CASA Designated Aviation Medical Examiners Handbook, December 2003, Section 2.1.4
http://www.casa.gov.au/manuals/regul...e/080r0201.pdf
The role of radial keratotomy in reducing refractive errors is a significant current issue in aviation medicine. Persons who have undergone this procedure are often subject to diurnal fluctuation in visual acuity. If this is significant, (i.e. loss of more than one Snellen line for professional licence applicants and more than two Snellen lines for private licence applicants) even if an applicant’s visual acuity is still within the pass standard, this fluctuation constitutes failure to meet the visual requirements of the standard(s) concerned.
Applicants who undergo radial keratotomy before their myopia has stabilised are at risk of continuing progression of their myopia.
The long-term consequences of radial keratotomy are not yet well documented, so it is impossible to predict any long-term implications for pilot licensing. Applicants should be reminded of this uncertainty as it may affect their chances of employment in the aviation industry.
Following radial keratotomy, the refraction takes some time to stabilise to its new value.
Flying is not permitted while the refraction is still plastic. Evidence of stability requires:
A variation not exceeding 0.25 dioptres in refraction
A visual acuity changing by not more than one Snellen line
Visual acuity, which at least satisfies the minimum standard for the class of licence, at three paired serial measurements.
These three paired serial measurements are to be part of a full ophthalmological examination, are to include measurements early in the morning and late in the day, and must be delayed for at least three months following surgery. Note that some eyes may not have stabilised even as late as a year after surgery.
A second problem associated with radial keratotomy is sensitivity to glare. This can cause considerable difficulty in the healing phase but tends to settle with time. Testing of visual performance with a bright light shining at the applicant should demonstrate any continuing glare sensitivity.
All applicants whose eyes have stabilised following radial keratotomy must thereafter have an ophthalmological assessment every two years for Class 1 and 3 and every five years for Class 2 Medical Certificates.
Photo-ablative Refractive Keratectomy (PRK)
This is a new technique, using a laser, for changing refraction. The long-term implications are as yet unknown. The requirements for assessing stability after radial keratectomy outlined above should be followed after photo-ablative refractive keratectomy.