Central and Paracentral Visual Field Defects and Driving Abilities

Clinical review of retinotopy

Two observations made 29 years apart are the cornerstones of this review on the contributions of Dr Gordon T. Plant to understanding pathology affecting the optic nerve. The first observation laid the anatomical basis in 1990 for the interpretation of optical coherence tomography (OCT) findings in 2009. Retinal OCT offers clinicians detailed in vivo structural imaging of individual retinal layers. This has led to novel observations which were impossible to make using ophthalmoscopy. The technique also helps to re-introduce the anatomically grounded concept of retinotopy to clinical practise. This review employs illustrations of the anatomical basis for retinotopy through detailed translational histological studies and multimodal brain-eye imaging studies. The paths of the prelaminar and postlaminar axons forming the optic nerve and their postsynaptic path from the dorsal lateral geniculate nucleus to the primary visual cortex in humans are described. With the mapped neuroanatomy in mind we use OCT-MRI pairings to discuss the patterns of neurodegeneration in eye and brain that are a consequence of the hard wired retinotopy: anterograde and retrograde axonal degeneration which can, within the visual system, propagate trans-synaptically. The technical advances of OCT and MRI for the first time enable us to trace axonal degeneration through the entire visual system at spectacular resolution. In conclusion, the neuroanatomical insights provided by the combination of OCT and MRI allows us to separate incidental findings from sinister pathology and provides new opportunities to tailor and monitor novel neuroprotective strategies.

Impact of photoreceptor density in a 3D simulation of panretinal laser photocoagulation

Background

During panretinal photocoagulation (PRP), the outer retina, especially the photoreceptors, are destroyed. During such procedures, the impact of the retinal photocoagulation, which is performed in the same photocoagulated area, may change if it is applied to different locations with different photoreceptor densities. Thus, we aimed to evaluate the influence of photoreceptor density on PRP.

Methods

We constructed a three-dimensional (3D) average distribution of photoreceptors with 3D computer-aided design (CAD) software using previously derived photoreceptor density data and calculated the number of photoreceptors destroyed by scatter PRP and full-scatter PRP (size 400-μm on the retina, spacing 1.0 spot) using a geometry-based simulation. To investigate the impact of photoreceptor density on PRP, we calculated the ratio of the number of photoreceptors destroyed to the total number of photoreceptors, termed the photoreceptor destruction index.

Results

In this 3D simulation, the total number of photoreceptors was 96,571,900. The total number of photoreceptors destroyed by scatter PRP and full-scatter PRP were 15,608,200 and 19,120,600, respectively, and the respective photoreceptor destruction indexes were 16.2 and 19.8%, respectively.

Conclusions

Scatter PRP is expected to have 4/5 of the number of photoreceptors destroyed by full-scatter PRP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-01945-z.

The Impact of Visual Field Loss on Driving Skills: A Systematic Narrative Review

Purpose

To review the evidence on the impact of visual field loss on skills required for driving.

Methods

A literature search was undertaken using a systematic approach. Papers within scope were identified by two independent reviewers, and papers were grouped into similar themes for discussion.

Key findings

Evidence suggests that both binocular and monocular visual field defects have a negative impact on driving skills. Both central and peripheral cause difficulties, but the degree of impact is dependent on the defect severity and compensation ability. Many factors that affect compensation to visual field loss and the effects of visual field loss on driving skills are discussed, including cognitive status, age and duration of visual field loss. In summary, in central visual field loss compensation, strategies include reduction of overall driving speed; whereas, in peripheral field loss, increased scanning is reported to aid adaptation.

Conclusions

For driving, there is evidence that complete and/or binocular visual field loss poses more of a difficulty than partial and/or monocular loss, and central defects cause more problems than peripheral defects. A lack of evidence exists concerning the impact of superior versus inferior defects. The level of peripheral vision loss that is incompatible with safe driving remains unknown, as compensation abilities vary widely between individuals. This review highlights a lack of evidence in relation to the impact of visual field loss on driving skills. Further research is required to strengthen the evidence to allow clinicians to better support people with visual field loss with driving advice.

Autoimmunity in visual loss

There are a number of autoimmune disorders which can affect visual function. There are a very large number of mechanisms in the visual pathway which could potentially be the targets of autoimmune attack. In practice it is the retina and the anterior visual pathway (optic nerve and chiasm) that are recognised as being affected in autoimmune disorders. Multiple Sclerosis is one of the commonest causes of visual loss in young adults because of the frequency of attacks of optic neuritis in that condition, however the basis of the inflammation in Multiple Sclerosis and the confirmation of autoimmunity is lacking. The immune process is known to be highly unusual in that it is not systemic and confined to the CNS compartment. Previously an enigmatic partner to Multiple Sclerosis, Neuromyelitis Optica is now established to be autoimmune and two antibodies - to Aquaporin4 and to Myelin Oligodendrocyte Glycoprotein - have been implicated in the pathogenesis. The term Chronic Relapsing Inflammatory Optic Neuropathy is applied to those cases of optic neuritis which require long term immunosuppression and hence are presumed to be autoimmune but where no autoimmune pathogenesis has been confirmed. Optic neuritis occurring post-infection and post vaccination and conditions such as Systemic Lupus Erythematosus and various vasculitides may cause direct autoimmune attack to visual structures or indirect damage through occlusive vasculopathy. Chronic granulomatous disorders such as Sarcoidosis affect vision commonly by a variety of mechanisms, whether and how these are placed in the autoimmune panoply is unknown. As far as the retina is concerned Cancer Associated Retinopathy and Melanoma Associated Retinopathy are well characterised clinically but a candidate autoantibody (recoverin) is only described in the former disorder. Other, usually monophasic, focal retinal inflammatory disorders (Idiopathic Big Blind Spot Syndrome, Acute Zonal Occult Outer Retinopathy and Acute Macular Neuroretinitis) are of obscure pathogenesis but an autoimmune disorder of the post-infectious type is plausible. Visual loss in autoimmunity is an expanding field: the most significant advances in research have resulted from taking a well characterised phenotype and making educated guesses at the possible molecular targets of autoimmune attack.

Driving with Central Visual Field Loss II: How Scotomas above or below the Preferred Retinal Locus (PRL) Affect Hazard Detection in a Driving Simulator

We determined whether binocular central scotomas above or below the preferred retinal locus affect detection of hazards (pedestrians) approaching from the side. Seven participants with central field loss (CFL), and seven age-and sex-matched controls with normal vision (NV), each completed two sessions of 5 test drives (each approximately 10 minutes long) in a driving simulator. Participants pressed the horn when detecting pedestrians that appeared at one of four eccentricities (-14°, -4°, left, 4°, or 14°, right, relative to car heading). Pedestrians walked or ran towards the travel lane on a collision course with the participant's vehicle, thus remaining in the same area of the visual field, assuming participant's steady forward gaze down the travel lane. Detection rates were nearly 100% for all participants. CFL participant reaction times were longer (median 2.27s, 95% CI 2.13 to 2.47) than NVs (median 1.17s, 95%CI 1.10 to 2.13; difference p<0.01), and CFL participants would have been unable to stop for 21% of pedestrians, compared with 3% for NV, p<0.001. Although the scotomas were not expected to obscure pedestrian hazards, gaze tracking revealed that scotomas did sometimes interfere with detection; late reactions usually occurred when pedestrians were entirely or partially obscured by the scotoma (time obscured correlated with reaction times, r = 0.57, p<0.001). We previously showed that scotomas lateral to the preferred retinal locus delay reaction times to a greater extent; however, taken together, the results of our studies suggest that any binocular CFL might negatively impact timely hazard detection while driving and should be a consideration when evaluating vision for driving.

Assessment of novel binocular colour, motion and contrast tests in glaucoma

The effects of glaucoma on binocular visual sensitivity for the detection of various stimulus attributes are investigated at the fovea and in four paracentral retinal regions. The study employed a number of visual stimuli designed to isolate the processing of various stimulus attributes. We measured absolute contrast detection thresholds and functional contrast sensitivity by using Landolt ring stimuli. This psychophysical Landolt C-based contrast test of detection and gap discrimination allowed us to test parafoveally at 6 ° from fixation and foveally by employing interleaved testing locations. First-order motion perception was examined by using moving stimuli embedded in static luminance contrast noise. Red/green (RG) and yellow/blue (YB) colour thresholds were measured with the Colour Assessment and Diagnosis (CAD) test, which utilises random dynamic luminance contrast noise (± 45 %) to ensure that only colour and not luminance signals are available for target detection. Subjects were normal controls (n = 65) and glaucoma patients with binocular visual field defects (n = 15) classified based on their Humphrey Field Analyzer mean deviation (MD) scores. The impairment of visual function varied depending on the stimulus attribute and location tested. Progression of loss was noted for all tests as the degree of glaucoma increased. For subjects with mild glaucoma (MD -0.01 dB to -6.00 dB) significantly more data points fell outside the normal age-representative range for RG colour thresholds than for any other visual test, followed by motion thresholds. This was particularly the case for the parafoveal data compared with the foveal data. Thus, a multifaceted measure of binocular visual performance, incorporating RG colour and motion test at multiple locations, might provide a better index for comparison with quality of life measures in glaucoma.

Driving with central field loss I: effect of central scotomas on responses to hazards

OBJECTIVES

To determine how central field loss (CFL) affects reaction time to pedestrians and to test the hypothesis that scotomas lateral to the preferred retinal locus will delay detection of hazards approaching from that side.

METHODS

Participants with binocular CFL (scotoma diameter, 7°-25°; visual acuity, 0.3-1.0 logMAR) using lateral preferred retinal fixation loci and matched controls with normal vision drove in a simulator for approximately 1½ hours per session for 2 sessions a week apart. Participants responded to frequent virtual pedestrians who appeared on either the left or right sides and approached the participant's lane on a collision trajectory that, therefore, caused them to remain in approximately the same area of the visual field.

RESULTS

The study included 11 individuals with CFL and 11 controls with normal vision. The CFL participants had more detection failures for pedestrians who appeared in areas of visual field loss than did controls in corresponding areas (6.4% vs 0.2%). Furthermore, the CFL participants reacted more slowly to pedestrians in blind than nonscotomatous areas (4.28 vs 2.43 seconds, P < .001) and overall had more late and missed responses than controls (29% vs 3%, P < .001). Scotoma size and contrast sensitivity predicted outcomes in blind and seeing areas, respectively. Visual acuity was not correlated with response measures.

CONCLUSIONS

In addition to causing visual acuity and contrast sensitivity loss, the central scotoma per se delayed hazard detection even though small eye movements could potentially compensate for the loss. Responses in nonscotomatous areas were also delayed, although to a lesser extent, possibly because of the eccentricity of fixation. Our findings will help practitioners advise patients with CFL about specific difficulties they may face when driving.

Vision and driving: the United States

Minimal visual standards for obtaining driving licensure in the United States principally use 2 measures: visual acuity and visual field. Although research studies have established a correlation between performance on these measures and safe driving, the correlations are weak and mostly retrospective. These measures remain in place in screening centers largely because they (especially visual acuity) are practical. A newer test of visual attention, called the useful field of view, may be more predictive of safe driving than the traditional measures, but it has not been widely applied in licensing bureaus.

Kompensatorische und restitutive Methoden des Gesichtsfeldtrainings

Gesichtsfelddefekte sind eine häufige Folge von Hirnschäden. Es existieren zwei Behandlungsansätze: 1. Kompensation durch Spiegelbrillen, Prismen, sakkadische Augenbewegungen, exzentrisches Lesetraining und 2. Gesichtsfeldvergrößerung durch ein spezielles visuelles Restitutionstraining. Spiegelbrillen und Prismen wurden vielfach kritisiert, tauchen aber auch in aktuellen Studien immer wieder auf. Kompensation durch ein Training sakkadischer Augenbewegungen in den blinden Bereich führt rasch zu Alltagsverbesserungen und ist als Methode weitgehend unumstritten. Für ein exzentrisches Lesetraining wurde aktuell ein computergestütztes System entwickelt. Erste Forschungsergebnisse des Restitutionstrainings wurden positiv bewertet, seit der Jahrtausendwende tauchte jedoch zunehmende Kritik auf – insbesondere bezüglich mangelnder Fixationskontrolle. Der Artikel setzt sich mit diesen Kritikpunkten auseinander und gibt einen Überblick über aktuelle Forschungsergebnisse, die zeigen, dass eine Gesichtsfelderweiterung zwar klein, aber durchaus möglich ist. Alternativerklärungen wie z. B. sakkadische Augenbewegungen und Veränderungen der Aufmerksamkeit konnten in neuen Studien weitgehend ausgeräumt werden. Hinsichtlich der Fahreignung können offenbar viele Patienten den Defekt gut kompensieren; Studien hierzu sind aber widersprüchlich. Empfohlen wird die bessere Verquickung von restitutiven und kompensatorischen Behandlungsstrategien, um Patienten optimale Hilfe zu geben.

Clinical disorders affecting mesopic vision

Vision in the mesopic range is affected by a number of inherited and acquired clinical disorders. We review these conditions and summarize the historical background, describing the clinical characteristics alongside the genetic basis and molecular biological mechanisms giving rise to rod and cone dysfunction relevant to twilight vision. The current diagnostic gold standards for each disease are discussed and curative and symptomatic treatment strategies are summarized.