They Eyes Have It

Last summer my optician used his new-fangled camera to take images of the back of my eyes. He thought he saw, in one, something untoward – a small patch of discoloration. This would not normally be cause for concern, but this particular patch was close to the macula – an area of the eye that determines the accuracy of our vision. It could (but was unlikely to) herald the early onset of Age-Related Macular Degeneration (AMD), the leading cause of visual impairment in the UK.

And so in the autumn I paid a visit to the eye clinic at the John Radcliffe hospital, for further examination. This involved using two medications on my eyes, the end result of which (beyond minor stinging) was highly dilated pupils, an inability to focus and a sensitivity to light.

The drugs used to achieve this have an interesting ethnobotanical history, laid out in a paper called Ophthalmology’s Botanical Heritage (published in the Survey of Ophthalmology in 1992). It says that many of the advances in pharmacology in the 19th century were made by ophthalmologists, eager to explore the autonomic nervous system through its visible effects on the eye.

Atropa belladonna - Wolfskers
Atropa belladonna, by Anne Tanne

They discovered that atropine and scopolamine dilate the pupil (an effect called mydriasis) by blocking the action of the pupillary sphincter. Later it was determined that they also cause cyclopegia – paralysis of the ciliary muscle, which causes a lack of accommodation (my inability to focus properly).

The two effects go hand-in-hand and are used during eye examinations because they make it easier to see the retina at the back of the eye. They are caused by plants in the Solanum (nightshade, potato) family, which were well known in Europe.

However, once they had succeeded in dilating the pupil, ophthalmologists wanted the ability to contract it (miosis) – and for that they had to look to plants beyond their experience. The Calabar bean was used as an ordeal bean, used to ‘determine’ the innocence or guilt of people suspected of witchcraft. When applied to the eyes it causes miosis and short-sight (through an effect on the ciliary nerves), caused by the presence of eserine (physostigmine). It was discovered that it also had an effect on intraocular pressure, and hence it was used as a treatment for glaucoma. It was followed by pilocarpine, isolated from a Brazilian plant.

n702_w1150
The Calabar Bean, from the Biodiversity Heritage Library

Returning from the ethnobotanical aside, there is no reason for me to be concerned about my eyes. The doctor issued what sounded like a standard set of advice for eye health – wear sunglasses when it’s sunny, don’t smoke, eat leafy vegetables and oily fish. I was intrigued by what’s in leafy vegetables and oily fish that would help, so I did some research.

It turns out that carrots, which are rich in vitamin A, are good for general health but not particularly for preventing AMD. That they will help you see in the dark is wartime propaganda – published partly to avoid the Germans learning that we’d invented radar and could see them coming at night, and partly to encourage the general public to eat their way through a carrot glut and reduce the demand for other foodstuffs. (An enterprising woman even came up with a recipe for carrot fudge!)

Oily fish (such as salmon, mackerel, anchovies, trout, herring and sardines) have higher levels of Omega-3, although it’s also found in other fish.

And it turns out that there are two carotenoids vital for eye health – lutein and zeaxanthin – and they are most abundantly found in dark green leafy veg such as kale, spinach and silver beet. They’re also found, in smaller quantities, in peas, pumpkin, Brussels sprouts (that Christmas dinner will have done wonders for your eye health!), sweetcorn and beans.

Which is good news, because all of those things will happily grow here in the UK. It would be interesting to find out which leafy greens are the best if you’re in other climates. I also came across a very interesting paper from 2005 that looks at the lutein values in nasturtiums (Tropaeolum majus), which came to the following conclusion:

“The edible T. majus flower is an excellent source of lutein, the yellow flowers having higher levels than the dark orange flowers. The leaf is a good source of lutein and the provitamin A β-carotene. More studies are warranted to promote the use of these materials as functional food.”

And so it seems that I should be adding nasturtium flowers and leaves to my diet to keep my eyes nice and healthy. The same paper suggests that egg yolks are another good dietary source of lutein, so it might be time to ditch the egg-white omelettes.

So… who’s up for having a salmon omelette with a kale and nasturtium side salad for tea? 😉


References
Macular Disease Foundation Australia. (2013). Nutrition and Supplements for Macular Degeneration. Available from: http://www.mdfoundation.com.au/page17334.aspx

Niizu, P. Y., & Rodriguez‐Amaya, D. B. (2005). Flowers and leaves of Tropaeolum majus L. as rich sources of lutein. Journal of food science, 70(9), S605-S609.

Packer, M., & Brandt, J. D. (1992). Ophthalmology’s botanical heritage. Survey of ophthalmology, 36(5), 357-365.