This page is an interesting compilation of cases demonstrating the strong link between the patient’s sleeping position and in asymmetrical cases, the side in which keratoconus is more pronounced.
For each case, the right and left corneal topographies are presented on the bottom row. On the top row are two pictures. The first picture, outlined in blue, shows the patient demonstrating his or her favoured sleeping position. The second picture, outlined in orange, documents the patient’s eye rubbing technique.
The correlation between the more affected eye and the preferred sleeping side is striking.
Moreover, when the patients are asked to demonstrate their technique of eye rubbing, in the vast majority of cases, when the patient rubs only one eye, it would be the eye that he sleeps on and the eye more affected by keratoconus. (A side note: we made sure that the patients’ hands were both free from any objects or gadgets before asking them to demonstrate their eye rubbing technique).
Such a strong correlation could be accounted for by the following explanations :
– 1) Chronic night time ocular compression may cause local inflammation, as well as the contamination of the ocular surface by dust mites, allergens and irritants from pillows, bed-linen or detergent, triggering ocular pruritus and the need to rub upon awakening.
– 2) The compression of the tip of the cornea by the hands, mattress or pillow may contribute to the central or paracentral thinning seen in keratoconus via ground substance redistribution.
– 3) Ocular compression exposes the cornea to an increase in temperature, which facilitates the activation of enzymatic cascades leading to protein degradation and cellular apoptosis (cell death)
– 4) Local heating, together with the physiological swelling of the cornea during sleep may induce weakening of the corneal tissue, making it more susceptible to the deleterious effect of rubbing at the time of awakening.
– 5) The forces exerted on a heated and swollen cornea by rubbing upon awakening or shortly after may favor the « tenderization » of the corneal stroma, making the central cornea more deformable over time.
In clinical practice, it is important to identify such unhealthy sleeping habits and positions and encourage patients to abandon or modify them. In some cases, the affected eye may be protected at night with a rigid eye patch or shield.
This is a limited series, but the correlation between the laterality of the sleeping position and the eye more afflicted with keratoconus is stunning, and based on the cases presented, is clinically if not statistically significant.