Thorough preoperative evaluation and meticulous operative technique are the best methods to prevent complications in blepharoplasty.

Mild pain, ecchymosis, eyelid edema, diplopia, lagophthalmos, blepharoptosis, subconjunctival hemorrhage, and diminished sensitivity of the eyelids usually resolve with supportive care.

Other complications such as persistent fat hernias, excess skin, or redundant orbicular ridges may be corrected later. 

Major complications such as blindness, hematoma, ectropion, hollow eye, corneal injuries must be prevented. The incidence of blindness in blepharoplasty is 1 in 20,000.

The most feared complication of blepharoplasty is retrobulbar hematoma.
Patients must be observed closely for, and warned of, the signs and symptoms of retrobulbar hematoma.
Typical postoperative pain is mild, but patients with retrobulbar hematoma experience severe orbital pain.

Patients also may complain of decreased visual acuity.
On physical exam the eyelids may be ecchymotic and the globe is tense and proptotic.
This typically occurs in the immediate postoperative period but has been reported up to 5 days postoperatively.
The exact mechanism of retrobulbar hematoma is unknown but it is thought that bleeding from either orbital fat or orbicularis muscle increases intraorbital pressure, increasing intraocular pressure, which may cause central retinal artery occlusion.

Another theory is that the increased intraorbital pressure may close the small ciliary arteries that feed the optic nerve itself.

Retrobulbar hematoma is a true emergency requiring quick, aggressive treatment since it is estimated that you have about 100 minutes to save the vascularly compromised eye. Initial management consists of opening the wound and evacuating any hematoma.
The eye may be massaged as well. If this fails to resolve the problem, aggressive medical management should be instituted.
Patients should receive Mannitol 1gm/kg and Diamox 500mg IV to try to reduce the intraocular pressure.
Steroids may be used as well.
The next step would be cantholysis and even orbital decompression.
This disorder requires the assistance of a good ophthalmologist.