SNR: What does it all mean?

I took a drive down to Knysna on Thursday for business purposes. It was the sort of journey that is equal parts pilgrimage and errand. Between the views of the unfolding Garden Route and the requisite coffee break at Storms River (Somehow it is always accompanied by a bathroom break), I got to go home!

I dropped by the Vision for Life clinic a couple of hours after I arrived in Knysna. It will always be known as the practice where I once worked, and it will be called “home” for as long as it exists.

I have many fond memories of this place and of Knysna and its people!

It's a strange sort of déjà vu, stepping into a room you once knew so well. The hum of the equipment, the scent of disinfectant and coffee, the rhythm of the day unfolding one patient at a time and of course, Mariska to greet one at the door. (Hands down the best part). It all came back! Shaking hands with the man whose name is on the door, Dr Dylan Joseph. It brought back many memories. The MS-39 and Pentacam diagnostic machines, still finicky, still producing the same occasional error messages that used to drive me (and I reckon everyone else) just a little bit nuts.

One in particular that I remember seeing often during my initial training was the SNR error. It's short for Signal-to-Noise Ratio, and it's a problem that pops up when the machine thinks that your scan isn't quite up to par, meaning that the signal it's getting is too weak, or that there's too much interference for it to be able to determine what it's seeing. This is largely problematic to say the least!

When I used to work as an ophthalmic technician, I would perform the corneal topography scans on the MS-39 and the Pentacam for most of our patients. The doctor I worked with was very particular about scan quality. The standards were high: well-centred, artefact-free reflection, stable fixation, minimal disturbances. If the SNR dropped to a certain point, the image was not reliable. No exceptions. It was a retake with different conditions. Either the patient would have to move their head slightly, the fixation point would have to be adjusted, one eye might have to be occluded, or, if the patient had dry eye, some lubrication would be necessary.

A low SNR could be anything: A blink mid-way through the scan, a watery tear film reflecting the light unexpectedly, the patient moving, or simply looking off-centre. The signal (the unadulterated reflection of light off the cornea) was being overpowered by noise (randomness of movement, disturbed tear film or distraction).

And that, standing there, got me thinking: isn't that basically life?

Signal. Noise. Repeat.

In ophthalmology, SNR is a measurable ratio. In real life, it isn't, but it should be.

The signal is whatever is really significant. The bright, stable thing we're meant to be focusing on. The noise is everything else: the distractions, the comparisons, the small doubts, the fears, the endless notifications and pseudo-urgencies we permit to clutter our mental filters.

If you linger too long in the noise, your own scan grows indistinct. The contours of focus and intention become background.

Steve Jobs did the same thing at Apple, actually. He often spoke of keeping a high signal-to-noise ratio, deeply focused on the extremely limited number of things that truly matter and cutting the remainder. He was renowned for saying "no" far more than "yes," and that, according to most accounts, was Apple's magic of clarity of purpose.

Maybe that's the moral of the story: the skill of a good life is the same as the skill of a good scan, i.e. get aligned, blink less, look at the focus point, and don't move for any reason at all, because if the input is jumbled, the data is useless.

In that brief moment, there I was, in Knysna, among technology that can perceive better than the typical human being, and I saw how soon we forget that rule. We're working towards productivity and efficiency, but we never ask ourselves if the signal that we're sending is even the right one. We let the noise invade until the image that is our focus, our purpose, is a blur of competing goals.

Perhaps life's periodic "SNR error" is not an error. Perhaps it's merely a courteous reminder to re-tune. To recalibrate. To refocus.

To find the most unobscured signal.

Euan