When you arrive for an eye exam at Cowichan Eyecare, you will spend the first portion of your eye exam experience with one of our highly trained technicians. The tests that are done prior to seeing your Optometrist are collectively called the “pretest.” The tests run depend on your age, the type of exam you are having, and any specific concerns you are having with your eyes or vision. However, the purpose of the pretest is always the same: to gather key information to aid the doctor in determining an accurate prescription and performing a thorough eye health assessment.
After the initial check-in process, a technician will ask to borrow your eyeglasses. The prescription in your lenses will be read through a process called lensometry. This approximates your prescription and also gives us information about the type of lenses that you are wearing, such as whether they are single vision, bifocals, or progressives. We can also identify if your glasses have certain features such as anti-reflective coatings and photochromic properties. We recommend that you bring any glasses that you currently use to your appointment. This is important so that your Optometrist can determine if and how much your prescription has changed and also make recommendations on lens styles or features that could improve your visual experience. It also allows our dispensing experts to clean, adjust, and make repairs to your glasses, if needed.
The next pretest step is autorefraction. The autorefractor is an instrument that gives an objective measurement of the refractive error of the eye. The patient simply views an image and the instrument measures how light reflects from the retina. It also provides an auto keratometry measurement of the curves of the front part of the eye called the cornea. Keratometry information is especially useful for fitting contact lenses and for monitoring certain eye conditions. Autorefraction data can be considered an estimate of the glasses and/or contact lens prescription for a patient and provides a starting point for the subjective refraction. Subjective refraction is the “better 1 or better 2” test that your Optometrist performs in the exam room to fine-tune your prescription. Autorefraction is generally fairly accurate but there are times when the readings may be variable due to cataracts or other ocular health conditions. This is why autorefraction alone is not used to prescribe glasses.
Stay tuned for another article about the second half of the pretest that involves intraocular pressure, peripheral vision testing and retinal imaging.
