I have no history of glaucoma, none in the family, and was initially, maybe 10 years ago, treated with drops to reduce my eye pressure, picked up in eye tests as being too high. [OK, it is worth adding the comment here that I had also been taking prescribed Statins for some time before this, as there is now the suggestion that glaucoma could be a side effect produced by Statins] This treatment continued for many years, with more drops, stronger drops, but eventually the field tests showed that I was losing vision in the lower two quadrants of both eyes, initially the left lower quadrant in one, and the right in the other, so I did not lose any overall vision when using both eyes.
I eventually changed hospitals as the specialists in the first were just rubbing their heads, giving more eye drops, and sending me away for another 12 months – they never mentioned Glaucoma: but they lost my notes continually, so started again twice and did not treat the condition seriously. In the second Hospital I was told I had severe open angle Glaucoma, told to advise the DVLA, and take a driving fields test at an opticians – that led to my car driving licence being withdrawn.
The driving field test does not really demonstrate to you how badly your vision is affected. When I can see the effect of the combined blind spots, just under my eye line, it is when talking to someone at normal face to face distance, maybe 2 feet, when if I look into their eyes I can’t see their lips moving: in fact I can’t see their mouth at all. It’s also surprising how a significant part of effective hearing relies on also observing the lip movement.
After 3-4 years at the next Hospital I had moved up the priority list, having been using two different drops to try to reduce the eye pressure – ineffectively. So I reached the end of a waiting list for an operation called a Trabulectomy.
It’s a frightening operation, more from the point of view of your own worries and not for any pain. The eye is immobilised, and anaesthetised, and my surgeon was very skilled. Nevertheless I would have liked some form of tranquiliser into the line they put into a vein in the back of my hand. Maybe I was so paralysed by fear, they thought I was calm. The objective is to put a slit into the eyeball, to allow the internal fluid to drain out through this slit, rather than through the normal route, which has probably furred up. (Maybe we should have bought a better water softener?) From the instrument engineer’s point of view, it’s a drain hole like a safety valve, an over-pressure valve, to let fluid out when the pressure gets too high. Say at over 20mm Mercury, to reduce the normal eye pressure – to the desirable level of 12-15mm Mercury.
The drops used after the operation are of two types: one seems to be an antibiotic, to stop germs getting inside; the other, a corticosteroid, is to ‘stop inflammation and swelling’. This also delays the healing process, so allowing the slit put in the eye to settle down without the edges healing together across the slit, keeping a drain slot open once the eye recovers. So the drop delivery immediately after the operation controls the slot width/gap, and the objective is to make this the right size to suit your condition – – and so it takes some tweaking. Hence the frequent return trips to the specialist to see what is happening.
What happens next?
Now I have one eye operated on, getting better after about three weeks, hopefully the pressure is going to be lower. I am now thinking about the next eye needing the same operation, but next time I’ll ask for something to tranquilise me. It’s a fairly long operation, about half an hour, with them working on the eye and you just lying there, so you can get a bit worried.
After effects are interesting. I’m an optical/telescope/photography guy, with a collection of over 200 telescopes, a few binoculars and other optical things: I’ve always worn glasses and could never bring myself to use contact lenses. I studied physics at University and specialised in wave theory, optics, refraction, etc. So I can see my own blind spots, know that the left eye (yet to be operated on) has a blind spot almost impinging on the centre line, to the right, such that I can check text reading backwards more easily than forwards, etc. Alternatively you can tip your head to the right so the line of text on the PC screen is angled above the line between the eyes.
Apparently the eye has a membrane over the outside surface: when the eye pressure is reduced, maybe this membrane does not shrink, like the outside of the eyeball does. So it is a little loose on the eye. The slot, that somehow in the operation they put in the actual eyeball, leaks fluid out as far as the inside this membrane (which somehow maybe they repair in the operation): it forms in a “bleb”, ie a bubble of fluid, like a lump, on the eye surface, and slowly disperses through the membrane. I think in the operation they inject something to form the basis of the ‘bleb’. Bleb is a real technical term.
But when like me you work on a PC, at night, with light radiated directly into your eye mostly, it appears that the folds or ripples in the surface of this membrane can appear to move across the pupil, and at certain angles the light is refracted into the eye, so you see occasional hair like white lines of light running across the field of vision. This presumably will stabilise/disappear as the membrane does shrink, and the eye diameter stops going up and down with pressure variations. I asked the Consultant about this, and he just commented that I was too observant. Trouble is, understanding what I could see, is what made me interested in optics to start with.
Just a final comment: how do you still use a telescope, with almost total blind spots in the lower two quadrants? I use them on aeroplanes, to see the registrations. These you read by almost taking a snapshot of a good sighting into the brain and processing it. The answer I thought was to use binoculars, but it’s not the same. The answer is that you have to use the top half of the eye view, the top two quadrants, for the snapshot, ie aim the telescope below the target of the registration, or whatever. Thank goodness for autofocus on digital cameras!
If the eye pressure is reduced by the dual Trabulectomy, the damage will be arrested, and I will not lose any further vision. But what has been lost, is lost, as it is caused by pressure damage cutting the optic nerve where it leaves the eye: so until they can get little biotic nerve bridging robots to repair that break (and spinal chord breaks in people who have neck injuries), that area of vision will remain cut off. The technique is being developed, with the research on stem cells etc, but not that fast.
Maybe there will be a follow up blog later. But I have to work out whether this is a post that should be used on the process control blog, where I always promote the use of optical techniques, or the Telescope Collector’s blog (for optical equipment enthusiasts, http://www.telescopecollector.co.uk)!
Filed under: Optical sensors, Technology developments | Tagged: Glaucoma, safety valve, Trabulectomy | 1 Comment »