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Results for “refractive error”

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At least 631 records · Page 35Linked to original sources
PubMed1979

Contrast (modulation) sensitivity functions measured in patients with high refractive error with emphasis on aphakia: II. Determinations of patients.

Measurements of Constrast Sensitivity Functions (CSF) were made on normal observers made artificially highly ametropic with spectacle lenses (with high back vertex) distance in order to determine the effect of retinal image size alterations upon CSF measures. While not an exact model for high ametropia per se, this experiment served to familiarize the experimenters with problems associated with the task. Image size alterations occur normally in aphakic patients and highly myopic patients. As a clinical trial, a series of aphakic observers were tested using an interferometric acuity device. CSF measures were made with the patient's spectacle corrections in place and again with correcting contact lenses substituted. The contact lenses reduce induced image size alterations in these cases. The use of contact lenses in such measures allows differentiation between artifactual low frequency fall off in aphakia due to lens effects and possible low frequency fall-off due to other causes.

Adult↗
PubMed1985

Visual acuity, refractive error, and astigmatism following corneal transplantation for pseudophakic bullous keratopathy.

Seventy-six corneal transplants performed by one surgeon for pseudophakic bullous keratopathy (PBK) were studied. The mean follow-up was 23 months (range 2-76). Of 41 eyes with lenses left in situ, the mean acuity was 20/45; 60.9% of the eyes saw 20/40 or better. In contrast, the mean acuity for 18 eyes with lens removal and 17 eyes with intraocular lens exchange was 20/52 and 20/62, respectively; 42.8% saw 20/40 or better. Eighty-three percent of all grafts remained clear. Vitreous loss, glaucoma, and cystoid macular edema were more common with eyes with lens removals and exchanges. The type of lens present at transplant for PBK did not affect visual outcome. Although the results were not statistically significant, this study suggests that lenses left in situ are associated with a better visual prognosis, and that there is no difference in the clinical results between aphakic and pseudophakic bullous keratopathy.

Aged↗
PubMed1976

Values, personality, physical characteristics, and refractive error.

A questionnaire containing: (a) a questionnaire of physical characteristics associated with psychosomatic symptoms, (b) questions to determine the presence of myopia or hypermetropia but not the amount of error, (c) a shortened version of the Gough Adjective Check List, and (d) the Heist and Yonge Omnibus Personality Inventory were administered to 782 introductory psychology students attending Washington State University. This group consisted of 297 self-identified myopes (117 males, 180 females), 439 emmetropes (207 males, 232 females), and 46 hypermetropes (15 males, 31 females). Results indicated that myopes and nonmyopes differed from one another with respect to their value systems, personality, and physical characteristics as assessed by the components of the questionnaire. Differences in these characteristics were consistently found by all assessment techniques to exist most often between myopes and hypermetropes and between emmetropes and hypermetropes rather than between myopes and emmetropes. In general myopes exhibited a personality pattern of introversion, whereas hypermetropes maintained a pattern described as extroverted.

Adult↗
PubMed2006

Refractive error after triple and non-simultaneous procedures: is the application of a standard constant keratometry value in IOL power calculation advisable?

PURPOSE: The purpose of this investigation was to determine whether or not the use of a standard constant keratometry value in cases of preoperative abnormal keratometry values in biometry for triple procedures is advisable. METHODS: Cataract surgery and penetrating keratoplasty were performed in 82 eyes; 53 eyes underwent triple procedures and 29 eyes underwent non-simultaneous procedures. A standard constant keratometry value of 42.50 D was applied in 18 triple-procedure eyes because the preoperative measured keratometry values were outwith the normal range (41-47 D). The spherical equivalent and expected values were compared after a mean follow-up of 20.5 months. RESULTS: Cases in the triple-procedure group that achieved spherical equivalent within +/- 2.0 D of expected values included nine of 18 eyes (50%) in which a standard constant keratometry value of 42.50 D was applied, three of 17 eyes (18%) in which keratometry values outwith the normal range were applied (p = 0.044), and eight of 18 eyes (45%) in which keratometry values within the normal range were applied (p = 0.862). Cases in the non-simultaneous procedure group that achieved spherical equivalent within +/- 2.0 D of expected values included 22 of 24 eyes (92%) in which keratometry values within the normal range were applied (p = 0.0025), and five of five eyes (100%) in which a standard constant keratometry value was applied. CONCLUSIONS: The application of a standard constant keratometry value of 42.50 D for intraocular lens power calculation in triple procedures can be recommended if abnormal keratometry values were measured previously. If possible, non-simultaneous procedures should take priority.

Biometry↗
PubMed2000

Choroidal retinoic acid synthesis: a possible mediator between refractive error and compensatory eye growth.

Research over the past two decades has shown that the growth of young eyes is guided by vision. If near- or far-sightedness is artificially imposed by spectacle lenses, eyes of primates and chicks compensate by changing their rate of elongation, thereby growing back to the pre-lens optical condition. Little is known about what chemical signals might mediate between visual effects on the retina and alterations of eye growth. We present five findings that point to choroidal retinoic acid possibly being such a mediator. First, the chick choroid can convert retinol into all-trans-retinoic acid at the rate of 11 +/- 3 pmoles mg protein(-1) hr(-1), compared to 1.3 +/- 0.3 for retina/RPE and no conversion for sclera. Second, those visual conditions that cause increased rates of ocular elongation (diffusers or negative lens wear) produce a sharp decrease in all-trans-retinoic acid synthesis to levels barely detectable with our assay. In contrast, visual conditions which result in decreased rates of ocular elongation (recovery from diffusers or positive lens wear) produce a four- to five-fold increase in the formation of all-trans-retinoic acid. Third, the choroidal retinoic acid is found bound to a 28-32 kD protein. Fourth, a large fraction of the choroidal retinoic acid synthesized in culture is found in a nucleus-enriched fraction of sclera. Finally, application of retinoic acid to cultured sclera at physiological concentrations produced an inhibition of proteoglycan production (as assessed by measuring sulfate incorporation) with a EC50 of 8 x 10(-7) M. These results show that the synthesis of choroidal retinoic acid is modulated by those visual manipulations that influence ocular elongation and that this retinoic acid may reach the sclera in concentrations adequate to modulate scleral proteoglycan formation.

Animals↗
PubMed2004

Measurement of refractive error and accommodation with the photorefractor PowerRef II.

The infrared photorefractor PowerRef II (PR II; PlusoptiX AG, Nurnberg, Germany) uses the principle of eccentric photorefraction. In eight subjects the mean non-cycloplegic refraction measured with the 'Full Scan' mode of the PR II at a far viewing distance (0.2 D) was significantly more hypermetropic by 0.6 D compared with subjective refraction. The mean accommodation differed by about this same amount between the PR II and the Canon R1 at three different viewing distances (3, 2 and 1 D). The PR II refraction at the 1 m reference distance was 0.25 D more hypermetropic compared with the subjective refraction at far (5 m); these measures were moderately correlated (r = 0.7). To determine temporal changes, the 'Dynamic Scan' mode was used over a 2-min period: the mean intraindividual standard deviation was 0.32 mm for pupil diameter and 0.29 D for accommodation, while the absolute measurement error of the 'Dynamic Scan' was found to be <0.12 D for the accommodation data. Interindividual reliabilities were satisfactory. However, the PR II did not provide a continuous stream of data and the specified sampling frequency of 25 Hz was rarely realized.

Accommodation, Ocular↗