The effect of cataract surgery on imaging optic nerve head topography with the Heidelberg Retina Tomograph.

Purpose. To determine whether phacoemulsification cataract surgery with intraocular lens (IOL) implantation interferes with measuring optic nerve head (ONH) topography using the Heidelberg Retina Tomograph (HRT). Methods. The study population consisted of 31 women and 12 men aged 63-81 years with no previous history of eye diseases, surgery, laser procedures, or medication. The patients underwent first eye cataract surgery for senile cataract. The HRT II with software version 1.6 was used to obtain 3-dimensional images of the ONH as a part of a comprehensive ocular examination. The quality of the HRT image was assessed using topography standard deviation (TSD). Topography measurements are considered to be unreliable if TSD is more than 50 µm. Re-examination took place 1 month after surgery. Results. Before surgery, the topography measurements were unreliable in 35% (15/43) of the eyes; in 3 of these cases, ONH topography could not be calculated at all. One month after cataract surgery, the ONH topography could be calculated in all eyes and only one displayed unreliable topography measurements. The mean TSD was 40 µm before and 22 µm after surgery when calculated for all eyes with measurable topographies. The change in TSD was statistically significant (p<0.0005). The image alignment between the HRT examinations before and after surgery was excellent in 67% (26/39). Magnification changes occurred in 21% (8/39). Conclusions. Phacoemulsification cataract surgery with IOL implantation improves the image quality of the HRT. However, because of magnification changes and image misalignment, HRT follow-up of the ONH after cataract surgery is often unreliable.