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Editors Selection IGR 15-3

Visual Function Tests: Relationship between VF and RNFL OCT

Comment by Alfonso Anton Lopez on:

21755 Mapping standard automated perimetry to the peripapillary retinal nerve fiber layer in glaucoma, Ferreras A; Pablo LE; Garway-Heath DF et al., Investigative Ophthalmology and Visual Science, 2008; 49: 3018-3025

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Ferreras et al. (1020) assess and describe the topographical relationship between standard visual field (VF) damage and retinal nerve fiber layer (RNFL) OCT measurements in glaucoma patients identified through optic disk photographs. This study deepens and widens the existing knowledge on objective mapping that began in the late 90s1,2 and, until now, had been based on optic disk data from confocal scanning laser ophthalmoscopy. More recently, a detailed topographical map based on RNFL data was developed by Garway-Heath,3 using non-quantitative assessment of RNFL photographs.

There may by an inter-individual variability in the structure-function topographical relationship

The present study uses factor analysis to identify factors ‐ groups of locations ‐ that explain or simplify the complex correlations between VF regions and RNFL, and this statistical approach seems particularly adequate for this complex task. The authors performed two independent factor analyses, one for the VF locations included in each hemifield. The analysis selected five regions in each hemifield that were not symmetrical. The mean thresholds of points in each factor or VF region were correlated with the mean RNFL thickness at the 12-hour sectors, assuming superior hemifield corresponds with inferior hemiretina and viceversa. Inferior hemiretina correlated more strongly with superior hemifield than superior hemiretina to inferior hemifield, and the weakest correlations were found at the 3- and 9-positions. Each RNFL sector had significant correlation with several VF sector indicating certain overlapping among RNFL zones. The resulting map is congruent with the anatomy but shows considerable overlapping of the representation of different VF regions on the RNFL. These results confirm previous findings of studies performing objective mapping1,2 and probably indicate the presence of inter-individual variability in structure- function topographical relationship, and/or the non-anatomic distribution of VF test locations. In summary, the map obtained complements previous knowledge and confirms that structure-function topographical correlation in glaucoma is complex.

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