Refractive errors are an important common cause of visual disturbance worldwide. The prevalence of types and degree of refractive errors may vary from region to region. Vitale et al., in their analysis of the United States, found astigmatism as the most common refractive error with a prevalence of 36.2%, followed by myopia with a prevalence of 33.1%, and least being hyperopia with a prevalence of 3.6%.
Further, myopia was more prevalent in females (39.9%) than males (32.6%). Sethu et al. found the prevalence of refractive error of at least 0.50 diopter (D) spherical, equivalent to 53.1%. Myopia and hypermetropia were found to be the most common refractive errors accounting for 27.7% and 22.9%, respectively.
Symptoms related to refractive errors are quite disturbing and may even disrupt the normal lifestyle of individuals. Refractive error patients form the majority of outpatient patients visiting an optometrist or ophthalmology clinic. A study by Schiefer et al. found refractive errors accounted for 21.1% of the patients presenting to an ophthalmologist.
The evaluation of these patients can be occasionally aided by topical agents called cycloplegic drugs. Thus refraction can be broadly divided into cycloplegic and non-cycloplegic refraction. Cycloplegic drugs are often used to evaluate patients for underlying refractive errors. Cycloplegics cause temporary paralysis of ciliary muscles allowing the determination of total refractive errors. Cycloplegic retinoscopy is also known as wet retinoscopy. Cycloplegics have been used since the 19 century to assess refractive errors by relaxing the accommodation.
Noncycloplegic refraction is performed without any drug administration. It doesn't affect the accommodation and pupil dilatation. The various listed methods of non-cycloplegic refraction are retinoscopy, autorefraction, and objective and subjective refraction. A detailed description of how to perform retinoscopy and refraction is beyond the scope of this chapter and is discussed in separate chapters.
Difference between Cycloplegic and Noncycloplegic Refraction
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