|Year : 2018 | Volume
| Issue : 3 | Page : 193-194
Keratoconus in high-prevalence populations: Is it time for a screen-and-crosslink approach?
Ahmed Zahir Al-Maskari
Department of Ophthalmology, Sultan Qaboos University Hospital, Muscat, Oman
|Date of Web Publication||29-Oct-2018|
Dr. Ahmed Zahir Al-Maskari
Department of Ophthalmology, Sultan Qaboos University Hospital, P.O. Box 38, Post Code 123, Al Khoudh, Muscat
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Al-Maskari AZ. Keratoconus in high-prevalence populations: Is it time for a screen-and-crosslink approach?. Oman J Ophthalmol 2018;11:193-4
Keratoconus continues to be a major cause for corneal blindness among adolescents worldwide. It is particularly a major problem in countries with known high prevalence. A recent study from Saudi Arabia reported keratoconus prevalence at 4.79% among 12–21-year-olds, highlighting the significant size of the problem. Another study, also from Saudi Arabia, showed the prevalence of keratoconus among patients seeking refractive laser surgery to be as high as 19.7%. In this issue of Oman Journal of Ophthalmology, AlMahrooqi et al. present the results of a study from Oman demonstrating the severity of keratoconus at presentation in the Omani population, particularly in children. The impact of poor vision at such a critical stage in life when hobbies, education, and career pathways are to be determined is immense. Unfortunately, keratoconus also remains the main cause for corneal transplantation in this age group, with a significant impact on quality of life and a big burden on health-care providers. Large epidemiological studies in high prevalence populations are now more important than ever before to enable us to set up targeted screening programs and design more efficient population-specific keratoconus monitoring and treatment pathways.
The last 15 years have seen a revolution in the diagnosis and management of keratoconus. The introduction of corneal cross-linking in 2003 has completely changed the way keratoconus is managed with an emphasis on early detection and monitoring. Modern tomographic machines equipped with artificial intelligence algorithms and user-friendly interfaces have made it very easy to detect corneal ectasia even at an early stage by non-cornea specialists. Despite this, late diagnosis continues to be a challenge particularly in countries with limited resources and without developed and accessible optometric services. Until keratoconus screening programs are initiated in high prevalence regions, the concept of targeted keratoconus screening should be emphasized to ophthalmologists and optometrists. Pediatric ophthalmologists are also encouraged to incorporate keratoconus screening as part of their management routine for all children with ocular allergy, atopy, connective tissue disorders, Down's syndrome, and family history of keratoconus.
Waiting for evidence of progression before proceeding with corneal cross-linking remains a troublesome concept, particularly with limitations in the precision of corneal tomographic machines and the lack of specific quantitative data to define significant progression. Distinguishing real change in corneal shape from measurement inaccuracies is still challenging in the monitoring stage of keratoconus. There are inter- and intra-observer errors as well as errors between different machines. All these need to be taken into consideration when trying to determine real keratoconus progression. Precision parameters become even less reliable as the cornea becomes more ectatic. Flynn et al. studied the precision of Pentacam HR measurements and reported 95% limits of inter-observer agreement for Kmax to range from −0.90 D to 1.01 D in Krumeich stages 1 or 2 and from −3.71 D to 3.86 D in Krumeich stages above 2. In other words, a minimum of 1 D change in Kmax is required to reliably demonstrate a change in corneal shape in the early stages of keratoconus. The reproducibility becomes poor in advanced stages making a decision on change in shape less reliable. Until we have tomographic machines with much higher precision, one way around this limitation is to use the mean of repeat measurements. Repeating the scan three times in each visit and then using the mean were found to significantly improve the 95% limit of inter-observer agreement for Kmax from 1.37 D to 0.78 D, thus enabling the use of lower thresholds to reliably determine progression. While this may not be practical in a busy clinical setup, the concept of repeat measurements and mean calculation should be easy to incorporate in future tomography analysis software.
Prompt corneal cross-linking without waiting for keratoconus progression is key in high-risk patients not only to prevent corneal transplantation but also to prevent the significant impact on vision-related quality of life. Delaying cross-linking to demonstrate significant corneal tomographic changes can lead to a large reduction in functional vision and may limit potential future refractive options if the corneal thickness drops below certain treatment thresholds. It is therefore imperative that cross-linking is considered at the point of diagnosis. It is time to stop relying only on tomographic numbers to decide on corneal cross-linking. There are several factors that can be taken into account to make an informed prediction on whether or not keratoconus will progress. Young age, advanced disease in the other eye, strong family history of advanced keratoconus, and atopy, all these are factors that can be used to justify proceeding with cross-linking without necessarily waiting to demonstrate progression. Chatzis and Hafezi reported in 2012 an 88% rate of keratoconus progression in children and adolescents aged between 9 and 19 years. It is unfortunate that there are still clinicians who wait for evidence of keratoconus progression in children despite the ample evidence, demonstrating the high rate of keratoconus progression and the safety of cross-linking in this age group. As eluded above, large population-specific epidemiological studies can also guide in quantifying the risk of progression and therefore help with early management decisions.
Although we are becoming more successful in stopping keratoconus progression and reducing the need for corneal transplantation, many patients will continue to have poor vision-related quality of life as they struggle with contact lens use and limited best spectacle-corrected vision. The ultimate aim in managing keratoconus should therefore focus on minimizing the impact on vision-related quality of life. That is to detect and stop the disease at a very early stage to maintain excellent spectacle-corrected visual acuity and reduce reliance on contact lenses. This can only be achieved currently with a screen-and-crosslink approach.
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