Figure 1. Home screen of the Estermate web application with the 120 test points in an Esterman grid layout. The user selects the unseen points, toggles them from white to black, and clicks the analyse button.
A new app is now available for optometrists and ophthalmologists who regularly perform Esterman testing. Estermate, developed by ophthalmologist Dr Jeremy Tan, a clinician-researcher with interests in visual fields and glaucoma, offers a practical way to work through driving eligibility criteria systematically, particularly when the defect pattern is complex or the applicability of a concession is uncertain.
The visual field (VF) is an integral component to driving safely,1 and the Esterman test has become the global standard in assessing the binocular VF for driving eligibility.2 In Australia, Austroads requires a minimum continuous horizontal VF span of at least 110º across the four rows adjacent to the horizontal meridian for a private, unconditional driver’s licence.
Certain formatting and design characteristics of the standard Esterman binocular visual field report, however, make this assessment less than straightforward. Firstly, the locations of the test points do not always align neatly with the numerical markings on the x-axis grid. Calculating the exact horizontal span between two seen points can be imprecise, and therefore, is often estimated.
Secondly, Austroads criteria permit certain defects to be disregarded, for example, a single cluster of up to three adjoining missed points unattached to any other area of defect, or a vertical defect of a single-point width but any length. These concessions exist to avoid penalising patients for small, isolated scotomas that are unlikely to be functionally significant. These defects, however, need to lie on or across the horizontal meridian. The concept of ‘adjacency’ is also not self-evident from the printout. Finally, even if a patient’s horizontal visual field span meets the minimum threshold, they must also satisfy the central visual field requirements to qualify for an unconditional licence. Specifically, the central visual field – defined as the area within a 20º radius of fixation – must be free from ‘unacceptable scotomas’. Under Austroads guidelines, an unacceptable central defect includes any of the following three patterns: a cluster of four or more adjoining missed points; a smaller cluster combined with additional scattered loss within the central 20°; or a central cluster that extends directly from a peripheral defect.
The complexity of applying these criteria to assess driving eligibility can therefore be highly subjective and variable, even between experts. Indeed, a recent study of ophthalmic experts from 32 countries tasked to apply the European VF standards for driving found only moderate levels of agreement for determination of pass/failure;3 only three of the 15 cases had full pass/fail agreement between the experts.3
Designing a Solution
Estermate (estermateapp.com) was developed to address this complexity. It is a publicly available web application that automates interpretation of the Esterman test according to Austroads criteria. The user toggles each of the 120 test points between seen and unseen on an interactive grid, and the application calculates the horizontal VF span and evaluates central VF criteria (Figure 1, above).
The horizontal span analysis works by finding the widest continuous band of seven points across the four midline rows, evaluated under three sequential criteria. Criterion one applies no concessions – every unseen point is treated as a defect. Criterion two allows a connected cluster of up to three unseen points touching the horizontal midline rows to be disregarded. Criterion three applies the vertical meridian concession. If multiple candidates for criteria two and three exist, the application chooses to disregard the cluster, which would maximise the patient’s horizontal span. The visualisations provided for both how horizontal and central visual field criteria are applied helps the clinician understand how these rules are being applied (Figures 2 and 3).
Figure 2. In this case example, the patient has two clusters of defects, one in the left mid-periphery (two points) and the other in the superior right central vision (three points). Without any concessions, the maximum horizontal span is 43º. Applying the Austroads concessions however, increases this to 103º and 76º for criteria two and three respectively. This patient may, therefore, be recommended a conditional private licence, but this will have to be assessed by the licensing authority.
Figure 3. In this second case example, the patient has a cluster of three unseen points in the right central vision. This cluster is connected to a peripheral cluster, as highlighted by the red circles, which would result in a failure of both Rules A and C.
A few caveats are worth stating clearly. Estermate reflects one interpretation of the Austroads criteria, and clinicians may read certain edge cases differently. Ultimately, this is a decision-support tool, not a substitute for clinical judgement.
The final determination of driving eligibility rests with the relevant licensing authority.
Collaboration with Austroads and licensing authorities is currently in progress to verify that these criteria are being interpreted accurately. Meanwhile, the application is freely accessible at estermateapp.com and requires no login or installation.
The launch of Dr Tan’s app coincided with the launch of a second app to help interpret driving eligibility, developed by Dr Simon Chen. Both apps are free to use.
Dr Jeremy Tan MD MMed FRANZCO is a clinician-researcher at the University of New South Wales and Prince of Wales Hospital with clinical and research interests in visual fields and glaucoma.
References
- Owsley C, McGwin G Jr. Vision impairment and driving. Surv Ophthalmol. 1999;43,535-550, doi: 10.1016/s0039-6257(99)00035-1.
- Bro T. Benjamin Esterman (1906-1994) and the binocular visual field scoring grid that became a world standard for assessing driver eligibility. Acta Ophthalmol. 2022;100(7):828-833. doi: 10.1111/aos.15096.
- Sudmann T M, Jonsdottir T E, RJørstad Ø K, et al. National application of the European visual field standards for driving: a survey study. BMJ Open Ophthalmol. 2022;7(1):e000904. doi: 10.1136/bmjophth-2021-000904.
