Imaging the porcine retina using adaptive optics scanning light ophthalmoscopy

Abstract

Purpose : We sought to examine the living porcine retina using an adaptive optics scanning light ophthalmoscope (AOSLO) due to its physiological similarity to humans.

Methods : A wild-type domestic swine (age: 5 months) was imaged on five occasions using a custom AOSLO, covering an area between 5° and 30° nasal to the optic nerve. Anesthesia was induced using telazol (6 mg/kg) and propofol (2 mg/kg) and maintained using 2-4% isoflurane. Body temperature was regulated using a Hot-dog convection heating pad (Augustine Temperature Management, Eden Prairie, MN) set to 39°C. Pupils were dilated with one drop each of 2.5% phenylephrine and 1% tropicamide, and isotonic saline drops were used during imaging to maintain corneal hydration. Dark-field, non-confocal split-detection, and confocal AOSLO images were captured using 790nm light. We obtained horizontal and vertical montages at 25° and 7-22° from the optic nerve, respectively. Eccentricity-matched regions were identified at separate time-points. Estimates of cone and RPE density were obtained at 20 separate retinal locations along these strips.

Results : Cone photoreceptors were seen on confocal and split-detection, while the RPE was visualized with dark-field imaging. An average cone density of 12,147 ± 952 cones/mm² was observed, which is consistent with previous histological data.¹ RPE cells for the same areas were found to have an average density of 1,736 ± 105 cells/mm², which is also consistent with histological data.^2,3 Cone density differed in eccentricity-matched images by ~1.3% and RPE density differed by ~6.0% between imaging sessions.

Conclusions : The photoreceptor mosaic and RPE of the porcine retina can be imaged consistently using AOSLO. The ability to non-invasively obtain quantitative estimates of cone and RPE cell density could enable longitudinal studies of retinal disease and treatment efficacy.

¹Hendrickson PMID:12076087
²Mannerström PMID: 11869882
³Zhang PMID:22201976

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

(A) The dashed box on the SLO image of the pig retina shows an area imaged with AOSLO in panels B-D. (B) The confocal image shows cone waveguiding, while (C) the split-detection image shows the corresponding cone inner segments. (D) Dark-field images show the RPE, though some “bleed-through” of cones can be seen. Scale bar: 100µm.