What is myopic defocus, and what is hyperopic defocus?
Both terms name where an image comes to focus relative to the retina, not what the eye's refractive error is. Myopic defocus is in front of the retina. Hyperopic defocus is behind it.
The distinction only matters because the retina is a curved surface and a lens does not focus every field angle onto it equally. A single-vision correction can put the fovea exactly on focus while the off-axis image shell falls somewhere else entirely — and in a myopic eye corrected with a spherical lens, that off-axis shell tends to fall behind the peripheral retina. Berntsen and Kramer (Optometry and Vision Science, 2013) measured exactly that: their spherical soft lens produced significantly more relative peripheral hyperopia than a centre-distance multifocal at multiple peripheral locations.
The term relative peripheral defocus appears in the same literature and means the peripheral value expressed against the central one, which is why it can be reported as a shift rather than an absolute. Berntsen and Kramer measured along the horizontal meridian at ±20°, ±30° and ±40° from the line of sight, at distance and at a 3.33 D near demand — a reminder that a defocus figure without its eccentricity and its viewing distance is not a result.
They also note the practical reason contact lenses appear in this conversation at all: a contact lens delivers a defocus profile 360° in the periphery because it stays relatively centred with eye movements. A spectacle lens does not, because the eye rotates behind it.
What is a treatment add, and how does it differ from a presbyopic reading add?
A treatment add is plus power placed outside the distance zone to move the peripheral image shell forward. A presbyopic reading add is plus power placed to give a presbyope usable near vision. The number looks the same and the job is not.
Three differences matter when an order is written:
- Where it comes from. A presbyopic add starts from a measured, written spectacle add and is converted to a starting contact lens add — the procedure on the Multifocal Contact Lens Calculator. A treatment add has no spectacle antecedent; there is nothing to convert.
- Who it is for. The wearer of a myopia control design typically accommodates normally and has no near demand the add is answering. The plus power is not there to be looked through at near.
- How much choice there is. Melanie Frogozo, OD (Review of Cornea & Contact Lenses, February 2026) records adds commercially available from +1.00 D to +4.00 D in gradient designs, while other designs ship a single universal defocus add with no selection at all.
The consequence for a fitter is that on a presbyopic fit the add is a starting value to be refined, and on a myopia control fit it is closer to a design property to be chosen among. What the printed LOW, MED and HIGH designations mean as labels is a separate question, answered on Low, Medium, and High Add of Multifocal Contact Lenses.
How do centre-distance and centre-near zones produce opposite peripheral defocus?
They put the plus power in opposite places. Centre-distance carries distance correction in the middle and plus outside it. Centre-near carries the full add in the middle and distance power outside it.
Berntsen and Kramer describe centre-near designs as full add power in the centre transitioning to distance power in the periphery, and note that this is the opposite of the power profile a peripheral-defocus design is built for. Centre-distance concentric ring designs, in their description, alternate rings of full distance and full near power and produce a peripheral myopic shift.
The direction is measurable, not theoretical. Hair, Steffensen and Berntsen (Optometry and Vision Science, 2021) compared four multifocal soft lenses — three centre-distance, one centre-near — and reported that the centre-distance designs caused myopic changes in defocus across the retina, varying by design, while the centre-near design caused peripheral hyperopic changes. The same study reported that the multifocal designs reduced low-contrast visual acuity by amounts that also varied by design.
Two things follow. The word “multifocal” on a box does not tell you the direction of the peripheral effect, and two centre-distance lenses with the same nominal add are not interchangeable, because the profile between the zones differs. That is why substituting one design for another is a refit, not a swap.
What are the three concentric zone geometries?
Frogozo groups the centre-distance soft designs into gradient, dual-focus and extended depth of focus, which differ in how the plus power is distributed across the optic zone.
| Geometry | How the plus power is distributed | Pupil dependence |
|---|---|---|
| Gradient (aspheric) | Distance in the middle of the optic zone, progressively increasing outward into the full near add | Theoretically pupil dependent — the full add is only reached at the optic zone periphery |
| Dual-focus (concentric ring) | A central annular distance zone with an adjacent annular add ring, then alternating annuli of distance and add | Full add reached independent of pupil size |
| Extended depth of focus (EDOF) | Central distance area, then peripheral defocus areas out to the edge of the optic zone; a continuous elongated focus rather than discrete focal points | Near add reached independent of pupil size |
Frogozo describes the trade in each direction. Discrete-focus designs can produce defocused light scatter, glare and halos; EDOF avoids that by having no discrete focal points, at the cost of some retinal image quality. Higher adds in any of them raise higher-order aberrations, which present as glare, halos and reduced contrast sensitivity — and where that degrades vision, she describes prescribing up to −0.50 D more minus in the distance zone to recover it. That is an over-refraction adjustment made on eye; verify it on the over-refraction calculator, not by re-converting the spectacle Rx.
Why can the phrase “add power” not be taken at face value here?
Because at least four different quantities are called an add, and only one of them is the optic on this page.
- The spectacle near add. The reading addition on a glasses prescription, which is a presbyopic refraction value at the spectacle plane. Add-by-age tables belong to that entity and have no corneal-plane conversion behind them. They are not this page and not this site.
- The contact lens ADD designation. The LOW, MED and HIGH bands a multifocal is ordered in, which are labels rather than dioptric values. Defined on Low, Medium, and High Add of Multifocal Contact Lenses.
- The starting multifocal add. The value a presbyopic fit begins with, derived from the spectacle add and refined on eye. Calculated on the Multifocal Contact Lens Calculator.
- The treatment add. The plus power a myopia control design carries outside its distance zone to place peripheral myopic defocus. That is the subject of this page.
One more collision is worth naming because it is not ophthalmic at all. A dual-focus lens in photography and in some spectacle catalogues is a different object entirely — a camera or spectacle lens with two focal regions, unrelated to peripheral retinal image shells. The dual-focus contact lens on this page is a concentric-ring soft lens design. If you arrived from a camera or spectacle context, this is not that entity.
What does the treatment optic change about the parameters you order?
Less than people expect on the power side, and more than people expect on the fit side.
The distance zone still needs a vertex-compensated sphere at the corneal plane, calculated the same way as for any soft lens on the Contact Lens Conversion Calculator. The treatment optic sits around that number rather than replacing it. What changes is that the design's zone sizes now matter: Frogozo notes that each myopia control design has its own optic zone sizes and power profiles, and that a lens sitting decentred on the eye does not deliver the profile it was designed to deliver. Centration is therefore part of the optic, not just part of the comfort assessment — check it at the slit lamp, as on contact lens fit assessment.
Base curve, diameter and zone size are fixed in most commercial designs. Frogozo notes that lathe-cut custom designs allow base curves, diameters and zone sizes for distance and add to be specified, which is the one place in this category where a fitter orders zone geometry directly rather than choosing a design that already has it.
Astigmatism is where the ordered set runs out. Most myopia control soft designs carry spherical distance powers only. Where a significant cylinder does not correct acceptably inside the chosen design, Frogozo describes considering a design that offers astigmatic correction, or spectacles over the lenses for the residual error. Starting toric parameters are calculated on the Toric Contact Lens Calculator, and the parameter-by-parameter comparison against a reshaping design is on Soft Multifocal or Corneal Reshaping: Comparing Lens Parameters.
What this page does not cover
The optics are here. The outcomes are not, and that is deliberate.
The sources cited on this page also report myopia progression and axial length results. Those figures are not reproduced here, and neither are candidacy criteria, starting ages, wearing schedules or review intervals. This site publishes lens optics and ordered parameters; how a treatment is chosen and followed for a particular child is clinical management, decided by a practitioner who has examined that eye.
Patient aside (Grade 8–9)
The extra power around the edge of these lenses is not a reading prescription. It changes where light lands on the outer part of the retina. It is part of the lens design, not a number your eye test produces. And none of that applies to a sore, red or light-sensitive eye: that lens comes out and the eye doctor is called the same day.
Read Starting Contact Lens Parameters Are Not a Prescription for the bound that applies across this site, and Myopia Control Contact Lenses: Optics and Ordered Parameters for the category this optic belongs to.
Sources
Clinical claims on this page are attributed to the publications below. Progression and axial length findings in these sources are deliberately not reproduced.
- David A. Berntsen and Charles E. Kramer, Peripheral Defocus with Spherical and Multifocal Soft Contact Lenses (Optometry and Vision Science, 2013) — measurement at ±20°, ±30° and ±40° along the horizontal meridian at distance and at a 3.33 D near demand; the spherical lens produced significantly more relative peripheral hyperopia than the centre-distance multifocal at multiple locations; centre-near designs carry full add in the centre transitioning to distance in the periphery; centre-distance concentric ring designs alternate rings of full distance and full near power; a contact lens delivers a peripheral profile 360° because it stays relatively centred with eye movements.
- Lea A. Hair, Elaine M. Steffensen and David A. Berntsen, The Effects of Center-Near and Center-Distance Multifocal Contact Lenses on Peripheral Defocus and Visual Acuity (Optometry and Vision Science, 2021) — three centre-distance and one centre-near design compared; centre-distance designs caused myopic changes in defocus that varied by design, the centre-near design caused peripheral hyperopic changes; low-contrast vision was reduced by amounts that varied by design.
- Melanie Frogozo, OD, Succeed with Soft Multifocals (Review of Cornea & Contact Lenses, February 2026) — gradient, dual-focus and EDOF geometries and their pupil dependence; commercially available adds +1.00 D to +4.00 D; lathe-cut designs allow customisable base curves, diameters and zone sizes; higher-order aberrations, glare, halos and reduced contrast sensitivity at high add, and up to −0.50 D more minus in the distance zone; each design has its own optic zone sizes and power profiles, and a decentred lens does not deliver the designed profile; astigmatism handling and over-spectacles.
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