8 Refraction
Refraction is a favourite exam topic (and one which is often very poorly performed!). Usually the candidate is asked to perform retinoscopy on one eye (often dilated and cyclopleged) followed by subjective refraction (depending on the length of the station). The patient is often a medical resident, carefully selected for their high myopia and astigmatism, so if the retinoscopy reflex is very dull, try putting up a high minus (or plus) lens early.
Equipment Required
In examinations, equipment will often be provided, but having your own retinoscope that you are familiar with is advantageous.
- Retinoscope (with charged / new batteries)
- Trial frame. Exam candidates should consider bringing their own, as some frames can take a bit of mastering
- Trial lenses (use left column of lenses for right eye and vice versa. Keeping the lenses ordered during the examination is not only good professional practice, but respectful to the candidate following you).
- Retinoscopy rack. It is personal preference whether this is used. Some clinicians find it faster to use a retinoscopy rack to roughly find neutralisation, which is then refined with trial lenses. Others find that this is achievable just as quickly (and more accurately) by using the trial lenses directly. Children may not tolerate use of a retinoscopy rack
- Jackson Cross Cylinder (JCC). Again, exam candidates should consider bringing their own for familiarisation. Different strengths of JCC are used for different purposes. Higher powers are used for determination of axis. Smaller powers (± 0.50D or even ± 0.25D are used when refining the final subjective refraction. It is convention that JCCs will be marked on their handle by twice the power of the lenses (e.g. a ± 0.50D JCC will be marked 1.00D on the handle)
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