A number of cool machines are used to determine the shape and condition of your eyes. These include:
- Auto-refractor - This machine measures the prescription in the eyes using a cone of infrared light. The infrared light is not visible to you. It is directed into your eye by the auto-refractor while you attempt to focus on an image within the machine's viewfinder. The auto-refractor changes the magnification of the image until it comes into focus for you.
- The auto-refractor has sensors that detect the reflections from the cone of infrared light. These reflections are used to determine the size and shape of a ring at the back of the eye called the ocular fundus. This is the part of the eye directly across from the pupil's opening. By measuring the ocular fundus, the auto-refractor can determine when your eye properly focuses on the image you are staring at. The auto-refractor monitors the magnification setting and calculates the approximate level of vision correction needed. This information is then fed into the phoropter for refinement of the prescription.
- Corneal topographer - The corneal topographer maps the clear cornea, determining its exact shape. You look into a purple, spiraled cone (sort of looks like a hypnotist's prop). Within the cone are sensors that detect infrared light.
It collects the light from a several hundred points across the eye. The topographer's mapping software then "connects the dots" to create an outline of the cornea's shape. This procedure is very accurate and can find anomalies in the cornea undetectable by other means.
The topographer is able to precisely measure the distance and depth of each point in relation to the other points. The topographer's mapping software then "connects the dots" to create an outline of the eye's shape. This procedure is very accurate and can find anomalies in the cornea undetectable by other means.
- Pupilometer - The other tool used during the pre-op exam is the pupilometer. This is a handheld device -- the one that Erika used for my exam looked like a ray gun from a sci-fi movie -- used to measure the exact diameter of the pupil. It does this using infrared light that is reflected back to a tiny sensor. Because the pupil reflects infrared light differently than the surrounding iris, the pupilometer's sensor can determine precisely where the pupil begins and measure the distance across it. Typically, measurements are taken with the lights on and then again with the lights off, so that the doctor can see the changes in pupil size.
Once all of the measurements are done, the ophthalmologist can determine if you are an ideal candidate. If you are considered a candidate, then you are given some information about the procedure and an opportunity to decide if you wish to continue.
If you decide to continue, then you must schedule an appointment for the surgery. You need to have someone accompany you since you will not be able to drive yourself home afterwards.