Keratoconus: what's new?
This article will cover the recent changes in keratoconus management in the Hospital Eye Service, including referral criteria since the introduction of corneal cross-linking on the NHS.
As expected, there has been a surge in referrals for KC since the introduction of corneal cross-linking (CXL). Primary care optometry has also shown excellent specificity in detecting pre-clinical and pre-symptomatic keratoconus (KC) using traditional methods such as retinoscopy, and increasingly, by use of corneal topographers and tomographers. But what happens to your referral and patient once they reach the hospital? In the short term, limitations in the IT systems in most hospitals mean that you may only rarely (if ever) receive feedback--a situation which Moorfields Eye Hospital and others are working to correct. This article covers the referral, treatment and monitoring pathways in the KC service at Moorfields Eye Hospital, including new treatments available now and those on the horizon.
CXL in 100 words
CXL has been around for long enough with plenty of articles written on the topic to not necessitate too much explanation here, but for background:
* The only treatment available to arrest disease progression in KC
* National Institute for Health and Care Excellence (NICE) approved in September 2013 (1)
* Performed under topical anaesthesia in an approximately 30-minute procedure
* Epithelium debrided, and Riboflavin 0.1% drops instilled every few minutes for 10-15 minutes
* Eight minutes pulsed (one second on/one second off) UVA radiation at 30mW/[cm.sup.2] (Moorfields CXL protocol.
* ther centres may differ)
* Soft 'bandage' contact lens inserted
* Stringent post-op drops instillation regime
* One-week post-op review with bandage lens removal.
The referral pathway
The Referral to Treatment Time (RTT) system ensures that a patient in the Hospital Eye Service (HES) is seen and (if required) treated within 18 weeks (see Figure 1). It is important to remember that the clock starts not when you send the referral, but when it reaches the hospital, prior to which there are several possible reasons why it might be delayed.
Empower the patient to take charge of this process by asking them to contact their general practitioner (GP) if they have not heard something within three or four weeks.
The monitoring pathway
The vast majority of patients who are referred for suspect KC are not treated on presentation since NICE guidance states that there must be "consideration of the likelihood of disease progression." (1) Some patients will never progress beyond the date of their first scan and while CXL is a safe procedure, there are risks with any intervention. In treating an already stable eye the risks, however small, outweigh the benefits.
Although each unit is slightly different in their management, there is general consensus among most about how to effectively monitor KC (see Figure 2, page 80). At Moorfields, patients can expect to undergo the following tests at most visits:
* Vision, visual acuity (LogMAR) and subjective refraction
* Corneal tomography using the Oculus Pentacam (currently the gold standard)
* Slit-lamp biomicroscopy
* Endothelial cell count
* Corneal biomechanics using the Oculus Corvis ST (from the patienf s perspective, an air-puff tonometer).
How do we define progression and high risk?
Previous work has shown repeatability of measurements taken on the Pentacam in early KC to be much tighter than in moderate to advanced disease. (2) Work is ongoing to further tailor progression criteria, but at present patients are classified into one of two groups: 'early' KC, where maximum keratometry (Kmax (Oculus Pentacam)) is less than 55D; and 'moderate/advanced' KC, where Kmax is greater than or equal to 55D (see Figure 3, page 81).
The definition of progression in KC is a constantly evolving landscape and the Pentacam is neither fully understood nor used to its full potential. It gathers well over 20,000 elevation points per scan, but due at least in part to historical reasons, only legacy keratometric indices of K1, K2, Kmax and pachymetry are typically analysed. Analysis of the remaining data available is ongoing and there is a lot more to learn.
The effect of contact lenses
Corneal tomography is seriously affected by corneal shape changes induced by both rigid gas permeable (RGP) and soft contact lenses (see Figure 4, page 80). The extent of the effect is dependent on a wide range of factors including corneal hysteresis (stiffness), lens fit, lens material, wearing time and time since lens removal.
Changes in corneal shape brought on by lens wear can range anywhere from negligible to >10D and predicting the extent of this is an impossible task. This is what makes tomography in contact lens wearers notoriously unreliable and why it is important to insist on two weeks out of lenses for RGP wearers and one week for soft lens wearers before any scans, wherever possible. These timescales are completely arbitrary with no published research thus far to back up this approach. However, an exploratory study at Moorfields led by Martin Watson and Inderpaul Sian will look at this in more detail in the coming months.
The treatment pathway
When a patient is listed for CXL, the RTT clock is ticking to ensure treatment is performed within the 18-week window. Practically speaking patients are booked for treatment approximately six weeks in advance with every effort made to prevent disruption to holidays, exams and work commitments. At Moorfields, the treatment is performed by highly skilled nurse practitioners under local anaesthesia in a 20 to 30-minute outpatient procedure. A short video produced by Moorfields on CXL and an interview with a patient who has undergone the treatment is available online. (3) A bandage soft disposable contact lens is placed on the eye and the patient returns home with a stringent drop regime and advice to self-certify for one week off work. Additional time off is occasionally necessary in cases of delayed healing. In cases of bilateral treatment, both eyes are treated at the same appointment. The procedure itself is not painful; however, postoperatively the first 48 hours are as uncomfortable for the patient as you would expect with a 9mm+ epithelial defect to be. Patients experience varying levels of discomfort, with younger patients usually reporting more than older patients.
Patients are seen one week later to remove the bandage lens and check for complications such as sterile infiltrates, delayed healing and infective keratitis, all of which are rare events. (4) Following this appointment, a six-month review is booked, and patients are advised that vision will be variable for the coming weeks and months as the epithelium remodels and post CXL shape changes take effect. If after five years of monitoring, analysis of tomography shows stability, patients are discharged back to their community optometrist.
Following treatment, patients are often keen to update their spectacles. At around three months post-CXL this is possible and can be done with their own community optometrist. However, patients should be advised that prescriptions can fluctuate for up to one year postoperatively. In cases where patients are in urgent need of spectacles earlier than three months, although refraction is still possible, patients should be warned that the chance of short term fluctuation is significant.
New treatments in KC
Despite its late approval by NICE and subsequent adoption by the NHS in 2013, CXL was actually first piloted in 2003. Since its introduction, a lot of work has been done to explore alternative treatment methods to improve post-operative comfort and enable visual rehabilitation.
Several 'trans-epithelial' riboflavin preparations have been brought to market (see Figure 5). (5) However, these are yet to be proven effective in large scale studies and although new iontophoresis protocols have shown promise, further research is needed.
Refractive procedures and CXL
Visual rehabilitation is a key part of management in KC. If we intervene with CXL early, spectacles and soft disposable contact lenses are usually more than sufficient. In more advanced cases, rigid lenses give excellent vision. Refractive laser procedures can be combined with CXL to produce a more regular corneal shape. It is important to remember that the primary aim of these laser procedures is not to correct refractive error but rather to improve spectacle-corrected acuity by reducing aberrations, for example, coma.
Trans-epithelial photorefractive keratectomy (TransPRK)
TransPRK is performed as a wavefront guided procedure using pre-operative scanned aberrometry data. Following PRK, CXL is performed to 'lock' the new shape in place. Figure 6 (see page 82) shows both pre- (middle column) and post-operative (left column) Pentacam scans for four different patients. (6) Difference maps are shown in the right column where red areas denote steepening and blue/ purple denote flattening. The correction of higher order aberrations can be seen in the reduction in hot/ red zones on the colour maps. Although TransPRK is not routinely offered on the NHS, it is available privately.
Refractive CXL or 'customised CXL' is a new iteration of CXL in which a bespoke treatment pattern is applied to the cornea. Its aim is the same as that of TransPRK--to smooth out surface irregularities thereby improving vision. From the patient's perspective, standard and refractive CXL are the same procedure. However, in refractive CXL, a UV light source of variable and targeted intensity is used to produce an improvement in shape. The technique is new, and although currently being offered privately is awaiting validation within an NHS set-up through a large scale prospective study soon to begin at Moorfields under the supervision of consultant ophthalmologists Daniel Gore and Bruce Allan.
Implantable collamer lens (ICL)
ICLs represent a suitable alternative to laser for correction of residual sphere and regular astigmatism where spectacle acuity is good. This is especially useful where there is significant and symptomatic anisometropia in the context of poor contact lens tolerance, with ranges of -18DS to +10DS and 6DC. (7)
Intrastromal corneal ring segments
These have been on the market for several years and remain a commonly performed procedure to improve corneal shape. After topography data is sent to the manufacturer, and a surgical plan is sent to the surgeon who performs the procedure. However, outcomes are very unpredictable, and patients are suitably counselled pre-operatively on the probability of success. Ring segment surgery is more common in countries without readily available specialist contact lens infrastructure. We are fortunate in the UK to have these contact lens services at our disposal, which provide a safer and more predictable means of improving the quality of vision in KC.
Primary care optometry referrals are how the vast majority of patients enter the HES. New treatments, increasing demand for services and improved early detection of disease has unsurprisingly resulted in additional strain on the HES; therefore, ensuring appropriate, high quality referrals can have a significant positive impact on resources.
The College of Optometrists' website provides clear guidance on making referrals and re-reading this short document is strongly recommended. (8) While all of the College guidance is relevant to referrals for KC, here are a few key points relevant to the condition:
* You are entitled to monitor certain patients yourself as long as it is within your competence or scope of practice
* Refer with the appropriate urgency--for KC, usually routinely
* Be clear, concise and thorough in your referral
* Ensure that the patient understands the routine nature of the referral and when they should expect to hear from the receiving practitioner/hospital, and what to do if they have not heard
* Provide a copy of your referral, including any scans you might have performed, to the patient. Sadly, originals often go astray during the referral process.
How urgently should I refer?
'Suspect KC' is a routine, and never an urgent referral. There are occasions where you might believe that your patient should be seen with some measure of urgency. This is perfectly reasonable but can only be actioned when appropriate reasons are given to expedite a referral, such as incidental additional ocular pathology, or if evidence can be provided of rapid progression.
Counselling your patients
Managing expectations about referrals into the hospital will make the patient's journey more pleasant and reduce anxiety. From the patient's initial consultation with you, it may take anywhere from 12 to 14 weeks for them to be seen in the hospital clinic.
In the event of a possible diagnosis of KC, patients should be reassured that:
* Treatment is available to prevent deterioration
* It is not a blinding condition. While this may seem obvious to the practitioner, the possibility of blindness is a very common source of anxiety among patients
* Referral need not be urgent. Progressive KC rarely happens over weeks, but over several months
* One eye seeing poorly does not have an adverse effect on the better eye. This is another very commonly held myth among patients and even clinicians.
Things to avoid in referrals for 'suspect KC'
* Do not refer unaffected family members for screening. It is unnecessary, and referrals are likely to be rejected. Siblings of patients diagnosed with the condition should be followed up annually until around age 30 by their community optometrist and referred only if they present with signs and symptoms suggestive of the condition
* It is difficult to diagnose KC without corneal tomography, so diagnosis should be avoided in referral letters
* Although CXL is one possible treatment in case of a diagnosis of KC, it is not always indicated, and suggestion of treatment options should be avoided
* Avoid urgent referrals unless clinically indicated, that is to say, not in the case of 'suspect KC.'
How can I improve my referral?
Refraction in early KC is a reasonably reliable indicator of progression and so full records of any changes that you have noticed over time can be very useful indicators of risk. Other helpful things to include:
* Atopic history including asthma, eczema, hay fever and eye rubbing
* Keratometry and/or scans. Remember to give copies to patients as they often go missing during the referral process.
Patient information on KC including advice for those that have been referred, (4) as well as up-to-date results on success of CXL can be found on the Moorfields website. (9)
Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 12 October 2018. You will be unable to submit exams after this date. Please note that when taking an exam, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article.
CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.
Visit www.optometry.co.uk, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.
Course code: C-60084 Deadline: 12 October 2018
* Be able to explain the options for management of keratoconus to patients (Group 1.2.4)
* Understand the use of contact lenses for managing keratoconus and recognise the impact they can have on measuring corneal tomography (Group 5.3.3)
* Be able to manage patients with keratoconus (Group 6.1.3)
* Understand the different treatment options available for the management of keratoconus (Group 1.1.2)
* Be able to explain to patients about keratoconus (Group 1.2.4)
* Understand the use of contact lenses for managing keratoconus (Group 5.1.1)
* Understand the management of patients with keratoconus (Group 8.1.3)
* Be able to explain the options for management of keratoconus to patients (Group 1.2.4)
* Understand the use of contact lenses for managing keratoconus and recognise the impact they can have on measuring corneal tomography (Group 5.5.3)
Marcello Leucci BSc (Hons)
About the author
* Marcello Leucci is the lead optometrist of the keratoconus service at Moorfields Eye Hospital. He is responsible for development of protocols on keratoconus monitoring and progression criteria and is actively involved in research into the effectiveness of both new and existing treatments for the condition.
Caption: Figure 1. The RTT pathway
Caption: Figure 2. The monitoring pathway at Moorfields Eye Hospital
Caption: Figure 3. Progression criteria
Caption: Figure 4. Effect of contact lens on tomography. Comparing top left and bottom right as done here, there is a clear topographic difference. Close examination of the notes however showed that 2014 (bottom right) was pre-lens fitting. Top left: lens dependence and removed the day before
Caption: Figure 5. Two-photon fluorescence images of tissue sections showing 'epi-off' versus several 'epi-on' CXL techniques--stromal riboflavin absorption. Whiter areas indicate riboflavin fluorescence. A--negative control; B--positive control (epi-off); C--Ribocross TE 0.125% 30 minutes; D--MedioCross TE 0.25% 30 minutes; E--Paracel 0.25% four minutes, VibeX Xtra 0.25% six minutes; F--Ricrolin+ 0.1% rnA five-minute iontophoresis
Caption: Figure 6 TransPRK tomography effects. Pre-treatment (middle column), post-treatment (left column) and difference maps (right column). Each row represents one of four patients presented. Hotter red colours indicate steeper areas of cornea. The post-operative scans show a greater symmetry and increase in regularisation
Figure 3 Figure 3 Progression criteria Early KC (Kmax < 55D) Moderate/advanced KC High risk patients One or more of the (Kmax [greater than One or more of the following or equal to]55D) following One or more of the following * [greater than or * [greater than or * [greater than or equal to]1D increase equal to]2.5D increase equal to]Previous in Kmax Kmax LASIK with secondary ectasia * [greater than or * [greater than or * Age [less than or equal to]1D increase equal to]2.5D increase equal to] 18 with in K2 or K1 front K2 or K1 front confirmed KC * [greater than or * [greater than or * Fellow eye hydrops equal to]0.5D increase equal to]22[micro]m or too advanced back K2 decrease minimum for treatment * [greater than or equal to]16pm decrease in minimum thickness
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|Date:||Sep 1, 2018|
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