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What is a Keratometer?

By J. Beam
Updated Mar 03, 2024
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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.

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Discussion Comments
By SarahSon — On Nov 28, 2012

Many times when I go to a doctor I am intimidated by all the big instruments in the room. If I don't know how they operate or what they do, I can be scared before the exam even begins.

Even though a keratometer can look big and intimidating, I am not bothered by these machines at all. All I have to do is sit up and look through the lenses and answer the questions.

It would be interesting to know how much one of these instruments costs. I am sure it is not cheap, but an eye doctor wouldn't be able to practice without one of these in his office.

By sunshined — On Nov 28, 2012
Isn't it interesting that the man who invented the keratometer suffered from his own vision problems? So many times a wonderful product is invented because someone is trying to find help for their own problem.

Even after all this time, the keratometer is widely used by doctors today. My mom has had more than one cataract surgery and so she is used to going through all kinds of eye tests. Every eye doctor she has visited has a keratometer instrument in his office.

By honeybees — On Nov 27, 2012

I think it would take a lot of training to know how to use a keratometer. When I go the my eye doctor for my eye exam, he quickly goes through moving various lenses and calculating refractions to determine if my vision has changed or not.

I have always had a little bit of astigmatism, but I have been able to correct it with glasses or contact lenses.

By anon129040 — On Nov 22, 2010

Thanks for the info. it has prepared me for my optics lab this morning knowing what one is!

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