Exhaustive Notes on Driving Vision Standards and Esterman Field Testing

General Investigation Policy: All applicants for a driving license must undergo an appropriate investigation to ensure they possess adequate visual acuity for driving power-driven vehicles.
Examination Triggers: If there is any reason to doubt that an applicant’s vision is adequate, they must be examined by a competent medical authority.
Specific Clinical Focus: During the medical examination, specific attention must be paid to the following visual functions and pathologies:
- Visual acuity.
- Field of vision.
- Twilight vision.
- Glare and contrast sensitivity.
- Diplopia (double vision).
- Other visual functions that have the potential to compromise safe driving.

Notification Process: If the Driver and Vehicle Licensing Agency (DVLA) is notified by a patient regarding a visual issue, a field check is required. The DVLA usually arranges these tests at local approved optometrists, such as Specsavers.
Horizontal Field Standards: The binocular visual field must be at least $120^\circ$ horizontally. This must extend at least $50^\circ$ to each side.
Vertical Field Standards: The field must extend at least $20^\circ$ above and below the horizontal midline.
Central Fixation Requirements: No significant defect should exist within $20^\circ$ above or below the fixation point.
- A "significant defect" is interpreted as a cluster of more than 3 points.
- A significant defect also occurs if a cluster is attached to a defect outside the central area.
- Single scattered points are considered acceptable and do not constitute a failure.

Binocular Esterman Program: The standard test used for driving field screening is the Binocular Esterman program, performed on an automated field screener.
Conceptual Origins: The test arises from the concept of "measuring" disability. It was originally utilized for determining disability benefits and compensation claims (e.g., quantifying a " $30\%$ loss of vision").
Developmental Logic: Esterman devised his "functional scoring of the binocular field" in 1982. The design was based on clinical intuition and experience rather than experimental data.
Weighting System: The grid is weighted with more points assigned to areas considered more functional.
- No points are tested beyond $60^\circ$ .
- Most points are concentrated in the central area.
- The lower field contains more points than the upper field.
Grid Overlay: The test works by overlaying a grid with specific points on a field plot and calculating how many points are seen by the patient.
Modern Implementation: Currently, most automatic perimeters include a pre-programmed Esterman protocol.

Stimulus Properties:
- The test uses considerably supra-threshold stimuli set at $10\,dB$ .
- In comparison, a standard threshold stimulus is approximately $30\,dB$ , making the Esterman test very lenient.
- Stimulus size: III, White.
- Background brightness: $31.5\,asb$ .
Test Parameters:
- Strategy: Two Zone.
- Test Mode: Single Intensity.
- Fixation Target: Central.
- Henson Esterman Program variation: Uses 112 points and a stimulus intensity of $100\,cd/m^2$ .
- Humphrey Esterman Program variation: Features a grid of 120 points.
Efficiency Scores:
- The Esterman Efficiency Score is calculated based on the ratio of points seen to total points presented (e.g., $\frac{120}{120}$ results in a score of 100; $\frac{69}{128}$ results in a score of 57).
- Reliability is assessed through fixation losses, false positive errors, and false negative errors.
- The DVLA requires a defect level of less than $20\%$

Sensitivity Differences: Because Esterman is a suprathreshold test, it may not capture the full extent of a visual field loss identified by a full-threshold test.
Case Studies in Sensitivity:
- Case 1: Full-threshold Humphrey central fields show left Bjerrum scotomas and a dense right arcuate scotoma down to fixation. However, the Humphrey Esterman binocular field only shows one or two missed spots within $20^\circ$ of fixation.
- Case 6: Full-threshold fields show a complete upper left quadrantanopia with inferior extension. The Esterman binocular field shows a cluster of 4 missed spots, with only 2 affecting the central $20^\circ$ .
Approved Screeners: While various visual field screeners are used, if a patient fails on a non-standard screener, the DVLA requires a follow-up test specifically on a Humphrey Visual Field Analyzer (VFA).

Driving Scenes: Chisholm (2008) highlighted functionally important areas of the visual field in typical driving scenes, emphasizing central and horizontal zones.
Critique by Glen et al. (2015): Research suggests the Esterman Visual Field Test (EVFT) grid may include irrelevant points. Specifically, many points in the inferior visual field correspond to the car's dashboard or internal structure rather than the road scene through the windscreen.
Hazard Perception Test: This is the second part of the theoretical driving test. Glen et al. (2015) research found that superior (upper) field defects had a greater average effect on hazard detection compared to inferior (lower) field defects. This has led to discussions regarding whether the Esterman test should be redesigned.

Monocularity:
- Group 1: Permitted if the driver has adapted to the condition. Adaptation is typically defined as a 6-month period.
- Group 2: Not permitted under any circumstances.
Diplopia:
- Group 1: Permitted if the condition is controlled via patching or prisms, or if the patient has adapted to it (usually requiring a $?6$ month period).
- Group 2: Not permitted. Neither patching nor the presence of diplopia is allowed.

Visual Acuity:
- Must pass the standard Number Plate Test.
- Must achieve $\frac{6}{7.5}$ in the better eye.
- Must achieve $\frac{6}{60}$ in the worse eye.
- The worse eye must have sufficient vision to bring the vehicle to a safe stop.
Refractive Limitation: If corrected with spectacles, the power must not exceed $+8.00\,DS$ .
Field of Vision:
- A horizontal field of at least $160^\circ$ is required.
- The field must extend $70^\circ$ to the right and left.
- The field must extend $30^\circ$ above and below the horizontal midline.
- Absolutely no defect is permitted in the central $30^\circ$ .

High Power Spectacles ( $>+8.00\,DS$ ): These are problematic due to the optical effects they create. Walsh and Pearce (2006) note that while pupil size mitigates some theoretical issues, high-power lenses can create scotomas or distort the peripheral field.
Spectacle Frames: The aperture of the frame limits the visual field.
- Decreasing the Back Vertex Distance (BVD) increases the field of view.
- However, decreasing BVD also increases the angular subtence (visual size) of the rim and the side-pieces, thereby increasing the size of the obstruction.
Esterman and Spectacles: Steel et al. (1996) investigated whether drivers take their spectacles off to pass the Esterman test to avoid frame-related obstructions (bridge or side-piece shadows).