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Justin Spaulding, Therese Sassalos, Nitin Kumar, Aldo Fantin; Proptosis and retrobulbar anesthesia: a technique to evaluate for subclinical retrobulbar hemorrhage.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):722.
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© ARVO (1962-2015); The Authors (2016-present)
This is a prospective pilot study to quantify the displacement of the globe and elevation in IOP from retrobulbar anesthetic injections. There is no prior studying measuring this phenomenon.
All patients were currently enrolled for PPV with a retrobulbar block (5cc of equal parts 0.75% Marcaine and 4% lidocaine) injected into the muscle cone. Baseline preoperative measurements were taken in a supine position with Hertel (HR) and Naugle (NU) exopthalmometers, IOP was measured using a tonopen. The patient was then given the 5cc retrobulbar block and immediately thereafter all measurements were repeated.Using AEL, K radius, and ACD measurements (from IOL Master) we will determine the location of the apex in relation to the lateral canthi in the case of the HR or the frontal and maxillary bone in the case of the NU. The increased exopthamomiters readings can then be converted into a volume of forward displacement based off these values.A paired t-test was used for statistical analysis.
From the 7 subjects enrolled to date, there are 5 males and 2 females, 4 OD and 3 OS eyes. All patients are Caucasian. The difference of pre and post HR and NU measurements are statically significant with a P=0.0008 and P=7.6E-5 respectively. The average amount of proptosis is 3mm (HR) and 2.9mm (NU). There is not enough data to compare across genders. Our goal is to enroll a total of 15-20 patients for the study.Justification for this goal is based on a conservative standard deviation estimate of 3.75 (using a range of 15 divided by 4 -- this is the range of millimeters of proptosis from 15-30mm) should be appropriate. Using that standard deviation along with a 2-sided alpha level of 0.05, the paired t-test would have a power of 0.80 to detect an underlying mean measurement increase of 3 if a total of 15 patients are used.
We hope in the end to have an average value of proptosis associated with the volume of injection. This is directly beneficial in the case of retrobulbar hemorrhage a rare complication of such injections. Any displacement past this average change in proptosis may indicate a subclinical retrobulbar hemorrhage.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Naugle exophthalmometer - uses fixation points above and below the superior and inferior orbital rims to measure the distance of the corneal apex. Hertel exophthalmometer - measurement is taken from the lateral orbital rim to the corneal apex.
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