Clinical evaluation of meibomian gland dysfunction in patients with keratoconus
Introduction
Keratoconus (KC) is a chronic bilateral disease characterized by asymmetric progressive thinning most commonly located in the inferotemporal and central corneal regions. Its prevalence in the different studies ranges from 0.17 to 47.9 per 1000 people [1] and its annual incidence from 1.3 to 25.0 per 100 000 people [2], [3], [4], [5], but it could be higher as there are probably many undiagnosed subclinical cases. It usually starts in puberty and progresses over time to stabilize in the third or fourth decades of life. Vision correction in this condition is often achieved with glasses or contact lenses in the mild and moderate stages of the disease, but surgery may be required in severe KC.
Although traditionally considered an ectatic non-inflammatory disease, several studies have demonstrated increased interleukine-6, interleukine-1β and interferon-γ levels in this disorder [6], [7], [8], [9]. A myriad of genetic, environmental, biomechanical and neurotrophic associated factors have also been described. In addition, systemic diseases such as thyroid disease, sleep apnea syndrome or asthma have recently been found to be associated [10], [11], [12], [13], [14], [15], [16], [17], [18], although the extent to which these different factors, including inflammation, may affect each other is unknown.
Meibomian gland dysfunction (MGD) is a chronic, diffuse abnormality of the meibomian glands characterized by terminal duct obstruction and/or qualitative/quantitative changes in glandular secretion, which may result in alteration of the tear film, clinical apparent inflammation, ocular surface disease and symptoms of eye irritation [19]. It is the most frequent risk factor for the development of dry eye disease [20], [21], [22] and its prevalence in population-based studies ranges widely from 3 to 65% probably because of differences in study populations and variable diagnostic criteria [22], [23], [24], [25].
Previous studies have reported an association of KC with DED [26], [27], [28], [29], [30], which can seriously affect quality of life [31], [32], [33]. A few investigations also suggest an increased prevalence of MGD in KC [26], [34], but there are no studies on the association of KC with MGD. The hypothesis of this study was that MGD might be an important associated factor in KC and that MGD might have distinct characteristics in patients with this disease. Being able to identify the role of MGD in KC would further the understanding of the pathophysiology of this condition and help to design strategies to manage DED in these patients. The purpose of this study was to investigate the association of KC with MGD as well as to describe the epidemiological characteristics of MGD in this disease.
Section snippets
Participants
In this observational study, the study group consisted of 120 patients previously diagnosed with KC, consecutively recruited from the corneal and external disease clinic of the Department of Ophthalmology of the Complexo Hospitalario Universitario de Santiago de Compostela from May 2015 to November 2016. The control group comprised 87 patients without this diagnosis recruited from the general ophthalmic clinic of the Department of Ophthalmology of the same hospital. Subjects were excluded from
Results
There were 65 men (54.2%) and 55 women (45.8%) in the KC group and 31 men (35.6%) and 56 women (64.4%) in the control group. Their mean age was 35.2 ± 11.3 years (range, 13–66 years) and 36.9 ± 14.2 years (range, 15–63 years), respectively (P = 0.372). A total of 35 patients in the KC group had only one eye analyzed because they had undergone KC surgery in the other: intrastromal corneal ring segment insertion (18 eyes), keratoplasty (11 eyes), corneal cross linking (3 eyes) and epikeratoplasty
Discussion
The main finding of this study was that MGD was nearly twice as common in KC patients as in controls and more prevalent in the more advanced stages of the disease. It was also found that KC patients exhibited more symptoms and signs than controls, although no differences were found with respect to the Schirmer test. The prevalence of MGD, or DED, in KC and in other pathologies varies substantially between studies [22], [23], [24], [25], [26], [27], [28], [29], [30]. These variable results may
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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