IOP must be monitored in refractive surgery patients

In eyes that have undergone corneal refractive surgery, non-Goldmann measurements of intraocular pressure (IOP) and continued examination of the optic nerve is essential as changes of the corneal shape can lead to falsely low IOP values, according to a report published in the January issue of the Journal of Refractive Surgery.

Alexander Friedrich Scheuerle and colleagues from the University of Heidelberg, Germany, reported on a case of advanced glaucomatous optic atrophy years after bilateral radial keratotomy in a 40-year old woman.

Multiple IOP measurements of both eyes were obtained using Goldmann applanation tonometry as well as air-puff and Schiotz tonometry. In addition to regular eye examinations, corneal thickness, surface and shape were examined using Orbscan and C-scan.

The cornea of both eyes did not show signs of thinning but flattening of the corneal surface was observed. The decreased corneal curvatures precipitated a misjudgement of IOP readings measured by central applanantion tonometry (12 to 18 mmHg), whereas impression and non-contact tonometry revealed elevated IOP values (21 to 27 mmHg).

The authors believe that changes in corneal shape, without corneal thinning, can lead to falsely low IOP values and therefore, in eyes that have undergone corneal refractive surgery, non-Goldmann measurements and continued examinations of the optic nerve are recommended.