Purpose:
To evaluate the role of mfERG and quantitiative OCT (qOCT) compared to Ganzfeld ERG in diagnosis of cone-dystrophies (CD).
Methods:
Prospective study in 43 patients with CD, 53 healthy controls. Participants characterized by: best corrected visual acuity (BCVA), slit lamp examination, Ganzfeld-ERG (ISCEV standard). CD patients were divided in 3 groups (severity of disease, characteristics in table1). Patients with accompanying diseases were excluded. OCT imaging done with Zeiss Stratus OCT 3. OCT images were analyzed calculating density profiles (longitudinal reflectivity profiles: LRP) from 20 scan-lines through the fovea. LRP averaged and analyzed quantitatively for retinal thickness + distances between different retinal reflectivity layers (intensity peaks). mfERGs were recorded binocularly on Veris® system, 61 hexagon stimulus. P1 amplitudes and latencies of central foveal segment and ring 2 were analyzed. qOCT and mfERG values are considered abnormal if altered by more than twice the standard deviation of average of controls. Sensitivitiy of mfERG and qOCT was compared to Ganzfeld ERG.
Results:
All patients with CD showed significant and typical changes of LRPs in qOCT, while all healthy controls had normal OCT findings. LRPs were significantly altered in CD (table 1) for reflectivities of: (i) the supposed layer of photoreceptor inner/outer segments (POS) and (ii) for external limiting membrane (ELM). Retinal thickness was significantly reduced only in groups 1 and 2. mfERG recordings were abnormal in 31/43 (72%) of patients with CD. All false-negative patients (28%) were in group 3 (mild CD). All controls had normal mfERG results.
Conclusions:
Quantitative OCT analysis shows excellent sensitivity in the diagnostic workup of patients with CD while recording of mfERG is not sensitive in patients with mild CD. qOCT should be preferred to mfERG as additional examination in patients with mild forms of CD.
Keywords: electrophysiology: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal degenerations: hereditary