Hysteresis was significantly higher in normal than in keratoconic eyes. It may be a useful measurement in addition to CCT, when assessing ocular rigidity, and may be of particular importance when trying to correct intraocular measurements for increased or decreased ocular rigidity. Long-term studies of change in hysteresis may provide information on the progression of keratoconus.

No abstract

Hysteresis and CRF were highest in OHT eyes. These factors may prove to be useful measurements of ocular rigidity and may help to understand role of the corneal rigidity in monitoring the progress of conditions such as NTG, POAG and OHT.

The ocular hysteresis reading was almost constant throughout the day, whereas the IOP readings showed highest values in the morning with a reducing trend being lowest in the afternoon. The CCT values were almost stable throughout the day. IOP appears to vary independently of a variation in hysteresis or CCT.

The results of these studies, albeit relatively small scale, indicate that in young or elderly individuals with essentially normal IOP and CCT measures, the tonometry values show only small differences with respect to CCT. The slope in the observed relationship was not that different from an average of 1.5 mmHg for a 10% different in CCT, as obtained from a literature analysis over a 30-year period. The magnitude of the effect does not provide evidence that pachometry needs to be routinely performed in glaucoma screening protocols based on tonometry. Notwithstanding, the finding of higher than expected tonometry values should be further investigated, by pachometry, especially in very young children and in the elderly.