The cycloplegic refraction is a cornerstone of the eye exam on young children. “Cyclo” drops, such as cyclopentolate or atropine are a class of drugs called cycloplegics. Cycloplegics paralyze the focusing muscle inside the eye. The focusing muscle inside the eye (ciliary body), when flexed, is able to help the eyes focus at near as well as overcome hyperopia (farsightedness). In children, their focusing muscles are very strong, allowing children to overcome very high amounts of hyperopia. In doing so, the child may test with 20/20 vision, but only because the focusing muscle is working so hard. Over the course of minutes to hours, however, this extra work may cause headaches or blurred vision as the muscle begins to fatigue.
So a child who’s prescription is +4.00, may test at 20/20 vision, can see the board at school well, but complain about headaches, especially when reading (when additional strain is placed upon the focusing muscle). Additionally, the two eyes cannot work independently. So if the prescription is plano in the right eye and +4.00 in the left the child may claim to see just fine, but this is only because they are only using the right eye, many times without even realizing it. The result is the +4.00 left eye never receives a clear image, the nerve pathway is never stimulated to develop, and unless is corrected by about the age of 8 becomes amblyopic (a lazy eye uncorrectable even with glasses).
What a cycloplegic refraction does, then, by paralyzing the focusing muscles of the eye, is allow the doctor to determine the full prescription in each eye without the child’s focusing muscles being able to hide any of it by being in a state of work. Countless times I can recall cases where a child’s “dry” refraction (without the use of cyclo drops) is plano, but because the child’s chief compliant is “headaches when reading” we placed cyclo drops in the eye and suddenly the manifest or retinoscopy refraction reveals the true prescription is +4.00 or higher. Additionally, other cases where the child has no visual complaints, their acuity is 20/20 in the right eye but only 20/60 in the left. “Dry” refraction reveals a prescription of plano in each eye, however when cyclo drops are applied the full true prescription of plano right eye and +4.00 left eye is revealed and suddenly the poor vision in the left eye has an explanation. In this case, a diagnosis of “refractive amblyopia” left eye can be made, and glasses along with a course of vision therapy (usually patching the right eye while wearing glasses to stimulate the lazy left eye to begin development) is initiated.
So, in summary, the cycloplegic refraction helps the doctor determine the full, true, prescription knowing none of it is being hidden by the child’s focusing muscles working overtime.
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