15 August 2010

Seeing probabilities

Filed under: aging, risks, Ultralase — David Wood @ 12:59 am

I thought of entitling this blogpost “Blinded by technology”.  Or, perhaps, “Almost blinded by technology”.  But that would have been unfair.

It’s now just over five weeks since I had my eyes lasered at the Ultralase clinic in Guildford, Surrey.  For more than 40 years, I had worn spectacles, to correct short sightedness.  My hope with the surgery was that I could dispense with spectacles and all the inconvenience that goes with them.

I had an idea what to expect.  Back in 2005, my wife had a similar operation, also from Ultralase, and has been very happy with the result.  I remember her being pleased with the outcome just a few moments after the operation, when, from the room next to the operating theatre, I could hear her excited voice on opening her eyes.  But my own experience turned out different.

One complicating factor is that I received a treatment called “monovision”, in which the two eyes are given treatments that optimise them for different viewing tasks.  My left eye was optimised for short-distance reading (such as computer screens, books, phone screens).  My right eye was optimised for medium-distance and long-distance.

The rationale for monovision is to address a decline in the power of eyes to change the distance where they’re focussing.  This is a condition called “Presbyopia” – sometimes known as “Aging eye”.  To quote from “The Eye Digest“:

A presbyopic eye loses its innate ability to clearly see all objects that are located at different distances. It can see some objects clearly but not all. In individuals who are less than 40 years of age, the eye can be thought of as an ‘auto-focus’  cameras. In an auto-focus camera, all one has to do to get sharp pictures is to point the camera in that direction, the auto-focus mechanism kicks in and you get sharp pictures. After age 40, the presbyopic eye can be thought of as a ‘fixed-focus’ camera. Fixed-focus cameras, the most basic of all cameras, have a nonadjustable lens. In general, a fixed-focus camera can take satisfactory photographs but it may produce a blurred picture if the subject is moving or is less than 6 feet (1.8 meters) away.

The presbyopic eye is also in a more or less ‘fixed-focus’ state. This means that a presbyopic eye will see clearly only at a particular distance. If you correct the presbyopic eye for distance with glasses or contact lenses, then it will clearly see all the distant objects and may read 20/20 on the distance vision eye chart, but there is no way it would be able to clearly read up-close with the distance vision correction. On the other hand if you correct the eye for reading up-close, then you will be able to read clearly, but there is no way you will be able to see distance objects clearly with the same correction. So reading vision is at the cost of distance vision and vice versa.

And as Wikipedia puts it:

Presbyopia is a health condition where the eye  exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been postulated as its cause.

Similar to grey hair and wrinkles, presbyopia is a symptom caused by the natural course of aging. The first symptoms (described below) are usually first noticed between the ages of 40-50. The ability to focus on near objects declines throughout life, from an accommodation of about 20 dioptres (ability to focus at 50 mm away) in a child, to 10 dioptres at 25 (100 mm), and levels off at 0.5 to 1 dioptre at age 60 (ability to focus down to 1–2 meters only).

The word presbyopia comes from the Greek word presbys (πρέσβυς), meaning “old man” or “elder”, and the Neolatin suffix -opia, meaning “sightedness”.

I can’t deny it: by these measures, I’m aging!  I turned 51 in February.  And I have presbyopia to show for my age.   (Not to mention wrinkles…)

Monovision is one of the options offered to patients with presbyopia.  Not everyone copes well with monovision treatment.  Apparently, some people get headaches, from the two eyes having different preferred focal lengths.  For this reason, Ultralase gave me special spectacles to wear, as an experiment, for six weeks before the intended date of the operation.  These spectacles mimicked the intended outcome of the operation: left eye great for short-distance, right eye great for everything else.  Happily, I had no headache, and was pleased with how these spectacles worked for me.

So I approached the operation itself with high hopes.  And I can report that my left eye has turned out exactly as hoped.  Without glasses, my short-range sight is excellent.

But  my right eye has ended up in a less optimal state.  Subsequent tests by Ultralase, repeated on several occasions, confirm that my right eye is about -0.75 compared to what was intended.  When I look into the middle distance or long distance, without wearing glasses, I see things as much fuzzier than before (when I wore glasses).  To see things more clearly, I have to squint, or stand up and walk closer.  In practical terms, it causes inconvenience when I’m in meetings at work.  I can’t see what’s displayed on screens in conference rooms.  I sometime struggle to see the prices on the menus behind the counter at coffee shops.  And so on.

But to say that I have literally been “blinded by technology” (by the short blast of a laser) would be putting things much too strongly.  I can get by fine, most of the time.

Nor was I figuratively “blinded by technology” – in the sense of being naively over-optimistic about the outcome of a technical fix to address the symptoms of aging.  The Ultralase surgeon had carefully explained matters to me before the operation.  He even got me to fill in some blank paragraphs in a form, using my own words to confirm that I understood the risks associated with the surgery.  One blank paragraph was headed, “Four risks with the operation”.  Another was headed, “How will I cope, if the treatment doesn’t work as well as I hope”.  It was sobering.

I knew, before the operation, that there was a one-in-six chance that I would need a “top up” operation six months (or so) further down the line.  And that looks like what will happen to me.  The risks were significantly higher in my case than for most patients, because of the monovision treatment, and because my eyesight was starting from such a poor threshold (around -8.0).

Medical treatments frequently involve probabilities.  As with many other difficult decisions in life, it’s important to be able to understand probabilities, and to plan ahead for possible unwanted outcomes.

It’s still possible that my right eye will continue to improve by itself.  I read of cases where it took several months, after laser eye surgery, for an eye to completely settle down.  That’s why Ultralase require several months of stability in eyesight before doing any follow-up surgery.  My current guess is that I’ll be visiting the surgery again some time around January.  In the meantime, I’m putting up with some haziness in my middle-distance and long-distance vision.

Has this experience changed my attitude towards the wonder-powers of technology (for example, to address the problems of aging)?

Not really.  I already know, viscerally, from my many years in the hi-tech smartphone industry, that technical solutions frequently fail.  A team can have many thoughtful, experienced, super-smart people, developing new technology in a careful way, but still the results can go wrong.  You can take measures to try to reduce risks, but you can’t make all the risks go away.  And, in many cases,  you shouldn’t seek to make all the risks go away.  That way, you’d miss out many benefits from when risky projects turn out good.  But you should be aware of the risks beforehand, and try to quantify them.

For me, a one in six chance of needing the inconvenience of a second operation was a risk well worth taking.  And I still see things that way.

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