Eye rubbing has been a long-standing risk factor for keratoconus, with many studies suggesting that repetitive and prolonged rubbing may alter corneal biomechanics and trigger or exacerbate the condition. But not everyone rubs their eyes the same way, according to new research—and each rubbing technique applies different forces to the eye.

The study included 57 patients (41 male and 16 female with an average age 34.8) with keratoconus and a history of eye rubbing. The researchers asked patients to perform their individual eye-rubbing movement.

They recorded the type of eye-rubbing movement and the force applied, measured in newtons (N), and identified three different types of eye rubbing: rubbing with fingertips (51%), rubbing with the knuckle (44%) and rubbing with the back of the fingernail (6%). Knuckle rubbing employed significantly more force than either of the others, 9.6 ±6.3N, compared with 4.3 ±3.1N for fingertip- and 2.6 ±3.3N for fingernail-rubbing.

The researchers hope the data will help shape future studies to better understand the possible correlations between the applied force of eye rubbing and keratoconus levels.