PubMed · 14856475
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J A EGAN. 1951. A modified cross cylinder.. https://doi.org/10.1001/archopht.1951.01700020159005
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We provide an adjustment factor for ablation algorithms used in photorefractive laser surgery that takes into account how laser polarization in reflection losses affects the cornea. We evaluate the influence of this factor on corneal radius and asphericity after surgery, showing that it is significant for visual performance (effective visual acuity is reduced) and for the correction of eye aberrations. Our data indicate that this adjustment factor should be included in the ablation algorithms (depending on the polarization state of each laser device) that are proposed for customized corneal ablation, which need great accuracy for minimization of eye aberrations.
According to optical diffraction theory, a visual acuity of 20/3.5 is possible in human eyes with pupil diameters larger than 6 mm. This theoretical value cannot be obtained in practice - in fact visual acuity is limited by the scale of the mosaic of the retinal cones. Anatomical data and the model by Helmholtz-Hering suggest that visual acuity of humans cannot be substantially higher than 20/10. Many young adult reach this visual acuity with their normal spectacles or contact lens correction. The human eye has higher-order aberrations which can be measured with a Hartmann-Shack aberrometer. A partial correction of these aberrations is possible by means of wavefront-controlled keratectomy and customized corneal ablation. A perfect eye completely free of ocular aberrations cannot be created by customized refractive surgery as, for example chromatic aberration cannot be corrected and the strength of ocular aberrations depends on the state of accomodation and varies with time.
OBJECTIVE: This article is a systematic review of the literature examining the anatomical and visual function outcomes after scleral buckle and/or vitrectomy for Stage 4 or 5 retinopathy of prematurity. MATERIALS AND METHODS: The literature published between 1994 through May 2003 was reviewed via a computer search accessing MEDLINE via OVID. Eight applicable studies were retrieved and analyzed. The study designs were descriptive, retrospective, non-comparative, consecutive case series. RESULTS: The postoperative anatomical outcomes varied dramatically between studies with retinal reattachment rates of 0.8% to 90%. Surgeries that achieved a 50% or higher rate of reattachment occurred primarily between 2 and 9 months of age. Surgeries that occurred between 7 and 11 months of age achieved a lower percentage of retinal reattachment. Further, the longer the duration of follow-up, the lower the percentage of retinas that remained attached. Most importantly, at least in these reports, the degree of retinal reattachment did not correlate well with the level of visual function. One report demonstrated no statistical correlation between visual and anatomical success. Poor visual outcomes were noted in both timely and delayed cases of surgical reattachment of the retina. Many of the reports described challenges in accurately measuring low levels of vision.