Abstract
Purpose :
The anatomical orientation of the retina with respect to the mouse orbit is relevant for research studies of opsin distribution, retinal degeneration, direction selective retinal ganglion cells, melanopsin ganglion cells, and retinal cell taxonomy. In particular, many studies have found that functionally distinct retinal ganglion cells have density and size gradients across the mouse retina. However, a review of the literature indicates that different groups report different methods to mark the topographic orientation of the retina (dorsal, ventral, temporal and nasal poles). Such variations in retinal landmark identification may result in discrepancies in the topographic distribution of retinal cells (such as melanopsin ganglion cells) as reported by different studies. The goal of this project was to create an accurate anatomical map of the mouse retina that includes all commonly used landmarks, including the rectus muscles, choroid fissure, temporal canthus, dorsal corneal, and opsin gradient.
Methods :
Four methods were followed as described in the literature to identify physical landmarks during enucleation and retinal isolation in adult C57 mice: 1) dorsal corneal burn, 2) tattoo dye at the temporal canthus, 3) cuts at rectus muscle insertion points, and 4) cuts at the temporal-nasal points of the choroid fissure. Retinas were fixed in 4% PFA, stained with s-opsin, imaged with Leica-TCS-SP5 confocal microscope, and analyzed with Leica-LASAF and ImageJ. All retinas were digitally re-stitched with Retistruct and aligned to the s-opsin gradient; polar plots of retinal landmarks were compared in Origin.
Results :
The rectus muscles were measured at 19.2±6.3, 82.0±9.6, 169.3±14.7, and 259.4±15.8 degrees for medial, superior, lateral, and inferior rectus, respectively (n=8). Nasal and temporal choroid fissure landmarks were measured at 7.5±3.1 and 172.3±8.5 degrees, respectively (n=8), and temporal and dorsal landmarks at 187.5±13.2 and 98.4±23.9 degrees, respectively (n=8). However, a 15 degree mismatch was found between choroid fissure and medial/lateral rectus landmarks. The lowest internal consistency was found in the dorsal burn dissection method.
Conclusions :
These results suggest that variations in dissection methods and retinal cuts may be a source of discrepancy between studies that use different dissection techniques to orient the retina.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.