T. Baba et al.
(nV)

(ms)

**P < 0.01

**
****
**

3140

P1 – N1 amplitude

P1 peak latency

3230

292827

Control Before
PRP1 mo

3 moAfter PRP

30

Fig. 4. Changes in the P1 peak latencies of the mfERG
obtained from 4 mfERG areas in 14 diabetic eyes before
and after PRP. The diabetic eyes were derived from9 patients with preproliferative or early proliferative
diabetic retinopathy showing no clinically significant
macular edema in this series. All values were expressed
as mean ± SEM. Each bar indicates SEM. ** indicatesP < 0.01 by Mann-Whitneyʼs U test. PRP, panretinal
photocoagulation; mo, month(s). Control: 15 normal
control eyes of 14 healthy volunteers.

**

**
**

**
**

*

**

*P < 0.05**P < 0.01
**
*
*

20

1006 mo**Control

Before
PRP

*
1 mo

3 mo

After PRP

6 mo

Fig. 5. Changes in the P1 – N1 amplitudes of themfERG obtained from 4 mfERG areas in 14 diabetic
eyes before and after PRP. All values were expressed asmean ± SEM. Each bar indicates SEM. * indicates P< 0.05, and ** indicates P < 0.01 by Mann-Whitneyʼs Utest. PRP, panretinal photocoagulation; mo, month(s).
Control: 15 normal control eyes of 14 healthy volunteers.

Symbols used in Figs. 4 to 6:

Area 1:

5 degrees

Area 2:7 degrees

Area 3: 10 degrees
Area 4: 20 degrees

9**

Response density

876**
*(�m)

*P < 0.05**P < 0.01
*
**

230

Foveal retinal thickness(nV/deg2)****543210**Control Before
PRP

**

*1 mo

3 mo

After PRP220210200190180170160150

6 moFig. 6. Changes in the mean response density levels ofthe mfERG obtained from 4 mfERG areas in 14 diabeticeyes before and after PRP. All values were expressed asmean ± SEM. Each bar indicates SEM. * indicates P< 0.05, and ** indicates P < 0.01 by Mann-Whitneyʼs Utest. PRP, panretinal photocoagulation; mo, month(s).
Control: 15 normal control eyes of 14 healthy volunteers.

*P < 0.05*Control Before
PRP1 mo

3 moAfter PRP

6 moFig. 7. Changes in the mean foveal retinal thickness
within 5 degrees on OCT in 14 diabetic eyes before andafter PRP. All values were expressed as mean ± SEM.
Each bar indicates SEM. * indicates P < 0.05 by MannWhitneyʼs U test. PRP, panretinal photocoagulation;
mo, month(s). Control: 16 normal control eyes of 12
healthy volunteers.

76Macular function before and after PRP in diabetic retinopathy

Before PRP
1 mo

After PRP
3 mo

6 mo

0.80�0.37

0.76�0.33

0.84�0.38

mfERG parameters

P1 peak latency(Area 1: 5 degrees)

P1 – N1 amplitude(4 mfERG areas)

Response density(4 mfERG areas)

Foveal retinal thickness(within 5 degrees)on OCT

Corrected visual acuity(mean � SD)

0.87�0.37

Fig. 8. Summarized data obtained in the present study before and after PRP in 14 diabetic eyes. In the mfERG parameters, the P1 peak latency from the area 1 (within a central radius of 5 degrees), the P1 – N1 amplitudes and themean response density levels from the 4 mfERG areas are presented at 1, 3 and 6 months after PRP following eachdata before PRP in addition to the mean foveal retinal thickness within 5 degrees on OCT. The mean corrected visual acuity in the 14 diabetic eyes is also presented throughout the course. PRP, panretinal photocoagulation; mo,months(s).

same tendency as in the P1 – N1 amplitudes, as
shown in Fig. 6. That is, the mean response density
levels from the 4 areas were remarkably decreasedin the 14 diabetic eyes before PRP as comparedwith those in the 15 control eyes at the 1% or 5%
level, followed by a maximum decrease in the parameter at 3 months after PRP. However, remarkable recoveries were detected in the mean response
density levels from the 4 areas at 6 months after
PRP at the 1% or 5% level.
The mean foveal retinal thickness within 5degrees on OCT was significantly increased in the14 diabetic eyes before PRP as compared with thethickness in the 16 control eyes of the 12 healthy
volunteers at the 5% level. Most remarkably, atransient increase in the thickness was detected in
the diabetic eyes at 1 month after PRP, followed bya tendency for recovery at 3 to 6 months after PRP(Fig. 7).

Discussion
As summarized in Fig. 8, in the mfERG parameters, the P1 peak latency from the area 1 (withina central radius of 5 degrees) was markedly prolonged in the 14 diabetic eyes before PRP as compared with that in the 15 control eyes, but a tendency for recovery was detected throughout the course
after the procedure (Fig. 4).
The P1 – N1 amplitudes and the mean response density levels from the 4 mfERG areas wereremarkably decreased in the diabetic eyes before
PRP as compared with those in the control eyes,
followed by a maximum decrease in both parameters at 3 months after PRP. However, remarkable
recoveries were detected in both decreased parameters from the 4 areas at 6 months after PRP (Figs. 5,6 and 8).
The mean foveal retinal thickness within 5
degrees on OCT was remarkably increased in thediabetic eyes before PRP as compared with the77

T. Baba et al.
thickness in the 16 control eyes. Most remarkably,a transient increase in the thickness was detectedin the diabetic eyes at 1 month after PRP, followedby a tendency of recovery at 3 to 6 months after theprocedure (Figs. 7 and 8).
This time, statistical analysis was not undertaken on the correlation between the corrected visual acuity and each data from the mfERG or OCT
examinations before and after PRP in each diabetic
eye due to the relatively small number of samples.
However, as demonstrated in Fig. 8, it is of notethat the mean corrected visual acuity before PRP
in the 14 diabetic eyes showed a gradual decreaseat 1 month, followed by a maximum decrease at
3 months and a tendency of gradual recovery at 6months after the procedure in each mean correctedvisual acuity in those eyes, as in the changes in theP1 – N1 amplitudes and the mean response density
levels of the mfERG obtained from the 4 mfERG
areas in the 14 diabetic eyes before and after PRP.
The OCT findings showed no coincidental
changes between mean foveal retinal thickness andmean corrected visual acuity in the 14 diabetic eyes
throughout the course after PRP. However, tendency of recovery in mean foveal retinal thickness
at 3 to 6 months after PRP may reflect a reversible
foveal function resulting in a gradual recovery of
the mean corrected visual acuity at 6 months after
the procedure in diabetic eyes (Fig. 8), although
we need to do further investigation on this point inmore subject patients.
The mfERG derived from the fundus area,
especially within 5 degrees of the central portion(Area 1) is supposed to reflect a cone-dominated response, which originates predominantly in the outer
70% of the retina, as in the full-field flash ERG(Hood et al., 1997; Palmowski et al., 1997; Fortuneet al., 1999).
Optical coherence tomography provides noninvasively a cross- sectional tomographic image ofthe retina as described above and is more sensitive
to small changes in retinal thickness than slit-lamp
biomicroscopy (Hee et al., 1995, 1998; Kang et al.,2004).
Thus, the results obtained in the present survey indicate that the mfERG and OCT examina-

tions are useful for assessment of macular function
before and after PRP in diabetic retinopathy, especially within 5 degrees of central portion, and thatthe effects of PRP on the macular function in thisentity seem to be reversible at the foveal region, although we need a further investigation in relation tothe outcome of visual acuity.
Acknowledgments: We express our sincere thanks toProfessor Yoshitsugu Inoue, Division of Ophthalmology
and Visual Science, Department of Medicine of Sensory
and Motor Organs, School of Medicine, Tottori University Faculty of Medicine, for his generous help.

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Received August 27, 2004; accepted September 24, 2004
Corresponding author: Akihiko Tamai, MD79