Yonago Acta medica 2004;47:71–79

Assessment of Macular Function by Multifocal Electroretinography and Optical Coherence Tomography before andafter Panretinal Photocoagulation in Diabetic Retinopathy
Takashi Baba, Yuji Sasaki, Shiro Hatta, Jiro Hasegawa, Atsushi Yamasaki, Ryoko Ishikura, Akiko Kakimaru, Kazuki Matsuura* and Akihiko Tamai†
Division of Ophthalmology and Visual Science, Department of Medicine of Sensory and Motor Organs, School of Medicine, Tottori University Faculty of Medicine and *Department of BiomedicalScience, Institute of Regenerative Medicine and Biofunction, Tottori University Graduate Schoolof Medical Sciences, Yonago 683-8504 and †Clinic of Ophthalmology, Hino Hospital Association
Hino Hospital, Hino 689-4504 JapanWe evaluated macular function before and after panretinal photocoagulation (PRP) indiabetic retinopathy using a multifocal electroretinogram (mfERG) and optical coherence
tomogram (OCT). In mfERGs, the 1st positive wave (P1) minus the 1st negative wave
(N1) amplitude (P1 – N1 amplitude), the P1 peak latency and the response density weremeasured in 7, 19, 37 and 103 hexagonal areas or elements (Areas 1, 2, 3 and 4) withina central radius of 5, 7, 10 and 20 degrees, respectively. The mean retinal thickness wasestimated from 9 calculation points at the foveal region within 5 degrees; the central andeach of the other 4 points at a distance of 250 µm and 500 µm from the central portion
on horizontal and vertical sections on OCT. The P1 peak latencies from the 4 areas wereremarkably prolonged in 14 eyes of 9 patients with preproliferative or early proliferative
diabetic retinopathy showing no clinically signiﬁcant macular edema before PRP as compared with those in 15 normal control eyes, without a tendency of recovery throughout thecourse after PRP except for area 1. The P1-N1 amplitudes and the mean response density
levels from the 4 areas were remarkably decreased in the diabetic eyes before PRP as compared with those in the control eyes, followed by a maximum decrease in both parametersat 3 months after PRP. However, remarkable recoveries were detected in both decreased
parameters from the 4 areas at 6 months after PRP. The mean foveal retinal thickness
on OCT was remarkably increased in the diabetic eyes before PRP as compared with thethickness in 16 normal control eyes. Most remarkably, a transient increase in thickness
was detected in diabetic eyes 1 month after PRP, followed by a tendency of recovery 3 to 6months after PRP. These results indicate that mfERG and OCT examinations are usefulin the assessment of macular function before and after PRP in diabetic retinopathy, especially within 5 degrees of the central portion, and that the effects of PRP on macular function in this entity seem to be reversible at the foveal region, although we need to do further
investigation in relation to the outcome of visual acuity.
Key words: diabetic retinopathy; macular function; multifocal electroretinogram; optical coherence
tomogram; panretinal photocoagulation
List of Abbreviations, p. 72.

71

T. Baba et al.
Panretinal photocoagulation (PRP) is a beneficial
procedure for the treatment of preproliferative or
early proliferative diabetic retinopathy (Diabetic
Retinopathy Study Research Group, 1981; Early
Treatment Diabetic Retinopathy Study ResearchGroup, 1991), even though vitrectomy has been
performed in many patients with severe and complicated diabetic lesions (Lewis et al., 1992; Massin
et al., 2003). On that occasion, the assessment ofmacular function is very important for predicting
the patientsʼ quality of vision after PRP. Several reports showed various changes in retinal sensitivity
after PRP in this entity, using mostly the Goldmannkinetic perimeter (Frank, 1975), the computed
static perimeter (Chee and Flanagan, 1993; Yoon etal., 1996) and the electroretinogram (ERG) (Frank,1975; Bresnick and Palta, 1987).
Using an optical coherence tomogram (OCT),Hee and his co-workers (1995, 1998) and Kang andothers (2004) quantified foveal retinal thickness
correlated with visual acuity in patients with clinically significant diabetic macular edema. Recently,
Palmowski and others (1997) and Fortune and others (1999) revealed local retinal dysfunction in themacular area in diabetic patients, with and without
retinopathy, using a multifocal electroretinogram(mfERG) (Sutter and Tran, 1992). In general,morphological changes in the retina are assessedby OCT examination because optical coherence
tomography offers high-resolution, cross-sectional
images of the retina and quantitative measurementof retinal thickness (Hee et al., 1995, 1998; Kang etal., 2004), while topical functional changes in theretinal layer are assessed with mfERG examination, using a multifocal technique (Sutter and Tran,1992; Palmowski et al., 1997; Fortune et al., 1999).
These tests allow a relatively fast, objective
evaluation of retinal function in their images andpatterns in contrast to subjective perimetric examinations such as the Goldmann kinetic perimeter (Frank,1975) and the computed static perimeter (Cheeand Flanagan, 1993; Yoon et al., 1996). However,
little attention has been paid to the assessment ofmacular function by mfERG and OCT examinations before and after PRP in diabetic patients withretinopathy. We therefore evaluated macular function before and after PRP in diabetic retinopathy bymultifocal electroretinography and optical coherence tomography in this survey.
Subjects and Methods
Nine patients (14 eyes) with preproliferative or
early proliferative diabetic retinopathy showing noclinically significant macular edema were referred
to us for this study. Their ages ranged from 51
to 77 years averaging 61.2 ± 8.6 years (SD). The
mean corrected visual acuity of the 14 diabetic eyes
before PRP was 0.87 ± 0.37 (SD), followed by 0.80
± 0.37, 0.76 ± 0.33 and 0.84 ± 0.38 at 1, 3 and 6months after PRP, respectively. They were examined using a VERIS Science System for the mfERG(Mayo Corp., Nagoya, Japan) and a Humphrey
OCT scanner (Carl Zeiss Co., Ltd., Tokyo, Japan)
before PRP and at 1, 3 and 6 months after the procedure, as described later.
Fourteen healthy volunteers (15 normal eyes)
aged 51.1 ± 13.1 years (SD) on the average served
as controls for the VERIS study, and 12 healthy
volunteers (16 normal eyes) aged 66.1 ± 12.5 years(SD) on an average served as controls for the OCT
study in the present estimation. These healthy volunteers were randomly divided into either study
group.
The diabetic patients were randomly chosen
for the present survey over the past 4 years (August1996 to September 2000) at the Department ofOphthalmology, Tottori University Hospital. The
tenets of the Declaration of Helsinki were followed.
Upon giving informed consent, all subjects including volunteers participated in the present study. Error of refraction did not exceed ± 3 diopters in thediabetics or normal controls. Eyes with cloudingof the media or subjected to previous surgery wereexcluded from the analysis.

Abbreviations: ERG, electroretinogram; ETDRS, Early Treatment Diabetic Retinopathy Study; mfERG, multifocal
electroretinogram; N1, 1st negative wave; OCT, optical coherence tomogram; P1, 1st positive wave; PRP, panretinal
photocoagulation72

Macular function before and after PRP in diabetic retinopathy

recording. The mfERG stimulus matrix consistedof 103 concentrically scaled hexagons, which covered the fundus area within a central radius of 20degrees (Fig. 1). Alternated color changes were set
in each hexagon between black and white in binary
m-sequences at a rate of 75 Hz. Luminance levels ranged from 5 to 200 cd/m2. A Burian-Allen
bipolar contact lens electrode was used for signal
derivation. A grounding electrode was attached toeither earlobe, a routine procedure. The pupil ofone eye was fully dilated with 2.5% phenylephrinehydrochloride, and the other eye was occluded.
The net recording time for each eye was 4 min.
The entire procedure was divided into eight 30-s
segments. The signals were amplified using theVERIS Science System with bandpass filters (10–300 Hz).
As demonstrated in Fig. 2, in the response
arrays of the mfERG consisting of the mean focal flash response (Fig. 2a), the 1st positive waveof each mean focal flash response (P1) minus the
1st negative wave of each response (N1) amplitude(P1 – N1 amplitude) in µV and the P1 peak latency
in ms were measured as mfERG parameters in 7,19, 37 and 103 hexagonal areas or elements (Areas1, 2, 3 and 4; 4 mfERG areas) within a central radius of 5, 7, 10 and 20 degrees, respectively (Fig.
1). Three-dimensional topography revealed the re-PRP procedure
Treatment with PRP on the diabetic patients wasperformed according to the Early Treatment Diabetic Retinopathy Study (ETDRS) protocol (Diabetic Retinopathy Study Research Group, 1981;
Early Treatment Diabetic Retinopathy Study Research Group, 1991). All patients underwent PRP
in 2 sittings 1 week apart, lower hemifield followed
by upper hemifield. Photocoagulation covered theentire mid periphery beyond the equator, and posteriorly to the area bordered by the temporal vasculararcades, nasal disc border and 2-disc diameter temporal to the fovea. All eyes were treated with eithera green argon laser (Coherent Inc., Palo Alto, CA)or a dye laser (Biophysic Medical Ins., ClermontFerrand, Cedex, France). Approximately 1,000
to 2,000 burns of a 200 to 500 µm spot size weremade 1 to 2 burn spaces apart through a 3-mirror
universal lens (Ocular Instruments Inc., Bellevne,WA) or a double aspheric lens Trans Equator orQuadr Aspheric (Volk Optical Inc., Mentor, OH).
mfERG examination
The VERIS Science System, which is a visual evoked response imaging system originally developedby Sutter and Tran (1992), was used for the mfERG

mfERG areas
Area 1:

5 degrees
7 elements

Area 2: 7 degrees

19 elements

Area 3: 10 degrees

37 elements

Area 4: 20 degrees

103 elements

73Fig. 1. The multifocal electroretinogram (mfERG) stimulus matrix consisting of 103 concentrically scaled
hexagons. The matrix was divided
into 7, 19, 37 and 103 hexagonal areas
or elements (Areas 1, 2, 3 and 4; 4
mfERG areas) within a central radiusof 5, 7, 10 and 20 degrees, respectively.