Atan, D

Foy, C

Scanlon, Peter H

Scanlon, PH

Explore Bristol Research

Reply to ‘Evaluation of the effect of JPEG and JPEG2000 image compression on the detection of diabetic retinopathy’

Name not available

Sir,
Reply to ‘Evaluation of the effect of JPEG and
JPEG2000 image compression on the detection of
diabetic retinopathy’
The authors found good agreement for diabetic
retinopathy (DR) detection between grading
uncompressed tagged interchanged files format (TIFF)
images taken with a nonmydriatic digital camera and
their joint photographic experts group (JPEG)
equivalents, compressed by JPEG2000 or classic JPEG
algorithms. Both performed well for the detection of
haemorrhages and microaneurysms (HMA), when
preselected ‘good quality’ TIFF images were compressed
at the lowest ratio. Our experience in the Gloucestershire
Diabetic Eye Screening Service, using a Topcon TRNW5s
camera and Sony DXC-950 tri-CCD colour video camera,
producing TIFF images of identical resolution (800 600
pixels) is that it cannot reliably detect small DR lesions
like HMA in the first place.
The TIFF images of 99 eyes with microaneurysms
within one disc diameter of the centre of the fovea
(masp1DD), identified by an experienced
ophthalmologist (PS) using slit-lamp bio-microscopy, and
their fellow 69 eyes with no DR were randomly
presented to two experienced and masked independent
medical retina specialists (EJ and VG) for grading among
other images from 472 eyes with a variety of retinopathy
levels. In Table 1, the grading of these TIFF images is
compared with the clinical grading as reference. Only 6.1
and 5.1% of masp1DD were detected by VG and EJ
respectively. Even allowing for the misclassification of a
microaneurysm as a haemorrhage, the detection rates
remained poor. Nevertheless, the system did perform
well for the detection of referable DR as reported in the
Gloucestershire study.1
In 2003, a Four Nations Working Group from England,
Scotland, Wales, and Northern Ireland2 recommended a
minimum camera resolution of 20 pixels per degree of
retinal image (equivalent to 1365 1000) for UK
screening programmes. The same year, a Health
Technology Assessment by Sharp et al3 reported that the
sensitivity and specificity of digital imaging for the
detection of early retinopathy were only 81% using a
Topcon TRC-50XT with Kodak Megaplus 1.41 CCD
camera (1024 1024 pixels in monochrome) compared to
slit-lamp bio-microscopy by ophthalmologists. Since
then, more high-resolution cameras and camera backs
are available to screening programmes resulting in large
uncompressed image file sizes.
Studies to determine the maximum acceptable level of
image compression have either scanned in high-quality
images from film4 or used images of lower resolution
such as Conrath’s study. Based on current evidence,
the English National Screening Committee recommends
the highest quality JPEG compression setting on the
digital camera back is used at capture (for example 12 : 1
rather than 20 : 1).2 Subsequent compressions are more
likely to result in the loss of clinically significant
information.
Further research is required to determine appropriate
levels of compression using higher resolution cameras
for both referable retinopathy and any retinopathy.
References
1 Scanlon PH, Malhotra R, Thomas G, Foy C, Kirkpatrick JN,
Lewis-Barned N et al. The effectiveness of screening for
diabetic retinopathy by digital imaging photography and
technician ophthalmoscopy. Diabet Med 2003; 20(6): 467–474.
2 NSC. A national screening programme for sight-threatening
diabetic retinopathy. In:www.nscretinopathy.org.uk, 2003.
3 Sharp PF, Olson J, Strachan F, Hipwell J, Ludbrook A,
O’Donnell M et al. The value of digital imaging in diabetic
retinopathy. Health Technol Assess 2003; 7(30): 1–119.
4 Wood I, Ritchings RT, Javadian S, Harding SP, Broadbent
DM. Assessment of JPEG compression on the diagnostic
quality of digitised diabetic retinopathy images. ARVO Invest
Ophthalmol Vis Sci 1999; 40: S698.
D Atan1, C Foy2 and PH Scanlon3
1Academic Department of Ophthalmology, Bristol
Eye Hospital, Lower Maudlin St, Bristol, UK
2Gloucestershire Eye Unit, Cheltenham General
Hospital, Sandford Road, Cheltenham, UK
3Gloucestershire Eye Unit, Cheltenham General
Hospital, Sandford Road, Cheltenham, UK
E-mail: Denize.Atan@bristol.ac.uk
This work was presented at the Oxford
Ophthalmological Congress in 2002 for which
Denize Atan was awarded the Founders Cup.
Eye (2008) 22, 471; doi:10.1038/sj.eye.6703019;
published online 9 November 2007
Sir,
Retinal pigment epithelial rip associated with
idiopathic central serous chorioretinopathy
Retinal pigment epithelial (RPE) rips have been
reported in association with age-related macular
degeneration and laser photocoagulation. Rarely, they
occur in central serous chorioretinopathy (CSCR),
particularly when the neurosensory detachment is
associated with an underlying large pigment epithelial
detachment (PED). We documented with fundus
imaging, a patient with idiopathic CSCR who developed
an RPE rip.
Table 1 Detection of micro-aneurysms or haemorrhagesp1DD
from the fovea in TIFF images compared with clinical grading as
reference
Sensitivity Specificity
No. (%) CI No. (%) CI
(i) Detection of micro-aneurysms alone p1DD from fovea
VG 6/99 (6.1%) 2.6–12.9 68/69 (98.6%) 91.5–100
EJ 5/99 (5.1%) 1.9–11.6 67/69 (97.1%) 89.4–99.8
(ii) Detection of micro-aneurysms or haemorrhages p1DD from fovea
VG 20/99 (20.2%) 13.4–29.2 66/69 (95.7%) 87.5–99.0
EJ 9/99 (9.1%) 4.7–16.6 67/69 (97.1%) 89.4–99.8
Cl¼ 95% confidence intervals.
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Eye (2008) 22, 471–474
& 2008 Nature Publishing Group All rights reserved 0950-222X/08 $30.00
www.nature.com/eye


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Reply to ‘Evaluation of the effect of JPEG and JPEG2000 image compression on the detection of diabetic retinopathy’

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