What are mini-scleral lenses?

Size is measured against your own eye

Older systems classified lenses by a fixed diameter, and the cut-offs varied between sources. One older scheme, as summarized in a 2024 paper, called lenses of 15.0 to 18.0 mm mini-scleral and 18.1 to 24.0 mm full scleral.^[1] The problem is that eyes differ in size, so the same lens can reach much further onto the white of the eye in one person than in another.

The Scleral Lens Education Society’s nomenclature takes a different approach. A lens that rests entirely on the sclera (the white of the eye) is a scleral lens. Within that group, a mini-scleral lens is up to 6 mm larger than your horizontal visible iris diameter, which is the width of the colored part of your eye as seen from the front. That works out to no more than about 3 mm past the cornea on each side. A large scleral lens is more than 6 mm larger than that width.^[1] A 2025 review notes that the older size-only system is no longer recommended because it doesn’t account for differing eye sizes.^[2]

As a worked example (not a typical value): on an eye whose visible iris is 12 mm wide, a lens up to 18 mm across would count as mini-scleral, and anything wider as large.^[1]

The Society later adopted an official terminology guide, developed by a committee of experienced fitters, to standardize how these terms are used.^[3]

How mini and large scleral lenses differ

Both sizes vault over the cornea and hold a pool of saline against it. The differences are about trade-offs:

• Mini-scleral lenses can be made thinner, which helps oxygen reach the cornea, and their lower mass and smaller movement can make them easier to tolerate.^[4] They usually sit with less clearance over the cornea, and they are less affected by an uneven scleral shape. On the other side, small lenses can fit more tightly and can be harder to remove.^[4]
• Large scleral lenses are often preferred for steep cones, pellucid marginal degeneration, keratoglobus, and ocular surface disease. They can hold a deeper vault and spread their weight over more of the sclera, but they are heavier, more affected by gravity, and can be harder to apply.^[4]

One review suggests starting with the smallest lens that suits the eye’s iris size and limbus (the border between the cornea and the white of the eye), and moving to a larger lens only when problems arise.^[5]

What sizes people actually wear

In an international survey describing 419 eyes, the average scleral lens diameter was 16.2 mm, with a range of 11.8 to 23.0 mm.^[7]

A single large specialty practice in the Netherlands reviewed 27,430 scleral lenses ordered between 2016 and 2022. Mini-scleral designs made up 60.8% of them, and their share of orders rose from 44% in 2016 to 74% in 2022 for every indication except corneal transplant. The median diameter was 16 mm for mini-scleral designs and 20 mm for large ones.^[6] That reflects one practice’s fitting approach, not a rule.

Size also affects how a lens behaves through the day. In a small study of 22 keratoconus eyes, smaller-diameter lenses settled deeper into the tissue over 8 hours than larger ones.^[8] See what is scleral lens settling?

Where the label matters, and where it doesn’t

The word “mini” can sound like a lesser version. It isn’t. A mini-scleral lens is a full scleral lens sized to clear your cornea with less overhang. What matters more is whether the lens clears your cornea and limbus, lands evenly on your sclera, and gives you comfortable, stable vision.

If you’re comparing practices, ask what range of sizes and designs a fitter works with rather than whether they offer “mini” lenses. A fitter who can go larger when your eye needs it, or smaller when it doesn’t, has more room to solve problems. For what to expect at the fitting itself, see what a scleral lens fitting involves.