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Edwin R Swann; The Association Between Normal Optic Nerve Cupping , Normal Visual Fields and Marijuana Use. Invest. Ophthalmol. Vis. Sci. 2014;55(13):567.
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The purpose of this study was to test for the association between normal optic nerve cupping, normal visual fields (VF) and a history of having smoked marijuana.The null hypothesis was that there is no difference in the odds of having a vertical cup disc ratio (C/D ratio) of less than 0.5, or normal VF in subjects who reports a history of having smoked marijuana compared those who had not smoked it.
The 2005-2008 NHANES data were imported into Stata/IC version10.0 (StataCorp LP, College Station, Texas). Variables analyzed were: "ever smoke marijuana", " the vertical C/D ratio" of each eye, race/ethnicit, gender, and age. Another variable examined was normal Humphrey Matrix VF as defined by an NHANES algorithm.The variable vertical C/D ratio was use to create a dichotomous variable "C/D ratio < 0.5". The variables for ever smoke marijuana, C/D ratio < 0.5 and normal VF were used to create dichotomous variables to represent those variables for each subject instead of for each eye. The logistic regression models for the dependent variables C/D ratio < 0.5 and normal VF were created using a backward elimination process. The model with C/D ratio < 0.5 as a dependent variable had remaining variables ever smoked marijuana and gender as independent variables. The model with normal VF as the dependent variable had a remaining variable of ever smoked marijuana. Permission to allow use of de-identified data from the NHANES in other studies was obtained from subjects at the time of their enrollment.
The adjusted odds ratio of subjects with a vertical C/D ratio < 0.5 was 1.26, 95% CL (1.03 - 1.58) with a "P" value = 0.037. The odds ratio of subjects with a normal VF who had smoked marijuana compared to those who had not was 1.4, 95% CL (0.91 - 2.16) with a "P" value = 0.119 .
This study shows a statistically significant increase in the odds of subjects with C/D ratios<0.5 having a history of having smoked marijuana. There was a lack of statistical significance for the odds of having a normal VF test in subjects who reported having smoked marijuana possibly related to the smaller sample size. These results suggest that the use of marijuana may have a protective influence on the optic nerve. Croxford (2003) has reported that cannabinoids "may be potent neuroprotective agents." Further studies could reveal that marijuana has neuroprotective properties .
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