It is important to have practiced this procedure on a cadaver in order to have the confidence to do it in vivo. Local anesthetic should be placed around the lateral canthus of the eye. Small straight scissors should be used to divide the lateral canthus down to the bone of the orbital rim and to the depth of the lateral sulcus of the conjunctiva. It is important to protect the globe in order to avoid a corneal abrasion or conjunctival damage (Fig. 12.18a-d). The lower lid is then retracted downward to expose the substance of the lower lid; the scissors are angled at 45° to the horizontal axis and
the lateral ligament and septum are divided. The globe and contents of the orbit will then prolapse forward. A little blood-stained exudate will come out, but do not expect much bleeding and do not probe into the posterior compartment of the eye. The pupil reflexes, the pressure of the orbit, and vision should all be checked. Over the next 2-3 days, the orbit will retract to its normal position and the incision will normally be almost imperceptible as it fades into the crowsfoot of the eye. It does not require suturing at any stage.
This procedure is normally sufficient to decompress the posterior compartment of the eye. If it is inadequate, a medial decompression should be undertaken as well. This can be done either endoscopically by removing the lamina papyracea widely and incising the orbital periosteum or externally via a Lynch-Howarth incision; the choice depends on the surgeon's experience. Do not be frightened about making an external incision if you are most comfortable with that approach. Preserving vision takes priority and comes before any embarrassment you may have about producing an external scar. In any event, an external incision normally heals well as long as the line is broken with a seagull shaped incision, as this will minimize the chance of webbing. If the orbit is decompressed by an external approach, the anterior ethmoid artery will not be found as it will have retracted into the substance of the orbit. It should not be sought, as this would cause more disruption and damage to the orbit.
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