Some additional thoughts on peripheral vision

In the past few days, as my vision has continued to improve, I couldn’t help but think about what exactly is going on with my peripheral vision. I had written a post about the effects of PRK on peripheral vision, with my first observation being about the blur on the extremes of my ‘far’ peripheral vision and another observation about the general discomfort of visual feedback from anywhere beyond about 40 degrees from central vision on either side. At this point, I feel much more comfortable with peripheral vision than I did back then. The blurring on the edges of my peripheral vision seems a bit milder and I am not bothered as much by near peripheral vision either. However, I’m not comfortable yet and the healing process is really just starting. It could get better or it could get worse and there are many factors that can influence the outcome. I have a feeling that my improvement with peripheral vision is largely an adaptation to it by my brain even though it is less in focus than before.

I was thinking about my first post on peripheral vision and it occurred to me that I may have missed something in my study of an article comparing PRK eyes with natural 20/20 eyes (emmetropes). The study found that the emmetropic eyes were superior through something called static quantitative perimetry testing. This measures the sensitivity of the eye in its ability to detect flashes of light centrally and then further away into the zones of peripheral vision. PRK eyes needed more intense light in the periphery than did the emmetropic eyes. However, what that particular study doesn’t consider is whether uncorrected near-sighted eyes behave any different from PRK eyes on the same test and whether glasses or contact lenses change the results if the uncorrected eyes are given them to simulate correction.

The idea of looking up this information came after I was thinking about the optics of the eye as its shape changes according to environmental stimuli during the age of development (mostly before 20 years of age). Depending on the level of de-focus of objects in the peripheral vision, the eye can elongate to accommodate to the type of visual exposure that it is routinely exposed to. There are also some genetic tendencies present, but I feel that the environmental factors have been proven at this point. Once the eye elongates, the optical properties are quite different from when it was spherical. Contact lenses and glasses are then prescribed that bring vision into focus centrally, but they have the peripheral image focusing behind the retina (hyperopic or far-sighted state). I have shown here an illustration of this from the article I linked above.

If the type of visual environment is still the same (which influenced myopic growth in the first place) and if it can still do so (depending on a variety of factors, likely genetics, age, etc.) the eye elongates further and myopia gets worse. It’s an interesting read with implications on approaches to treat the development of near-sightedness. The optimal correction to slow down or stop myopia progression is suggested to be the one on the very right of the illustration. Why then have the traditional optics of correction had the peripheral vision in a hyperopic state rather than myopic. Was there an initial medical reason? Perhaps there are some sort of limits or difficulties with lens design? Either way, these advances in knowledge are great news for the next generation of potential myopes who can prevent or mitigate this condition, but it’s already too late for me – my eyes are already elongated and have now been lased.

What I’m interested in right now is whether the elongation of the eye affects scores on static quantitative perimetry testing. Based on what I have read so far (and information is, as usual, not easy to locate), it seems like it does. If the type of correction done with PRK creates an optical system exactly like the one shown for traditional correction in the illustration above, then it’s possible that both PRK eyes and myopic eyes corrected with glasses (or contact lenses) would score less than perfect on static quantitative perimetry testing. After all, peripheral vision is in a hyperopic state so it will be blurry and thus sensitivity will decrease. Uncorrected myopic eyes may score even worse. But regardless, all of these eyes (PRK or myopic with/without glasses) will be worse than eyes that are emmetropic, which speaks a lot for myopia prevention over laser correction. Laser correction is a patch job for screwed up vision, but it won’t ever restore the optics back to how good they were with a normally shaped eye. It can make it better but it likely won’t make it perfect. That’s water under the bridge for me now, but it is information that I hope will make a difference for the generations that follow mine – particularly those that are young and just starting to read.

In terms of comparing eyes pre- and post-PRK on static quantitative perimetry (or other forms of perimetry testing), I have had a tough time finding studies with this information. However, some comparisons between pre- and post-LASIK eyes do exist and show a decrease in scores after the procedure (type of testing is slightly different, kinetic vs. static perimetry, but the information is similar). I also found it interesting that it is mentioned in another article how peripheral vision is myopic after LASIK. I wonder, is this the same with PRK as well? I think so. This would mean that laser vision correction creates optics that are different from traditional correction where peripheral vision is hyperopic rather than myopic. It would look more like optimal correction in the illustration shown earlier in this post. However, that’s optimal for slowing myopia, not necessarily for vision.

My personal opinion is that peripheral vision can be made worse by PRK when the treated area is small enough to affect a significant part of the peripheral vision or if the healing process does not go well with hazing. Poorly selected sizes for treated area is at least not as significant of a problem these days as it was in the past. Newer laser systems and treatment plans allow for better design and matching of the optical zone to the treated eye’s pupil, which diminishes negative impacts on peripheral vision. Hazing is also better controlled than it was in the past.

With a perfect or near-perfect PRK procedure and recovery, I would wager that the post -PRK peripheral vision would be comparable to pre-PRK measurements. Evidently the vision won’t be as good as emmetropic eyesight. I may be wrong (maybe i missed something else) and I still have a lot more than I would like to learn, so I will keep monitoring this particular topic and the recovery of my own peripheral vision.

Related articles

• • Peripheral Vision after PRK (myprkupgrade.wordpress.com) on my blog
  • Smith EL, III., Charles F. Prentice Award Lecture 2010: A case for peripheral optical treatment strategies for myopia. Optom Vis Sci. 2011;88:1029–1044.
  • Aung T, Foster PJ, Seah SK, Chan SP, Lim WK, Wu HM, et al. Automated static perimetry: the influence of myopia and its method of correction. Ophthalmology. 2001;108:290–295.

  • Visual field changes after laser in situ keratomileusis
    Sandra M. Brown, Jay C. Bradley, Ke Tom Xu, Alicia A. Chadwick, David L. McCartney
    Journal of cataract and refractive surgery 1 April 2005 (volume 31 issue 4 Pages 687-693 DOI: 10.1016/j.jcrs.2004.09.036)