The DVLA has just announced some new health-related rules for drivers. For car drivers, there is a new stipulation regarding epilepsy; however, for bus and lorry drivers, visual acuity requirements have been relaxed.

Previously the threshold was 0.8 (6/7.5) in the better eye and at lease 0.5 (6/12) in the poorer eye. These values are now 0.8 and 0.1 (6/60), respectively.

Driving is an unusual visual task inasmuch as there are large eye movements than in most everyday tasks. It might be that with the specific angles of wing- and rear view-mirrors, there are different implications for ‘poorer right’ and ‘poorer left’ drivers, and they might notice a difference between right-hand and left-hand drive cars.

Overall, though, it seems this is all of little functional consequence. This 1991 paper suggests little or no practical difference between monocular and binocular drivers.

An interesting question arose in our contact lens clinic last week: are myopic corneas steeper than those of ametropes or hyperopes? Anecdotally, it was felt that perhaps myopes had flatter corneas. Most optometrists should be aware that most refracts errors are axial: myopes have big eyes and it’s the reverse for those who are longsighted. However, myopes having flatter corneas would be counter-intuitive.

Ametropia can be due to a normal length eye hosting a cornea that’s the wrong shape (too steep or too flat). However, I wasn’t sure if this was a general trend – do myopes tend to have steep corneas?

So, to the literature. This paper describes a study in Taiwan of 500 subjects aged 40 and over. The authors measured a range of ocular parameters and whilst a strong (ish) correlation was found between refractive error and axial length (r-value -0.65), no such relationship was demonstrated between refractive error and corneal curvature (r = -0.02). Overall, then, randomly selected hyperopes will have similar corneal curvature to a group of randomly selected myopes.

A slightly different story arises from this very large study from Canada. This work, on over 3,000 eyes finds a general increasing of corneal power with more myopia. It’s not a very strong relationship (r = -0.25) but it’s the sort of finding you can get with large data sets.

So, our anecdotal feeling-in-our-water was incorrect. Overall, myopes do have steeper corneas, but it’s a rather weak relationship and they are much more likely to have longer eyes.  Predicting K readings from refractive error for an individual is unlikely to be accurate.

Anecdotally, it seems the optometrists who are members of the College of Optometrists are generally unaware that they have access to 28 scientific journals as part of their membership package.  This access is processed via the Athens system where organisations and institutions purchase access rights for their members or staff to specified journals within the academic literature.

College members have access to a range of optometric, ophthalmological and contact lens titles, including the College’s own title Ophthalmic and Physiological Optics, Optometry and Vision Science, Investigative Ophthalmology and Visual Science and Contact Lens and Anterior Eye.   Those wishing to gain access need to contact the College’s Library Manager as explained here.