T. Baba et al.

mfERG parameters
1: P1 – N1 amplitude(nV)2

2: P1 peak latency(ms)P1

1

3: Response density(nV/deg2)

N13abFig. 2. Multifocal electroretinogram (mfERG) parameters calculated in this survey. The P1 and N1 indicate the 1st
positive and negative wave of each mean focal flash response in the response arrays of the mfERG (a), respectively.
The 3-dimensional topograph (b) represents the response density in each hexagonal area (amplitude per retinal area:nV/deg2). The mfERG parameters, that is, the P1 – N1 amplitude, the P1 peak latency and the response density aredemonstrated as 1, 2 and 3 in this figure, respectively.

sponse density in each hexagonal area in amplitude
per retinal area (nV per degree squared: nV/deg2) inthe topograph (Fig. 2b). The response density wasalso adopted as one of the mfERG parameters (Fig.
2) and measured in the 4 mfERG areas in this survey. The recording procedure was repeated at thetime when spurious potentials from eye blinks on
ocular movement were involved.

beam on the fundus so that the location of eachscan on the retina could be monitored. A computer-controlled light placed in the visual field fixatedthe eye being scanned. Fine positioning for theOCT examination on the retina was accomplishedby keyboard control for scan length, angular orientation and position relative to the patientʼs fixation
point.
The mean retinal thickness was estimatedfrom 9 calculation points at the foveal region within
5 degrees in the thickness estimation in the averaged OCT scans by our computer program, thatis, the central and each of the other 4 points at adistance of 250 µm and 500 µm from the central
portion on horizontal and vertical sections in linear
pattern on OCT (Fig. 3). Retinal thickness wasmeasured at the distance between the strongest 2
edges in each tomogram, which most likely corre-

OCT examination
Optical coherence tomography was used for measurement of retinal thickness in µm. The opticalcoherence tomography system was interfaced using
fiber optics to a conventional slit-lamp biomicroscope and a fixed +78-diopter condensing lens forretinal examination. An infrared-sensitive video
camera provided a view of the scanning probe74

Macular function before and after PRP in diabetic retinopathy

OCT calculation points
500 µm
250 µmFoveolaFig. 3. Calculation points on optical coherence tomogram (OCT). The mean retinal thickness was estimated from
9 calculation points at the foveal region within 5 degrees; the central and each of the other 4 points at a distance of
250 µm and 500 µm from the central portion on the horizontal and vertical sections on OCT. Horizontal and verticalcross-sectional tomographic images are inserted in this figure.

sponded to the vitreoretinal interface and the retinal pigment epithelium, respectively.
We not only used the retinal thickness program, but also hard copies of each OCT image forchecking errors, because the layer of cystoid macular edema was sometimes detected as the edge ofthe retinal pigment epithelium and the detachedvitreoretinal membrane was also detected as theedge of the vitreoretinal interface. In OCT measurement, the subjectʼs pupil was fully dilated with
2.5% phenylephrine hydrochloride.

Results
The P1 peak latencies obtained from the 4 mfERG
areas were significantly prolonged in the 14 eyes of
the 9 patients with preproliferative or early proliferative diabetic retinopathy who showed no clinicallysignificant macular edema before PRP as comparedwith those in 15 normal control eyes of 14 healthy
volunteers at level of 1%, with no tendency for recovery throughout the course after PRP except forarea 1 (within a central radius of 5 degrees) (Fig. 4).
The P1 – N1 amplitudes obtained from the 4
mfERG areas were significantly decreased in the 14
diabetic eyes before PRP as compared with those in
the 15 control eyes at the 1% or 5% level, followed
by a maximum decrease in the parameter 3 months
after PRP. However, significant recoveries weredetected in the decreased P1 – N1 amplitudes fromthe 4 areas at 6 months after PRP at the 1% or 5%
level (Fig. 5).
The mean response density levels obtained
from the 4 mfERG areas also showed almost theStatistical analysis
All values obtained in the mfERG and OCT examinations were expressed as mean ± SEM. Statisticalanalysis was performed with Mann-Whitneyʼs U
test. A P value of < 0.05 was considered statistically significant.

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