Noninvasive instruments (Oculus Keratograph 5M, Germany; K5) are used for automatic non-invasive tear breakup time (NIBUT) measurements.
[6] Evaporative dryness can also be seen in conditions like lagophthalmos, proptosis, Parkinson's disease, computer vision syndrome, contact lens use, drugs (antihistamines, beta blockers, antispasmodics, diuretics) and vitamin A deficiency, amongst others.
In annon-invasive tear breakup time measurement procedure, a grid or concentric ring pattern is projected onto the cornea and the patient is asked to blink.
[8] Ocular protection index (OPI) is used to quantify the interaction between tear film break-up time and blink intervals of a person.
[9] It is based on the idea that, even when the TBUT is normal, if the blink interval is too slow it may cause breakage of tear film due to increased evaporation.
The ocular Protection Index can be calculated by dividing tear break-up time by inter blink interval (IBI).