Pattern electroretinogram (PERG) in the early diagnosis of normal-tension preperimetric glaucoma: a case report

Abstract

Introduction: The purpose of this case is to present the use of pattern electroretinogram (PERG) in the early diagnosis of normal-tension preperimetric glaucoma in 56 years old woman.

Methods and results: At baseline the results were as follows: distance-corrected visual acuity in the right eye (RE) and left eye (LE) 1.0 and 0.7, respectively (Snellen table), normal anterior segments in both eyes, normal fundus in the RE and abnormal cup to disc ratio (0.6) in the LE. Intraocular pressure (IOP) was within normal limits in both eyes: RE-14 mmHg, LE-18 mmHg (Goldmann tonometer). Results of standard automated perimetry (SAP), short wavelength automated perimetry (SWAP) and nerve fiber analyzer (GDx) were normal in both eyes. PERG result was normal in the RE but in the LE reduced amplitudes of P50 and N95 waves were observed. After topical treatment (Xalacom to the LE), a reduction of IOP to 13 mmHg was achieved and was accompanied by amplitudes increase of PERG waves. After discontinuation of the therapy, IOP increased to 18 mmHg and P50 and N95 amplitudes decreased to the values before treatment, suggesting the influence of IOP lowering therapy on electrical function of retinal ganglion cells. After 4 years from the baseline, static perimetry results were still normal, but abnormalities in retinal nerve fiber layer thickness were detected in GDx.

Conclusions: PERG was a useful test not only for the early diagnosis of normal-tension preperimetric glaucoma, but also in evaluating the effectiveness of antiglaucomatous treatment.

Fig. 1

Fundus photographs of the right (a) and left (b) eyes. Increased cup-to-disc ratio (0, 6) in the left eye was detected

Fig. 2

Gdx results in both eyes within normal limits

Fig. 3

Right eye (left side): PERG amplitudes of P50 and N95 waves within normal limits. Left eye (right side): lower PERG amplitudes of P50 and N95 waves

Fig. 4

Left eye: increase in PERG amplitudes after instillation of Xalacom (right side), in comparison with the score before treatment (left side)

Fig. 5

Left eye: decrease in PERG amplitudes after 1-month discontinuation of Xalacom therapy (left side treated eye, right side without treatment)

Fig. 6

Left eye: gdx result after 4 years of follow-up: abnormal thickness of RNFL in the lower quadrant and a pathological nerve fiber index (NFI) = 43