ACQUIRED BRAIN INJURY

While acquired brain injury (ABI) can have significant implications on a patient’s ability to drive, many patients do recover and there are a variety of established treatment options. At a conference on traffic medicine here, Patricia Logan FRCSI, FRCOphth, Beaumont Hospital, Dublin, discussed diagnosis and treatment options for common neuro-ophthalmology issues caused by ABI. She pointed out that the general public commonly believes that visual ability is simply linked to the eyes, and sometimes find it hard to understand the role of the “complex” visual pathway, and how eyesight can be negatively affected by an ABI or neurological medical condition. Sudden onset of diplopia, loss of visual acuity and field, and oscillopsia are the main visual issues that neuroophthalmologists deal with, Ms Logan told the meeting.

“Vision is the most important source of information when driving, so visual assessment for driving is a major public health issue”

ABI-related visual issues can occur due to severe head trauma, stroke, tumours, certain diseases such as multiple sclerosis (MS), and as a result of neurosurgery. She said that typically these issues have a rapid and sudden onset and can occur in young, otherwise healthy patients with good visual acuity and can significantly affect driving ability. While many ABI issues will resolve with time or are treatable, some patients will never be able to drive again, which may impact on their ability to work, and this can be devastating for them, Ms Logan noted. Many of these patients who may not recover perfect visual ability can adapt quite well, which needs to be recognised in relation to their driving ability, she pointed out.

Treatment

Those who develop diplopia are commonly treated with prism therapy and occlusion therapy or occasionally eye muscle surgery, depending on the amount of muscle damage. However, not all will recover binocular vision, Ms Logan said. She explained that cranial nerve palsies, such as third cranial nerve palsy, can result from head injuries, aneurysms, haemorrhages, tumours or diabetes, and affect eye orientation, causing diplopia and affecting driving ability. Some palsies resolve spontaneously after a period of time. Others can be treated in a similar fashion to diplopia by patching, prisms or surgery, she elaborated. “Many stroke patients with visual field loss may recover it within six months, though if they don’t significantly improve within six months then they are not likely to improve any further,” she explained.

Non-progressive lesions may stabilise and allow adaptation. Progressive lesions, on the other hand, require monitoring and frequently have more negative outcomes in relation to ability to drive, she explained. “So if someone has a visual field defect due to a progressional lesion from a tumour it’s very hard to predict how their vision will turn out so that requires constant monitoring,” she said. Other serious visual issues that can be caused by tumours include bitemporal hemianopia; a reduction in vision in both the right and left visual fields, which can obviously be quite dangerous for driving. Discussing treatment approaches to serious ABI visual pathway issues, Ms Logan said visual rehabilitation may help to improve patients’ refixation saccades, while prism therapy may also increase their useful field of vision. However, both rarely allow patients to fulfil the required driving visual criteria.

Patients with conditions like MS may experience a sudden loss of visual acuity from optic neuritis and have painful eye movements. “Fortunately about 85 per cent of these patients recover, so again it is a matter of time,” Ms Logan noted. However, in patients who experience traumatic (eg, head injury), compressive (eg, tumour), or especially ischaemic optic neuropathy, the outcomes can be less positive and quite difficult to resolve, she informed the meeting. Visual driving guidelines As president of the Irish College of Ophthalmologists (ICO) Ms Logan also discussed the new medical fitness-to-drive guidelines that were formally launched in Ireland in February.

“The eye doctors of Ireland welcome and fully support this collaboration between the Irish Road Safety Authority and the Department of Traffic Medicine in the Royal College of Physicians of Ireland in providing clear guidelines on the visual criteria for driving,” Dr Logan commented. She reiterated that understanding the impact of a visual condition on driving is a vital aspect of road safety. “Vision is the most important source of information when driving, so visual assessment for driving is a major public health issue. The measurement of visual acuity, contrast sensitivity, fields of view, twilight vision and vision under glare conditions are of the utmost importance,” she stated. Ms Logan voiced her support for Irish proposals for a validated on-road driving assessment for patients who do not strictly fulfil the visual criteria, but whom the treating consultant believes is competent to drive. She also supported proposals for the creation of a special driving licence restricted to daylight driving for certain visually impaired patients.