What is Contact Lens Calc?
The site converts spectacle SPH/CYL/axis into ordered starting power using disclosed vertex, optional spherical equivalent, and 0.25 D rounding. Related tools isolate vertex, transpose cylinder notation, start a toric or multifocal power, and combine an over-refraction with the trial lens.
The glasses number is not hiding from you; the vertex distance moved.
It is not:
- A contact lens prescription, a fitting, or medical advice
- A manufacturer portal that maps a refraction onto a brand SKU
- An impersonation of OptiExpert, simplifit, FittingHub, or Barrett toric (an IOL formula, out of scope)
Brand tools and independent peers are described, not copied, onContact Lens Calculators: OptiExpert, Simplifit, and Independent Tools. The fitting bound isStarting Contact Lens Parameters Are Not a Prescription.
Who is it for?
Eye-care practitioners, students, and technicians who need a starting power without being pushed into one manufacturer’s portfolio. Educated patients may read along to understand why a glasses number is not a contact lens number. Patients should not order lenses from calculator output.
Clinical review of the formulas, assumptions, and copy is attributed to Optom. Deepak Ghimire on this page. Calculator output remains starting parameters, not a prescription. Who he is, and what that review covers, is listed below.
Who publishes this site?
This site is published under the name Contact Lens Calc. The calculators are manufacturer-agnostic starting-parameter tools. They are not a clinic portal and not a Drishti Eye Care product.
Calculator input stays in the browser, and advertising is disclosed. How data and cookies are handled is on theprivacy policy.
Who reviewed the formulas and copy?
Reviewed by Optom. Deepak Ghimire, B. Optometry, PGDOVS — Consultant Optometrist, Myopia & Contact Lens Specialist.
- Name
- Optom. Deepak Ghimire
- Qualification
- B. Optometry; PGDOVS
- Role
- Consultant Optometrist, Myopia & Contact Lens Specialist
- Organization
- Drishti Eye Care
- NHPC registration
- A-1356 OPT
- Experience
- 6+ years, as listed by Drishti Eye Care
- Locations
- Kalanki, Chabahil, and Drishti @OM, Kathmandu
Optom. Deepak Ghimire is listed byDrishti Eye Careas Consultant Optometrist, Myopia and Contact Lens Specialist. That page lists qualification as B. Optometry; PGDOVS, NHPC registration A-1356 OPT, and 6+ years of experience. Locations listed there are Kalanki, Chabahil, and Drishti @OM, Kathmandu.
HisResearchGate profilelists consultant optometrist at Drishti Eye Care Centre and a bachelor in optometry and vision science. One listed paper isCase Report: Front surface eccentricity of scleral lens: Its impact on visual quality in eyes with higher-order aberrations induced by refractive surgery(Deepak Ghimire, Manish Bhagat, Kiranmayi Chappidi, Simmy Chaudhary; listed December 2025).
He is also listed as a member ofDrishti Eye Foundation Nepal. That is a nonprofit team listing. It is not a claim that the foundation operates or endorses these calculators.
Review means clinical and technical review of the formulas, assumptions, and copy on this site: vertex identity Fc = Fs ÷ (1 − d × Fs), the gate at or above about ±4.00 D, spherical equivalent after vertex, cylinder transposition, RGP D = 337.5 ÷ r, and over-refraction examples attributed to Moran CORE. The site still outputs starting parameters, not a prescription. Review does not mean he endorses a specific lens order, brand, or patient result. Fit, comfort, and final power remain on-eye decisions by the licensed practitioner using the tool.
How are formulas sourced?
Every calculator page discloses the method it uses. The full set — vertex formula, 12 mm default when unspecified, about ±4.00 D gate, spherical equivalent only when a spherical lens is intended, 0.25 D rounding — lives onHow we calculate.
Those defaults are locked against published conversion references such as Wikipedia’s Vertex distance page and the ODReference Contact Lens Conversion Calculator. Copy is written to match the calculator code, and unit tests pin the arithmetic. This page does not repeat those formulas.
Why does this site exist?
We built independent calculators so a starting power is not a brand decision. CooperVision OptiExpert, ACUVUE simplifit, and MyAlcon FittingHub map a glasses Rx into that manufacturer’s parameters. This site converts the same optical job and stays manufacturer-agnostic.
According to CooperVision’s tools footnote, those calculators aid eye-care practitioners and are not a replacement for a professional contact lens fitting. According to Johnson & Johnson’s simplifit disclaimer, that calculator is for educational and convenience purposes and is not a substitute for independent professional judgment. We agree on the bound. We do not impersonate those tools.
Corrections
If a formula, threshold, or table row is wrong, it should be corrected in code and tests, then reflected on the matching explainer. Send corrections to the site inbox,hello@contactlenscalc.com, or through thecontact page. Name the page and the source you checked against.
The reviewer's listing is verified onOptom. Deepak Ghimire's Drishti Eye Care page. That page belongs to his practice, not to this site; use it to verify who he is, not to reach this site.
Compare the implemented method against your own source on themethodology page.