Figure 3. Cataract had significantly progressed in the left eye.
Piggyback contact lens systems have, to a great extent, been superseded by modern technology. However, Jessica Chi writes, for some complex patients they still have their place.
In the February 2024 edition of mipatient, I detailed the case of Ray Henson,* a then 60-year-old male with keratoconus and markedly elevated blood glucose of 28 mmol/L and consequent diabetic retinopathy.1 He subsequently developed bilateral cataracts, more advanced in the right eye. He was hospitalised until glycaemic control was achieved, then proceeded to have right cataract surgery, unfortunately complicated by cystoid macular oedema (CMO). Despite sustained glycaemic control, both his diabetic retinopathy and CMO persisted.
When we left Mr Henson, his left cataract had progressed, reducing his contact lens acuity to L 6/18. Although aware that surgery might improve his vision, he was unwilling to risk CMO in his remaining functional eye. Living close to work in inner-urban Melbourne, he had elected to cease driving and was managing adequately with his vision as it was.
Nearly three years on, despite continued tight glycaemic control and regular anti-VEGF injections (Eylea or Vabysmo) every six to seven weeks, diabetic retinopathy persisted in both eyes with ongoing right CMO (Figures 1 and 2).
Figures 1 and 2. Persistent diabetic retinopathy in both eyes with ongoing cystoid macular oedema in the right eye, despite tight glycaemic control and regular anti-VEGF injections.
An epiretinal membrane had also developed in the right eye, appearing to contribute to his recalcitrant oedema. His right eye vision had declined to 6/60, improving only to 6/38 with pinhole. Contact lenses offered no further improvement in vision. The left cataract had progressed significantly (Figure 3, above), with contact lens acuity now also reduced to 6/38=, although an over-refraction of L –1.50 DS improved this to L 6/24+.
Mr Henson was struggling with his current level of vision. At the time of publishing, he and his retinal surgeon had agreed to await stability in the right eye before proceeding with left cataract surgery, and Mr Henson was two months into a three-month course of monthly Eylea injections. Should the response prove insufficient, the plan was to perform vitrectomy with epiretinal membrane peeling and ongoing intravitreal therapy.
Mr Henson was hoping to proceed with cataract surgery within weeks. As he was essentially monocular, the over-refraction represented a useful gain in functional vision – however, given that, cataract surgery would alter his refraction and likely render a new rigid gas permeable (RGP) lens redundant. Instead, a daily disposable silicone hydrogel lens of –6.00 DS was prescribed as a piggyback system to be used with his existing RGP. With this combination, his over-refraction was plano and he achieved a contact lens acuity of 6/24 – a practical and cost-effective interim solution while he awaited surgical intervention.
Piggyback Contact Lens Systems
Traditionally, piggyback contact lens systems – in which a soft lens is worn beneath a rigid gas-permeable (RGP) lens – represented a useful addition to the contact lens practitioner’s toolkit. For patients who struggled to tolerate RGP lenses, yet required them for the superior visual correction they afford in cases of corneal irregularity or high ametropia, the soft lens acted as a cushioning intermediary, improving comfort without compromising vision.
Today, however, piggyback fitting is far less common. The development of modern hybrid and scleral lens designs has largely superseded this approach, offering comparable – and in most cases superior – comfort alongside the convenience of only requiring a single lens per eye.
Handling
Piggyback systems are not often enjoyed by patients. Those who are visually compromised without correction face particular challenges, as soft lenses are larger and flimsier than RGPs and therefore more difficult to insert and remove. In addition, the soft carrier typically contributes minimal power to the overall system, making it difficult for the patient to confirm the lens is correctly positioned – or indeed present at all. It is not uncommon for patients to be uncertain whether they have successfully removed the soft lens, inadvertently resulting in unintentional extended wear.
It is also important to emphasise that the correct wearing order is critical: the soft lens must always be inserted first, with the RGP placed on top. Wearing the RGP beneath the soft lens risks the rigid lens rubbing or binding.
Oxygen Transmissibility
The layering of two lenses inevitably restricts corneal oxygen supply, and this remains an important clinical consideration. Fortunately, there are now many high-Dk materials available in both silicone hydrogel and rigid lens materials, providing adequate oxygen transmissibility for safe open-eye wear.
Solution Compatibility
Rigid lens solutions are not compatible with soft lens materials and must be thoroughly rinsed from the RGP before it is placed over the soft lens. In practice, simplifying to a single soft lens storage solution for both lenses – where a reusable soft lens is used – is often the more pragmatic approach. More convenient still is the use of a daily disposable – of which there are now many silicone hydrogel options with high oxygen transmissibility.
Power Calculation
And then there is the question of the overall power of the system – are the two lens powers additive? Due to the interaction between the lens surfaces in a piggyback system, the soft lens contributes only approximately 20–23% of its power to the overall correction of the system.2 For example, a –1.00 D soft lens will contribute approximately –0.25 D to the overall system. Where the RGP alone provides the correct prescription, a low-powered soft carrier will have little effect on the overall power of the system. However, where a more significantly powered soft lens is used, careful selection is required to achieve the desired outcome. In Mr Henson’s case, we took advantage of this relationship, selecting a soft lens of sufficient power to meaningfully modify the overall system correction.
Soft Lens Fit
The soft lens can also influence the fit of the overlying RGP. Plus-powered lenses are convex in shape; they steepen the anterior surface on which the RGP rests, and can improve centration and stability in low cones. This would have been useful for Mr Henson; however, it would have increased his under-correction rather than resolving it.
Minus-powered lenses present a flatter front surface for the RGP to rest on, which may be advantageous in smoothing out an irregular corneal surface. This can be particularly useful in oblate corneas, such as those seen following refractive surgery. For a low, inferiorly sagging cone such as Mr Henson’s, however, this can encourage inferior decentration of the RGP, which was indeed observed in his case. Fortunately, centration remained adequate for the interim, and the improvement in acuity was of far greater significance to this patient than the decentration.
A further consideration in irregular corneas is that the soft lens may simply not fit. In cases of advanced ectasia, tilted or proud grafts, the soft lens may fail to drape adequately over the ocular surface, resulting in the soft lens fluting. This can cause discomfort and instability of both lenses, and may increase the risk of localised hypoxia, inflammation, and infection. If piggybacking is the desired modality, custom made-to-order soft contact lenses can be prescribed. Fortunately, Mr Henson’s keratoconus was not so advanced that standard soft contact lenses did not fit.
Mr Henson’s case serves as a practical reminder that piggyback systems, while no longer a first-line modality, retain a place in the contact lens practitioner’s toolkit – particularly as an interim measure. The ability to modify both the power and the fit of the overall system through a soft lens worn with a rigid lens can help to increase comfort, stability, and vision.
The ability to modify both the power and the fit of the overall system through a soft lens worn with a rigid lens can help to increase comfort, stability, and vision.
Addendum
Another application of a ‘piggyback’ system, or rather a ‘reverse-piggyback’ system is during scleral lens fitting. During scleral lens fitting, practitioners may often send patients away to allow lenses to settle for a period of time. If the patient has a prescription significantly different to that of the fitting lens, this may cause visual discomfort and asthenopia. A nifty little trick is once the over-refraction is performed, a soft contact lens with this power (vertex-corrected) can be placed over the scleral lens to allow the patient to see. In this scenario, the maths is far simpler – the powers of the scleral lens and the soft contact lens are simply additive.
*Patient name changed for anonymity.
References
- Chi J, Pondering the Imponderable, mivision. 2024;197:79-80. Available at: mivision.com.au/2024/02/pondering-the-imponderable [accessed July 2026].
- Woo M, Weissman BA. Effective optics of piggyback soft contact lenses. Contact Lens Spectrum. 2011;26(11):50-2.
