Eleven patients (six men and five women, mean age: 49.3 ±
8.2, range: 36–62 years) with a diagnosis of OAG and eight patients
(four men and four women, mean age: 48 ± 6.7, range: 40–57
years) with OHT were included in the study. Diagnosis of OAG was
established on the basis of an elevated IOP (>21 mm Hg on two separate
occasions), an open angle, the presence of abnormal white-on-white
perimetry (Humphrey 30-2; Humphrey Instruments, San Leandro, CA) with a
typical reproducible defect (arcuate and/or paracentral scotoma or
nasal step; three or more adjacent points, not contiguous with the
field borders, with a ≥5 dB loss, or two or more adjacent points, not
contiguous with the field borders, with ≥10 dB loss) and glaucomatous
optic disc, evaluated by slit lamp biomicroscopy and 78-D lens, with a
cup-to-disc ratio greater than 0.6 (or an interocular cup-to-disc ratio
asymmetry ≥0.2) and one or more of the following disc abnormalities:
excavation, thinning of the rim, notching, nerve fiber layer defects,
or parapapillary atrophy. Field loss was graded from early to moderate
in all patients, with Humphrey 30-2 mean deviation ranging from −1.2
to −6 dB. Patients with OHT had an elevated IOP (>21 mm Hg on two
separate occasions), normal Humphrey perimetry, and normal clinical
optic disc appearance. All patients were selected by an experienced
ophthalmologist (AC) specializing in glaucoma. Eight normal subjects,
whose sex and age distribution was comparable with that of patients
(four men and four women, mean age: 48.7 ± 6.4, range: 38–59),
provided normative ERG values. In
Table 1 , clinical findings obtained in individual patients with OHT and
OAG are reported. In all patients, analysis of the optic disc was
performed by confocal scanning laser ophthalmoscopy (Heidelberg Retina
Tomograph, [HRT]; Heidelberg Engineering, Heidelberg,
Germany) according to a previously published protocol.
16 Among the various morphometric parameters obtained by HRT, those most
sensitive and specific for glaucoma damage
17 18 19 were
considered in the analysis: the cup-to-disc area ratio and the cup
shape measure. Cup-to-disc area ratio is the ratio of cup to disc
surface determined by means of the current HRT software algorithm (2.01
ver.). The cup shape measure is a structural index summarizing in one
number the depth variation and steepness of the cup
walls.
18 Its value is typically negative in normal eyes
and less negative or positive in glaucomatous eyes.
18 These measurements were compared with the 95% confidence limits
established in 18 normal eyes (18 subjects; mean age: 44 ± 6.5
years, range: 38–59 years), with disc area in the ranges of 1 to 2
mm
2 (
n = 9; mean cup-to-disc area
ratio = 0.15, upper 95% confidence limit = 0.22; mean cup
shape measure = −0.29, upper 95% confidence limit = −0.14)
and 2 to 3 mm
2 (
n = 9; mean
cup-to-disc area ratio = 0.23, upper 95% confidence limit =
0.36; mean cup shape measure = −0.23, upper 95% confidence
limit = −0.06). Subjects providing normative HRT and
electroretinographic data belonged to independent groups. Cup-to-disc
area ratio was significantly altered in 2 of 8 OHT eyes and in 7 of 11
OAG eyes, whereas cup shape measure was normal in all OHT eyes and
abnormal in 2 of 11 OAG eyes. In
Table 1 , in addition to the Humphrey
mean deviation derived from the 30° field, a central mean deviation
calculated from a field area of 12° × 12° is reported for each
patient. This mean deviation value was obtained by averaging the local
losses in decibels found in the total deviation plot of the Humphrey
30-2 and was used for correlation purposes with the
electroretinographic responses, elicited from the same central 12° ×
12° stimulation area (see below). Informed consent was obtained from
every subject or patient after the procedures used in the study were
fully explained. The research followed the tenets of the Declaration of
Helsinki.