Results indicate that there was a significant difference between HEVF and HVF. The findings of the study demonstrated that more subjects passed the new driver’s license visual field requirement using the HEVF when compared to the HVF.
Results indicate that the HVF is still the predominant visual field test for the detection and diagnosis of visual field defects in glaucoma, but in the case of driver’s license screenings, the HEVF can be as effective as the HVF in detection of central defects in cases of advanced glaucoma.
Crabb et al in 1998 described a method known as integrated visual field (IVF) to simulate a binocular visual field using data from monocular visual fields
]. The IVF is estimated from monocular results, taking the best sensitivity values from corresponding visual fields locations from the two eyes. The authors found a substantial agreement between the simulated binocular results and HEVF in classifying glaucomatous patients
]. These results were even corroborated by Nelsson-Quigg et al., which demonstrated general agreement between results from the HEVF and an integration of two monocular visual fields into one binocular field
Since the current study did not use IVF data compilation it was not possible to make direct comparisons to previous research. Further studies must be done to determine agreement between the IVF and the HEVF in classifying a glaucomatous subject’s legal fitness to drive according to the guidelines of the Swedish Transport Agency. Probably the HEVF can be replaced by the IVF improving visual field evaluation and saving resources.
According to the new regulations, consideration is given not only to the central visual field, but also the peripheral portions of the visual field. In previous studies, testing was focused only on the central 20° of the visual field. A higher ”pass” rate for the HEVF could be due to the fact that even though most of the subjects had peripheral visual field defects, the defects were not large or deep enough to constitute a ”fail” result (see Figures
) under the new binocular testing regulations. The Figures
belong to the same subject who failed both the HFV and the HEVF.
Figure 1 HVF of one subject’s right and left eyes. Even though the bilateral field defects resulted in a “fail” result for the HVF, the subject passed the HEVF (see Figure
Figure 2 The same subject’s HEVF shows only a few missed points. The remaining defect is not in the vertical area 20° from the center of the visual field (denoted by thick black tick marks), and the missed adjacent points are outside of the horizontal (more ...)
Figure 3 An HVF test from one of the subjects included. Missed test points can be seen with sensitivity values below 10 dB within the area of defect; there are many missed adjacent points in the required field. The test is therefore classified as “fail”. (more ...)
Figure 4 The same subject’s HEVF shows lot of missed points. The defects (denoted by thick black tick marks) are situated in the vertical area 20° and the horizontal 50° from the center. In this area 3 adjacent defects were detected, therefore (more ...)
These new Swedish regulations are intended to be closure to regulations in other European countries. In the UK a driver should have a binocular horizontal visual field of at least 120° assessed using a Goldmann III4e target or similar and have no significant defect
]. The European Union Member States have their individual driver’s license requirements and guidelines, but the European Union regulations can potentially overrule these. According to the European Union Commission Directive put into effect August 25, 2009 (amending a directive from 1991), new visual requirements were recommended in the European Union for obtaining a driver’s license. Applicants shall have a visual acuity of at least 0.5 when using both eyes together. Moreover, the horizontal visual field should be at least 120 degrees; the extension should be at least 50 degrees left and right and 20 degrees up and down
]. However, no description of which visual field test to be used has been included in the European Commission’s regulations.
The new Swedish regulations for fitness to drive have no stated any influence in fitness to drive and where the visual field defects are localized. It does not matter if visual defects are placed in the nasally or temporally part. Theoretically temporal defects would alter more driving capabilities than nasal defects. In case of nasal visual field defects, the visual fields from the other eye will compensate. Furthermore, vehicles coming from the sides will be detected mostly with the temporal part of the visual field. Information about influence of placement of visual field defects and fitness to drive are scarce in the literature. Racette & Casson found no difference in driving capabilities tested on-road driving with different locations of visual field defects when testing subjects that were affected of cerebral vascular accident
]. The authors even concluded that the results must be reconfirmed because of a large individual difference and small sample size. Driving performance is difficult to measured as it was pointed out by Crabb et al , because of accident rates are low in the general population, driving simulators are difficult to utilise and other factors than visual defects can alter driving fitness in glaucoma subjects like age and cognitive skills
According to the Swedish Transport Agency is up to the ophthalmologist to decide to use whether the monocular or the binocular visual field tests for determining fitness to drive. The decision should be based on clinical findings. Subjects included in the present study showed moderate visual field impairment due to glaucoma (MD
dB). Haymes et al evaluating glaucoma subjects with slight glaucoma damage (MD
dB) found no increased difficulties while driving using a real-world setting compared to normal subjects
]. It is very possible that subjects affected by slight glaucoma damage would passed both tests as same as subjects with great visual field damage would failed in both tests. Further investigations should be done to correlate results from monocular and binocular tests methods with “real life” situations during driving. Studies using “driving simulators” would add more valuable information.