As analysis of the VF is essential in the evaluation of glaucoma progression, and in order to avoid abnormal VF results related to previous examination of the eye, glaucoma patients often have the VF test performed just prior to the ophthalmological consultation. IOP is the only parameter amenable to treatment, with proven efficacy on glaucoma progression, so its measurement during the consultation has a direct impact on the therapeutic decision. However, it has been stated that VF testing might increase IOP in some patients. This could be of particular importance and may justify performing the VF test at a separate time from that of the consultation. It is well known that environmental factors have an effect on IOP. Erb et al. showed that psychological stress can induce an IOP elevation, possibly due to a sympathetic response increasing blood pressure and heart rate . Patients who see the VF as a difficult performance test could be stressed, and this could be a factor causing an elevation in IOP after the VF test. VF’s are also performed in a dark room, and Gloster et al. showed that mydriasis induced by confinement in a dark room resulted in an IOP elevation of 4 mmHg (not only in angle closure glaucoma), with the return to the original IOP taking approximately 10 minutes . In our study we found no impact of the VF test on IOP (global model fit R²=0.12), whether based on the duration of the VF test (P=0.18) or the MD (P=0.7) after adjustment for age, gender, CCT and history of glaucoma surgery, analysing all patients. Patients with a ≥ 2 mmHg IOP elevation had a mean VF test duration of 12.8 ± 2.6 min, which was a longer test duration than for other subjects (P=0.002, table 3), suggesting an effect of VF testing on IOP for patients with longer VF test durations. However, this was only found on a subgroup analysis, and there were no correlations observed on multivariate analysis between IOP change and VF test duration.
In the literature, several studies have already studied this subject and have led to conflicting results. Two studies showed an impact of VF testing on IOP. Recupero et al. reported a significant mean increase in IOP after automated VF testing (P<0.01) in 94 glaucomatous eyes . The mean IOP increase was 2.38 ± 3.49 mmHg (range - 6 to 11 mmHg). They also found that elderly glaucoma patients showed a significantly higher IOP elevations than younger patients, which was not confirmed in our study. They suggested rejecting IOP measurements in glaucomatous eyes if measured soon after VF testing. Interestingly, in this study, test duration ranged from 7 to 21 minutes, using the central 30–2 full-threshold program, which is typically a VF test with a longer duration. This longer duration of the VF test might be associated with psychological stress, inducing an IOP elevation [16, 19]. Similarly, our patients with a transient IOP elevation also had a significantly longer duration of tests. Another retrospective study of 109 eyes by Ni et al.  reported that the mean IOP measured after VF testing (14.9 ± 4.7 mmHg) was significantly higher than both the previous (13.7 ± 4.4 mm Hg, P<0.001) and following visits without VF examinations (13.8 ± 4.4 mmHg, P<0.001). They explain the rise in IOP by a stressful perception of VF testing by the patients, leading to a sympathetic response that transiently elevates IOP . Nevertheless, they did not find any correlation of IOP variation with age or use of β-blockers (BB) or α-2-agonists (AA). In this study, IOP measurements were not compared immediately before and after VF testing, but were compared to the previous visit and the following visit. Factors other than the VF test might have interfered with IOP and could explain these different results.
Conversely, three studies showed no differences. Rebolleda et al.  studied 52 eyes (27 patients) with POAG and did not observe any significant IOP variations immediately after VF testing or one hour later. They did not find any significant IOP change in a group of 12 eyes (6 patients) who underwent Goldman tonometry immediately before and after VF testing. They used the same patients as a control group and repeated tonometry 72 hours later, in the same time frame but without VF examinations, and they did not find any significant IOP variations either. They used a control group, because they believed that the IOP variations found by Recupero et al. could be due to fluctuations in the IOP inherent to glaucomatous eyes and not to an effect of VF testing. Martin et al.  studied 61 patients with glaucoma, OHT or suspected glaucoma, measuring IOP immediately before and after VF testing, and the mean differences were not significant. Lee et al.  studied 45 patients (71 eyes) with OAG with the Icare® rebound tonometer (RBT). The IOP’s measured immediately and 20 minutes after VF testing were not different, and the IOP measured 10 minutes after VF testing was significantly lower (-0.57 ± 1.84 mmHg) but within the margin error of the RBT. In the present study, IOP measurements were taken using a non-contact tonometer, which is not considered as the gold standard for tonometry measurement, as is Goldman applanation tonometry . The reason was to avoid disturbing either the visual field or the second IOP measurement with anesthetics and/or repetitive procedures and manipulations of the eye and the patient. In addition, we excluded patients with pathological corneas or other conditions that could cause errors in IOP measurements, which might have affected the reliability of IOP measurement. Moreover, the two measurements before and after the VF were taken by the same method and on the same machine. This may have limited the issue of subjectivity in Goldmann tonometry and avoided measurement bias. Our study measurements were done within a maximum of 5 minutes before and after VF testing for every patients, allowing observation of a direct effect of VF testing if it existed. In addition, no difference was found with regard to severity of glaucoma, history of glaucoma surgery, use of glaucoma medication or age. As usual in clinical practice, patients had different types of VF tests performed during the consultation, including HFA 24-2 alone or combine with 10-2, Octopus G2 alone or combine with Octopus C08, and FDT matrix 24-2. Nevertheless, only 2 patients had a HFA 10-2 alone (2,1%) and only one patient (1,1%) had a FDT alone and his MD value was not considered for statistical analysis. Although it would have been interesting to analyse the effect on IOP of the different types of VF, the low number of patients in each group did not allow this subgroup analysis in our study.