24-hour IOP monitoring with the SENSIMED Triggerfish contact lens: effect of sleep position and assessment of upward drift

Abstract

 

Purpose

 

To determine the difference in relative IOP measured by the SENSIMED Triggerfish (TF) in flat compared to 30 degree head-up sleeping positions in patients with glaucoma and describe an IOP “drift” phenomenon observed after 24h monitoring session.

 

Methods

 

Patients with progressive POAG or NTG (defined as a new or recurrent optic disc haemorrhage) were included in this prospective, randomized, cross-over comparative study. IOP fluctuation was monitored for 24hr using the TF sensor in 2 separate sessions. Patients were randomly assigned to sleep flat one night and 30 degree head-up the other. TF IOP-monitoring curves in arbitrary units were obtained. Comparisons of IOP (measured by applanation tonometry), corneal central thickness (CCT) and spheric equivalent before the sensor fitting and after its removal were performed. Sleep period was defined as 22-6h. Mean TF outputs between sleep positions were compared. A potential association between IOP change from baseline and last mean TF values before sensor removal (17-18h) was studied.

 

Results

 

Twelve subjects were included in the study. One subject withdrew consent after the first session and was excluded from the analysis. Mean hourly TF values during sleep from 22-6h were significantly higher in 5 of 11 subjects in flat position (p <0.05). However, no differences in overall mean hourly TF values between positions were found (p >0.05 for each interval). A marked increase from baseline in the TF output (>100mVEq) over 24 hours was detected (“DRIFT” phenomenon, fig.1) in 8 of 11 subjects with a mean ± SD increase of 106,9 ± 208,2 mVEq and in 6 of 11 subjects with a mean of 81,33 ± 153,03 mVEq in flat and head-up position, respectively. An IOP increase of 1,6 ± 2,8 mmHg (p = 0.08) in flat and 2,8 ± 3,0 mmHg (p=0,006) in head-up position after 24h was found. No significant correlation was found between IOP change and last mean TF values (17-18h) before sensor removal (fig.2). The sensor caused a myopic shift (p<0.05) but no significant increase in CCT was found.

 

Conclusions

 

Sleep position seems to affect the IOP as measured by TF in some patients with progressive glaucoma. However, the upward drift in TF output detected in more than 50% of the subjects needs to be taken into account when interpreting TF output. Further studies are required to establish whether this drift is an artefact or real.

 

 

TF output with drift

 

 

Keywords: 568 intraocular pressure