You can’t directly turn a glasses script into contacts; a fitting sets base curve, diameter, brand, and any vertex change for safe vision.
Switching from spectacles to contact lenses isn’t a copy-paste move. A contact lens sits on the cornea, not 12–14 mm away like a spectacle lens, so the final power can shift. A safe swap also needs fit data that doesn’t exist on a spectacles script. This guide walks you through what changes, what stays the same, and how an eye-care visit turns your current values into a working contact lens order.
What Makes A Contact Lens Script Different
A spectacles script lists sphere, cylinder, and axis. That’s only part of the story for contacts. A contact lens script adds fit geometry and product details, and it’s tied to a specific brand and material because each design drapes on the eye in its own way. You’ll also see a wear schedule and a renewal window. Those elements protect comfort and corneal health while matching the vision you’re used to in spectacles.
Prescription Fields At A Glance
The first table shows which fields appear on each script and what they mean for the swap.
| Term | Glasses Script | Contact Lens Script |
|---|---|---|
| Sphere (SPH) | Overall power for near/far | Adjusted for on-eye position; may differ from spectacles |
| Cylinder (CYL) | Astigmatism strength | Toric value in set steps; matched to available lens designs |
| Axis | Astigmatism angle | Mapped to toric stabilization angles available in the brand |
| Add | Near boost for multifocal spectacles | Mapped to discrete multifocal “adds” and optical zones |
| Prism | Occasional for eye alignment | Usually not in soft lenses; specialty options exist |
| PD | Pupillary distance for lens centering | Not used; lens centers on the cornea |
| Vertex Distance | 12–14 mm typical; affects strong powers | Zero; lens rests on the cornea |
| Base Curve (BC) | Not listed | Fit radius chosen during fitting |
| Diameter (DIA) | Not listed | Overall size chosen during fitting |
| Brand/Material | Not listed | Named product required; prescriptions are brand-specific |
| Wear Schedule | N/A | Daily/biweekly/monthly and replacement plan |
| Expiration | Set by clinic | Set by clinic; tied to on-eye evaluation |
Turning A Glasses Script Into Contact Lenses: What Changes
Two things drive the change: the zero vertex position and the need to fit a specific lens geometry. Power can shift a little for modest nearsighted or farsighted scripts. Larger shifts appear once the spectacles power passes about ±4.00 D. Astigmatism needs a toric design with fixed steps in cylinder and axis. Multifocal wearers move to set “add” tiers rather than continuous ranges.
Why A Direct Copy Doesn’t Work
A spectacles power assumes a small air gap. Move that power onto the cornea and the effective strength changes. A contact lens also must drape smoothly without edge lift or tightness. Base curve and diameter set that drape, and those values vary by brand. Without those, the same numbers that look fine on paper can feel dry, ride high, spin, or blur on blinks.
Step-By-Step: From Spectacles To Contacts
1) Gather Your Current Values
Have your most recent spectacles script handy. Note sphere, cylinder, and axis for each eye, plus any near add. Jot your typical wearing time and dryness history. That context helps the fitter pick a starting material and schedule.
2) Book An Exam And Fitting
The fitter measures corneal width and curvature, checks tear film, and screens the surface. That yields a starting base curve and diameter. A trial set then dials in the brand and power while the lenses sit on your eyes for a few minutes. Rotation, centration, and movement are checked before power is finalized.
3) Adjust Power For On-Eye Position
With modest myopia or hyperopia, the on-eye power often matches the spectacles value. Once the power gets stronger, a vertex adjustment brings the number closer to what your eye needs at zero distance. Your fitter may nudge by 0.25–0.50 D at first and refine after a short settling period.
4) Map Astigmatism To Toric Steps
Soft toric lenses come in set cylinder steps (often −0.75, −1.25, −1.75, −2.25) and axis steps (commonly every 10° or 5° in some lines). The chosen brand must stabilize in the same place over repeat blinks so your axis holds. If the rotation drifts, the fitter compensates by selecting the nearest axis that lands correctly on eye. Rigid gas permeable designs remain an option when soft toric stability is tricky or when clarity target is higher.
5) Test Vision And Comfort
After a few minutes of wear, you’ll read the chart, blink through, and look at contrast. Dry spots, fluctuating blur, or ghosting tell the fitter to tweak material, base curve, or power. Multifocal designs need a short conversation about your reading distance, screen distance, and lighting, and you might try two add tiers before locking in a final pick.
6) Finalize The Brand And Schedule
Daily disposables suit sensitive eyes and low-maintenance routines. Biweekly or monthly lenses save cost but need steady care. Your script will name the product, base curve, diameter, sphere, and—if needed—cylinder and axis. That brand-tie is part of the prescription, not a shopping suggestion.
7) Get A Copy Of Your Script
U.S. rules require a copy after the fitting is complete. That lets you order where you like. See the Contact Lens Rule for exact rights and obligations. The FDA also explains how a valid script protects buyers; see Contact lens prescription guidance.
Power Changes: A Simple Way To Think About It
When a lens moves from an air gap to the cornea, the effect of power shifts. Nearsighted values often get slightly weaker on eye; farsighted values can trend the other way. The table below shows common starting points that fitters use for quick trials. Final power comes after on-eye checks.
Typical Vertex Adjustment Guide (Myopia)
| Spectacles Power | Starting Contact Power | Notes |
|---|---|---|
| −0.25 to −3.75 | Same as spectacles | Usually no change |
| −4.00 to −5.00 | Often −0.25 lower | Check clarity after settle |
| −5.25 to −6.50 | −0.50 lower | Fine-tune on eye |
| −6.75 to −8.00 | −0.50 to −0.75 lower | Brand and tear film matter |
| Over −8.00 | Use calculator, then test | Specialty fitting often needed |
What About Hyperopia?
With stronger farsighted values (+4.00 D and above), the starting contact lens number can bump up by a small step. Many clinics start with the same or +0.25 D, then refine during the fit. The brand’s optic profile and your near work can sway the final choice.
Astigmatism: Picking A Toric Design That Holds Steady
Astigmatism needs a lens that stays lined up. Soft toric lenses use ballast or other stabilization features so the axis doesn’t drift. If your spectacles cylinder is mild, some wearers accept a spherical lens and a tiny blur trade-off; many still prefer true toric clarity. When cylinder is higher or the cornea is irregular, rigid gas permeable designs can sharpen edges and reduce ghosting.
Axis Mapping Tips
Axis values in spectacles run from 1° to 180°. Toric lenses come in standard steps. During the fit, the lens might settle a few degrees off. Your provider notes the rotation and picks the axis that lands the optics in the right place after rotation. That’s why an in-chair trial beats a straight mail order guess.
Multifocal Wearers: How The “Add” Translates
Multifocal contacts don’t copy the spectacles add one-to-one. Designs come in Low, Med, and High (names vary). The center zone can be set for near or distance. You and your provider match the add tier to your reading tasks and choose a center profile that suits your day. Minor compromises are normal: a bit more near clarity or a bit more distance snap, based on your target.
Care, Follow-Up, And Legal Basics
After you pick a brand and power, you’ll get care steps and a renewal window. If comfort or clarity drifts, circle back. A fresh corneal check is part of a renewal because the surface can change with dryness, allergy, or new screen habits. In the U.S., prescribers must release a copy of your contact lens script at the end of the fit, and sellers must verify before shipping. The FTC guide explains how release and verification work across clinics and retailers.
Common Mistakes When Moving From Spectacles To Contacts
Skipping The Fit
Buying by spectacles values alone risks poor vision or red eyes. Without base curve and diameter, the lens may ride off-center, dry out, or rotate.
Ignoring Tear Film And Wear Time
Daily disposables help many dryness-prone wearers. If you sit in air-conditioned rooms or work long screen hours, bring that up during the fit so the brand choice matches your day.
Ordering A Different Brand “With The Same Numbers”
Designs aren’t interchangeable. Even with the same power, a new brand can sit tighter or looser. Stick to the named product on your script unless your clinic approves a swap.
Quick Checklist You Can Save
- Bring your latest spectacles script and wear time notes.
- Ask for daily, biweekly, or monthly options that match your routine.
- For strong powers (past about ±4.00 D), expect a vertex tweak.
- For astigmatism, plan on a toric trial to lock axis stability.
- Test reading distance, laptop distance, and night driving clarity.
- Get the final script in hand; it must list brand, BC, DIA, and power.
- Order only with a valid script; sellers must verify before shipping.
FAQ-Free Notes On Special Cases
High Myopia Or Hyperopia
Expect a few power trials and close follow-up. Targets are crisp acuity and stable comfort over a full day, not just a sharp chart right after insertion.
Dry Eye Or Allergy
Daily disposables, higher water designs, or specific materials can ease symptoms. Care solutions also change outcomes; some pairs feel fine with one solution and sticky with another.
Occupational Needs
Drivers, coders, and tradespeople may want different balances. Mention your main tasks so the fit lands on the right compromise between distance, midrange, and near.
Second Table: Fit And Power Tuning Roadmap
This compact roadmap shows how fit, power, and wear choices come together near the end of the process.
| Decision Point | Typical Options | What To Check |
|---|---|---|
| Base Curve / Diameter | Brand-specific pairs | Centering, movement, edge comfort |
| Power Finalization | 0.25 D steps | Chart acuity after settle time |
| Astigmatism Control | Toric vs. RGP | Axis stability across blinks |
| Multifocal Profile | Low/Med/High adds | Near vs. distance balance |
| Wear Schedule | Daily / biweekly / monthly | Comfort by hour 10–12 |
| Care System | Peroxide / multipurpose | Morning feel, deposits, redness |
Safe Ordering And Follow-Up
Only buy from sellers that request and verify your contact lens script. That check isn’t red tape; it’s there to match the exact lens and geometry that sat well on your eyes in the chair. If your eyes feel gritty, vision fluctuates, or lenses shift late in the day, book a quick recheck. Small nudges to brand, care solution, or power can turn a good fit into an easy all-day wear.
The Takeaway
A spectacles script gives you a starting point, not a complete contact lens order. A fitting adds base curve, diameter, brand, and any power tweaks tied to on-eye position. With a short chair time and a proper release of your script, you can order with confidence and wear with comfort.