A patient's refraction is −3.00 DS / −2.00 DC × 90. What is the equivalent sphere (spherical equivalent) of this prescription?

• A −3.00 D
• B −2.00 D
• C −5.00 D
• D −4.00 D ✓

Explanation

Spherical equivalent = Sphere + (Cylinder / 2) = −3.00 + (−2.00 / 2) = −3.00 + (−1.00) = −4.00 D. This is used clinically to convert compound astigmatic prescriptions into a single power for purposes such as contact lens fitting, laser refractive surgery screening criteria, and IOL selection when toric IOL is not available.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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