There are a couple of articles [Friberg et al., 2008: (http://www.ncbi.nlm.nih.gov/pubmed/18055020); Friberg et al., 2000: (http://www.ncbi.nlm.nih.gov/pubmed/11099749)] reporting that symptoms of depression are highly correlated with self-report of visual dimming. Visual dimming is discussed in many different mitochondrial disorders and cases of papilledema (optic disc edema due to mildly elevated intracranial pressure). It's important to note that a person who has visual dimming should see a doctor and tell his or her doctor about it. It could be a sign of optic neuropathy or a serious complication from a medication or other medical condition, and one shouldn't assume that visual dimming is simply a symptom of depression. It could be a sign of impending loss of vision and may be very serious and not mild. I just wanted to mention that, in any case. It's hard to make a lot of results show up in succession in a search, but here are some attempts [(http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=mitochondrial+dimming+vision+OR+visual); (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=%22dim+vision%22+OR+%22dimming+vision%22+OR+%22visual+dimming%22)]. Those searches are not showing this well. One sees, in the second search, that exposure to some AChE inhibitors can produce visual dimming and miosis, and one explanation for visual dimming might be the cholinergic hypersensitivity that's frequently been associated with depression. I think it's a result of mitochondrial dysfunction, as some of the articles citing the Friberg et al. (2000) article (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&cites=5337751757716500786) are getting at. But people report visual dimming in many different neurological conditions and mitochondrial disorders. Any neurological problem that causes miosis, which is pupillary constriction and is sometimes described as "pinpoint pupils," could produce visual dimming, and, in some case reports, researchers report that the visual dimming gets worse when the pupils are more constricted. But I've seen it reported a lot in case studies of people with mitochondrial disorders or metabolic disorders, including nonketotic hyperglycinemia, and in reports of people with pseudotumor cerebri (which is idiopathic intracranial hypertension, a.k.a. benign intracranial hypertension), with or without papilledema (optic disc edema). In other words, optic disc edema is not always a result of elevations in intracranial pressure but is not infrequently associated with it, and the intracranial pressure can be elevated without producing optic disc edema that's necessarily going to be obvious or measurable or even exist at all. The rate of cerebrospinal fluid production is regulated by the adrenergic innervation of the choroid plexuses (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=%22choroid+plexus%22+adrenergic), for example, but I think it's more likely that there's some hypometabolic state that's causing low-level dysfunction of the blood flow to part of the brain or very mild optic neuropathy or something. Or there might be low-level venous sinus thromboses. Unfortunately, no one's followed up on those articles. Those are potentially important articles, and I'm surprised no one's followed up on this in the last several years.
Incidentally, the authors of some articles make statements implying that elevations in intracranial pressure usually or always cause severe headaches or blurring of the vision, etc. Those aren't accurate statements, and there are numerous reports of vitamin A intoxication (producing intracranial hypertension), for example, producing only psychiatric symptoms and no headaches or blurring of the vision, etc. Here's a crude search that looks like it includes some articles describing the subtlety of the symptoms (or lack thereof) associated with elevations in intracranial pressure (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=subtle+pseudotumor+OR+pseudotumour+OR+papilledema+OR+%22intracranial+hypertension%22). It's probably missed fairly frequently, and I wonder if the presently-available measuring devices are even all that useful. The CSF pressure can also be translated into the lymphatic fluid in the ears (elevating the "perilymphatic pressure," etc.) and cause ear pain or pressure or tinnitus or specific forms of hearing loss, and those can be the only symptoms [Sismanis, 1987: (http://www.ncbi.nlm.nih.gov/pubmed/3302575); Larsen, 1982: (http://www.ncbi.nlm.nih.gov/pubmed/7102299); (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=otologic+pseudotumor+OR+pseudotumour+OR+papilledema+OR+%22intracranial+hypertension%22)]. The point is that mild elevations in intracranial pressure could occur in people and only produce psychiatric symptoms and visual dimming or other subtle symptoms.
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