August 23, 2021
2 min read
August 23, 2021
2 min read
Keratoconus, like many ocular diseases, has genetic, systemic and environmental associations that affect prevalence.
One of the systemic conditions where keratoconus incidence is much higher is in the Down syndrome (DS) population.
DS is a genetic condition where the affected individual gets three (full or partial) copies of chromosome 21 (trisomy 21). According to the National Down Syndrome Society, one in 700 babies in the U.S. is born with DS, making it the most common chromosomal disorder.
As keratoconus (KCN) awareness continues to rise, disease prevalence studies are variable, but the trend continues to show higher incidence than previously thought.
Certain regions show higher patient numbers, but using a recent systematic global review, the authors concluded about one in 750 patients develop KCN (Hashemi et al.). In patients with DS, KCN prevalence has a larger range depending on inclusion criteria to define it, but a recent literature review showed a condensed range of 8% to 36% (Kristianslund et al.). This aligns with reported incidence of KCN being 10 times to 20 times higher in a patient with DS compared to the general population (National Keratoconus Foundation).
Although the exact mechanism is unknown as to why the KCN incidence is higher in the DS population, these patients need our expertise on exam. Examining a patient with DS should start with an inviting tone and only inclusive terms and language. Remember, communication can be more difficult with some DS patients, and some of these patients may be nonverbal. In these cases, utilize a parent or family member who likely has a communication method that may include gestures, pictures or touch. During your introduction to the patient and their loved ones, closely watch for and inquire about mechanical eye-rubbing. In all KCN patients, relying on visual symptoms can delay early diagnosis, but in a child or patient with DS, expressing visual change may be difficult to report.
In the exam, prioritize shorter, objective tests when available. When KCN is suspected, this includes using an autorefractor, autokeratometer, retinoscope, corneal topographer/tomographer and others depending on each patient’s comfort level. In all KCN patients, subjective phoropter refractions are widely variable, and in a patient with DS this may lead to ambiguity or even a roadblock.
Undilated and dilated retinoscopy can uncover refractive error, ocular misalignment (strabismus) and KCN, all of which have increased incidence in the DS population (Alio et al.). During childhood and early to mid-adolescence, completing a corneal topography/tomography exam to review corneal shape is extremely useful. In a patient with DS, corneal mapping on a yearly basis during the KCN years can greatly aid in early diagnosis.
So much of this review focuses on early diagnosis, because after the first step of diagnosis, now stabilizing these corneas is of the utmost importance. In a patient with DS, who, in my experience is more prone to eye rubbing, halting ectatic progression with corneal cross-linking (CXL) should be a priority. Earlier diagnosis coupled with CXL helps maintain optical rehabilitation options. Some DS patients with KCN may excel and adapt well to specialty contact lenes, but glasses are more commonly the first choice due to ease of care and handling.
Additional support for CXL in DS patients with KCN comes from the precarious last resort alternative of corneal transplantation in these individuals.
Managing KCN in a patient with DS can present challenges but also a unique opportunity to prevent further vision loss. Emphasizing the mantra of earlier diagnosis, followed by halting disease progression and, finally, optical rehabilitation will serve these patients well.
Alio J, et al. JAMA Ophthalmol. 2018;doi:10.1001/jamaophthalmol.2018.2373.
Hashemi H, et al. Cornea. 2020;doi:10.1097/ICO.0000000000002150.
Kristianslund O, et al. BMJ Open Ophthalmology. 2021;doi:10.1136/bmjophth-2021-000754.
National Down Syndrome Society. What is Down syndrome? https://www.ndss.org/about-down-syndrome/down-syndrome/. Accessed August 23, 2021.
National Keratoconus Foundation. Crosslinking for patients with Down syndrome. https://nkcf.org/crosslinking-patients-syndrome/. Accessed August 23, 2021.