Vision Quick Look: Refraction Example 1
High Symmetric Myopic Astigmatism
This series on auto-refractor ‘strips’ is for therapists interested in learning more about the basics of human vision so they might respond better to their clients’s core sensory needs. Read the introduction to the series here.
Progressive nearsightedness (myopia) is an increasing concern among some populations where daily exposure to daylight is limited or restricted. Nearsighted literally means to have one’s sight clear at near distances. Light or moderate nearsightedness has long been associated with superior academic outcomes and as a rule, nearsighted kids fare better in classrooms where books and computers are the primary vehicles for instruction. Nearsighted eyes are oversized, meaning the light is focused somewhere inside the eyeball in front of the retina’s receptor cell layer. Indeed, many of the medical concerns associated with myopia relate to damage related to stressed tissues and nerve fibre layers from this stretching out of the globe.
The eyes represented by the strips above (Right Eye, RE, aka ‘OD, and Left Eye, LE, aka ‘OS’) are roughly equally highly nearsighted (myopic) with a touch of astigmatism. Clinically, this state is called compound myopic astigmatism, or CMA. Since astigmatism is generally clinically significant for most purposes at values greater than 0.75D, the (-)0.75 in the RE and (-)0.50 in the LE are not especially significant in this overall picture. For practical purposes, the slight astigmatism does add some degree of additional blur as well as adding to the overall nearsightedness.
In the strip, the first digits are the sphere values (minus values for myopia, plus values for hyperopia/farsightedness), so in the first RE reading, -7.25 represents 7.25D of myopia. The next two numbers (-0.50×172) indicate 0.50D of astigmatism at an angle of 172 degrees, referred to as ‘with the rule astigmatism’. The angle of astigmatism through the three readings in each eye shows some mild variability indicating an active accommodative system and a lens that is still malleable enough to respond to muscle tension of the ciliary body.
We can infer a few things about this strip and what it tells us about the owner of these eyes:
- Rough math: This patient’s eyes are in the -8.00D (diopter) range. We can estimate the far point of focus by taking the inverse of this, so 1/8 of a meter. In the real world, this patient is bringing targets up to the 12-15 cm range for inspection. This is very close indeed, too close for comfortable reading for any length of time, and well too close for computer work.
- The multiple readings RE and LE are reasonably similar, respectively, for both sphere and astigmatism readings. So, for each eye, the focusing machinery (accommodative reflex) is stable throughout with minimal variability or reshaping of the lens during repeated readings. Clinically, I would say these eyes are happy, relaxed, and still have some accommodative range to them.
- Myopia above 0.75D is a practical nuisance for most people who rely on distance clarity. Myopia in the range of 8D is debilitating and requires optical correction for daily living. It also poses unique health risks.
- Uncorrected myopia in this range (>4D) will exclude most people from participating in most activities and some sort of optical compensation is necessary for daily living.
- The fact that the two eyes have nearly equivalent refractive states suggests minimal inter-ocular/bi-ocular dissonance – functional tension resulting from differing focusing needs (anisometropia) and resulting magnification differences in spectacles (aniseikonia).
- Myopes can be more reserved than their hyperopic peers and will be more likely to succeed in academics due to their natural tuning for near tasking.
Typically we would find high myopia like this in late adolescence or early adulthood if left untreated. Treatment can often prevent dramatic progression such as this. Contact lenses can be a nice option for high myopia such as this since these reduce minimizing effects of high minus lenses.