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What is a refraction?

Photo of an auto refractor used during eye exams.

We have A LOT of patients ask, “Why do I have to do that air puffer thingy?!” Here’s what that pretty rad piece of technology does:

When we bring a patient back for a vision exam, the first thing we do is start in our screening room. One of the machines we use is this one, called an Automatic Refractor. This device offers us a piece of the puzzle that, once your exam is complete, helps us formulate the perfect ocular prescription for your eyes. The information obtained through this screening is a great baseline for us to then hone in on your best vision.

But what does it actually do, and why does it matter? This machine does two things. It refracts to assess optical error and it tests intra-ocular pressure. Here’s why that is important:
When an eye sees clearly, it means that the shape of the eye creates the ability for light to focus directly on the retina. The retina is the light sensitive tissue at the back of the eye. In contrast to that, the length of an eyeball creates changes in the shape of the cornea, which results in image distortion, also known as a “refractive error.” During the refractive phase of this screening, the machine uses infrared technology to assess the curvature of the lens of the eye in order to determine what the patient’s refractive error is, and what prescription is necessary to improve a patient’s vision. The doctor uses this mechanical assessment combined with his expertise, and the patient’s described perception to really dial in a great prescription.

The second phase of this screening is called Tonometry. This machine uses non-contact tonometry also known as every patient’s favorite: THE AIR PUFFER!, which determines intra-ocular pressure of the eye. High eye pressure can be a symptom of glaucoma or certain other ocular conditions, so it’s important to determine whether or not ocular pressure presents within normal range. To do this, the machine uses a rapid air pulse to flatten the cornea. Corneal flattening is detected via an electro-optical system.
Intra-ocular pressure is estimated by detecting the force of the air jet at the instance of flattening. That estimation is shown to us as a number, which conveys to us where on the spectrum that pressure presents.

Once we have obtained the information needed from these screenings, we are ready to move forward with the rest of our standard comprehensive exam. Dr. Goodwin and his staff want you to know our commitment goes beyond our patient’s just seeing clearly. We want you to see your best. That is why we spend time conducting tests that go beyond routine. It is our goal to explain what and why we are doing certain tests, and to explain to you what we are seeing while we are doing them. This way you will have a better understanding of eye health and eye care.