Parapapillary Autofluorescence and its Correlation with Neurovascular Fundus Anomalies in Primary Open Angle Glaucoma

Abstract

 

Purpose

 

To study the area, polar distribution and intensity of parapapillary autofluorescence (AF), its progression and its correlation with retinal nerve fiber layer (RNFL) thinning and focal arterial narrowing (FAN) in primary open angle glaucoma (POAG).

 

Methods

 

Patients with POAG were randomly selected. Those with a condition interfering with the measurement of AF (ex. cataract, keratopathy, haemorrhage, AMD, 4⁺-dioptre ametropia) were excluded, as were patients with an optic neuropathy. AF images and parapapillary RNFL thickness were acquired using a confocal scanning laser ophthalmoscope. The RNFL polar coordinate system was used to locate the AF areas and the FAN, after registering the RNFL with the AF images via vascular markers. AF areas were segmented using automatic region growing with a floating threshold and manually selected seed points. FAN were manually identified.

 

Results

 

32 fundi were divided into 4 groups (Jonas' classification). There were no statistically significant differences between the groups in regard to sex, age, ethnicity, maximum IOT, pachymetry and BCVA. The number of AF areas, their size and their polar distribution were strongly correlated with the stage of glaucoma (Spearman, ρ=0.61, 0.74 and 0.73 respectively, p<0.01). AF areas were almost exclusively located temporally in stage 1; they appeared nasally in later stages and were equally distributed in stage 4 (Χ² goodness-of-fit test, p<0.01). The presence of AF was strongly correlated with borderline RNFL thinning (p<0.05) (Spearman, ρ=0.49, p<0.01). Only 9.7% of AF areas weren't matched to a RNFL anomaly; these areas could precede measurable RNFL thinning. FAN were more often located near AF areas (±15°) associated with pathological (p<0.01) than with normal RNFL thickness (1 in [4.2;32.3] vs 1 in [21.4;∞], p=0.03). AF minimal intensity was lower when associated with pathological than with normal RNFL thickness (48.9±5.7 vs 58.2±4.3, 256 shades of gray; Student, p=0.01); this could reflect the destruction of the RNFL and its supporting RPE where lipofuscin is stored. AF intensities did not differ statistically significantly between stages.

 

Conclusions

 

AF correlates with neurovascular fundus anomalies in POAG and could be used to track its progression. A prospective study will determine if AF precedes detectable RNFL destruction; if so, AF could help us act before visual field defects appear.

 

 

 

Keywords: 550 imaging/image analysis: clinical • 582 ipofuscin • 629 optic nerve