CET Continuing education

A n active ciliary body controls the eye’s accommodation process, allowing near focusing to occur. The ciliary body is made up mainly of smooth muscle, known as the ciliary muscle. Accommodation occurs when the muscarinic receptors within the ciliary muscle are stimulated by the parasympathetic neurotransmitter, acetylcholine (see Part 1 Optician 29.06.12). The ciliary muscle then contracts, pulling the ciliary body forward. Tension in the suspensory ligaments supporting the crystalline lens is reduced. As a result, the lens becomes more convex, and thereby increases its refractive power. Adequate focus for nearer targets is then achieved.1 To obtain the true distance correction, it is imperative that refraction takes place when the patient has relaxed his/her accommodation. For most adults and some children, this can be achieved by directing the patient to view a non-accommodative distance target. However, in some individuals, particularly the young, this is not sufficient and other methods must be employed to ensure an accurate result. Cycloplegia means ‘paralysis of the ciliary body’. In this state, the eye cannot accommodate and the latent prescription can be determined. To obtain cycloplegia, practitioners use drugs known as cycloplegic agents. These are muscarinic antagonists which block the muscarinic receptors within the ciliary muscle (muscarine is a chemical that early neurology researchers found to effectively block the acetylcholine receptors at the post ganglionic neurone action site of the parasympathetic system). If acetylcholine can no longer reach the ciliary muscle, accommodation cannot occur. Cycloplegic agents are particularly valuable within paediatric optometry (Figure 1). They are also beneficial beyond this age group when examining patients with particular refractive needs. Furthermore, cycloplegia is occasionally desirable for patients receiving ophthalmological care. This article explores the diagnostic uses of In the second of our series looking at drugs and their use in optometric practice, Catherine Viner discusses cycloplegics, how they work, when they should be used and how to undertake cycloplegic refraction. Module C19478, one general CET point for optometrists and dispensing opticians