Multifocal Contact Lens Calculator

What starting multifocal parameters does this calculator return?

Starting multifocal parameters are converted distance sphere, equal-add start, dominance labels, and the vertex assumption used.

The following four values make up that starting set:

• Starting distance sphere at the corneal plane
• Starting add from the spectacle add, at equal-add start
• Dominant and non-dominant labels as entered
• Vertex distance in millimeters, or a flag that distance was already converted

Those four fields are diagnostic starting parameters. According to the ACUVUE simplifit calculator, multifocal calculations take a functional add in addition to sphere, cylinder, and axis. We keep the functional-add input and drop the ACUVUE trial-lens picker.

Spectacle-to-contact conversion of distance power is the upstream step. Run that path on the Contact Lens Conversion Calculator when the sphere still sits at the spectacle plane. This URL isolates starting add.

Takeaway: the returned add is a trial start, not an ordered SKU.

How does spectacle add become a starting contact lens add?

Spectacle add becomes a starting contact lens add after a least-minus, least-add refraction, equal-add start, and rounding to 0.25 D steps.

Glasses add is not a brand LOW, MED, or HIGH bin. According to Pal, Review of Contact Lenses, Do You Follow These Fitting Principles? (November 2018), basic multifocal steps begin with a “least minus, least add” refraction, then eye dominance, then initial lenses from the spherical-equivalent vertex refraction and add power. According to Hay, Eyes On Eyecare, 15 May 2017, always start with equal adds. Unequal adds, or a sphere in the dominant eye and a multifocal in the non-dominant eye, are an endpoint, not a starting point.

The following table maps add from the spectacle plane to the starting contact lens value.

Takeaway: add survives as a starting parameter; distance still converts first.

1. Perform a least-minus, least-add refraction.
2. Convert distance power at a disclosed vertex.
3. Enter the spectacle add equally in both eyes.
4. Round the starting add to the nearest 0.25 D.

According to MyAlcon, FittingHub, Alcon rounds ADD up to the nearest 0.25 D. That is Alcon’s product rule. We round to typical 0.25 D steps. According to the Bausch + Lomb, Multifocal Fitting Calculator, that tool’s add dropdown lists 0.00 D then 0.75 D to 2.50 D in 0.25 D steps. Those values are that tool’s input grid, not a market-wide strength chart.

If cylinder stays indicated, calculate starting SPH, CYL, and AX on the Toric Contact Lens Calculator. Do not auto-replace that cylinder with spherical equivalent.

Why convert distance power before the add?

Distance spectacle power is converted before a starting multifocal add is selected.

According to Moran CORE, Contact Lens Over-Refraction (Noell Acord, OD, and David Meyer, OD, FAAO, dated 6/30/22), vertexing spectacle refractions before selecting a new contact lens power saves over-refraction time later. That page states any meridian at or above about ±4.00 D should be vertexed. The same gate appears on the ODReference conversion page. Default vertex is 12 mm when unspecified. The ACUVUE simplifit calculator includes 12 mm vertex calculation across each power meridian. The Bausch + Lomb multifocal calculator likewise says to adjust for vertex if necessary.

This site converts spectacle power to the corneal plane. It does not reverse a contact lens prescription to glasses. The inverse vertex relationship is Fs = Fc ÷ (1 + d × Fc), published on Wikipedia, Vertex distance. This site does not apply that inverse.

Takeaway: an unvertexed distance sphere corrupts the add trial that follows.

How does eye dominance change a multifocal starting fit?

Eye dominance is a fitting heuristic you test and label. It does not calculate a new diopter on this page.

According to Hay, always test eye dominance when fitting monovision or multifocals. Pal lists “Determine eye dominance” as the second basic multifocal step. Equal adds remain the start. Dominance tells the fitter which eye to bias if over-refraction later needs a one-eye change. Hay’s overlapping-hands test is a chairside method, not an optical formula. This calculator does not compute dominance from sphere and add.

Moran CORE’s 0.25 D dominant-eye minus (distance) and non-dominant plus (near) sequence belongs to verification, not to the starting-add output.

Takeaway: label dominance at the start; change add later, one step at a time.

How do you verify a multifocal trial with over-refraction?

A multifocal contact lens is verified with binocular loose-lens over-refraction in 0.25 D steps, not behind a phoropter.

According to Pal, let the initial lenses settle 20 to 30 minutes, then evaluate binocular vision with real-world tasks. Pal: keep the lights on, over-refract with trial lenses rather than the phoropter, and make only one change at a time.

The following sequence comes from Moran CORE and from Contact Lens Spectrum, The Contact Lens Exam (Schafer, June 2007):

1. Let the trial settle, then work binocularly in free space.
2. Find the highest plus that still gives clear distance vision.
3. Use 0.25 D steps: minus for distance complaints, plus for near complaints.
4. For leftover near blur, add plus over the non-dominant eye before changing add.
5. Confirm the patient accepts the new power at both distances.
6. Change one parameter, then recheck.

According to Moran CORE, extra plus at distance also helps near. More plus than expected often means the spectacle refraction was over-minused or the contact lens power was not vertexed. Hyperopes may accept more plus in a contact lens than expected. Some front-surface center-near aspheric designs provide more distance minus than the vertexed spectacle refraction predicted. Schafer: start at the distance that needs the most help.

Residual error after that trial calculates on the Over-Refraction Calculator for Contact Lens Parameters. Starting add still belongs on this URL.

Takeaway: multifocal over-refraction is binocular, plus-biased at distance, and 0.25 D stepwise.

Why can't I read with multifocal contacts?

Near blur with multifocal contacts is usually a starting-parameter and expectation problem, not a missing brand add.

Convert distance power first, then start equal adds. According to Guide to Fitting Contact Lenses for the Presbyopic Population, always start with equal adds after an accurate refraction. Unequal adds are an endpoint, not a start. That guide begins with the lowest add and stays conservative with plus. Patients should expect functional vision for most daily tasks, not glasses-level near, and may still need low-power magnifiers on occasion.

According to The Contact Lens Cheat Sheet: Multifocals, Dailies, Sclerals, and More, set that bound before the trial: multifocals give functional distance and near, not glasses clarity. The goal is a balance, using as much plus at distance as the patient can tolerate.

According to Do You Follow These Fitting Principles?, today’s multifocal designs do not follow the old shortcut of raising add for every near complaint. According to the Bausch + Lomb Multifocal Fitting Calculator, update the spectacle refraction and ADD, then adjust for vertex if necessary, before choosing a trial. This page returns equal-add starting parameters after that conversion. It does not pick a Bausch SKU. Let the trial settle, over-refract binocularly with real-world tasks, and change one parameter at a time. Output remains starting parameters, not a prescription.

How does an independent multifocal calculator differ from brand fitting tools?

An independent multifocal calculator maps spectacle add to manufacturer-agnostic starting parameters. Brand fitting tools map the same Rx onto one manufacturer’s grid.

The following table states what brand and independent tools map to, and what this page does. It is a purpose map, not a clone spec.

ACUVUE multifocal fitting calculators are brand-specific tools. Those portals, plus NaturalVue’s Quickstart calculator, are named on Contact Lens Calculators: OptiExpert, Simplifit, and Independent Tools. We do not impersonate simplifit, Bausch’s fitting-guide PDF, FittingHub, OptiExpert, or NaturalVue.

Takeaway: independence means a starting add without a SKU grid.

What should you do after the starting add is calculated?

After the starting add is calculated, convert remaining distance power if needed and verify the trial on eye. Contact lens parameters at the corneal plane remain a trial start.

Follow this five-step path:

1. Confirm distance power was converted at a disclosed vertex.
2. Trial equal adds from the starting add this page returned.
3. Fit dominance on eye with real-world distance and near tasks.
4. Verify power with over-refraction after the trial lens.
5. Treat the output as starting parameters, never as a prescription.

Patients must not self-prescribe. Convert spectacle prescription to contact lens parameters on the conversion calculator when the distance sphere is still a glasses number. Calculate vertex-compensated contact lens power when meridians are at or above about ±4.00 D. You still fit a starting toric or multifocal contact lens in the chair. Verify power with over-refraction after the trial lens.

Sources

• Pal, Review of Contact Lenses, Do You Follow These Fitting Principles? — least minus, least add; eye dominance; 20–30 minute settle; one change at a time.
• Hay, Eyes On Eyecare, 15 May 2017 — equal-add start; always test dominance.
• The Contact Lens Cheat Sheet: Multifocals, Dailies, Sclerals, and More — functional distance and near, not glasses clarity; plus-biased distance start.
• Moran CORE, Contact Lens Over-Refraction — vertex spectacle refractions before selecting contact lens power; meridians at or above about ±4.00 D; 0.25 D binocular over-refraction sequence.
• Contact Lens Spectrum, The Contact Lens Exam — binocular loose-lens multifocal over-refraction; start at the distance that needs the most help.
• MyAlcon, FittingHub — ADD rounds up to the nearest 0.25 D as Alcon’s product rule, not this site’s rounding.
• Bausch + Lomb, Multifocal Fitting Calculator — spherical equivalent plus ADD OU; add dropdown 0.75 D to 2.50 D as that tool’s input grid.
• CooperVision, OptiExpert — sphere, toric, multifocal, and toric-multifocal calculator categories; clariti 1 day multifocal recommendation named only.