Contact Lens Prescription Calculator

Converting Spectacles into Contact Lenses

Converting a spectacle prescription to a contact lens prescription and calculating the spherical equivalent are critical processes in optometry to ensure accurate and comfortable vision correction. When transitioning from spectacles to contact lenses, it is essential to account for the vertex distance—the space between the spectacle lens and the cornea—since this distance affects the effective power of the lens. High-powered lenses, in particular, require this adjustment to maintain the intended visual correction. The spherical equivalent is calculated to simplify the prescription by averaging the sphere and cylinder values, thus creating a single value that approximates the overall refractive power. This calculation is especially useful for determining the initial power of contact lenses or when prescribing lenses for patients with low levels of astigmatism. By carefully converting the spectacle prescription to account for the vertex distance and calculating the spherical equivalent, optometrists can ensure that the contact lenses provide the correct refractive power directly on the cornea, thereby enhancing visual acuity and comfort. Mastery of these conversions is crucial for delivering precise, personalized vision care and improving patient satisfaction with their contact lens experience.

Calculator:
Spectacle Rx to Contact Lens Rx & Spherical Equivalent

Spectacle Rx
EyeSphereCylinderAxis
OD
OS