At the completion of this article, the reader should be able to improve keratoconus management. Including:
- Understand the risk factors and symptoms for keratoconus
- Know how new technologies have improved keratoconus patient outcomes
- Understand the rationale behind updated keratoconus referral protocols
- Know the elements vital for an informed keratoconus referral
Many ideas about keratoconus are changing. As DR BRENDAN CRONIN points out, there are new diagnosis and therapeutic technologies available, prompting changes in the optometrist’s role. Increasingly, keratoconus patients will rely on informed optometrists to notice and act on their symptoms early to ensure the best outcomes.
Dr Brendan Cronin
MBBS (Hons) DipOphthSci B.Com LLB FRANZCO
Queensland Eye Clinic, South Brisbane, QLD
Queensland Eye Clinic, Clayfield, QLD
What is keratoconus?
Our diagnosis, understanding and treatment of keratoconus over a number of years. Improved diagnostics have enabled earlier detection and better estimates of the prevalence of keratoconus in the community. A better understanding of the pathophysiology of the disease has also led to a greater range of more effective treatments to alter its natural history.
Traditionally, in the Australian population, the rate of keratoconus was thought to have been around 1 in 2,000. More recent studies using corneal tomography and topography have demonstrated rates of keratoconus to be up to 1.2% of the population – or 1 in 84 people1; this takes the condition from being one that was considered to be quite rare and not hugely relevant from a public health perspective to being one that is quite common.
Given the significant lifelong visual complications associated with keratoconus, there is an enormous public health benefit in early diagnosis and treatment. This requires a thorough understanding of the condition and excellent communication and collaboration between optometrists and ophthalmologists for ongoing patient care.
Keratoconus has traditionally been described as a non-inflammatory condition however, it is now widely accepted that it is an inflammatory disease.2 We understand that allergic eye disease and in particular, eye rubbing, is a very significant risk factor and can significantly exacerbate the condition. A family history of keratoconus is also one of the other major risk factors.3
Importantly, even subclinical keratoconus is a risk factor for offspring developing the disease. Given the documented high prevalence of the condition in the population, diagnosing even asymptomatic keratoconus in older patients has a significant public health benefit in that it will facilitate screening of other members of the family.
Identification and diagnosis of the condition
The hallmark symptoms of keratoconus along with the other corneal ectatic disorders are reduced visual acuity and increased sensitivity to light and glare, particularly flaring of lights at night.
Optometrists have always been very well-positioned and particularly adept at identifying patients with these presenting symptoms along with a reduced best corrected spectacle acuity, particularly in the setting of increasing astigmatism, and identifying this as likely keratoconus. Clinical tricks such as the scissor reflex or the Charleaux/oil droplet sign on retinoscopy can be diagnostic of the condition.
In recent years more highly advanced diagnostic equipment has become much more commonplace in optometric practices. Even fairly basic equipment such as autorefractors can be beneficial in diagnosing the condition when patients still have a good best corrected visual acuity due to the presence of distorted mires on autorefraction machines (Figure 1). Obviously if there is a history of allergic eye disease, eye rubbing or a family history of keratoconus, this makes the index of suspicion that much higher, even in patients presenting with good vision.
The availability and reduced cost of topographers has been a game-changing development for the early diagnosis of keratoconus. Cheap but effective placido disc-based topographers are commonplace in optometric practices. As a result, a definitive diagnosis of keratoconus can be made in a primary care setting very early on in the disease. These days, many optometry practices also have tomography which can further document keratoconus by looking at the posterior elevations in corneal topography and also the characteristic corneal thinning that occurs in the disease.
Additionally, Some OCT machines now perform not only retinal OCT but also OCT-based topography, making this once very specialised and expensive diagnostic tool more readily available.
Referral patterns
Prior to the development of corneal cross-linking, referral to an ophthalmologist for a patient with keratoconus was only advantageous to either confirm the diagnosis or to offer surgery for visual rehabilitation of a patient intolerant of contact lenses. Because there are a range of treatments now available, referral patterns need to change accordingly. A delayed referral may have a profound difference in the long-term outcome for a patient and the treatments available to them.
Children
It is critical that children with a suspicion, or confirmed diagnosis, of keratoconus are referred urgently for review. Typically, the younger a patient is at presentation, the more aggressive the disease. In adolescence and young teenagers their best corrected acuity can plummet over a matter of weeks to a few months.4
While there are regional and interpersonal differences in what clinicians qualify as progression, the threshold for what is considered to be progression is generally considered to be significantly lower in patients who are younger. For example: if a patient has ever had an objective documentation of normal visual acuity and then presents with reduced visual acuity and documented keratoconus, many clinicians would argue this is an adequate indication of progression.
In short, optometrists should not wait to document any type of refractive visual or topographic progression in children or adolescents with the condition. Referral should be made immediately on suspicion of the disease. The referring optometrist should include any previous visual acuity with the referral. It is also vital to stop any eye rubbing and manage any allergic eye disease immediately in these young patients.
Adults
In adults, particularly those in their mid 20s and over, the requirement for referral can be divided into two broad groups. In the first group: those with a new diagnosis of keratoconus. These patients should all be referred for an opinion on treatments to halt the progression of the disease. In these cases, however, some type of objective documentation of their visual history is important. It is advantageous if referrals can include documentation of any refractive or topographic change over a period of time as this is required by Medicare to justify cross-linking.
In the second group are the large number of patients who will have stable keratoconus either due to their age or those who have potentially had cross-linking. If these patients have good visual acuity either in glasses or well-fitting contact lenses, there really is little need for them to be referred for ophthalmic assessment. If, however, they have any reduction in their visual acuity or quality-of-life due to issues with wearing contact lenses, the availability of new treatments makes referral of these patients appropriate in the absence of progression of the disease.
Co-management
Optometrists are crucial to the public health campaign to avoid both habitual and allergy-related eye rubbing in adolescence to help reduce the incidence and progression of keratoconus. This applies to all patients who have any allergic eye disease but this is especially important for patients with keratoconus.
Typically, once a patient has been cross-linked, it will be their optometrist who follows them up annually for ongoing contact lenses or spectacles, so it is imperative that ocular allergies are being managed adequately on a long term basis. Diagnosing the condition in family members is another critical role in the primary care optometry setting to reduce the burden of disease.
Patients can still progress despite corneal cross-linking. Severe or rapid progression is quite rare but it is important to understand that, particularly in adolescents, there is a peak in the risk of progression around seven years after their initial collagen cross-linking procedure is performed. The reason for this is not entirely well understood but this is an important point to be aware of in the co-management of the condition.
As optometrists will often be the person primarily responsible for the visual rehabilitation of the patient, either with glasses or contact lenses, they are very well positioned to monitor patients for progression of their disease and to recommend further treatment options that may be available.
New technologies
It isn’t just the early diagnosis of keratoconus that has altered the course of the disease for many patients. New technologies exist both in the optometric and ophthalmic spheres to ensure people with keratoconus do not have to struggle with poor quality vision. These days, it is actually very rare for a patient to require a full thickness corneal transplant. There are numerous ways to avoid the long-term complications and morbidities associated with this procedure, although it is unfortunately sometimes still required.
On the simplest level, even spectacle technology has improved for keratoconus. Lenses can now be ground to incorporate wavefront measurements of the eye. This can minimise higher-order aberrations and improve spectacle visual acuity. Shaw lenses can also be used to minimise anisocoria when significant anisometropia exists.
Prescribing and dispensing these glasses requires specialised equipment that is not available in all optometry practices. It is important that optometrists are aware that referral to another optometrist with access to these lenses may be appropriate in mild cases.
Contact lenses
New technology in contact lenses has improved the vision correction and comfort in contact lenses for keratoconus. While small diameter RGP lenses were the mainstay of visual rehabilitation for keratoconic patients for many years, the development of both wavefront contact lenses and other types of scleral lenses has made contact lenses much more comfortable for patients but it has also enabled optometrists to be able to fit much steeper and more ectatic corneas.
Corneoscleral topography and profilometry allows contact lenses to be made with customised landing angles and sagittal depths. These extremely high levels of individualisation and customisation can facilitate the fitting of previously unfittable corneas so that even patients with very steep cones, other complex corneal ectasias, ocular surface conditions and decentred or mildly dehisced corneal grafts can achieve high quality vision with minimal higher order aberrations.
Unfortunately, not all patients will be able to tolerate or insert and remove contact lenses due to a variety of reasons. Thankfully developments in the surgical treatment of keratoconus have progressed in the same way that optometric treatments have. There are numerous routine procedures available that may assist in improving a patient’s topography and therefore their best corrected spectacle acuity.
Procedures
Topography-guided cross-linking shows promise in providing a degree of corneal regularisation in patients. The advantage of this procedure is that a very wide range of corneas can be treated as no tissue is removed. There are very few corneas that can’t undergo this procedure, however it can also only provide a certain degree of topographic regularisation.
Topography-guided phototherapeutic keratectomy is a routine procedure for keratoconus. In this procedure, an excimer laser regularisation of the cornea is planned using the patient’s topography. Depending on the corneal thickness, the refraction, the topography and the higher-order aberrations, it may be possible to factor the patient’s refraction into the ablation profile, however generally these treatments are intended to improve a patient’s best corrected visual acuity, not to improve their uncorrected visual acuity. This is often combined with cross-linking, either due to the patient’s progression or to restore some of the corneal biomechanics that will be removed due to the stromal ablation.
Kerarings are a plastic insert that can be inserted into the cornea typically using a femtosecond laser to provide a mechanical regularisation of the corneal topography. While these can be very successful in some patients, a number of patients will experience issues due to the plastic insert.
Corneal allogenic intrastromal ring segments (CAIRS)
A newer procedure, corneal allogenic intrastromal ring segments (CAIRS), shows great promise. In the same way that Kerarings are inserted in a circular corneal pocket, CAIRS (Figure 2) uses non-viable corneal stromal tissue in exactly the same manner. This is performed as a routine day surgery procedure. CAIRS is currently undergoing rapid adoption around the world. The current three-year safety and efficacy data is very positive so hopefully longer term studies continue this trend.
Femtosecond laser assisted lamellar corneal grafting techniques are very much in their infancy but potentially show promise. Segments of lamellar corneal stromal tissue may be implanted into a patient’s cornea to thicken up very weak and/or thinned areas of the cornea and provide a resultant improvement in topography and best corrected visual acuity.
Conclusion
Collaborative care in keratoconus in Australia is very much alive and well. Optometrists, ophthalmologists and general practitioners currently enjoy an excellent working relationship for co-managing a wide variety of ocular diseases. It is important to ensure that all parties understand the developments in diagnostic and therapeutic technology that can alter the appropriate indications in the well-established referral framework that already exists.
References
1. Chan E, Et Al. Prevalence of Keratoconus Based on Scheimpflug Imaging: The Raine Study. Ophthalmology. 2021 Apr; 128 (4): 515-521.
2. Galvis V, Sherwin T, Tello A, Merayo J, Barrera R, Acera A. Keratoconus: an inflammatory disorder? Eye (Lond). 2015 Jul; 29 (7): 843-59.
3 Hashemi, Hassan MD Et al. The Prevalence and Risk Factors for Keratoconus: A Systematic Review and Meta-Analysis. Cornea. 2020 Feb; 39 (2): 263-270
4. Mukhtar S, Ambati BK. Pediatric keratoconus: a review of the literature. Int Ophthalmol. 2018 Oct; 38 (5): 2257-2266.
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