significant associations were found between accommodation, near acuity, HOA, and comalike aberration for right eyes only. Mean spatial frequencies (+/- SDs) corresponding to contrast values of 0.1 for right and left eyes were 14.96 (5.71) for right group A eyes and 22.02 (6.85) for right group B eyes (P = 0.074), and 15.11 (7.80) for left A eyes and 21.41 (9.00) for left B eyes (P = 0.271). Mean spatial frequencies (+/- SDs) corresponding to contrast values of 0.5 for right and left eyes were 2.86 (0.63) for right group A eyes and 3.21 (0.35) for right group B eyes (P = 0.596), and 2.76 (0.98) for left A eyes and 3.22 (0.27) for left B eyes (P = 0.194). CONCLUSIONS: Compared with normal eyes, in previously myopic eyes treated with first-generation PRK lasers there is a tendency for (1) the optical quality of the retinal image to be reduced at low contrast, (2) the aberrations attributed to the corneal surface to increase, and (3) both measured subjective accommodation and near acuity to be greater than expected. We postulate that the corneal aberrations induced by PRK for myopia may reduce the quality of the retinal image for distance but enhance near acuity by way of a multifocal effect that can delay the onset of age-related near vision symptoms.

Accommodation, Ocular↗

PubMed2005

Crystalline lens optical dysfunction through aging.

PURPOSE: To evaluate the optical and densitometric changes that take place in the crystalline lens with aging. DESIGN: Cross-sectional study. PARTICIPANTS: Seventy-two eyes of 72 patients of different ages (8-80 years) with a clear lens, a visual acuity of 20/25 or better, and no ocular disease. METHODS: In each case, the lens thickness, optical density, modulation transfer function (MTF), and intraocular aberrations were measured. MAIN OUTCOME MEASURES: Embryonic and fetal nucleus density, lens thickness, intraocular high-order aberration (HOA), and 0.1 MTF. RESULTS: Embryonic, anterior, and posterior fetal nucleus densities show a positive correlation with age (P<0.0001, P<0.0001, and P<0.0001, respectively). Lens thickness also shows a positive correlation with age (P<0.0001). Total ocular and corneal HOAs for a 6-mm pupil show a positive correlation with age (P = 0.036 and P<0.0001, respectively). Ocular and corneal Zernike polynomials Z4i+Z6i and intraocular spherical aberration (Z4(0)) also show a positive correlation with age (P = 0.001, P = 0.039, and P = 0.001, respectively). Intraocular coma aberration (Z3(-1)) shows a negative linear correlation with age (P<0.0001). In addition, 0.1 MTF decreased with age from 18.557 to 10.100 cycles per degree. CONCLUSION: There is a degradation of the optical quality of the crystalline lens with aging that is associated with morphological changes (thickness and density). These results are important for the consideration of lens replacement in the absence of evident cataract.

Adolescent↗

PubMed2005

Retinal image quality after microincision intraocular lens implantation.

PURPOSE: To evaluate the modulation-transfer function (MTF) in eyes implanted with a conventional intraocular lens (IOL) and 2 IOLs designed for microincision cataract surgery (MICS). SETTING: Research, Development, and Innovation Department, Instituto Oftalmológico de Alicante, Alicante, Spain. METHODS: This prospective nonrandomized consecutive series comprised 30 eyes implanted with 1 of the following IOLs: conventional acrylic foldable (AcrySof MA60BM, Alcon Laboratories) or the UltraChoice 1.0 ThinOptX (ThinOptX Inc.) or the Acri. Smart 48S (Acri.Tech) MICS IOL. The 0.5 MTF and 0.1 MTF following MICS were calculated 3 months after implantation with the Optical Quality Analysis System (OQAS) for a 5 mm pupil. The differences were statistically analyzed with the Mann-Whitney U test. RESULTS: The values of 0.5 MTF for AcrySof, UltraChoice, ThinOptX, and Acri. Smart IOLs were, respectively, 2.647 cycles per degree (cpd) +/- 0.833 (SD), 2.601 +/- 0.986 cpd, and 3.453 +/- 0.778 cpd. The mean 0.1 MTF values for the same IOLs were 8.720 +/- 3.074 cpd, 8.814 +/- 4.380 cpd, and 11.418 +/- 2.574 cpd, respectively. Statistical analysis did not show significant differences in 0.5 MTF and 0.1 MTF between the conventional IOL and MICS IOLs. CONCLUSIONS: Microincision cataract surgery IOLs showed excellent MTF performance when implanted after cataract surgery, equal to that of conventional IOLs. An in vivo MTF study may be an excellent option to evaluate IOL performance in the eye.

Acrylic Resins↗