Structure–function relationship in ocular hypertension and glaucoma: interindividual and interocular analysis by OCT and pattern ERG
- 309 Downloads
Pattern electroretinogram (PERG) and optical coherence tomography (OCT) represent objective probes to investigate respectively the function of retinal ganglion cells and their structure as retinal nerve fiber layer (RNFL) thickness. We examined interindividual (II) correlations of PERG amplitude and RNFL thickness, as well as correlations between interocular (IO) differences in both measures, in ocular hypertension (OHT) and early glaucoma (EG) patients.
Thirty-one OHT, 34 EG (mean deviation: −1 to −6 dB) and 16 age-matched controls were examined in both eyes. Participants had clear optical media, no or moderate refractive errors and no concomitant ocular or systemic diseases. PERGs were elicited by counterphased (16.28 reversals/second) gratings (1.6 cycles/degree spatial frequency). The Fourier isolated 2nd harmonic PERG amplitude and phase were measured. RNFL thickness was quantified by means of OCT Stratus according to a standard protocol. Average, superior and inferior RNFL thicknesses were considered.
Mean PERG amplitude was decreased (p < 0.01) in both OHT and EG patients compared to controls. Mean RNFL thicknesses were reduced (p < 0.01) in EG patients compared to both OHT and controls. In OHT patients, PERG amplitude did not correlate significantly with RNFL thickness in both II and IO analysis. In EG patients, PERG amplitude was positively correlated with RNFL thickness in both II (p < 0.005) and IO (p < 0.001) analysis. The slope of the correlation predicted that PERG losses exceeded systematically RNFL losses when the latter were between 0 and −0.25 log units.
Both II and IO analyses revealed a lack of structure–function relationship in OHT, suggesting that, at this disease stage, PERG losses appear to affect primarily retinal/optic nerve head function. In EG they reflect both dysfunction and RNFL loss.
KeywordsGlaucoma Ocular hypertension Pattern electroretinography Optical coherence tomography Retinal ganglion cells Optic nerve
Intramural Grant from Ministero della Ricerca Scientifica, Fondi di Ateneo ex 60%.
- 6.Budenz DL, Anderson DR, Varma R, Schuman J, Cantor L, Savell J, Greenfield DS, Patella VM, Quigley HA, Tielsch J (2007) Determinants of normal retinal nerve fiber layer thickness measured by stratus OCT. Ophthalmology DOI 10.1016/2006.08.046
- 15.Kim TW, Zangwill LM, Bowd C, Sample PA, Shah N, Weinreb RN (2007) Retinal nerve fiber layer damage as assessed by optical coherence tomography in eyes with a visual field defect detected by frequency doubling technology but not by standard automated perimetry. Ophthalmology DOI 10.1016/2006.09.015