Why a soft lens struggles with an irregular cornea
A standard soft contact lens is thin and flexible. It drapes over the cornea, the clear front window of the eye, and largely takes on its shape. That’s what makes soft lenses comfortable and easy to wear, and it works well when the cornea is smooth and the prescription is regular.
It’s also why a soft lens struggles when the cornea isn’t smooth. If the cornea is cone-shaped, scarred, or uneven after surgery, a lens that follows its contours passes most of that unevenness straight through to your vision.
A scleral lens works the other way round. It’s rigid, so it holds its own precise shape. It rests on the white of the eye and arches over the cornea, and the space underneath is filled with sterile saline. The fluid fills in the cornea’s bumps, and the smooth front of the lens becomes the surface you see through.
Specialty soft lenses for irregular corneas
Between a standard soft lens and a rigid one sits a group of specialty soft lenses designed for keratoconus and other irregular corneas. They are custom-made and usually thicker in the center, so they drape less and mask more irregularity, while keeping much of the comfort of a soft lens.
The evidence for them is encouraging but small:
- KeraSoft IC. A 12-month prospective study enrolled 43 adults with irregular corneas. High-contrast vision improved significantly from baseline, though low-contrast vision did not. Two minor adverse events were reported among 84 enrolled eyes, and wearers reported better comfort and vision than with their previous correction. The study was not compared against rigid or scleral lenses.[2]
- A custom soft lens for people who couldn’t tolerate rigid lenses. A Japanese retrospective study followed 20 people (36 eyes) with keratoconus who had given up rigid lenses. Seventeen (85%) were still wearing the soft lens. Of the three who stopped, two were unhappy with their vision and one had trouble handling the lens. No serious complications were reported.[3]
- Toric soft lenses compared with rigid lenses. In a study of 22 people with keratoconus, toric soft lenses reduced some of the eye’s optical distortion, but the patients’ habitual rigid lenses gave better low-contrast vision. High-contrast vision wasn’t significantly different.[1]
Some fitters also use piggyback wear, where a soft lens sits under a corneal rigid lens to cushion it.
Side by side
| Standard soft lens | Specialty soft lens | Scleral lens | |
|---|---|---|---|
| Rests on | The cornea, extending just past its edge | The cornea, extending just past its edge | The white of the eye (sclera), over the conjunctiva |
| Touches the cornea | Yes | Yes | No. It vaults the cornea over a layer of saline |
| Irregular corneas | Masks very little irregularity | Can help mild to moderate irregularity | Works across a wide range, including severe irregularity |
| Dry eye | Relies on your own tears | Relies on your own tears | Keeps the cornea bathed in saline while worn |
| Comfort | Comfortable for most healthy eyes | Often comfortable. Studied in people who can’t tolerate rigid lenses | Often comfortable, especially on a damaged eye surface |
| Handling | Familiar and simple | Similar to a standard soft lens | Larger, filled with saline, usually inserted with a plunger |
| Cost drivers | Stock lenses, routine replacement | Custom design, refits, replacement schedule | Fully custom design, more chair time, often more than one lens ordered, saline and care products |
| Who it suits | Regular prescriptions on a healthy cornea | Mild to moderate irregularity, or people who can’t tolerate rigid lenses | Moderate to severe irregularity, or eyes that need surface protection |
When scleral lenses make more sense
Moderate to severe corneal irregularity. That’s what scleral lenses are mostly used for. In a 2020 survey of fitters, a median of 84% of the scleral lenses they fitted were for corneal irregularity, 10% for eye surface disease, and 2% for an uncomplicated prescription.[5] An international survey of individual patients found a similar pattern: 87%, 9%, and 4%.[8]
A damaged or very dry eye surface. A soft lens sits on your tears. A scleral lens holds a pool of saline against the cornea for as long as it’s worn. A specialist referral center reviewed its patients with eye surface disease. Of the 115 who completed a scleral fitting, treatment goals such as better comfort, protecting the surface, or healing of the cornea were met in all but 2. Patients in the series had tried an average of 3.2 other treatments first.[6] Scleral lenses usually aren’t the first step for surface disease. In a survey of scleral fitters, lubricant drops were the most common first treatment, with scleral lenses considered after drops, gland treatments, prescription anti-inflammatory drops, and plugs.[7]
When a regular prescription is the only issue, scleral lenses are rarely the answer. In a one-year study of 95 scleral wearers, 77% of those with irregular corneas were still wearing their lenses at 12 months, compared with 58% of those with regular corneas.[4]
Questions to ask your fitter
- Is my irregularity mild enough that a specialty soft lens might work?
- If I can’t tolerate rigid lenses, which soft options would you try first?
- What vision can I realistically expect in a soft lens compared with a scleral lens?
- If my eye surface is dry or damaged, what should we try before or alongside lenses?
Common questions
Can a soft contact lens correct keratoconus?
A standard soft lens usually can't correct much of the irregular distortion, because it takes on the shape of the cornea underneath. Specialty soft lenses made for keratoconus are thicker and custom-designed, and small studies show good results for some people, particularly with milder disease or intolerance of rigid lenses.
Are scleral lenses more comfortable than soft lenses?
Not as a rule. Soft lenses are comfortable for most people with healthy eyes. Scleral lenses are often more comfortable than soft lenses for people with a damaged or very dry eye surface, because the cornea stays covered in saline. Comfort is individual, so it's worth trying.
Could I wear scleral lenses just for a normal prescription?
Some people do, but it's uncommon. Most scleral lenses are prescribed for irregular corneas or eye surface disease. In a one-year study, success rates were lower in people with regular corneas than in people with irregular ones.
What is piggyback lens wear?
It's a technique where a soft lens is worn under a corneal rigid lens, to cushion the rigid lens on the cornea. Some fitters use it when a rigid lens alone is uncomfortable. Ask your fitter whether it suits your eye.