Goldmann applanation tonometry over daily disposable contact lens: Accuracy and safety of procedure

Abstract 

Purpose

To study accuracy and safety, related to sensation (discomfort) and trauma, when using Goldmann applanation tonometry (GAT) on eyes wearing daily disposable soft contact lenses.

Methods

The intra-ocular pressure (IOP) of 136 normal eyes of 68 subjects was measured by Goldmann tonometer. Measurements were made in one eye with a contact lens (hilafilcon A) without anaesthetic drops and then without the contact lens using one drop of 0.4% oxybuprocaine hydrochloride. Each contact lens used was identical as to back optic zone, back vertex power. Standard Goldmann procedure only was used for the fellow eye of each subject. Subjective sensation (discomfort) responses to both procedures were studied in a subgroup (66 eyes) using a scale of discomfort, from 1 (no sensation) to 5 (highest sensation). Epithelial staining after tonometry was evaluated for this subgroup.

Results

No significant differences were found for the IOP with and without contact lens (t<1; p=0.63) for the IOP range studied. There was a good correlation between the two procedures (r=0.81; p<0.05). Lowest sensation was found with tonometry on the anaesthetized cornea; this condition was significantly different from other conditions (p<0.005). No difference was found among the other conditions (contact lens insertion, tonometry on contact lens and application of topical anaesthetic).

Corneal epithelial staining following the standard tonometry procedure was significantly higher than following the procedure with a contact lens (p<0.00005).

Conclusions

Measurement of IOP by GAT over a daily disposable soft contact lens is accurate, compared to the standard procedure and within the IOP's normal range studied here. Also using a contact lens results in less trauma whilst discomfort is similar.

Keywords: Tonometry, Contact lenses, Intra-ocular pressure