What a piggyback system is
A piggyback system is two contact lenses on the same eye: a soft lens sits on the cornea, and a small rigid gas permeable (RGP) lens sits on top of it. The rigid lens gives a smooth focusing surface over an irregular cornea, just as a rigid lens alone would. The soft lens underneath acts as a cushion.
In a study of 29 eyes of 16 people with keratoconus who couldn’t wear rigid lenses, the reasons for using a piggyback system were to stabilize the rigid lens, to improve comfort, and to protect the cone from the rigid lens rubbing on it.[1]
A scleral lens solves the same problem differently. It’s one large rigid lens that rests on the white of the eye and vaults over the cornea, with a layer of saline between the lens and the cornea. Nothing rests on the cone at all.
Side by side
| Piggyback (rigid on soft)[1][4] | Scleral lens[9] | |
|---|---|---|
| What it is | Two lenses: a soft lens with a small rigid lens on top | One large rigid lens |
| Rests on | The cornea, cushioned by the soft lens | The white of the eye (sclera) |
| Touches the cornea | Yes, through the soft lens | No. Vaults over it with saline |
| Vision | Similar to a rigid lens alone, sometimes better because the lens centers more steadily | Usually sharp, even in advanced keratoconus |
| Comfort | Better than a rigid lens alone for many people | Often comfortable once fitted |
| Oxygen to the cornea | Reduced by stacking two lenses. High-oxygen materials help | Passes through one lens and the saline layer under it |
| Handling | Two lenses per eye, often with two care systems | One lens per eye, but larger and needs filling with saline |
| Fitting | Uses standard soft and rigid lens designs | Custom lens, often several visits |
| Who it suits | People who see well in rigid lenses but find them uncomfortable or unstable | People who need sharp vision and can’t tolerate lenses on the cornea, including advanced cases |
What the research on piggyback lenses shows
The evidence is a handful of small studies, mostly older, all in keratoconus.
- Vision and comfort. In the 29-eye study above, vision was significantly better than in glasses for every patient. Compared with rigid lenses alone, vision improved in 89.7% of eyes and was unchanged in the rest. Most people wore the piggyback system for a limited time (on average 6 months) and then tolerated the rigid lens alone, except two patients.[1]
- Longer-term use. A US clinic reviewed the charts of 205 people with keratoconus and found 16 wearing piggyback systems. Their vision and wearing time were stable or better compared with when they wore rigid lenses alone. Two developed new blood vessels growing into the cornea and one developed giant papillary conjunctivitis, an allergic-type reaction under the eyelid. Corneal problems present before piggyback wear all resolved.[2]
- People who couldn’t wear rigid lenses. In a Japanese study of 11 people with keratoconus who couldn’t wear hard lenses because of pain or poor fit, 10 were successfully treated with a piggyback system. One needed a corneal transplant.[3]
- Compared with a hybrid lens. A small study of 30 eyes compared piggyback lenses with a hybrid lens over six months and found no difference in markers of surface inflammation or cell changes.[6]
The oxygen question
Stacking two lenses means less oxygen reaches the cornea. A lab study measured the oxygen level under several soft-plus-rigid combinations on normal eyes and found it was between 6.9% and 11.2%, expressed as the equivalent percentage of oxygen in the air. Among the 10 patients the same clinic followed after dispensing, none showed signs of corneal swelling.[4] Another lab study found that combining the highest-oxygen soft and rigid materials gave the smallest increase in the cornea’s oxygen demand, and that blinking made no measurable difference to the cornea’s oxygen supply under piggyback systems.[5] That’s why the choice of materials matters so much for a piggyback fit.
How common each one is
Piggyback systems are a niche option. At one US academic eye clinic, the lenses prescribed to people with keratoconus in 2020 were 60% corneal rigid lenses, 22% scleral lenses, 12% soft toric lenses, 5% hybrid lenses and 1% soft spherical lenses. Piggyback systems weren’t listed as a category. The people wearing scleral lenses had the steepest, most advanced corneas.[8]
Piggyback systems can also involve a scleral lens. In one case report, a child who couldn’t tolerate a scleral lens wore a soft lens, then a soft lens under a scleral lens, and eventually a scleral lens alone.[7]
What scleral lenses offer, and where they fall short
A scleral lens avoids the two biggest drawbacks of a piggyback system: there’s only one lens per eye, and nothing presses on the cone. In a study of 157 keratoconic eyes, average corrected vision improved from 0.50 logMAR in glasses (about 20/63) to 0.08 logMAR in scleral lenses (about 20/24).[9]
Questions to ask your fitter
- Do I see well in a rigid lens alone? Is comfort the main problem, or vision?
- Would a piggyback system let me keep using lenses I already know how to handle?
- What materials would you use, and how much oxygen will my cornea get?
- How would cleaning work with two different lenses?
- If piggyback doesn’t work, what’s the next step: a hybrid lens, a scleral lens, or something else?
See also scleral vs RGP lenses, scleral vs hybrid lenses, and our keratoconus page.
Common questions
Is a piggyback lens the same as a hybrid lens?
No. A hybrid lens is a single lens with a rigid center and a soft skirt bonded together. A piggyback system is two separate lenses, a soft one with a rigid one on top. A small study comparing the two in keratoconus found similar effects on the eye's surface over six months.
Do I need two cleaning systems for piggyback lenses?
Usually you're caring for two different lens types, and soft and rigid lenses often use different solutions. Your fitter will tell you exactly which products to use for each lens.
Can a piggyback system be a step toward scleral lenses?
Sometimes. One case report describes a child who moved from a soft lens to a soft-plus-scleral piggyback system and then to a scleral lens alone. It's a single case, so ask your fitter whether that kind of step-by-step approach makes sense for you.
Is piggyback wear temporary?
It can be. In one study, most people wore the piggyback system for a few months and were then able to wear the rigid lens alone. Others wear piggyback systems for years.