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Response to Fine’s perspective
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To the Editor:
I. Howard Fine, MD’s “Perspective” (Calibrated gauge simulates force of patient manipulation after cataract surgery, Ocular Surgery News, June 25, 2013, page 18) is always thought-provoking and interesting to the readership.
His first comment mentions that postoperative infection occurs far less commonly than does wound leak, raising question as to the clinical relevance of the latter and of our study. Factors that induce postoperative infection are multiple, including, but not limited to, host resistance, microbial load and capsule rupture. However, from the Wallin et al study, we know that wound leak noted on the first postoperative day is associated with a 44-fold increase in postoperative infection. For that reason, I cannot understand why Fine would dismiss the significance of wound leakage.
Fine questions the use of ounce as a measure of force. Actually, the ounce can be a liquid measure, mass or unit of force, the ounce-force (one-sixteenth of a pound-force), which is commonly converted to newtons, according to a dictionary of units of measurement from the University of North Carolina and Wikipedia. The ounce-force may also be used to measure torque. The force gauge developed in our investigation was derived from an instrument employed in orthodontics. We opted to employ the measurement units of the manufacturer rather than to recalibrate to another unit of force measurement.
Samuel Masket
He also questions the value of the force gauge to simulate the effect of patient eye rubbing. While one cannot estimate how firmly or with what point load a given patient will rub the eye at each and every event, we tested the device to measure the change in IOP that was reported in the literature as associated with digital pressure on the eye. In turn, elevating IOP with force can distort the incision, potentially inducing wound leak with hypotony and subsequent inflow of surface fluids into the anterior chamber.
Finally, Fine comments on the use of optical coherence tomography to evaluate wound leak in the early postoperative period. Unfortunately, OCT has not been demonstrated to be a valuable tool in determination of incision competence and wound leakage, although it more than adequately reveals incision morphology. Additionally, the curvilinear appearance of the incision on OCT described by Fine has been reported by others to be transient and indicative only of distortion of the tissue by swelling in the early period after surgery.
The calibrated force gauge reported in our investigation provides a tool to evaluate the effect of wound distortion by measurable external ocular force. It may be used to investigate varying forms of incision construction as well as the competence of several means for incision closure, including sutures and tissue adhesives.
Samuel Masket, MD
Los Angeles
Disclosure: Masket is a consultant, medical monitor and shareholder for Ocular Therapeutix.