What is the significance of keratometry?

What is the significance of keratometry?

Keratometry (K) is the measurement of corneal curvature, which is used to evaluate the cornea’s power. Astigmatism is caused by differences in power across the cornea (opposite meridians); thus, keratometry quantifies astigmatism. It can be obtained manually or through automated ways using a variety of devices.

Keratometry (K) is the measurement of corneal curvature, which is used to evaluate the cornea’s power. Astigmatism is caused by differences in power across the cornea (opposite meridians); thus, keratometry quantifies astigmatism. It can be obtained manually or through automated ways using a variety of devices. It can be measured in a more finite area of the cornea, such as with a manual keratometer or the IOL Master, or it can be measured in a more sophisticated way, such as with topographers that measure a cornea across a large number of points (Carl Zeiss Meditec). The IOL Master also incorporates K readings and measures axial length as well as other ocular characteristics (such as anterior chamber depth and white-to-white measurements).

Automated vs. manual

Personally, I prefer manual keratometry since it provides a clear insight of the pre-corneal tear film’s integrity as well as a dynamic perspective of the cornea’s surface. You may see the reflections caused by the tear film directly using manual keratometry. You can spot locations where the corneal surface is uneven or compromised. The quality of the measurements will be affected if the tear film is greasy or disturbed, or if the cornea shows mild dystrophy or degeneration (akin to the changes of a pebble tossed into a placid lake). You have a much better idea of the quality and precision of your measurements now.

Acquisition is static with automated measurements. The measurements are taken at a specific point in time and then processed by a computer. As the instrument operator, you have no idea how precise the “measured minute” is.

Because measurement errors are matched 1:1 to refractive results, keratometry is an essential measurement in cataract surgery. You’ll get a 1.00 D refractive surprise if your K measurements are off by 1.00 D. If your K is off, you’ll have an unpleasant refractive surprise after surgery. A refractive miss result is exceedingly frustrating to both the doctor and the patient in current generation of cataract surgery with premium intraocular lenses (IOLs). In cataract postoperative patients, residual ammetropia may necessitate a second surgical treatment, such as IOL exchange, piggybacking of an extra IOL, or a surface procedure.

If you have any doubts about your K readings, repeat them on another day. If there is any hint of a problem or if the measurement is difficult to get, we will repeat K readings. I usually measure the right eye first, then the left, and then double-check.

If I’m not happy with any part of my measurement—for example, if the patient has dry eye disease or is using contact lenses—I’ll have them return after receiving dry eye therapy and not wearing contact lenses for 1 to 3 weeks, depending on the lens type. It’s possible that the first K measurement you took isn’t the one you’ll need during surgery. It’s the first thing you should do before infusing drops, doing gonioscopy, or doing anything else that can affect the corneal surface if you’re getting ready for cataract surgery.

Although manual K is simple to master, it does require some practice to ensure precise measurements. Before you write down your findings on a piece of paper, you must be confident in your measurements. Only doctors, including residents, will perform keratometry for patients undergoing cataract surgery at Omni Eye Surgery.

For their surgeries, some surgeons prefer the most up-to-date automated K. Because each approach evaluates various parts of the cornea, it’s a good idea to compare manual and automated measurements to obtain a better sense. You should also expect a match between the measured corneal cylinder and the patient’s spectacles.

The significance of a correct reading

It’s critical to take care of the corneal surface before undergoing ocular surgery. Patients are occasionally referred for cataract surgery; nevertheless, the fundamental concern is the corneal surface, not the cataract. Patients who had their corneal surface repaired have opted out of cataract surgery in some circumstances since the issue was more about the bad corneal surface than the cataract. During keratometric measures, clinical signs can be picked up that can assist you identify more mild cornea deterioration, such as basement membrane dystrophy, that is more difficult to detect and easy to neglect with a slit lamp examination. Patients with corneal dystrophy should be informed that, while their vision will improve following cataract surgery, they will still have a corneal issue that could impact their post-operative vision.

If an operator is having trouble generating a measurement, try to figure out why right away. Dry eye, a damaged cornea, meibomian gland dysfunction, corneal illness, or even poor patient positioning or fixation during testing could all be contributing factors.

It is critical to have a strong understanding of keratometry. With those measurements in your hands, the surgeon is putting the surgical result of the patient in your hands. It is your responsibility to ensure that they are clean and to raise a red signal if they are not.

Keratometric readings are also important when fitting contact lenses, especially gas permeable lenses, to monitor corneal disease and detect keratoconus. Keratometry is frequently used to identify keratocones.


Keratoconus is a corneal degenerative condition that causes abnormal and irregular steepening (and irregular astigmatism) of the cornea, resulting in decreased vision, scarring, and the possibility of corneal perforation. Occasionally, a patient will present with unexplained visual loss until the technician gets K measurements. Then we discover that the cornea is completely aberrant, resulting in blurred vision. Corneal crosslinking, gas permeable contact lenses, Intacs (embedded stromal rings), and penetrating keratoplasty are among treatment possibilities for keratoconus (corneal transplant).

If the K readings are beyond of what is considered a normal range, or if the mires are irregular, you are immediately alerted to the possibility of keratoconus pathology. With corneal crosslinking, the sooner we detect it, the sooner we can stop corneal steepening from progressing.

Some practitioners favor automatic keratometry, while others prefer manual keratometry. The most essential aspect is that we may obtain these measures in a variety of ways. They should all make sense and be connected. If the measurements differ significantly, they should be retaken and examined to rule out other pathology.

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