Purpose To analyze the errors associated to corneal power calculation using the keratometric approach in keratoconus eyes after accelerated corneal collagen crosslinking (CXL) surgery and to obtain a model for the estimation of an adjusted corneal refractive index (nkadj ) minimizing such errors. Methods Potential differences (ΔPc) among keratometric (Pk ) and Gaussian corneal power (PcGauss)...

PURPOSE To analyze the effect of birth weight on ocular morphology, refraction and visual function in early adolescents aged 12-15 years. MATERIAL AND METHODS We conducted a secondary data analysis using the public use files from the National Health and Nutrition Examination Survey of the period from 1999 to 2008. Study participants aged 12 to 15 years were included with data on birth weight ...

PURPOSE To study the prevalence of and relation between refractive and corneal astigmatism in white school children in Northern Ireland and to describe the association between refractive astigmatism and refractive error. METHODS Stratified random clustering was used to recruit 1053 white children, 392 aged 6-7 years and 661 aged 12-13 years. Eye examinations included cycloplegic autorefractio...

OBJECTIVES To describe the refractive results of cataract surgery after photorefractive keratectomy (PRK) for patients with myopia, and to find a more accurate method to predict intraocular lens (IOL) power in these cases. DESIGN Nonrandomized, retrospective clinical study. PATIENTS AND METHODS Nine patients (15 eyes) who underwent cataract surgery after prior PRK to correct myopia were ide...

PURPOSE To investigate the changes in central and peripheral anterior corneal curvatures after myopic laser in situ keratomileusis (LASIK) and to correlate them with the manifest refractive change to discuss how such results could affect post-LASIK corneal topography profiles and midterm stability and their implications in postsurgical contact lens fitting. METHODS Topographic and refractive ...

PURPOSE To derive a method of quantifying corneal topographic astigmatism (CorT) that accurately represents manifest refractive cylinder. SETTING Private practice, Melbourne, Australia. DESIGN Retrospective study. METHOD Axial power measurements obtained using topography in right eyes and left eyes were analyzed. For each Placido ring, an astigmatism value was calculated. The ring astigma...

The frequent occurrence of spherical myopia after penetrating keratoplasty for keratoconus is partly the result of the excessive dioptric power of the grafted cornea which occurs when the diameter selected for the donor button is greater than the diameter of the host incision. This excessive power could be reduced by eliminating disparity between the diameters of the graft and host. To determin...

We calculate whether deviations of Lambert-Beer's law, which regulates depth ablation during corneal ablation, significantly influence corneal refractive parameters after refractive surgery and whether they influence visual performance. For this, we compute a point-to-point correction on the cornea while assuming a non-linear (including a quadratic term) fit for depth ablation. Post-surgical eq...

Corneal hysteresis (CH) is a parameter which measures the viscoelastic behaviour of the cornea, indicating its biomechanical integrity1. Some clinical conditions such as keratoconus, Fuchs corneal dystrophy, high myopia, glaucoma and corneal refractive surgery, may induce changes in corneal biomechanical properties, leading to a decrease in CH2-6. Astigmatism, a refractive error related to corn...

This paper customizes Bennett's equation for calculating lens power in chicken eyes from refraction, keratometry and biometry. Previously published data on refraction, corneal power, anterior chamber depth, lens thickness, lens radii of curvature, axial length and eye power in chickens aged 10-90 days were used to estimate Gullstrand's lens power and Bennett's lens power for chicken eyes, and t...