Paper 30

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Change in Iris Vessel Density in Ocular Coherence Tomography Angiography For Detection of Anterior Segment Ischemia after Strabismus Surgery

 Federico G. Velez, MD; Juan P. Davila-Gonzalez, MD; Andrea Diaz; Marcela Lonngi, MD; David Sarraf, MD; Stacy L. Pineles, MD
Jules Stein Eye Institute, University of California Los Angeles
Los Angeles, California

Introduction:  Anterior segment ischemia (ASI) is a serious but rare complication of strabismus surgery.  Indocyanine green angiography (ICG-A) has been utilized to reveal iris-filling defects to assess a patient’s risk of ASI However, ICG-A is limited by its invasive, time-consuming nature and possibility to image unilaterally, as well as by potential side effects.  Recently, optic coherence tomography angiography (OCT-A) has been introduced and used to image iris vasculature in normal subjects and for iris tumors.

Methods:  Adults undergoing strabismus surgery on at least one vertical muscle were prospectively recruited to undergo iris ICG-A and OCT-A pre-operatively and post-operatively.  A masked examiner evaluated all images and determined whether filling defects were present, qualitatively (ICG-A and OCT-A and quantitatively (for OCT-A using software to calculate vessel density by quadrant).

Results:  Seven patients  were enrolled.  Two patients with dark irides were excluded due to poor imaging quality. One patient was found to have a qualitative filling defect on ICG-A, and had a similar defect on OCT-A. There was a significant decrease in the mean vessel density of the iris quadrant adjacent to the operated muscle from 56.2% to 52.2% postoperatively (P<0.05). In non-operated quadrants, there was no difference between the mean preoperative (56%) and postoperative (55.9%) vessel density (p=0.93).

Discussion:  OCT-A is comparable to ICG-A for determining iris vessel filling defects.  In addition, OCT-A gives quantitative vessel density values that can be compared pre- and post-operatively.

Conclusion:  OCT-A is a useful tool in the evaluation of ASI in patients undergoing strabismus surgery.

References:
1. Chan TK, Rosenbaum AL, Rao R, et al. Indocyanine green angiography of the anterior segment in patients undergoing strabismus surgery. Br J Ophthalmol 2001;86:214-8.
2. Allegrini D, Montesano G, Pece A. Optical coherence tomography angiography in a normal iris. Ophthalmic Surg Lasers Retina 2016; 47:1138-42.
3. Skalet AH, Li Y, Lu CD. Et al. Optical coherence tomography angiography characteristics of iris melanocytic tumors. Ophthalmology 2017; 124:197-204.

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