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Introduction
Diabetes is a multiorgan disease which is known to affect the
capillary density on the conjunctiva and perilimbal area (1-2).
Different techniques like capillarscopy (3), conjunctival
vessels morphometry (4), computer – assisted intravital
microscopy (5) and automated analysis of red free images (6,7)
have been employed to quantitatively study the microcirculation
of the conjunctiva and perilimbic area in diabetic patients.
The new advancement in fluorescein angiography equipments allows
one to quantify the perilimbal microcirculation. Furthermore,
digital image format of vascular networks allow image
manipulation, resulting in better visualization and objective
analysis using computer-aided techniques. These computer
softwares analyze digital images and convert positions and
measurements in an image after calibration from pixel to real
world dimensional measurements such as millimeters, microns,
feet, miles, etc.
The aims of this study were to describe a new simple technique
in assessing the capillary density in perilimbal area in digital
fluorescin angiography images and to correlate the changes with
grades of diabetic retinopathy.
Patients and methods
Participant selection:
A case control study was carried out at the Departments of
Ophthalmology, Almowasat Clinic (Tripoli, Libya) and First Eye
Hospital (Lublin, Poland).
100 participants with diabetes mellitus were recruited from
diabetic patients referred for fluorescein angiography. 81
participants in control group were recruited from non diabetic
patients referred for fluorescin angiography. Table I.
Diabetic retinopathy was graded clinically as no retinopathy,
mild non-proliferative, severe non-proliferative or
proliferative diabetic retinopathy in accordance with accepted
criteria (8).
Exclusion criteria were contact lens wearing, active anterior
segment disease, history of ocular surgery or long term use of
ocular topical medication. The study was performed from July
2005 through March 2006.
Technique of angiography:
5 ml of 10% fluorescein were injected in the anticubital
vein of the participants.
Two kinds of digital fundus camera were used for anterior
segment photography; Kowa RC– XV3 (Almowasat clinic, Tripoli –
Libya), and Heidelberg Retina Angiogram 2 (First eye hospital,
Lublin – Poland). 5 – 6 digital photographs were taken during
the first two minutes. The photographs were concentrated on the
lower quadrants of the bulbar conjunctiva. Posterior segment
photographs were taken during the same session.
Technique of measuring the perilimbal intercapillary surface
area (PIA):
The UTHSCSA Image Tool program (developed at the University Of
Texas Health Science Center at San Antonio, Texas and available
from the Internet from ftp://maxrad6.uthscsa.edu) was used to
measure the Perilimbal Intercapillary Area (PIA). PIA provides
capillary density estimation in the perilimbal network. The
intercapillary areas are highlighted with the cursor in the
digital image. Fifty randomly selected areas surrounded by
capillaries are marked. The area described by the cursor is
measured with the image tool program to obtain its surface area
in µm².
Statistical Analysis
Mean values and standard deviations are given for all
samples with normal distribution (Kolmogorov-Smirnov test). The
Student’s t test was used for unpaired (independent) samples
with normal distribution. Findings with an error probability of
<0.05 were considered to be statistically significant. The
perilimbal intercapillary areas (PIA) were log transformed to
give percentage differences. All the statistical calculations
were performed using SPSS software version 14.0 for Windows (SPSS
Inc. Headquarters, 233 S. Wacker Drive, 11th floor Chicago,
Illinois 60606, USA).
Results
Mean and standard deviation of PIA for control and diabetic
participants and the percentage change in diabetic participants
with different grade of retinopathy are given in table II.
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Discussion
The present study adopted a new approach of using digital
fluorescein angiography with digital image analysis technology.
This technology gives high magnification with excellent
resolution enabling more precise study of conjunctival and
limbal capillaries
Measurement of capillary density is a valuable diagnostic tool
for differentiating capillary loss (9-12).
Our study describes a simple technique for quantitative
assessment of capillary density in the perilimbal area by
measuring the perilimbal intercapillary surface area (PIA) using
image analysis software in digital fluorescin angiography images.
Measurement of intercapillary area in digital fluorescein images
was first introduced by Arend and colleagues in 1991, for
evaluating the perifoveal capillary network. It has been proven
to be a valid and accurate tool in assessing the perifoveal
capillary density in different ocular and systemic conditions
(9).
Our results showed clearly the strong association between the
capillary drop out in the perilimbal area and the grade of
diabetic retinopathy.
The effect of diabetes mellitus on the microvascular system of
the conjunctiva and limbus have been discussed in the ophthalmic
literature mainly during the past few decades using different
methods.
For instance, Ioseliany using Quantitative capillarscopy noted
that patients with diabetes mellitus with still no visible
changes in the retina showed statistically significant reduction
in the amount of functioning capillaries of the limbus (3).
Using the conjunctival morphometry, Worthen and colleagues, have
noted that there is a decrease in the capillary vascularity by
25% among diabetic patients when compared to normal subjects
(4).
Using red-free conjunctival images and an automated computer
algorithm Owen CG and colleagues, have shown A strong positive
association between the duration of diabetes and overall mean
vessel width, resulting from changes in larger vessels (>80 µm
in width). Conversely, the duration of diabetes showed a strong
inverse association with vessel area that appeared to be driven
by the trend observed in smaller vessels (<40 µm in width).
He also observed a 25% reduction in vessel density in those with
type 1 diabetes and a 14% reduction in those with type 2
diabetes. The difference in the size of effect for type 1 and
type 2 diabetes was accounted for by duration of diabetes,
reflecting the longer duration of disease in those with type 1
diabetes compared with those with type 2 diabetes (median
duration, 26 years and 7 years respectively). They also noted
that grade of diabetic retinopathy showed less strong
associations with the changes in conjunctival vessel indices
(7).
Comparing with the present study, we found higher percentage of
capillary loss due to diabetes (31.7%), and more strong
association between the grade of diabetic retinopathy and
perilimbal capillary loss.
We concluded the perilimbal capillary drop and ischemic changes
associated with diabetic retinopathies showed strong
correspondence.
References
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Praca wpłynęła do Redakcji 20.07.2006 r. (911)
Zakwalifikowano do druku 20.12.2006 r.Reprint
requests to:
Dr. Abdrahman Benzaglam
Tripoli Eye Hospital
P.O.Box : 93173
Zawiat Eldahmany, Tripoli, Libya | |
