Anyone who has ever been in a car near Paris (France) knows about the crucial 'Boulevard Périphérique' - the always busy and chaotic giant ring road around the city of lights. Recently I was in Phoenix, Ariz. (less chaotic I can assure you) at the successful OAA meeting. One of the most interesting topics (and there were many) was the finding that corneal topography performed over a multifocal soft lens results in almost the same topographical pattern as the treatment effect from an orthokeratology lens (although with a somewhat smaller optical zone diameter). Myopia progression reduction has been reported in some kids using these lenses. Whether this is a potential treatment option has yet to be seen, but it appears that this finding supports the theory that the midperipheral changes induced by orthokeratology indeed contribute to a myopia progression reduction effect. And that we indeed may have to take 'le périph,' as locals call it, to get to the desired endpoint.

Eef van der Worp

 

We are not really used to thinking about the posterior pole of the cornea, simply because it couldn't be measured easily until recently. But is has been shown that higher order aberrations (HOA) - primarily coma - are higher on both the anterior and the posterior poles in keratoconic eyes compared to normal eyes. And in fact: residual irregular astigmatism in keratoconus patients wearing (R)GP lenses can be estimated by measuring the HOA from the posterior corneal surface alone.

 

The Gas Permeable Lens Institue (GPLI) in the USA is probably the world's best resource when it comes to (R)GP lenses. One of the most useful resources on the GPLI website is the Grand Rounds Troubleshooting Guide. It consists of a series of more than 50 case reports on all kinds of (R)GP lens fits, ranging from spherical lenses to multifocals, high astigmatism, keratoconus/irregular cornea, post-surgical fitting and corneal reshaping. Click the link below to see the complete series with free and open access to all case reports.

 

Our attention regarding irregular astigmatism typically focuses on managing it with contact lenses. However, it is interesting to know that there is a whole world of other correction methods out there. A book published under the title 'The Irregular Astigmatism' by Ming Wang (ophthalmologist, editor) and Tracy Swartz (optometrist, co-editor) contains an impressive 31 chapters just on irregular astigmatism. Section I of the book (chapters 1-9) covers the optics, etiology and clinical presentation of the irregular cornea. Section II (chapters 10-31) focuses on the management of the irregular cornea, with only one chapter devoted to 'the nonsurgical treatment for irregular astigmatism' (e.g. contact lenses).