Br J Ophthalmol 1998;82:121-130 ( February )
Scanning laser tomography Z profile signal width as an objective
index of macular retinal thickening
Chris Hudson,a b
John G Flanagan,a c
George S Turner,a
David McLeoda
a University Department of Ophthalmology,
Manchester Royal Eye Hospital, Manchester M13 9WH, b School of Biomedical Sciences, University of Ulster,
Coleraine, Northern Ireland, c Department of
Ophthalmology, University of Toronto, The Toronto Hospital, Toronto,
Ontario M5T 2S8, Canada
Correspondence to: Chris Hudson, PhD, School of Biomedical Sciences, University
of Ulster, Coleraine, County Londonderry, BT52 1SA, Northern Ireland.
Accepted for publication 18 September 1997
AIMS (i) To evaluate the relation between retinal
thickness and the Z profile signal width of a scanning laser
tomographer in selected patients exhibiting clinically manifest and
circumscribed macular retinal thickening; (ii) to compare the Z profile
signal width values of a group of age similar normal subjects with
those of the patients with macular retinal thickening; and (iii) to
present the methodology underlying the Z profile signal width derivation.
METHODSThree patients with the following
conditions were selected: widespread diabetic macular oedema; localised
diabetic macular oedema; and macular hole. The patients were selected
because they exhibited clinically manifest and circumscribed macular
retinal thickening. Patients underwent fundus photography and a
clinical examination which included fundus biomicroscopy. Fourteen age similar normal subjects were also assessed. The Heidelberg retina tomograph (HRT) was utilised to acquire seven topographic images of
each macula. Z profile signal width data were analysed using custom
software. Signal width was measured at 50% of the maximum intensity.
RESULTSFor each patient with macular retinal
thickening, Z profile signal width analysis (after normalisation to
reduce the influence of variation in reflectance intensity between
successive images) revealed a significant (p<0.0001) localised
increase of signal width which agreed with the HRT topographic analysis
of retinal height, and also the clinical assessment of retinal
thickness. The mean normalised Z profile signal width for the normal
subjects (assessed over the whole image) ranged from 0.278 (SD 0.039)
to 0.444 (0.063); these values compared with those obtained from patients in areas of macular retinal thickening of 0.761 (0.224) to
0.953 (0.194). Z profile signal width test-retest data for the patient
with localised diabetic macular oedema were plus or minus 0.159 which
compared with a mean signal width value of 0.761.
CONCLUSIONThe evidence of this study, based upon
three selected patients with macular retinal thickening and 14 normal
subjects, would suggest that Z profile signal width analysis offers a
non-invasive, objective, topographic, and reproducible index of macular
retinal thickening. Studies employing larger sample sizes are required to determine the true clinical worth of the technique.
Keywords:
diabetic macular oedema;
retinal thickening;
scanning laser tomography;
Z profile
© 1998 by British Journal of Ophthalmology
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