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Incidence and Prevalence of Idiopathic Corneal Ectasias, Active Component, 2001–2018

Keratoconus. Credit: © 2019 American Academy of Ophthalmology. Keratoconus. Credit: © 2019 American Academy of Ophthalmology.

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BACKGROUND

Corneal ectasias are a category of eye diseases characterized by progressive steepening and thinning of the collagen-based corneal stroma.1 Individually, these conditions are part of their own unique primary disease process or can occur as result of refractive surgery. Conditions characterized as corneal ectasias include keratoconus, pellucid marginal degeneration (PMD), keratoglobus, and post-refractive surgical ectasia. These disorders can be differentiated based on the pattern and location of corneal thinning, age of onset, and surgical history. Keratoconus, the most common corneal ectasia, usually presents around puberty, progresses until approximately 40 years of age, and is characterized by inferior thinning and protrusion of the cornea at its thinnest point.2 PMD is a rare disorder more common among males. It typically presents between 20–40 years of age and is characterized by inferior corneal thinning.3 Keratoglobus is most often congenital, although it may be acquired secondary to systemic conditions and consists of generalized thinning of the entire cornea and globular protrusion.4 Post-refractive corneal ectasia is corneal thinning with a clinical appearance similar to keratoconus; however, it is secondary to prior laser-assisted in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), or small incision lenticule extraction (SMILE).

Corneal ectasias cause progressive and often unpredictable decreases in best-corrected vision. Early in the course of the disease, this effect on vision may be adequately corrected with eyeglasses. As the disease progresses, medical contact lenses (to address the abnormal curvature of the cornea) are often required or corneal cross-linking can be used to slow or halt the progression of keratoconus. When these methods are no longer effective, surgical procedures such as intracorneal ring segment implantation or full or partial thickness corneal transplantation are required to maintain visual function.5

The current report summarizes the frequencies, rates, and temporal trends of idiopathic corneal ectasias among active component service members during 2001–2018.

METHODS

The surveillance period was 1 January 2001 to 31 December 2018. The surveillance population included all individuals who served in the active component of the U.S. Army, Navy, Air Force, or Marine Corps at any time during the surveillance period. Diagnoses of corneal ectasias were ascertained from records maintained in the Defense Medical Surveillance System (DMSS) that document outpatient encounters of active component service members. Such records reflect care in fixed military treatment facilities of the Military Health System (MHS) and in civilian sources of health care underwritten by the Department of Defense.

Case-defining diagnoses of corneal ectasias are shown in Table 1. For surveillance purposes, an incident case was defined by at least 1 outpatient medical encounter with a qualifying diagnosis in any diagnostic position. The incidence date was the date of the first qualifying outpatient encounter, and an individual was counted as an incident case only once per lifetime. For the incidence rate calculations, person-time at risk included all active component military service time before the date of incident diagnosis, termination of military service, or the end of the surveillance period, whichever came first. Because some corneal ectasias may have resulted from refractive surgical procedures, incident cases of corneal ectasias with any prior outpatient encounter that included a Current Procedural Terminology (CPT) code for refractive surgery (CPT: S0800 or S0810) in any CPT position were excluded from the analysis and person-time was censored at the time of the first-occurring refractive surgery procedure. Incidence rates were calculated as incident idiopathic corneal ectasia diagnoses per 100,000 person-years (p-yrs). Prevalent cases (i.e., service members with case-defining diagnoses occurring before the start of the surveillance period) also were excluded from the analysis of incidence.

Lifetime prevalence of each type of disorder was calculated for each year in the 18-year surveillance period. An individual was identified as a prevalent case during a given year of the surveillance period if they were in active component service at any time during the given year and were diagnosed as an incident case on or before that year (including those who were diagnosed as an incident case before the start of the surveillance period). The denominator for the annual prevalence calculations consisted of the total number of service members in active component service during each year. Annual prevalence estimates were calculated as the number of prevalent cases per 100,000 active component service members.

RESULTS

During 2001–2018, a total of 10,562 active component service members received incident diagnoses of idiopathic corneal ectasias, for a crude overall incidence rate of 45.3 per 100,000 p-yrs. Rates among male and female service members were relatively similar. Overall rates were highest among service members 30–34 years of age (54.2 per 100,000 p-yrs) and lowest among those less than 20 years old (30.3 per 100,000 p-yrs). Incidence rates were higher among officers compared to enlisted service members. Rates of idiopathic corneal ectasias were highest among Army personnel (52.6 per 100,000 p-yrs) and lowest among Marines Corps members (27.6 per 100,000 p-yrs). Across military occupations, overall incidence rates of idiopathic corneal ectasia diagnoses were highest among healthcare workers (58.5 per 100,000 p-yrs) and lowest among pilots/air crew (27.9 per 100,000 p-yrs) (Table 2).

During the surveillance period, crude annual rates of incident diagnoses of idiopathic corneal ectasias rose and then fell during the period 2001 through 2010, but rates from 2011 through 2018 were consistently higher than the preceding decade and peaked at 65.1 cases per 100,000 p-yrs in 2016 (Figure 1). Rates among Army and Air Force members peaked in 2016, while rates among Navy members peaked in 2017 and rates among Marine Corps members peaked in 2012 (Figure 2). During 2001–2018, the greatest increase in rates was seen in the Army (122.5%) followed by the Navy (86.0%), the Air Force (66.5%), and the Marine Corps (22.3%). Annual lifetime prevalence rates of idiopathic corneal ectasias increased steadily throughout the surveillance period, from 123.7 per 100,000 service members in 2001 to 315.6 per 100,000 service members in 2018 (Figure 3).

EDITORIAL COMMENT

This report demonstrated a crude overall incidence rate of idiopathic corneal ectasia diagnoses of 45.3 per 100,000 p-yrs among active component service members during 2001–2018. Early studies in Olmstead County, MN, estimated the incidence of keratoconus at 1 in 2,000 in that population, with a corresponding prevalence rate of 54.5 per 100,000 persons (per year).However, these data were collected before widespread use of computerized corneal topography and tomography devices, which provide more accurate and repeatable measurements of the cornea and its structure, including progression analysis of the disease. As recently as 2017, in conjunction with the advent of these newer and more sensitive computerized diagnostic methods, the annual incidence and prevalence of keratoconus in a civilian population were shown to be 5- to 10-fold higher than previously reported.7 While these estimated rates of keratoconus among civilian populations provide some reference, there are no currently available reports allowing for direct comparisons for the wider group of corneal ectasias. The results of the current analysis provide a baseline for future surveillance of corneal ectasias and evaluation of interventions among military populations. Of note, the relatively lower rates observed for Marine Corps personnel may be due to the younger age range of this group. Additional studies are warranted to explore the factors other than age that are associated with rate differences.

This report is subject to several limitations. There is established coding guidance for conditions such as corneal ectasias, which may lead to incomplete capture of cases. Because the current analysis used administrative data, questions requiring detailed review of clinical records for optimal mapping of signs and symptoms could not be addressed. The Armed Forces Health Longitudinal Technology Application (AHLTA) was introduced across the MHS in 2006, and this electronic health record may have influenced coding accuracy throughout the surveillance period. Finally, the new electronic health record for the MHS, MHS GENESIS, was implemented at several military treatment facilities during 2017. Medical data from sites that are using MHS GENESIS are not available in the DMSS. These sites include Naval Hospital Oak Harbor, Naval Hospital Bremerton, Air Force Medical Services Fairchild, and Madigan Army Medical Center. Therefore, medical encounters for individuals seeking care at any of these facilities during 2017–2018 were not included in this analysis.

This report demonstrated increasing rates of idiopathic corneal ectasias among active component service members over the course of the surveillance period. The increasing incidence rates reported here may be due to multiple factors, including increased recognition and improved diagnostic capabilities. The steadily increasing annual prevalence rates of idiopathic corneal ectasias are reflective of the chronic nature of these conditions once diagnosed. Corneal degenerations and keratoconus are disqualifying conditions for appointment, enlistment, or induction into the U.S. military.8 When vision is only correctable by contact lenses because of disease progression, service members must be evaluated for fitness for duty.9 Corneal ectasias carry high potential for impact on the readiness and retention of trained and experienced service members. Healthcare providers, both eye care professionals and providers responsible for tracking readiness indicators, must be aware of the signs/symptoms of and treatment options for service members suspected of having or diagnosed with these conditions.

Author affiliations: Department of Defense/Veterans Affairs Vision Center of Excellence, Defense Health Agency Research and Development Directorate (COL Reynolds, Dr. Morgenstern, and Dr. Mallia); Defense Health Agency, Armed Forces Health Surveillance Branch (Dr. Stahlman)

Disclaimer: The contents, views, or opinions expressed in this publication are those of the author(s) and do not necessarily reflect the official policy or position of the Defense Health Agency, Department of Defense, or the U.S. Government.

REFERENCES

1. Garcia-Ferrer FJ, Akpek EK, Amescua G, et al. Corneal Ectasia Preferred Practice Pattern®. Ophthalmology. 2019;126(1):P170–P215.
2. Vazirani J, Basu S. Keratoconus: current perspectives. Clin Ophthalmol. 2013;7:2019–2030.
3. Jinabhai A, Radhakrishnan H, O’Donnell C. Pellucid corneal marginal degeneration: a review. Cont Lens Anterior Eye. 2011;34(2):56–63.
4. Wallang BS, Das S. Keratoglobus. Eye (Lond). 2013;27(9):1004–1012.
5. Rabinowitz YS. Keratoconus. Surv Ophthalmol. 1998;42(4):297–319.
6. Kennedy RH, Bourne WM, Dyer JA. A 48-year clinical and epidemiologic study of keratoconus. Am J Ophthalmol. 1986;101(3):267–273.
7. Godefrooij DA, de Wit GA, Uiterwaal CS, Imhof SM, Wisse RP. Age-specific incidence and prevalence of keratoconus: a nationwide registration study. Am J Ophthalmol. 2017;175:169–172.
8. Office of the Under Secretary of Defense for Personnel and Readiness. Department of Defense Instruction 6130.03. Medical Standards for Appointment, Enlistment, or Induction in the Military Services. 6 May 2018.
9. U.S. Department of the Army. Army Regulation 40–501. Standards of Medical Fitness. 27 June 2019. Department of the Army, Washington, DC.

Numbers of incident cases and incidence rates of idopathic corneal ectasias diagnoses, active component, Armed Forces, 2001–2018

Annual incidence rates of idiopathic corneal ectasias diagnoses, by service, active component, Armed Forces, 2001–2018

Numbers of prevalent cases and annual lifetime prevalence rates of idiopathic corneal ectasias diagnoses, active component, U.S. Armed Forces, 2001–2018.

ICD-9 and ICD-10 diagnostic codes used to identify cases of corneal ectasias

 Numbers and rates of incident diagnoses of idiopathic corneal ectasias, by demographics and military characteristics, active component, U.S. Armed Forces, 2001–2018

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