Do you sometimes feel like the world is a little blurry? When you're driving at night, do the lights of cars in front of you seem a little blurry? Or do you feel like you can't see clearly even when you use your glasses? One of the main reasons for this could be a slight difference in the shape of your eyes. Today, we're going to talk about a simple, painless test that can help you find out.
What is Keratometry?
The name may sound a bit complicated, but it's actually quite simple. Simply put, keratometry is a test that measures the curvature, or shape, of the cornea in your eyes.
Now you may be wondering what the cornea is. Think of our eye as a good camera. The transparent, thin layer in front of this camera is what we call the cornea. It's like the protective glass over the camera lens on your phone. Light enters our eye through this cornea. So, it's very important for the shape of this cornea to be correct in order to have clear vision. The keratometry test measures that shape.
Why is this test important? What will it find?
The main and most common condition detected by this test is astigmatism . This is a very common condition that causes blurred vision.
Let's understand this more simply.
Normally, the cornea of a healthy eye is shaped nicely, like a baseball, so that light entering the eye is focused on one spot, allowing us to see a clear image.
But the shape of the cornea of a person with astigmatism is not a perfect circle. It may be slightly elongated, like a rugby ball. Or it may be curved to one side, like the back of a spoon. When this happens, light entering the eye is not focused in one place, but in several places. That's why vision is blurred and images appear stretched.
So, the main purpose of a keratometry test is to determine exactly whether you have astigmatism, and if so, to what degree.
This test is also important in several other situations:
- Before putting on contact lenses: To choose a contact lens that fits your eye perfectly, you need to know the exact measurements of your cornea.
- Before cataract surgery: During this surgery, an artificial lens (IOL) is inserted into the eye. These keratometry measurements are essential to choose the lens that best fits your eye.
How is this Keratometry test performed?
This is a very quick and painless test. It can be done during your regular eye exam. You don't need to set aside a separate day for it.
A device called a 'Keratometer' is used for this. At first glance, it looks like a small telescope. However, it does not look at distant stars, but at your eyes very close. Let's take a step-by-step look at how the test is performed.
| Steps | What is happening? |
|---|---|
| 1. Preparing yourself | You will be asked to sit in a chair, place your chin in a special place on the machine, and place your forehead on a special bar. This is to keep your head in one place during the test. The doctor will then adjust the machine so that your eye is in the correct position. |
| 2. Viewing through the device | You will be asked to look through a small hole in the machine (the eyepiece). It is like looking through binoculars. You may also want to close the other eye that is not being examined at this time. |
| 3. Looking at the image inside | Inside the machine, you will see an image that looks like three circles, or a positive (+) and negative (-) sign. You are instructed to stare at it without blinking. |
| 4. Recording measurements | As you look at that image, the doctor is turning the knobs on the machine to create those images. At one point, those two plus (+) signs touch each other. At that exact moment, he records the measurements. |
| 5. Checking the other eye | Once one eye is finished, the other eye is tested in the same way. The entire test takes a very short time, about a few minutes. |
Are there any risks or disadvantages to this test?
Absolutely not. This is a 100% safe test . It does not cause you any risk or pain . Although the light from the machine is a little bright, it will not harm your eyes or vision.
But there is one small thing. Rather than calling this a "disadvantage," think of it as an awareness of the nature of this test. A keratometry test is not a 100% accurate measurement of your cornea, but rather a very good estimate.
I'll explain why simply. Think of a globe. It's beautifully round and smooth. But we know that our Earth is not really that smooth, there are tall mountains like the Himalayas, deep oceans like the Mariana Trench, and many other things like valleys. And the Earth is not a perfect sphere either. But a globe is a great help in understanding where Sri Lanka is and where America is, isn't it?
The keratometry test is similar. It measures the shape of our cornea, assuming it is a perfect sphere. In reality, our eyes are not perfect spheres, and there are naturally small variations in them. But it is a very useful and valuable tool for quickly and fairly accurately determining whether you have astigmatism.
Nowadays, some ophthalmologists also use more advanced tests, such as corneal mapping, which can provide more accurate measurements.
What are these keratometry readings (K readings)?
The results obtained after this test are what we call a 'K reading' . The unit in which these are measured is called Diopters .
Don't be alarmed by these numbers and details. These are for your doctor to understand. He will look at these results and determine the exact cause of your vision changes.
| Eye condition | The nature of K reading |
|---|---|
| A healthy, round cornea (Normal Cornea) | The entire cornea has the same, constant K value. This value is usually around 43 diopters. |
| An eye with astigmatism | You will see two K values. One for the steepest part of the curve, and the other for the flattest part. The difference between these two values indicates your level of astigmatism. |
This K reading will guide your doctor in choosing the right pair of glasses, contact lenses, or, if necessary, the right lens for surgery.
When should I see my doctor?
Your doctor will tell you how often you should have your eyes checked. It's important to follow that schedule.
The shape of our eyes naturally changes over time, so the level of astigmatism can change. However, if you notice a sudden, significant change in your vision, especially if it's much more blurry than usual, don't ignore it. It could be a sign of a condition like keratoconus that requires immediate treatment. So if you notice a sudden, significant change in your vision, see your doctor right away.
Remember, this is not a test that you can pass or fail. It is just a test to see how well your eyes are doing. No matter how severe your astigmatism is, you can still see clearly with the right glasses, contact lenses, or other treatments.
Take-Home Message
- Keratometry is a simple, painless, and safe test to measure the curvature of your cornea.
- This mainly identifies the common vision impairment called astigmatism.
- The results of the test (K readings) will help your doctor choose the best glasses, contact lenses, or post-operative lenses for you.
- If you experience a sudden or significant change in your vision, do not ignore it and see an eye doctor immediately.
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