Ocular Disease Case Study Week—created in partnership with ZEISS Professional Education—brought together optometrists across the globe to increase disease knowledge through the sharing of unique case studies, diagnostic scans, and workflow protocols.
After sharing the top four cases on the @eyesoneyecare.optometry channel from December 5th-9th, 2022, followers voted on their top picks.
Below is the third-place case study. Keep reading to see what made Denise A. Valenti, OD, FAAO, stand out.
Third place: Denise A. Valenti, OD, FAAO
Case Study: Acute marijuana use: Functional findings of retinal ganglion cell impairment
Background and Methods:
We evaluated, using basic screening protocols, two participants who reported to have self-dosed with their own legal recreational marijuana twenty minutes earlier. Additionally, we used a visual field screening technology assessing visual field function within the central forty degrees of vision. We elected to use the instrument’s threshold strategy rather than screen program. Tests of psychomotor performance; including tests of visuospatial field perception, have the potential to demonstrate the impact of cannabis consumption.
Cannabis impacts vision with reports of increased function in periphery1 and decreases in other functions.2
Understanding deficits associated with cannabis is particularly critical for tasks such as driving.
The stimulus is a low spatial frequency grating of 10°, presented at 1 of 17 test locations, shown below. The grating alternates at 25 Hz. The frequency doubling illusion is the subjective perception that the grating has twice the number of dark and light bars (i.e., its spatial frequency appears to be 0.50 cpd), as shown in the diagram.
Cannabinoids and the Retina:
Cannabinoid receptors exist throughout the retina.3 Cannabis depletes retinal dopamine.4 Retinal amacrine cells are involved in processing acetylcholine and cannabinoids disrupt this neuroprocessing in the retina.5 To the right is an image of the retina. Cannabinoid receptors are shown in green, acetylcholine is yellow, and dopamine is depicted with red.
Outcome: Retinal Ganglion Cell Dysfunction:
Disruptions in neurotransmitter balance due to disease, medications or drugs can result in dysfunction in the retinal ganglion cells (RGCs). Chronic cannabis use, as well as acute use, causes dysfunction in the RGCs.6 Functional tests can demonstrate such losses. Below is an example of retinal ganglion cell dysfunction specific to dopamine depletion in Parkinson’s.7
The next image is an example of acetylcholine inhibition secondary to medication, methotrexate.8 The three images below are the results of the cannabis group. The far left is a normal result from a person who had not used cannabis. The others are from two males, age 24 years old and 22 years old, who had used marijuana twenty minutes earlier.
Conclusion:
Acute use of marijuana has already been reported to cause retinal ganglion cell dysfunction. These cases demonstrate the functional impairment that is caused by marijuana use. Further study is important as the functional deficits that this measures; contrast and temporal processing, are important for safe driving.
