Continuous monitoring of experimental macaques showed that this mindless habit can increase intraocular pressure, predisposing the individual to eye conditions like glaucoma and keratoconus.
A seemingly harmless habit like rubbing the eyes can greatly increase IOP and theoretically predispose the person to certain eye conditions. (Source)
Eye rubbing has been shown associated with the development of some eye diseases, such as keratoconus, keratoglobus, corneal astigmatism, and glaucoma. The increase in IOP that results from eye rubbing is thought to result from the direct force, anterior segment indentation, or both.
In this study, the IOP elevations that occur with eye rubbing were measured in vivo using bilateral continuous IOP telemetry. Three male rhesus macaques (4-6 years of age) were selected for this study.
Results showed that the mean IOP elevations because of eye rubbing was 109 ± 26 mmHg above baseline IOP, with as much as 310 mmHg more than baseline. Greater increases in IOP were noted with rubbing using the back of the hand or the wrist, instead of the fingers or knuckles. These elevations were followed by transient IOP reductions in the magnitude of 1-4 mmHg.
While this study only had 3 test subjects, this study supports the hypothesis of innocuous behavior resulting in mechanical damage to ocular structures, which may predispose to the development of eye diseases.
Turner, D., Girkin, C., & Downs, J. (2019). The Magnitude of Intraocular Pressure Elevation Associated with Eye Rubbing. Ophthalmology, 126(1), 171-172. doi: 10.1016/j.ophtha.2018.08.025