# Retinal Nerve Fiber Layer in Patients with Alcohol Use Disorder
## 4 Discussion
### Correlation Between Retinal Thickness and Cognitive Impairment  
It has been estimated that between 50 and 70% of patients who suffer from an AUD exhibit cognitive impairment to some extent [22; 23]. These impairments mainly affect anterograde and retrograde memory, visual-spatial thinking, cognitive skills, and attention [24].  
The use of neuroimaging techniques has revealed structural and functional changes in the brains of alcoholic patients [22]. To the best of our knowledge, no studies to date have been carried out using OCT to assess the cognitive impairment caused by alcohol consumption. In the present study, we found significant differences in the macular area and in the nerve, which correlated with a more intensive cognitive impairment as assessed by the TEDCA scale.  
Although there are no previous studies in which retinal impairment has been correlated with cognitive impairment caused by alcohol consumption, multiple studies have described these same findings regarding retinal thickness in other illnesses in which cognitive impairment presents, such as Alzheimer's disease. Using the same technique as in our study, OCT, a reduction in the RNFL was found when comparing patients to the control group. In this way, OCT has been proposed as non-invasive for early diagnosis [25].  
In recent meta-analyses [26; 27] it was concluded that reductions in the RNFL were significantly higher in patients diagnosed with Alzheimer's disease or mild cognitive impairment (MCI) compared to controls. Some studies report that these findings affect all the retinal quadrants, whereas others conclude that only specific areas are impaired, with some studies focusing on the superior quadrants and others on the inferior quadrants [28].  
As in our sample, there are also some studies that have found a significant correlation in the macular area. More specifically, in a study that used the mini-mental state examination (MMSE) to assess the severity of cognitive impairment, a significant correlation was found between scores on the MMSE and the reduction in the volume of the macula [29].  
Regarding specific changes within the retina, a huge field of research remains open, as the reason why some specific quadrants, the macula or optic nerve, are more severely impaired compared to others has not yet been completely explained.  
During the last few years, several studies carried out on patients suffering from different neurodegenerative diseases such as sclerosis [9; 30; 31] have found reductions in the RNLF of the retina. However, to the best of our knowledge, our study is unique because no other studies have been carried out to date comparing the thickness of the different layers of the retina in patients with AUD.  
A limitation of this study is the small sample size, which limits the generalization of our results. This fact could explain the difference in statistical significance in certain quadrants and between the two eyes of the study groups. Another limitation of the study is that there were no variables such as diet or water intake that may be related to changes in the retina. However, as OCT is an objective and easily quantified technique, the doors remain open to replicate our findings in future studies.