by Hazlin Hassan
For refractive surgery patients, new technologies are available for the detection of corneal disorders, thereby potentially improving outcomes.
This is among the good news that delegates heard at the 37th Congress of the European Society of Cataract and Refractive Surgeons (ESCRS Paris 2019) during the EuCornea Symposium called ‘Approaches to the Diagnosis and Management of Important Corneal Disorders in the Cataract and Refractive Patient’.
Diagnostic Imaging of the Irregular-Keratoconic Cornea
Prof. Georgios D. Kymionis of Jules-Gonin Eye Hospital and University of Lausanne, Switzerland, explained that keratoconus – a disorder where the cornea thins into a cone-shape and distorts vision – occurs in one of 2,000 people, with 7 percent having family history of the disease.
The incidence of keratoconus differs according to geographical location and environmental factors may also contribute to the wide variation in prevalence. Areas with sunshine and hot weather like India and the Middle East have a higher prevalence (2.3%), compared with places with less sunshine such as Finland, Denmark and Russia (0.0003%).
“Thus, ultraviolet light-induced oxidative stress may have a role to play,” said Prof. Kymionis.
Keratoconus impacts the patient’s quality of life. “Vision-related quality of life was worse in keratoconic patients due to low visual acuity,” he explained, adding that using contact lenses to maintain visual acuity (VA) may improve vision-related quality of life. Keratoconic patients also had significantly lower values in social functioning, mental health, role difficulties and overall composite scores.
Diagnostic imaging technology is essential for corneal analysis, especially in the early stages of disease. It’s used for screening subclinical keratoconus and evaluating the disease’s progression, preoperative screening of refractive (excluding patients with subclinical keratoconus) and cataract patients – especially in those where a premium intraocular lens (IOL) is used. It’s also important in the evaluation of corneal irregularities in post-refractive surgery patients and in the determination of possible retreatment.
Diagnostic imaging technology for corneal analysis includes topography, tomography, corneal thickness maps, epithelial thickness maps, aberrometers and artificial intelligence (AI).
Comparing corneal topography to tomography, Prof. Kymionis said that corneal topography is limited to evaluating the anterior surface of the cornea and has decreased sensitivity and specificity for patients with subclinical keratoconus. On the other hand, corneal tomography measures the elevation maps of both the anterior and posterior corneal surface, lens thickness and opacification, as well as higher order aberrations.
High order aberrations of the anterior and posterior corneal surfaces are good indicators for diagnosing keratoconus and for classifying the stage of the disease, with sensitivity and specificity of 98 and 99 percent, respectively.
“The diagnosis of irregular corneas is complex and depends on many factors. One device by itself is not a good predictor of the condition. Predictive models can be obtained in combination with other indicators,” concluded Prof. Kymionis.
New Technologies for the Detection of Corneal Disorders in Refractive Surgery Patients
According to Prof. Burkhard Dick from the University Eye Hospital Bochum, Germany, new technologies are now available for the early detection of corneal disorders in refractive surgery patients. “Early detection of keratoconus is a serious need. The lack of affordable tools is holding us back,” he explained.
Millions of patients are at risk for keratoconus based on corneal curvature alone, revealed Prof. Dick. There are 309 million patients with >46D corneal curvature or >2D cylinder. Some 90 percent of these patients live in Asia-Pacific countries, while 60 percent live in India and China. A total of 1.7 million patients are between the ages of 15 and 30-years-old. And while there are 4,000 cornea specialists, around 75 percent of physicians worldwide do not have topography capability in their offices.
This is where the Delphi EyeTopo System – a small, fast and cost-effective smartphone-based topography system at around $1,800 per unit – can help fill the gap. It’s equipped with AI-enhanced, cloud-based analytics and backed by the entire Nidek Magellan topography library, available to the smartphone and cloud environment.
Genetic testing can also be done to identify patients at risk. Genomic deoxyribonucleic acid (DNA) is extracted from a buccal swab sample, and next generation sequencing (NGS) analysis is carried out using a custom panel, primarily targeting the coding regions of 75 genes identified to be involved in the eye structure and function.
The test screens for over 70 mutations that lead to transforming growth factor beta-induced (TGFBI) corneal dystrophies. This allows for the analysis of a larger number of collected positives and control samples, greater detailed information on individual variant contribution to keratoconus progression, and therapeutic use.
There is a need for technology that is easy to adopt, and AI will further improve diagnosis of the disease. Genetic testing is a new addition to the clinician’s toolbox. Add this to existing optical and scanning methods, and at-risk patients can be identified earlier, perhaps before any changes are detected on current devices. With improved monitoring, doctors can implement preventative treatments.
Preoperative evaluation in refractive surgery can help determine the individual’s potential to progress to keratoconus, which can be a deciding factor in procedure selection or against a corneal procedure.
Preventing the Onset and Progression of Keratoconus
Dr. Mario Nubile, MD, PhD, from the University of Chieti Pescara, Chieti, Italy, provided tips on how to prevent the onset or progression of keratoconus.
“Avoid eye rubbing and use topical steroids or cyclosporine eye drops,” he advised, noting that hybrid lenses offer higher satisfaction and vision-related quality of life, as compared to rigid lenses. Larger diameter contact lenses are associated with decreased lens awareness and enhanced on-eye stability.
On corneal transplants, he said that deep anterior lamellar keratoplasty (DALK), a safe procedure for all levels of keratoconus, is preferred in phakic eyes or in patients with mental disability. It spares the recipient’s endothelium, there is a lower risk of rejection and a higher graft lifespan, and it’s less prone to increases in intraocular pressure (IOP).
“Penetrating keratoplasty (PK) to treat advanced keratoconus with endothelial failure has a higher risk of rejection and deep central corneal scarring,” added Dr. Nubile.
The 37th Congress of the European Society of Cataract and Refractive Surgeons (ESCRS) took place from September 14 to 18 at Pavilion 7, Paris Expo, Porte de Versailles, Paris, France. Reporting for this story also took place at the ESCRS 2019.
