Tonometry can serve as tool in CME prevention

July 10, 2019

Research offers guidance on NSAID use, identifies etiologic role of abnormal IOP

Research studies find that normalization of IOP at the end of cataract surgery can reduce the risk of cystoid macular edema (CME) and mitigate the need for adjunctive perioperative NSAID treatment in routine cases involving patients without diabetes.

Reviewed by John S. Jarstad, MDThe use of tonometry to check and guide adjustment of IOP immediately at the end of cataract surgery can reduce the risk of cystoid macular edema (CME). After that, patients can receive a topical corticosteroid postoperatively; perioperative nonsteroidal anti-inflammatory drug (NSAID) use may not be essential in routine cases.

Adjunctive NSAID treatment, however, is essential to reduce the risk of CME in all patients with diabetes and is also recommended in any case where there is an intraoperative complication or other risk factor for CME, said John S. Jarstad, MD. Dr. Jarstad’s comments were based on studies conducted at the Department of Ophthalmology, University of Missouri School of Medicine, Columbia, where he is associate professor of clinical ophthalmology and director of cataract and refractive surgery.

“Our study looking at the effect of NSAIDs on CME is the largest study to date on this topic, but it is retrospective,” he said. “The findings on omitting NSAIDs in routine cases if IOP is accurately assessed and adjusted into the normal range in the operating room should be investigated in a future controlled randomized trial.”

The incidence of CME in eyes operated on without perioperative NSAID use was investigated in a single surgeon retrospective study conducted by Dr. Jarstad as primary surgeon with the collaboration of Van Nguyen, MD, ophthalmology resident, and Carli Wittgrove, medical student.

The study included data from 930 eyes that underwent femtosecond laser-assisted cataract surgery (FLACS) or microincisional cataract surgery (MICS) between July 2016 and January 2018. “The period chosen for the study was a time when we were not using perioperative NSAIDs because of a supply shortage,” Dr. Jarstad explained.

“Rick Fraunfelder, MD, department chairman, suggested we review patients’ outcomes to investigate his impression that NSAIDs were not needed to prevent CME in routine cases.”

In all cases, IOP was checked and adjusted with BSS to between 16 mm Hg and 21 mm Hg using a sterile 27-gauge cannula with a Tono-Pen (AO Reichert) and sterile cover immediately after completion of surgery while the patient was still on the operating table. Patients whose visual acuity did not correct to 20/20 during follow-up were evaluated over the next several weeks with optical coherence tomography (OCT) of the macula to detect CME.

RELATED: Rebound Tonometry Useful Tool To Measure IOP In ChildrenCME was diagnosed by imaging in two eyes (8%) of 25 patients with diabetes but in only 13 eyes (1.4%) eyes of 905 patients without diabetes, he said.

“A Cochrane analysis including 948 eyes from 6 studies reported that the incidence of CME ranged from 1.2% to 4%,” he said. “Our study results fall within this incidence range, providing evidence that NSAIDs may not be essential to prevent CME in routine cases in non-diabetic patients if IOP is adjusted immediately after surgery.”

IOP as a risk factor

The value of checking IOP with tonometry and adjusting it to between 16 and 21 mm Hg was shown a previous study published by Dr. Jarstad and colleagues [Jarstad JS, et al. Korean J Ophthalmol. 2017;31:39- 43], which included 176 consecutive eyes that underwent FLACS or MICS.

The study was conducted to assess the accuracy of IOP determination by palpation and had an unexpected finding that abnormal immediate postoperative IOP was a cause of CME in routine cataract surgery. Cases were performed by two cataract surgeons and four senior residents.

IOP was estimated at the end of surgery by “feel,” and after the value was recorded, IOP was measured with a sterile handheld Barraquer surgical tonometer and a Tono-Pen. IOP was adjusted on the table if the Tono-Pen reading was ≥30 mm Hg or >10 mm Hg.

Data showed good agreement between the two instrument measurements. There were, however, large differences comparing the palpated IOP values with tonometry data. Immediate postoperative IOP thought to be safe (10 to 30 mm Hg) when estimated by surgeons’ feel ranged from 9 to 67 mm Hg when verified with tonometry.

Dr. Jarstad noted that when the paper was submitted, one of the reviewers commented that experienced surgeons can tell what the IOP is by feel.

“Our study refutes that belief,” he said. “I have done over 25,000 cataract cases, and in the study, I did no better than my residents at accurately judging IOP.”

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Researchers did find that the ability to predict IOP accurately by palpation improves when practicing immediate verification with tonometry and by using a quick “double tap” through the side-port incision if IOP is too high.

An analysis investigating the idea that abnormal IOP is a CME risk factor found that compared with eyes with an adjusted IOP between 16 mm Hg and 21 mm Hg eyes with an IOP <16 mm Hg had a fourfold greater incidence of CME and those with an IOP >21 mm Hg had a 2.5-fold greater risk.

The study also indicated normalizing IOP at the conclusion of surgery can help prevent postoperative IOP spikes, the most common complication after cataract surgery.

The study found there was a <5 mm Hg average IOP change comparing the immediate postoperative value to the measurement obtained in the clinic on the first postoperative day.

The opportunity for cost savings by checking IOP in the OR was indicated by data showing that as many as 33% of postoperative patients without IOP adjustment in the OR required an adjustment on the first day after surgery compared with just 5% of patients whose IOP was adjusted immediately after surgery. 

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Disclosures:

John S. Jarstad, MD
E: jarstadj@health.missouri.edu
Dr. Jarstad has no relevant financial interests to disclose.