In the optical system of the human eye, total refractive power consists mainly of corneal and lenticular components. Approximately two-thirds of the eye's converging power is at the air–cornea (tear film) interface; one-third is in the lens. Total corneal power is determined by corneal anterior and posterior curvature, corneal thickness, and the corneal refractive indices. Traditionally, anteri...

When a triple procedure is planned, calculation of the intraocular lens becomes a problem. Postoperative corneal power bears no relation to preoperative power, and the axial length of the globe also changes. A prospective study of 24 keratoplasties revealed a close relationship between postoperative corneal power and donor corneal power. Changes in axial length were found to be too small to pro...

Evidence is presented for an active corneal component of accommodation in chicks. Using anesthetized chicks, consistent increases in corneal curvature were observed during accommodation produced either by electrical stimulation of the Edinger-Westphal nucleus or by topical application of 0.4% nicotine sulfate to the cornea. Electrical stimulation produced a mean accommodative amplitude of 9.2 d...

The corneal maps displayed on commercially available corneal topography instruments are really one-dimensional, defining quantities only along a meridian, and ignoring shape information along any other direction. Both axial and instantaneous power have the drawbacks that there is a singularity at the center data point on the videokeratograph axis, and the computed powers and appearance of the c...

PURPOSE To quantify the error introduced by videokeratographic corneal topography devices in using a paraxial formula to calculate power over the entire corneal surface, including areas removed from the central paraxial region where the formula is known to be invalid. METHODS Corneal refractive power and two paraxial power approximations were computed as a function of distance from the apex f...

PURPOSE To compare the relative advantages and disadvantages of four different representations of corneal power--identified as instantaneous, axial, position, and refractive--based on curvature, slope, coordinate position, and focal properties, respectively. METHOD The four types of corneal power were evaluated by examining their interrelationship for 12 hypothetical corneal shapes chosen to ...

BACKGROUND In our clinical experience we discovered that EEG band power may be correlated with corneal nerve injury in retinoblastoma patients. This study aimed to investigate biomarkers obtained from electroencephalography (EEG) recordings to reflect corneal nerve injury in retinoblastoma patients. MATERIAL AND METHODS Our study included 20 retinoblastoma patients treated at the Department of ...

PURPOSE To obtain an accurate algorithm for calculating the keratometric index that minimizes the errors in the calculation of corneal power assuming only a single corneal surface in the range of corneal curvatures of the normal population. METHODS Corneal power was calculated by using the classical keratometric index and also by using the Gaussian equation. Differences between types of calcu...

PURPOSE To determine if a direct relationship exists between the two common measures of corneal topography--axial and instantaneous powers--that are based on corneal slope or curvature, respectively. METHOD The theoretical relationship between axial and instantaneous powers was derived for unrestricted shapes using equations of basic calculus. RESULTS It was found that axial power at any po...

AIM To compare postoperative keratometric corneal refractive changes after phacoemulsification surgery between pre-incision and single stepped clear corneal incision techniques. PATIENTS AND METHODS This prospective clinical study included 40 eyes of 40 patients who underwent clear corneal cataract surgery. Twenty eyes were operated using pre-incision technique (Group A), and 20 eyes using si...