Keratometry - Purpose, Procedure, Results Interpretation, Normal Values and more

Keratometry is a diagnostic test used in ophthalmology to measure the curvature of the cornea, the clear, dome-shaped surface of the eye. The cornea plays a crucial role in focusing light onto the retina, and its shape and curvature significantly affect vision. By accurately measuring the corneal curvature, keratometry provides essential data for diagnosing and treating a variety of eye conditions, including astigmatism, keratoconus, and refractive errors. It is also an important test for preparing for eye surgeries such as cataract surgery and refractive lens exchange.

What is Keratometry?

Keratometry is a test that measures the curvature of the cornea’s surface. The cornea is responsible for focusing light onto the retina, and its shape and curvature are vital in determining how well a person sees. An accurate measurement of the corneal curvature helps eye care professionals assess and correct refractive errors such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism.

Keratometry is often used to determine the steepness and flatness of the cornea by measuring the radius of curvature of the corneal surface in different meridians. This data is used to diagnose conditions, assist in fitting contact lenses, and plan eye surgeries.

The Keratometry Process

1. Measurement of Corneal Curvature: During a keratometry test, a light source is projected onto the cornea. The light reflects off the cornea and returns to a special sensor in the machine, which calculates the shape of the cornea based on how the light rays are reflected.
2. Instrument Used: The device used for keratometry is called a keratometer or ophthalmometer. It consists of a light source, a series of reflective rings, and a sensor to measure the light’s reflection and curvature.
3. Recording the Data: The results of the keratometry are usually displayed in terms of diopters, which measure the optical power of the cornea. The curvature is expressed as the radius of curvature, measured in millimeters.
4. Outcome: The test results indicate the shape and steepness of the cornea, which helps diagnose various visual impairments.

Why is Keratometry Performed?

Keratometry is an essential test in eye care for a variety of reasons. It is used to assess the cornea’s shape and curvature, which can affect vision and determine the best course of treatment for different eye conditions.

• Diagnosing Refractive Errors: Keratometry helps detect and diagnose refractive errors, including:
  • Astigmatism: A condition in which the cornea is irregularly shaped, causing blurred vision.
  • Myopia (Nearsightedness): When the cornea is too steep, causing difficulty in seeing distant objects.
  • Hyperopia (Farsightedness): When the cornea is too flat, leading to difficulty seeing nearby objects.
• Assessing Corneal Health: Keratometry can detect abnormalities in the shape of the cornea that may be indicative of certain conditions, such as:
  • Keratoconus: A progressive condition in which the cornea thins and bulges into a cone shape, leading to significant vision impairment.
  • Post-surgical Corneal Changes: After refractive surgeries like LASIK or cataract surgery, keratometry can help monitor the cornea’s shape to ensure optimal healing.
• Contact Lens Fitting: For people who need contact lenses, keratometry is essential in determining the curvature and size of the cornea. Correct measurements are critical in fitting the right lenses, particularly for those with irregular corneas or astigmatism. The test helps in determining the optimal curvature of the contact lenses for comfort and clarity.
• Pre-surgical Planning: Keratometry is commonly used as part of the preoperative assessment for patients undergoing cataract surgery, refractive lens exchange, or corneal transplant. The curvature measurements help surgeons plan the best surgical approach and select the appropriate intraocular lens (IOL) for patients.
• Monitoring Conditions: For patients with conditions that affect the cornea, such as keratoconus or following surgeries, keratometry helps track changes in the cornea over time. This allows healthcare providers to assess whether the condition is progressing or if further intervention is required.

How to Prepare for Keratometry

Preparing for a keratometry test is simple and involves a few key steps to ensure accurate results:

• Remove Contact Lenses: If you wear contact lenses, you may be asked to remove them at least 24 hours before the test. Contact lenses, especially rigid ones, can alter the shape of the cornea, leading to inaccurate readings.
• Inform Your Doctor of Any Eye Conditions: Before the test, inform your eye care provider if you have any existing eye conditions, such as dry eye syndrome, glaucoma, or if you’ve had recent eye surgery. This information will help the doctor interpret the results appropriately.
• Avoid Eye Irritation: If your eyes are irritated or inflamed, it is best to reschedule the test. Ensure that your eyes are well-rested and free from infection before undergoing keratometry.
• No Special Diet or Fasting Required: Unlike some medical tests, keratometry does not require fasting or dietary restrictions. You can eat and drink normally before the test.
• Relax Before the Test: While keratometry is a simple, non-invasive procedure, it is still recommended to relax before the test. This will help ensure your eyes are comfortable and that you stay still during the test for accurate results.

Test Results Interpretation

The results of the keratometry test are primarily used to assess the curvature of the cornea. These measurements are expressed in diopters and radius of curvature. Here’s how to interpret the results:

Normal Results

In a healthy eye, the cornea typically has a radius of curvature between 7.5 mm and 8.0 mm, with the diopter measurement ranging between 42.00 and 45.00 D (diopters). These measurements are considered within the normal range and indicate that the cornea is sufficiently round and evenly shaped for optimal vision.

Astigmatism

If the cornea is more oval-shaped rather than round, the test will show different curvature measurements along different axes. The presence of astigmatism is indicated when the cornea’s curvature differs significantly along different meridians. The diopter measurement will be higher along one axis than the other, with the difference suggesting the degree of astigmatism.

Keratoconus

In patients with keratoconus, the cornea may show a steepening or cone-shaped appearance. The keratometry measurements will reflect an abnormal curvature with a pronounced difference between the horizontal and vertical meridians.

Post-surgery Changes

After refractive surgeries such as LASIK, keratometry can reveal changes in the cornea’s shape. The curvature may flatten after the procedure, which helps with vision correction. Surgeons use the results to determine whether additional treatment may be needed.

Contact Lens Fitting

For individuals needing contact lenses, the keratometry readings are used to find lenses that match the shape of the cornea. A steep or flat cornea will require special consideration when selecting hard contact lenses or soft lenses for comfort and clarity.

Normal Range for Keratometry

There is no universally defined “normal range” for keratometry, as measurements vary depending on individual factors like age, gender, and overall eye health. However, a typical normal range for corneal curvature is:

• Radius of Curvature: 7.5 mm to 8.0 mm
• Diopter Measurement: 42.00 D to 45.00 D (for a healthy, non-astigmatic cornea)

Anything outside of these ranges may indicate an abnormality, such as astigmatism, keratoconus, or other conditions that affect the shape of the cornea.

Uses of Keratometry

Keratometry is used for a variety of purposes in both diagnostic and treatment settings. Some of the key uses include:

• Diagnosing Refractive Errors: Helps detect astigmatism, myopia, hyperopia, and other visual impairments.
• Assessing Corneal Health: Used to monitor conditions like keratoconus or corneal scarring.
• Contact Lens Fitting: Assists in selecting the appropriate lenses for people with irregular corneas or astigmatism.
• Pre-Surgical Planning: Provides essential information for surgeons performing cataract surgery, LASIK, or other refractive procedures.
• Monitoring Changes After Surgery: Used to track changes in the cornea’s shape after refractive surgery or other eye treatments.

10 Frequently Asked Questions About Keratometry

• What is Keratometry? Keratometry is a test that measures the curvature of the cornea to assess vision and diagnose conditions like astigmatism or keratoconus. It is an essential tool in ophthalmology and optometry.
• How is Keratometry performed? The test is non-invasive and involves focusing a light source onto the cornea and measuring its reflection. The data is used to calculate the curvature of the cornea.
• Why do I need Keratometry? It helps diagnose refractive errors, monitor eye health, and assess the shape of your cornea, which is crucial for fitting contact lenses and planning surgeries like LASIK.
• Does Keratometry hurt? No, keratometry is a painless procedure. It typically takes just a few minutes to complete, and you may be asked to focus on a light during the test.
• How should I prepare for a Keratometry test? Avoid wearing contact lenses for at least 24 hours before the test. You should also inform your doctor about any eye conditions, medications, or previous surgeries.
• Can Keratometry detect astigmatism? Yes, keratometry is essential in detecting astigmatism, as it measures the curvature of the cornea, revealing if it is irregularly shaped.
• What if my Keratometry results are abnormal? Abnormal results may indicate conditions like keratoconus or astigmatism. Your doctor will provide further guidance on treatment or corrective lenses.
• Can Keratometry be used to assess contact lens fit? Yes, keratometry is often used to ensure that contact lenses fit well, especially for people with irregular corneas or those needing special lenses.
• How often should I get a Keratometry test? The frequency of testing depends on your eye health and any conditions you’re monitoring. People with astigmatism or undergoing eye surgery may need regular tests.
• Can Keratometry help in post-surgery assessment? Yes, keratometry is commonly used after refractive surgery to evaluate changes in corneal shape and ensure the procedure was successful.

Conclusion

Keratometry is an essential diagnostic tool for evaluating the curvature of the cornea and diagnosing various vision problems, including astigmatism, keratoconus, and refractive errors. It plays a critical role in contact lens fitting, pre-surgical planning, and post-surgery assessments, helping healthcare professionals provide accurate treatments and ensure the best outcomes for patients.

Understanding how keratometry works and why it’s performed can empower you to take charge of your eye health. Whether you’re preparing for an eye exam, considering refractive surgery, or managing a condition like astigmatism, keratometry can offer valuable insights that contribute to your overall vision care.