A contact lens photostimulator for surgical monitoring

Vep

“…For cranial surgery such as for removal of tumors and other lesions of the anterior pathways, Harding et al observed that "transient abolition of the VEP seen under many circumstances did not correlate with the outcome of surgery, but absence of a previously normal VEP for greater than 4 min during surgical manipulation within the orbit correlated with postoperative vision impairment." [ 46,54 ] However, few if any seem to have adopted this warning criteria and perhaps for good reason. It is been reported that complete absence of F-VEPs is consistent with normal visual recovery, and, conversely, preservation of the responses does not exclude the possibility of impaired vision post surgery [ 3,21 ] .…”

“…Though some claim the resulting responses were more robust than those later obtained with LED stimulation (especially through dilated eyes) [ 46 ] , use of contact lens for IOM has lost favor due to the invasive nature of the technique, (e.g., lid sutures to keep the corneal lens recording/stimulating device in place) and the potential risk of corneal abrasions and ulcerations with their use. The American Electroencephalographic Society (AEEGS) Guidelines for IOM, recommend such hard lens stimulators be kept on the eyes for a maximum of 45 min (limiting their practical use for a majority of surgical procedures) and that users need to carefully examine the safety data from the stimulator's developer before employing such lenses in the OR [ 47 ] .…”

“…Fiberoptic haptic lens [ 46 ] and scleral contact lens [ 14 ] connected to photostimulators were developed to provide flash stimuli in the 1970-1980s. Though some claim the resulting responses were more robust than those later obtained with LED stimulation (especially through dilated eyes) [ 46 ] , use of contact lens for IOM has lost favor due to the invasive nature of the technique, (e.g., lid sutures to keep the corneal lens recording/stimulating device in place) and the potential risk of corneal abrasions and ulcerations with their use.…”

Time to revisit VEP monitoring?

“…LEDs are typically mounted onto goggles or eye patches for stimulus delivery through closed eye lids. Contact lens type stimulators [7] have raised concern about corneal lesions [2]. High-intensity stimuli have brought some improvement [12]; direct electrical stimulation of the optic nerve is another promising suggestion [1].…”

Visuell evozierte Potenziale und Elektroretinogramm

“…B. die Kraniotomie selbst eine Latenzverzögerung, deren Ursache unklar ist. Harding et al (1987) konnten mit in Kontaktlinsen eingebauten Photostimulatoren bessere Ergebnisse erzielen. Sie fanden bei Eingriffen in der Orbita, dass ein länger als 4 min dauernder Verlust der VEP während des Eingriffs in allen Fällen mit einer postoperativen Visusverschlechterung korrelierte (Harding et al 1990).…”