Should my myopia prescription include astigmatism?
Jun 29, 2022
Source: Cainiu Health
Dr. Chen You
Introduction
The degree of myopia combined with astigmatism depends on the magnitude of the astigmatism. The myopic correction should be the lowest acceptable power necessary to eliminate all pseudomyopia. Accurate measurements are typically obtained following cycloplegia. If the measured astigmatism is 150 diopters, corrective lenses are usually prescribed at either 100 or 150 diopters, as visual acuity often corresponds to approximately 50 diopters less than the actual measured value.
Myopia, in simple terms, refers to clear near vision but blurry distance vision. There are two main types: axial myopia and refractive myopia. Axial myopia occurs when the eyeball’s anteroposterior diameter is longer than normal. As a result, light rays entering the eye—after passing through the cornea and other ocular structures—focus in front of the retina rather than directly on it. Does the myopic prescription need to include astigmatism correction?
Should astigmatism be added to the myopic prescription?
The decision to incorporate astigmatism into the myopic prescription depends on the magnitude of the astigmatism. The myopic correction should ideally be the lowest possible power that fully eliminates pseudomyopia. Accurate measurement typically requires cycloplegic refraction (i.e., pupil dilation). For example, if the measured astigmatism is 150 diopters (D), corrective lenses with either 100 D or 150 D of astigmatism correction are commonly prescribed. Since visual acuity is generally unaffected by an undercorrection of approximately 50 D, both prescriptions usually achieve 20/20 (1.0) visual acuity.
If astigmatism measures only 50 D, correction may not be necessary—primarily because adding an astigmatic lens can induce visual distortion, and the brain requires time to adapt. Children generally adapt well due to their greater neural plasticity; however, adults often find adaptation challenging. Therefore, adults typically opt to forgo partial visual refinement in favor of ocular comfort.
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