Early macular retinal ganglion cell loss in dominant optic atrophy: genotype-phenotype correlation

PURPOSE

To assess the peripapillary retinal nerve fiber and macular retinal ganglion cell (RGC) loss in patients with dominant optic atrophy (DOA) stratified by OPA1 mutation type.

DESIGN

Cross-sectional study.

METHODS

We studied 39 patients from 28 pedigrees with DOA harboring heterozygous mutations in the OPA1 gene along with 45 age-matched healthy subjects. The retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GC-IPL) of patients with DOA were evaluated by optical coherence tomography (OCT) and compared to those of controls. Patients' eyes were divided into 4 groups based on increasing severity of visual loss (DOA1 to DOA4) and were stratified by OPA1 mutation type.

RESULTS

The average thicknesses of the RNFL and GC-IPL were smaller in patients with DOA than in healthy controls (P < 0.0001). RNFL analysis showed a significant reduction of the average, superior and inferior quadrants thicknesses in the DOA4 group compared to the DOA1 group (P = 0.001, P = 0.002 and P = 0.001, respectively). GC-IPL analysis showed a significant thinning in the superotemporal and superior sectors in the patients with DOA2 compared to those with DOA1 (P = 0.046 and P = 0.04, respectively). Stratifying by mutation type, average, superior and nasal RNFL thinning was significantly more severe in missense mutations and had a presumed dominant-negative effect compared to mutations causing haploinsufficiency.

CONCLUSIONS

The present study demonstrates that in DOA, loss of macular RGCs is the earliest pathologic event, better reflected by GC-IPL measurements, whereas RNFL thickness is a measure of spared axons in late stages of the disease. Thus, mild cases (DOA2) show significant macular RGC loss as opposed to substantial maintenance of RNFL thickness, which is significantly decreased only in severe cases (DOA4). A clear genotype/phenotype correlation emerged, stratifying OCT measures by OPA1 mutation type, missense mutations being the most severe.

Evidence for retrochiasmatic tissue loss in Leber's hereditary optic neuropathy

Patients with Leber's hereditary optic neuropathy (LHON) have loss of central vision with severe damage of small-caliber fibers of the papillomacular bundle and optic nerve atrophy. The aim of this study was to define the presence and topographical distribution of brain grey matter (GM) and white matter (WM) injury in LHON patients using voxel-based morphometry (VBM). The correlation of such changes with neuro-ophthalmologic findings and measurements of peripapillary retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (OCT) was also assessed. Dual-echo and fast-field echo scans were acquired from 12 LHON patients and 12 matched controls. VBM analysis was performed using SPM5 and an ANCOVA model. A complete neuro-ophthalmologic examination, including standardized automated Humphrey perimetry as well as average and temporal peripapillary RNFL thickness measurements were obtained in all the patients. Compared with controls, average peripapillary RNFL thickness was significantly decreased in LHON patients. LHON patients also had significant reduced GM volume in the bilateral primary visual cortex, and reduced WM volume in the optic chiasm, optic tract, and several areas located in the optic radiations (OR), bilaterally. Visual cortex and OR atrophy were significantly correlated with average and temporal peripapillary RNFL thickness (P < 0.001; r values ranging from 0.76 to 0.89). Brain damage in patients with LHON is not limited to the anterior visual pathways, but extends posteriorly to the OR and the primary visual cortex. Such a damage to the posterior parts of the visual pathways may be due either to trans-synaptic degeneration secondary to neuroaxonal damage in the retina and optic nerve or to local mitochondrial dysfunction.