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Sphero-Cylinder Over Refraction Formula:
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Sphero-Cylinder Over Refraction is a technique used in optometry to determine the final prescription by combining the patient's current glasses prescription with the over-refraction findings. This method helps refine the prescription for optimal visual acuity.
The calculator uses the following formula:
Where:
Explanation: The formula accounts for the vertex distance and the interaction between spherical and cylindrical components during over-refraction.
Details: Over refraction is crucial for fine-tuning prescriptions, especially for patients with high refractive errors or those wearing multifocal lenses. It helps optimize visual acuity and comfort.
Tips: Enter all values in diopters. The Old Sphere and Over Sphere can be positive or negative values, while Over Cylinder is typically entered as a negative value (following the conventional notation in optometry).
Q1: When should over refraction be performed?
A: Over refraction is particularly useful when examining patients who wear high-power lenses, progressive lenses, or when the subjective refraction doesn't match the current prescription.
Q2: Why multiply the cylinder by 0.5?
A: The 0.5 factor accounts for the spherical equivalent of the cylindrical component, which affects the overall spherical power needed in the new prescription.
Q3: Does this calculation account for vertex distance?
A: Yes, the formula inherently accounts for vertex distance changes that occur during over-refraction behind the existing glasses.
Q4: How accurate is this calculation?
A: While this provides a good estimate, final prescriptions should always be verified with subjective refraction and patient feedback.
Q5: Can this be used for contact lens over-refraction?
A: The same principle applies, but additional considerations like lens power availability and fitting characteristics must be considered for contact lenses.