Perioperative Ocular and Visual Disturbances

Abstract

Visual loss after anaesthesia and surgery is an unexpected and a devastating complication. Symptoms and signs of eye injury associated with visual loss are not generally familiar to most anaesthesiologists. The incidence of visual loss postoperatively has been estimated at 0.003% and 0.0008%. Cases can be divided into retinal ischemia, Ischemic Optic Neuropathy (ION), cortical blindness and acute glaucoma. Blood supply to the retina and the optic nerve depends on the intraocular perfusion pressure. This perfusion pressure is defined as the difference between the mean arterial pressure and the intraocular pressure (IOP). High IOP impairs the blood supply, leading to a loss of optic nerve function. After an incision in the globe is made, factors that would increase IOP can cause prolapse and loss of intraocular contents; this can cause permanent vision loss. A decrease in mean arterial blood pressure diminishes ocular perfusion pressure (the difference between mean arterial and retinal venous pressure). Increases in IOP decrease retinal and choroidal blood flow. Changes in hematocrit may alter ocular blood flow. Hemodilution increased retinal blood flow by 71% and preserved retinal oxygen delivery while producing a significant 19% decrease in choroidal blood flow. Visual symptoms could be misdiagnosed as delirium on awakening from anaesthesia, whereas blurry vision may be attributed to the anaesthetics or to the use of ointments in the eye. Focal neurologic complaints such as unilateral weakness suggest a concomitant stroke, a frequent feature with cortical blindness. Pupil signs in the postoperative period are easily overlooked or misdiagnosed, particularly after narcotic-based anaesthetic techniques or with the use of postoperative, parenterally administered analgesia. However, a unilateral pupillary defect in a patient complaining of visual loss should trigger further evaluation. Central (CRAO) or branch retinal artery occlusion (BRAO) may be accompanied by extraocular muscle dysfunction (i.e., impaired eye movements). Facial or periorbital oedema may be present in patients with associated venous obstruction. Ophthalmologic consultation is indicated for patients complaining of postoperative visual loss or blurry vision. A detailed neurologic examination is indicated if a cerebral cortical cause for the visual loss is suspected or to rule it out. When using a facemask, care must be taken to avoid applying undue pressure to the eye. Another potential complication is corneal abrasion; proper eye care with taping of lids with or without ocular lubricants provides protection. If a patient emerges from general anaesthesia with eye pain or foreign body sensation, then must be followed up to ensure improvement, if left untreated corneal abrasions can progress to corneal ulcers. The associated factors, in the perioperative period, with Retinal Artery Occlusion (RAO), ION, acute glaucoma or cortical blindness may include: age, unstable angina, diabetes, prior stroke or transient ischemic attack, previous CABG surgery, history of vascular disease. Transient visual loss may occur after TURP, Where visual disturbances occur only with Glycine as an irrigating fluid, range of visual loss: diming of vision to Light Perception to No Light Perception. The onset is from 30 minutes to 6 hours where Fundus Examination, (IOP) and Visual Evoked Potential (VEP) are normal. Vision returns spontaneously to normal from 2 hours to 12 hours after onset, as the cause is that Glycine is an inhibitory cerebral chemical neurotransmitter so when its level increases it inhibits the visual pathway. The most serious injuries that are most likely to result in blindness are RAO and ION. Even with avoidance of inadvertent pressure on the eye, many of these complications still occur, particularly after spine, cardiac, and head and neck surgery. The etiology of many of the injuries appears to be multifactorial, but the risk factors remain incompletely explained, and more studies are necessary.