• Neuro-Ophthalmology/Orbit

    Review of: Visual field deficits following laser ablation of the hippocampus

    Donos C, Rollo P, Tombridge K, et al. Neurology, March 2020

    Laser interstitial thermal ablation (LITT) has become an increasingly popular option for the treatment of mesial temporal lobe epilepsy (MTLE) due to its minimally invasive nature and higher rate of preservation of language and memory function. Visual field defects in these patients are usually unnoticed by the patient until formal visual field testing is performed. It is not always clear whether the defects are caused by a lesion in Meyer’s loop in the optic radiations in the temporal lobe or in the lower banks of the calcarine sulcus of the occipital lobe along the laser probe trajectory.

    In this study, researchers assessed visual field deficits following LITT for MTLE and compared them with anterior temporal lobectomy (ATL).

    Study design

    Of the 32 patients undergoing LITT, 22 underwent ablation of the left and 10 of the right amygdala and hippocampus. The results from LITT were compared with 25 studies describing visual field deficits after ATL.

    Outcomes

    The incidence of visual field defects after LITT was much lower than after ATL. Of the patients undergoing LITT, 37.5% developed a visual field deficit in either eye. The most common deficit was a superior vertical octantanopsia. Visual radiations were at greater risk during surgery for the left MTLE than the right. The authors conclude that LITT was superior to ATL in achieving seizure control and resulted in fewer visual field defects. Visual field tractography incorporated into LITT planning may reduce the occurrence of visual field defects.

    Limitations

    Although the study eliminated 14 deficits in order to avoid contamination of postablation visual field data analysis, this step only controlled for false-positive visual field deficits; preexisting asymptomatic contralateral superior temporal quadrantanopias would still have be included. The authors findings also require further validation.

    Clinical significance

    This study confirms that less invasive approaches to treatment of temporal lobe seizures may result in fewer and smaller homonymous visual field defects, most of which are not noticed by patients and do not appear to cause any significant problems with visual function.