The corneal endothelium plays a crucial role in maintaining health and transparency of the cornea and is subsequently essential for optimal vision [1]. It functions as an active pump, continuously moving ions and water molecules from the corneal stroma towards the aqueous humor. Additionally, it supplies nutrients to the cornea and removes metabolic byproducts [2]. Pachymetry can be used to assess the function of the corneal endothelium, as the endothelium plays a role in regulating central corneal thickness (CCT) and maintaining it within normal limits between 0.474 mm and 0.596 mm (95% CI) [2], [3], [4]. When endothelial cell density (ECD) falls below 500 cells/mm2, the corneal endothelium loses its ability to maintain corneal dehydration, leading to corneal edema and a pathological increase in corneal thickness [2], [5]. Human corneal endothelial cells are unable to regenerate and ECD is expected to decline with age at a reported rate of 0.3–0.6% per year [6], [7].

Many factors may affect ECD and CCT. Age significantly decreases ECD and causes thinning of CCT [8], [9], [10]. Females have been found to have higher ECD than males [11]. Differences in corneal endothelial density and morphology were described among races and ethnic groups [12]. Other factors that can alter endothelial function and decrease the ECD include previous intraocular surgery (e.g., cataract and glaucoma surgeries), and diabetes mellitus [13], [14].

Eye rubbing is a common behavior, particularly among patients with ocular allergy or dry eyes [15]. However, it causes alterations in corneal biomechanical properties inducing a transient softening of the cornea, and it is associated with the development of keratoconus [16], [17]. Sleeping position, especially lateral and prone positions, has been proven to increase IOP, and is associated with unilateral or highly asymmetric keratoconus [18], [19].

To date, the effect of eye rubbing and eye-pillow contact on corneal ECD and CCT has yet to be determined. Given that these factors may exert mechanical trauma on the cornea, a better understanding of their effects on the corneal endothelium is of clinical importance. This led us to hypothesize that eye rubbing and prolonged eye-pillow contact may be correlated with changes in ECD and CCT. To the best of our knowledge, no published studies have directly investigated this hypothesis. Therefore, the aim of this paper is to assess the association between these factors and corneal ECD and CCT.