This article considers the options for the long-term management of keratoconus by discussing when it may be appropriate for patients currently wearing contact lenses to consider alternative treatment interventions.
Keratoconus – then and now
Keratoconus presents many challenges for contact lens practitioners. The condition is usually satisfactorily managed with contact lenses but an in-depth knowledge of the treatment options beyond this and the potential impact on a patient are also crucial for practitioners to understand.
Keratoconus management in the UK is largely carried out in the outpatient hospital environment, but an increasing contribution is being made by community optometry, which does not have the same access to ophthalmology support. Up to the late 1970’s, there were a small number of specialist contact lens clinics, mostly confined to major city centres. Only a small percentage of the workload seemed to be keratoconus cases with a higher representation by aphakic or high, but uncomplicated myopia. Judging by the increased caseload, there seems to have been a huge proliferation of keratoconus presenting in our clinics, and along with it, many more practitioners willing to take on this work. Contact lens materials and clinical skills improved rapidly in the early 1980’s, as did the prospect of better surgical outcomes. The same period saw a massive increase in public awareness and expectation. While there are still relatively few keratoconic patients in an older age group, the average age does now seem to be increasing. Therefore, the longer term considerations and managing an ageing keratoconic population are increasingly important.
Onset of keratoconus is typically in the late teenage years or early twenties, just when most people are building careers and relationships. These aspirations can be severely hindered by a debilitating visual disability of comparatively rapid onset and can have a devastating impact in severe cases (see Figure 1: Advanced keratoconus corneal profile. The cone base is small and downwardly decentred. A depression is clearly seen just above the visual axis, giving rise to a highly irregular surface and consequently very poor and distorted vision with no improvement possible with spectacles). It is not an easy condition to understand, and most keratoconics spend a lifetime explaining to family, friends and work colleagues why they cannot wear glasses or have laser surgery. Some clearly do not appreciate the problem themselves as is evident by the same questions asked in our clinics many years after diagnosis. High expectations from keratoconic patients should not come as a surprise, and it must be very frustrating if they are not met, in spite of the best efforts from the clinicians to deliver a solution.
Contact lenses or surgery?
Successful contact lens wear is an immediate, non-invasive and generally a lasting functional solution. However, the keratoconus patient group frequently attend appointments equipped with information from the internet and other sources and are not slow to ask if they are suitable for a surgical alternative. Most of these questions relate to collagen cross-linking (CXL), intra-corneal ring segments (ICRS) or keratoplasty. Unfortunately, much of the information sourced by patients can be misleading, so a crucial part of the keratoconus management process is to rectify misconceptions. Surgery in general is sometimes presented and perceived as a quick fix but in fact is not always straightforward. Despite potential problems being discussed in advance of treatment, a post- surgical conversation along the lines of ‘I didn’t appreciate such and such could happen after the surgery’ is not uncommon.
There is evidence that timely CXL slows the progression of 1,2 keratoconus. The principal objective of this treatment approach is to stabilise the condition.3 However, it seems that the topography is regularised in some cases and may give an improvement in vision under some circumstances. There are also advocates of simultaneously carrying out other procedures to modify the topography in conjunction with CXL.4
In essence, riboflavin activated by bombardment with UV light stiffens the stroma. As a result, some stromal fibrils change their orientation from transverse to longitudinal, hence the term cross-linking. It has been likened to an acceleration of the corneal ageing process during which the progression appears to slow naturally. The epithelium is impervious to riboflavin, so is usually debrided preceding a slow application of riboflavin into the stroma. There are studies currently being carried out to see if there are ways to avoid removing the epithelium.5,6 The two methods are referred to as ‘epi-on’ and ‘epi- off’. The current evidence base is incomplete, but for now ‘epi-off’ remains the mainstream option.
The patient may well be wearing contact lenses before CXL is discussed. Regular topographic assessment and pachymetry have become a crucial part for the continuing management of keratoconic patients so that an appropriate referral for CXL assessment can be carried out.3
It is important to consider for how long contact lens wear should be avoided both prior to assessment of progression, and also following CXL treatment. Some CXL centres ask for RGP lenses not to be worn for two weeks, and soft lenses for one week prior to each topographical assessment. A period without lenses of two to three weeks after the procedure is also usually advised to allow regeneration of the epithelium. Some centres recommend up to three months, which represents a long and disruptive time for a patient not to be able see well during this period. Even two weeks prior to the on-going assessments can be a difficult request for many patients to comply with.
Appropriate timing for CXL
One school of thought is that the first presentation of keratoconus proves progression is evident; therefore, immediate CXL is advisable across the board. Another view is that progression does not always happen, so it is preferable to see visible signs of progression by monitoring the patient at the clinic (see Figure 2: Consectutive Pentacam plots of keratoconic cornea seperated by an eight-month period. The most recent plot, furthest to the left, indicates an enlargement of the steepest region of the cornea. The difference between the two is plotted graphically in the third image, furthest right. The numerical details on Pentacam images are too small to be visible here, but the tangential and sagittal radii are both significantly steeper, by 0.21mm and 0.26mm respectively, and the Kmax reading has increased by 3.30D to 60D. Also, and most critically, the corneal thickness at the apex has reduced . These are clear signs of progression, indicating CXL should be offered without too much delay. Image courtesy of Dr Vijay Anand, Moorfields Eye Hospital, London). There is a minimum corneal thickness less than which renders CXL too risky and unpredictable: the current thinking is that the cornea should be no less than 375μm at its thinnest point. One reason for this cut off point is that there is an increased risk of irreversible endothelial cell damage as there would be greater exposure to the UV radiation administered during the procedure. Awareness of the implications of timing for CXL is crucial to the practitioner as there is a clearly defined window of opportunity in which the procedure can be carried out. The patient may also find it disconcerting that a decision must be made fairly urgently as there is limited opportunity to reduce the chance of progression.
Intra-corneal ring segments
Some surgical centres have shown visual benefit and successful outcome with the use of intra- corneal ring segments (ICRS) in mild to moderate keratoconus.7,8 Minute semi-circular PMMA rings are slid into a groove cut into the stroma (see Figure 3: ICRSs inserted into the corneal storma after a protracted intolerance to RGP corneal lenses. Some recipients report an improvement, maybe in unaided vision if intolerant to contact lenses. This was one of the relatively unusual examples seen in a contact lens clinic. Use of the ICRS did not make much difference in this case and a scleral lens was fitted, hence the small bubble at the lower limbus). INTACs, KeraRings and Ferrara Rings are three in common use. The designs are different so one may perform better than the others, but the clinician’s preference seems to be as important a factor as anything else. The objective is to create a bulging of the cornea in the mid- periphery thereby flattening the corneal profile. As with CXL, the practitioner should be aware that a minimum corneal thickness is a pre-requisite as it is not possible to insert the rings if the cornea is less than 450μm at the site of insertion, ie at the perimeter of a circle 6mm in diameter.9
ICRSs are not very often seen in keratoconus contact lens clinics. The irregular front surface is not entirely eradicated; so successful contact lens wearers would probably not achieve a comparable level of vision with ICRS as an alternative. Therefore, they are unlikely to opt for the procedure, and there does not seem to be much to be gained by encouraging such a move.
If contact lenses are not giving a good enough result, either in terms of the visual improvement or contact lens tolerance, the patient may well seek alternative advice or investigate ICRS of their own volition.
Ophthalmology opinion regarding the outcome is mixed, but some patients report some improvement, more often in unaided vision than best-corrected acuity. Others report little or no gain. Most that are seen in the author’s contact lens clinics seem to make little difference and are left in situ. If unsuccessful, the next recommendation is likely to be a keratoplasty, so a return to the contact lens clinic may not happen.
Early and moderate stage keratoconus is usually well managed with contact lenses. However, if they do not provide either satisfactory vision, become too unstable for topographical reasons, or are simply not well tolerated, a keratoplasty is the only remaining way to restore vision.
Keratoplasty is a major undertaking and potentially life changing for the patient. Provided there is not excessive attendant atopic co-pathology, keratoconus indicated keratoplasty is relatively low risk. Contact lenses are also not free from complications and problems: serious contact lens associated infections can have sight-threatening implications, but wearers can exercise some control and minimise the risks. A vascularised cornea, possible as a complication of contact lens wear, could also increase the risk of rejection of a future keratoplasty.
In the later stages, when a keratoplasty is under consideration, best contact lens vision may be functional but often deteriorating as the condition continues to progress. There is a prospect of a significant improvement following a successful operation, but requires a decision to walk away from contact lenses and opting for an irreversible surgical intervention. Therefore, the process has to be sensitively dealt with after consideration of all the relevant risk/benefit factors.
Penetrating or deep anterior lamella keratopasty?
Deep anterior lamella keratoplasty (DALK) is becoming increasingly offered as an alternative to a penetrating keratoplasty (PKP).9 For a DALK, the minimum possible amount of stroma, Descemet’s membrane, and the endothelium from the host are left in place. There may be a reduced acuity if there are any residual opacities at the donor/endothelium interface, but the minimal endothelial cell loss and virtual elimination of endothelial rejection or failure represents a significant potential advantage for DALK over PKP.
Contact lenses or a graft?
A plethora of information is readily available on the Internet for keratoconic patients but reliable is intermingled with questionable. Robust information is also in the public domain for anyone who wishes to access it, but presented in a more complex format and reiteration may be required at future consultations. Conversations with patients suggest that contact lenses or a keratoplasty is sometimes presented as a choice between the two. A choice at some stage may be to abandon contact lenses and decide on an irreversible surgical intervention, but choosing a keratoplasty without investigating contact lenses beforehand is no choice at all. That is not to say keratoplasty should only be offered as a last resort, but that it is a valid discussion when it is clear there is a reasonable chance of significant improvement on the balance of probabilities. While there can be no guarantee of a successful or complication free outcome from a keratoplasty, an appropriate perspective for the practitioner is to emphasise that the chance of a good result massively exceeds the chance of a bad one. There are some patients regularly attending contact lens clinics with PKPs carried out over 40 years ago: the longest surviving example seen by the author still providing a functional level of vision is currently 54 years and may never need to be replaced in the patient’s expected lifetime. It is also worth pointing out that surgical techniques improve over time, so the outcomes with more recently performed PKPs are likely to be better.
About the author
Ken Pullum FCOptom, DCLP, is an experienced optometrist with a special interest in complex contact lens fitting. He holds posts at Moorfields Eye Hospital, Oxford Eye Hospital and Queen's Hospital, Romford, in addition to his private contact lens practice in Hertfordshire.
- Wittig-Silva C, Chan E, Islam FM, et al. A randomized, controlled trial of corneal collagen cross-linking in progressive keratoconus. Ophthalmology 2014;1–10. doi:10.1016/j.ophtha.2013.10.028
- O’Brart DPS, Chan E, Samaras K, et al. A randomised, prospective study to investigate the efficacy of riboflavin/ultraviolet A (370 nm) corneal collagen cross-linkage to halt the progression of keratoconus. Br J Ophthalmol 2011;95:1519–24. doi:10.1136/bjo.2010.196493
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- Kanellopoulos J. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg Thorofare NJ 1995 2009;25:S812–8. doi:10.3928/1081597X-20090813-10
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- Soeters N, Wisse RPL, Godefrooij DA, et al. Transepithelial versus epithelium-off corneal cross-linking for the treatment of progressive keratoconus: A randomized controlled trial. Am J Ophthalmol 2015;159:821–8.e3. doi:10.1016/j.ajo.2015.02.005
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- Coskunseven E, Kymionis GD, Tsiklis NS, et al. One-year results of intrastromal corneal ring segment implantation (KeraRing) using femtosecond laser in patients with keratoconus. Am J Ophthalmol 2008;145:775–9. doi:10.1016/j.ajo.2007.12.022
- Kasbekar SA et al. Corneal transplant surgery for keratoconus and the effect of surgeon experience on deep anterior lamellar keratoplasty outcomes. Am J Ophthalmol 2014;158:1239-1246