The Purpose of the Pretest: Part 1

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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.

Written by Trevor Miranda

Dr. Miranda was raised in Simcoe, Ontario and graduated from the University of Waterloo with his Doctorate of Optometry in 1995. Following graduation, he moved to beautiful Vancouver Island, where he continues to serve the eye care needs of the Cowichan Valley. Trevor is also an active member of the Third World Eye Care Society and has participated with other professionals to improve the vision of the less fortunate. Dr. Miranda was named Optometrist of the Year by the British Columbia Association of Optometrists in March 2015. This prestigious honour recognized Dr. Miranda’s commitment to providing every patient with exceptional care while mentoring optometrists across Canada. Outside the office, you will find Trevor enjoying hockey, coaching soccer, involved with the South Cowichan Rotary Club, and spending time with his wife Cheryl and their three children. Trevor looks forward to continuing to care for the eyes of the Cowichan Valley and welcomes new patients without a referral. Dr. Miranda is available for appointments in our Duncan and Cobble Hill.
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