A keratometer is a medical instrument that eye care professionals use to measure the curvature and reflection of the anterior surface of the cornea. Also sometimes called an ophthalmometer, this device is primarily used to diagnose the presence of astigmatism, and to determine its degree and how it can be treated. Astigmatism is a condition of the eye in which the cornea or lens is misshapen and can result in vision problems.
The original keratometer was invented in the late 19th century in a collaborative effort by French ophthalmologist Louis Émile Javal, who was the founder and director of the ophthalmology laboratory at the University of Sorbonne in Paris, and Javal's joint director and former student, Hjalmar Schiotz. Javal's study of medicine and the subsequent development of technology in ophthalmology was likely a result of his own vision problems, which he suffered from for most of his life.
The modern instrument uses optical sensors and computerized technology to measure comparisons and contrasts of the cornea against a predetermined value. The values determined by it are called keratometric values and enable eye care professionals to determine the presence and degree of astigmatism. There are two types of astigmatisms: the most common is a misshapen cornea, but sometimes, the lens, located behind the cornea, can be misshapen. A normal cornea is spherical, but in the case of astigmatism, the cornea is oblong. The keratometer measures the cornea at different points and helps determine a proper corrective prescription, the degree of correction, and whether concave or convex lenses are required to restore vision to an acceptable level.
The device is also frequently used to assist an eye surgeon in certain surgical procedures. An operative keratometer provides an LED light as a point of focus for the patient and refracts the proper meridians, enabling the surgeon to make precise incisions during cataract and other corrective eye surgeries. Just as the instrument has evolved with technology, so have other instruments and procedures pertaining to vision and eye care. Today, it's not only possible for eye care professionals to determine the exact cause of vision problems, but also to surgically correct many conditions that affect both vision and eye health.