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contact lens power calculation from BVD

https://medqpractice.blogspot.com/ A common royal college exam question. How to calculate contact lens power from the spectacles dioptric power, and the back vertex distance. This video explains how to calculate contact lens power from a patient’s spectacle prescription using the back vertex distance (BVD). A fundamental concept frequently tested in Royal College ophthalmology exams, this topic is essential for both clinicians in training and practicing optometrists. Two worked examples are demonstrated step by step: 1. Myopic correction example (-10.00 D spectacles at 20 mm vertex distance) 2. Hyperopic correction example (+10.00 D spectacles at 15 mm vertex distance) Learn how to apply the formula: F₂ = F₁ / [1 – (d × F₁)], where F₁ is the spectacle lens power and d is the back vertex distance in meters. By the end of this tutorial, you will understand: How to correctly convert mm to meters. When and why vertex distance adjustments are most clinically significant. How to select the correct multiple-choice answer in exams when rounding is required. This concept is commonly featured in FRCOphth, Refraction Certificate, and professional optometry exams.