Histamine and Sight : A Collection of Research Shows Histamine Does More In The Eye Than Produce Itching & Watering

A 1987 study noted that histamine is found in the human eye. They found that histamine in the human eye is higher in individuals suffering from ''endophthalmitis''; an inflammation of the internal coats of the Eye. They also found it to be moderately elevated in those with glaucoma.

However, up until a few years ago, the medical community and scientists haven't been able to pinpoint exactly how histamine affects vision. A 1985 summary `Histaminergic mechanisms in the vertebrate visual system` attempted to elucidate the molecular mechanisms of histamine signaling within the retina and optic nerve system. Then there was the 1990 citation : Histamine in the retina: recent progress and perspectives. These were minor in comparison to the newest paper on the topic.

What they found was that histamine dramatically affects light sensitivity, primarily by modulating dopaminergic neuron activity in the retina (see paragraph 2 under discussion of the final link above).
This essentially means that histamine 'regulates' the activity of other nerves.
To put it in real-life scenarios, histamine would be expected to.

1. Decrease sensitivity to the light when release is at its maximum in the human retina.
2.  Increases adaptation to dark/night time (as long as H1-receptors are available)
3. Allows one to distinguish objects and 'filter' the light when necessary.

That's just a start.

Read this paper to find out more about it, and for a better understanding of that particular function of histamine in relation to light sensitivity & ON Ganglion Cells.

The next paper we are going over, is a 2009 study titled "Histamine H1 receptor blockade predominantly impairs sensory processes in human sensorimotor performance".

What they found is that...

• Histamine is necessary for visual acquisition (learning by visual experience), visual perceptual processing (proper perception of all things and people in sight) and for distinguishing detail (intensity of lights, colors, depth etc).
• Histamine plays an even larger role in REACTION TIME. It is vital for proper performance and vigilance during activities like driving, tracking, target practice/shooting etc.
• Histamine plays a role as well in environmental observation, including of layouts, maps, and anything in which multiple objects, variables or codings are present in the same area at the same time etc, therefore antihistamines could impair mathmatical, particularly geometry skills, as well as oversight skills such as on a construction job etc. This is consistent with the advertisements you see on commercials and the literature we see in school books and high-grade medical school books.

Another paper, dated for May 14, 2012, named ''Retinopetal Axons in Mammals: Emphasis on Histamine and Serotonin'', goes into specific retinal axons, axons are 'long thread-like part of the nerve cell in which impulses are conducted from the cell body to other cells'. 

In other words, axons are our brains and organs lightning rods, they conduct the electrical nerve impulses, or jolts, nerve jolts, to other cells and have the longest 'reach', it's the literal 'long-body' of the nerve sending electricity. 

In this reference, it talks about how "our retinas, human retinas, receive input from the brain via axons emerging from the optic nerve''.

It goes on to talk about how histamine interacts with not only neurons, but also blood vessels in the retina. Histamine plays a role in inflammatory responses in the eye, as cited in the beginning of this article, so under conditions of allergy or allergic reaction, histamines increase and there is not only itching, and watery eyes, but also possibly changes in light sensitivity, floaters, and other uncomfortable symptoms.

Given histamines widespread effect on blood vessels everywhere, not just in the eye, this explains the epithelial vasodilation, or increased blood flow to the skin, and increased sensitivity of the skin during allergic reaction or allergen exposure.

See these links/papers.

➪Histamine Induces Vascular Hyperpermeability by Increasing Blood Flow and Endothelial Barrier Disruption

➪The Effect of Histamine on the Pulmonary Circulation in Man

➪The effect of histamine on the human fingertip circulation.

➪Allergy and the cardiovascular system.

➪Dynamics of the skin blood flow response to histamine. Comparison of the effects of cetirizine and loratadine on the skin response to a histamine dry prick test monitored with laser-Doppler flowmetry.

                                                     IN CONLUSION          

1. Histamine affects our sensitivity to light, generally decreasing it but also increasing dark adaptation or ability to adapt to night-time and night-time light patterns.
2. Histamine is needed for sensorimotor performance, including visual perception, orientation, identification, reaction time and observation of visual detail, thus, is crucial in concern to geometric tasks, spatial patterns, driving, target practice, oversight jobs, environmental work, observation/analysis of moving or still objects in the environment, of which histamine H1-receptors play a primary role but H2-receptors and H3-receptors also play important roles.
3. Histamine also affects vision, and ocular inflammation is under the predominant control of histamine, among others like leukotrienes etc.
4. Histamine causes floaters in some cases, and itchiness, redness, watery eyes etc, when exposed to allergens etc.
5. Histamine directly affects blood vessels which then affects ocular function and retinal nerve function. Histamine impacts blood flow, affecting the opening and closing of various coronary blood vessels as well as pulmonary targets.