I've been researching eye problems, and the role of vision, in Parkinson's Disease. I discovered much information which is both profound and unfamiliar, but very important for people with Parkinson's (PwP) to grasp. As usual, I have self-experimented with ideas developed from these concepts, and have indeed found practical solutions which are helping me. I am therefore now sharing this full report on the subject, in case it is helpful to others too.
Eye Problems and Vision Symptoms of Parkinson's Disease
The following is based on the major scientific review article:
A number of studies have found strong evidence for significant visual problems in the PwP population. These eye issues tend to worsen when a PwP is an "off" state, but improve again when they are "on" due to l-dopa supplementation. Visual problems that are strongly correlated with PD include:
- visual acuity;
- contrast sensitivity;
- color vision;
- motion perception;
- visual disturbances, hallucinations.
Sufficient evidence exists that these can be linked to dopamine deficiencies in the retina, and cannot all be ascribed to just being age related or to the cognitive decline (brain damage) of PD. Indeed, physical and structural changes to the eye and retina are also implicated in PD, as determined by a number of modern eye examination methods.
"The Parkinsonian retina may therefore exist in an inappropriately dark-adapted ([ow contrast vision] state. This, in turn, [leads] to lower spatial and temporal resolving potential and an ultimate impact on visual acuity, and colour perception. Evidence is now emerging that visual dysfunction directly contributes to [the] more traditional ‘motor’ complications of PD "
The Role of Dopamine in the Eye
Note in the above, I emphasized dopamine and its shortage is important in the eye. For most PwP, this link between dopamine and vision will come as unexpected, because, while we are informed at diagnosis that our PD is due to dead dopamine producing cells in a small part of our brains called the Substantia Nigra, we are typically not being properly informed that the dopamine deficiency issues are much more widespread, including in the gut
but also in the retina too.
Indeed, according to the scientific review article mentioned above, the role of neurotransmitters in the eye has been known since at least the 1960s, when dopamine producing cells - dopaminergic neurons - were found in the retinas of animals, and later in humans. Since then, several types of dopaminergic neurons have been discovered in the retina and it is now known their functions are strongly affected by light levels. They have a pivotal role in the processing of visual information through the retina. Different types of photo-receptors in the eye can either be switched on or off due to the concentration of dopamine in the retina.
It has also been found that there is a significant diurnal variation in levels of dopamine in the eye, with higher levels in the day and lower levels at night, and hence time of day and even the weather/seasons impact on the complex feedback between the functions of the photo-receptors and dopamine concentration in the visual system - and ultimately on PD symptoms.
"This circadian rhythm is in counterphase with the retinal concentrations of melatonin, and indeed, dopamine and melatonin have mutually inhibitory effects on each other's production—acting as a ‘biological clock’ for the retina. Because of this light-sensitive variation in dopaminbe concentration, it has been postulated that dopamine plays a role in the transition from a dark- to light-adapted state".
Dopamine is therefore important in the eye at multiple levels, and helps to control the processing of visual information in a complex way, stimulating some photo-receptors and inhibiting others. Neuro-chemical measurements found evidence for depleted levels of dopamine in the eyes of PwP. Post-mortem studies of PwP indicated that the level of dopamine in the retina after death was much lower if the person had not taken any l-dopa medications within about a day of the death, as compared to those who had taken their last l-dopa pill more recently.
Epithelial Layers in the Eye
In my article,
we discussed how leakage issues with epithelial cell membranes, a special form of protective and moisturizing tissue, are prevalent in PD. The malfunctions of these epithelial layers are due, for example, to chronic dehydration, nutritional deficits, infection. Places where epithelial layers occur include in the skin, the gut lining, the blood brain barrier, the mouth and sinuses - all of which are implicated in the major and common symptoms of PD.
Such epithelial layers also occur in the eye. For example the retina-blood barrier, which has functions including, but not limited to, light absorption, nutrient transport from blood to eye, secretion and immune response. These retinal cells, like those in the Substantia Nigra, are meloncytes - they are black. The Conjunctiva also contain epithelial cells, lining the inside of the eyelids and covering the white of the eye. Conjunctiva help lubricate the eye with mucous and tears, with immune surveillance, and protection of the eye against microbes. Given that problems with epithelial layers are common in PD, it is highly probable that malfunctions of the eye's epithelial cells are also widespread in PwP. Indeed, dry eye and eye strain problems are very common, for example.
These epithelial layers and their associated mucous membranes also appear to be places where natural microbiomes are being found to have essential roles in our health. The role of imbalanced gut bacteria profiles in particular is coming to the fore in the treatment of Parkinson's Disease, for example. Interesting, it is now also emerging that the eye also has its own microbiome, and imbalances in the types of bacteria here too can affect health or be used as indicator for problems.
Compounding Side-Effects of Parkinson's Drugs
Unfortunately, according to Drugs.com, many of the common PD medications can exacerbate eye problems in PwP. Possible side-effects related to the eye are listed as:
ropinerole: "double vision or other eye or vision problems";
sinemet: "inability to move the eyes; increased blinking or spasms of the eyelid; large, hive-like swelling on the eyelids; blurred vision; double vision";
amantadine: "irritation and swelling of the eye; decreased vision or any change in vision";
Interventions (nutritional support, movement therapies, mental health support, stress management techniques, etc.) which can help minimize PD drug burden may therefore be appropriate for helping to keep eyes as healthy as possible.
What Can We Do?
Armed with the above knowledge, is there anything we can do about it? I have been implementing various strategies to see if these help and I do strongly believe these are cumulatively benefitting me and reducing my symptoms over time.
The main thrust is to look after our eye health. In this regard, many of the strategies I discussed for blood-brain-barrier health follow over directly: keeping our bodies very well hydrated; avoiding inflammation and stress as best we can; making sure our nutritional support is maximized. In terms of nutrition specifically for the eyes, Dr Axe recommends two special anti-oxidants, Lutein (the "eye vitamin") and Zeaxanthin, as well as Zinc and Omega 3 supplementation too. I have been taking all of these for several weeks and do feel my eyes are less sore and dry now. The A, C, E vitamins are also recommended by Dr Axe.
Like most of the rest of our body parts, exercising the eyes and visual brain functions will also be most important to maintaining their health. In this regards, I recommend the work of Dr Eric Cobb of Zhealth Education. Dr Cobb gives a lot of free information on his blog about vision health and provides powerful, but quick exercises to practice daily, as well as running a commercial "vision gym" for pro-athletes. Importantly, Dr Cobb shows us just how - unexpectedly - important the eyes and vision are in direct connection to movement and stress reduction: hence eye exercise has very profound relevance for people with PD. I also recommend stimulation of the cranial nerves which are responsible for the muscles that move the eyes:
Bright light therapy continues to be one of the most impactful and safe, long term answers to reducing PD symptoms, and I hope the above article helps to explain why I am such a proponent in strategic light therapy for Parkinson's and strongly recommend PwP to consider this too.