Contrasting the HRT II and the HRT III in Leber's Hereditary Optic Neuropathy

Abstract

Purpose:: Since the HRT II and the HRT III assess the retinal nerve fiber layer (RNFL) by vastly different methods, we compared the two in fully documented cases of Leber’s Hereditary Optic Neuropathy.

Methods:: Fifteen consecutive eyes of 8 affected individuals (one eye of one subject could not be imaged) from a previously reported 11778 LHON Brazilian pedigree (SOA-BR) were studied. Inclusion criteria included optic atrophy, VA below 20/400, grossly abnormal visual fields and high quality (Topography SD under 30 u) HRT images. Using the most recent HRT analysis packages, the HRT II Moorfields Regression Analysis (MRA) was compared to the HRT III Glaucoma Probabilitiy Score (GPS).

Results:: The new HRT III analysis package yielded far more abnormal findings than did the HRT II and was more concordant with the findings from traditional testing, including visual fields. Specifically, the HRT II was in general agreement in 5 of 15 eyes whereas the HRT III matched the clinical findings in 13 of 15 cases.

Conclusions:: The HRT II always uses an arbitrary reference plane in the papillomacular bundle (PMB) in order to assess the RNFL thickness. However, the PMB is very thin in many non-glaucomatous optic neuropathies (such as LHON), therefore use of such a reference plane may lead to erroneous data with HRT II. In contrast, the HRT III does not use a reference plane but determines the curvature of the RNFL, an approach that predictably should be more accurate. These results indicate that the HRT II should not be depended upon in LHON (and perhaps in other non-glaucomatous optic neuropathies). The HRT III clearly demonstrates a superior ability in analyzing the nerve fiber layer in LHON and probably in analyzing the nerve fiber layer in other non-glaucomatous optic neuropathies as well.

Keywords: imaging/image analysis: clinical • neuro-ophthalmology: optic nerve • nerve fiber layer