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At least 289 records · Page 16Linked to original sources
PubMed2005

Astigmatism in monkeys with experimentally induced myopia or hyperopia.

PURPOSE: Astigmatism is the most common ametropia found in humans and is often associated with large spherical ametropias. However, little is known about the etiology of astigmatism or the reason(s) for the association between spherical and astigmatic refractive errors. This study examines the frequency and characteristics of astigmatism in infant monkeys that developed axial ametropias as a result of altered early visual experience. METHODS: Data were obtained from 112 rhesus monkeys that experienced a variety of lens-rearing regimens that were intended to alter the normal course of emmetropization. These visual manipulations included form deprivation (n = 13); optically imposed defocus (n = 48); and continuous ambient lighting with (n = 6) or without optically imposed defocus (n = 6). In addition, data from 19 control monkeys and 39 infants reared with an optically imposed astigmatism were used for comparison purposes. The lens-rearing period started at approximately 3 weeks of age and ended by 4 to 5 months of age. Refractive development for all monkeys was assessed periodically throughout the treatment and subsequent recovery periods by retinoscopy, keratometry, and A-scan ultrasonography. RESULTS: In contrast to control monkeys, the monkeys that had experimentally induced axial ametropias frequently developed significant amounts of astigmatism (mean refractive astigmatism = 0.37 +/- 0.33 D [control] vs. 1.24 +/- 0.81 D [treated]; two-sample t-test, p < 0.0001), especially when their eyes exhibited relative hyperopic shifts in refractive error. The astigmatism was corneal in origin (Pearson's r; p < 0.001 for total astigmatism and the JO and J45 components), and the axes of the astigmatism were typically oblique and bilaterally mirror symmetric. Interestingly, the astigmatism was not permanent; the majority of the monkeys exhibited substantial reductions in the amount of astigmatism at or near the end of the lens-rearing procedures. CONCLUSIONS: In infant monkeys, visual conditions that alter axial growth can also alter corneal shape. Similarities between the astigmatic errors in our monkeys and some astigmatic errors in humans suggest that vision-dependent changes in eye growth may contribute to astigmatism in humans.

Animals↗
PubMedDate not supplied

The role of patient's age in regression of holmium:YAG thermokeratoplasty-induced correction of hyperopia.

PURPOSE: Hyperopic correction can be induced with holmium:YAG laser thermokeratoplasty, which changes corneal curvature by shrinking stromal collagen. The thermal effectiveness of pulsed Ho:YAG laser depends on the water content of the corneal stroma, which should be related to age. This study investigated the presumed effect of age on the stability of the results of Ho:YAG laser thermokeratoplasty. METHODS: Ho:YAG laser thermokeratoplasty was done in 63 eyes of 45 patients for low to moderate hyperopic correction (up to 5 diopters). Patients were treated with one or two rings of 8 spots each, with an optical zone of 6 or 7 mm diameters respectively. RESULTS: Regression of the therapeutic effect was evaluated on the basis of the difference between the attempted to achieved correction ratio on the first postoperative day and at the last visit. The regression ratio was 18% in the patients older than 20 years. Patients younger than 20 years showed a ratio of 48%. Achieved correction was +2.40 D in older patients and +2.05 in younger patients. These values are respectively 43% and 35% of the attempted corrections. CONCLUSIONS: It appears that age-dependent corneal factors do influence the effectiveness of thermal energy on stromal collagen.

Adolescent↗
PubMedDate not supplied

Holmium: YAG laser to treat astigmatism associated with myopia or hyperopia.

The Summit Technology, Inc. (Waltham, Mass.) holmium:YAG laser was used to treat astigmatism in 31 myopic and 8 hyperopic eyes. There was slow but continuing regression of effect even 1 year after treatment. This regression was particularly seen in hyperopic astigmatism, larger amounts of myopic astigmatism, and younger patients. In some cases keratometry readings returned to their pretreatment values. Males and females had similar results. The mean myopic shift in 9 myopic astigmatism eyes at 9-month follow up was 1 D.

Adult↗
PubMedDate not supplied

Posterior chamber collamer phakic intraocular lens for myopia and hyperopia.

PURPOSE: To assess the feasibility of correcting refractive errors using a foldable posterior chamber phakic intraocular lens. METHODS: Thirty-four foldable posterior chamber phakic intraocular lenses (STAAR Collamer intraocular lens) were consecutively implanted by the same surgeon (PMP) in 19 myopic eyes and 15 hyperopic eyes. In myopic eyes, mean preoperative spherical equivalent refraction was -16.65 +/-3.37 D (range, -8.12 to -21.25 D). In hyperopic eyes, mean preoperative spherical equivalent refraction was +7.77+/-2.08 D (range, +4.75 to +11.75 D). Mean follow-up was 12 months (range, 6 to 18 mo). Two hyperopic eyes were not included in the data analysis because of removal of the intraocular lens due to pupillary block. RESULTS: Myopic eyes (n=19)-Mean spherical equivalent postoperative refraction was -1.51+/-1.37 D (range, -5.50 to+0.38 D). Postoperative refraction was within +/-0.50 D in 4 eyes (21.05%) and within +/-1.00 D in 8 eyes (42.10%). Uncorrected visual acuity was 20/40 or better in 12 eyes (63.15%) and 20/25 or better in 3 eyes (15.78%). No eye had an uncorrected visual acuity of 20/20 or better. Spectacle-corrected visual acuity was 20/40 or better in all eyes, 20/25 or better in 12 eyes (63.15%), and 20/20 or better in 1 eye (5.26%). Spectacle-corrected visual acuity was unchanged in 10 eyes (52.63%) and improved in 9 eyes (47.36%). A retinal detachment developed in 1 eye (5.26%). Hyperopic eyes (n=15)-Mean spherical equivalent postoperative refraction was +0.02+/-0.64 D (range, -1.00 to +1.50 D). Postoperative refraction was within +/-0.50 D in 9 eyes (69.25%) and +/-1.00 D in 12 eyes (92.30%). Uncorrected visual acuity was 20/40 or better in 6 eyes (46.15%) and 20/25 or better in 3 eyes (20.25%). No eye had an uncorrected visual acuity of 20/20 or better. Spectacle-corrected visual acuity was 20/40 or better in 7 eyes (53.84%), 20/25 or better in 6 eyes (46.15%), and 20/20 or better in 2 eyes (15.38%). Spectacle-corrected visual acuity was unchanged in 10 eyes (76.92%), significantly improved in 2 eyes (15.38%), and worse in 1 eye (7.69%). Two of 15 eyes (13.33%) developed a severe pupillary block necessitating removal of the implants. One eye (7.69%) developed an anterior subcapsular cataract. CONCLUSIONS: Refractive predictability appears better for hyeropia than for myopia using the STAAR Collamer foldable posterior chamber phakic intraocular lens. In hyperopic eyes, development of pupillary block may occur.

Adult↗