Fluorescin angiography shows lack blood flow the disc

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Blood Bank recommends hemoglibin-8gm/dl, the National Institutes of Health consensus conference of perioperative blood transfusion suggests 7gm/dl, the American College of Physicians advocates waiting for a deterioration of vital signs or until patient develops symptoms before blood is transfused. Importantly, the patients are now more likely to be maintained at lower average intraoperative hemoglobin levels than they were previously. A low hematocrit in the presence of other factors, particularly hypotension, may be the precipitating cause of postoperative ION, and one may need to transfuse blood at a higher hematocrit than is recommended for otherwise healthy patients.

Diagnosis of PVL

The onset of PVL usually occurs immediately on awakening but may be delayed upto seven days. Other confounding reason, such as, patient may not report the problem (believing it to be postoperative phenomena), misdiagnosis (confused state, delirium), and personnel not accepting the problem, may further complicate the clinical presentation. Judicious use of the following investigation may delineate the actual problem

The differential diagnosis of PVL is difficult especially when there is an overlap. Following are common situations that may lead to PVL:

Ischemic AION- Optic disc oedema on initial examination and occasional improvement in vision is possible. Typically occurs in one eye but the other eye gets afflicted after variable period. Visual acuity may improve in 30% of patients despite persistent pallor of disc.

Atypical situations

Intravitreal Gas

Transurethral Resection of Prostate Syndrome (TURP): One of the most alarming complications of “TURP syndrome” is transient blindness. The vision becomes foggy, one sees halos around the objects and pupils are typically dilated and unresponsive. The reason put forward is retinal dysfunction secondary to glycine toxicity.

Functional Endoscopic Sinus Surgery (FESS):Irreversible blindness due to electrocoagulation undertaken to gain control of delayed bleeding after FESS is a well-known but fortunately rare complication. Several anatomic structures in the nasal area lies in close proximity to one another, including; anterior cranial fossa, orbit,etc. Intranasal ethmoidectomy is considered ‘blindest’ and the ‘most dangerous’ of all endoscopic nasal surgeries. The area between posterior ethmoidal and sphenoid sinus is of critical significance because it is here where anatomic variation can predispose to inadvertent injury. Two mechanisms by which visual loss may occur during FESS are:

Drugs:Patients on anticoagulants, phosphodiesterase group-5 inhibitors (sildenfil, vardenafil, todafil) prescribed for erectile dysfunction, and intranasal α-agonists has been reported to cause AION. Patients on the above stated drugs are predisposed to PVL during prospective surgery (if any) under anesthesia. Local anesthetic (viz: bupivacaine, dyclomine, lidocaine, tetracaine) allergy/toxicity may result in blurring of vision, which may sometimes be construed as PVL.

Venous Air Embolism (VAE): Typically, VAE causes cortical blindness. Following surgeries are infamous for such an occurance: Open heart surgery involving cardiopulmonary bypass, lower segment cesarean section, laryngectomy, neurosurgery and neck dissection.

As patients with ION have not shown to be at higher risk for transient ischemic attacks/episodes, and myocardial infarction than unaffected patients, “optic nerve is now considered to be a critically sensitive watershed area”.

Despite the best of diagnosis and management methods, therapy is not uniformly successful and the results appear to depend on severity of the presenting symptoms. Following steps may help prevent PVL;