Adres Infrastructure
Hardware
A commercially available non-mydriatic retinal fundus camera optimized for low light level imaging of the retina (TOPCON, TRC-NW100) with capability to provide up to 2.3 million pixel image resolution images, with 45° field that gives high quality spatial, contrast and color resolution was used for fundus photography, preferably through a pupil at least 4 mm in diameter. It was interfaced with ADRES 3.0 (image capture and telemedicine software developed in-house) to acquire standard single-frame digital color images of the retina.
The camera’s dimensions are 272 (W) mm x 505 (D) mm x 560 (H) mm, it weighs 24 kilograms, and works on a power source of frequency 50 to 60 hertz AC 110/120/230/240V, with a power consumption of 400VA at maximum. The camera and interface are available at the retinal clinic and also in a mobile tele-ophthalmology van; this study was performed only on images acquired at the clinic set-up.
The recommended specifications for the acquisition unit include a Windows XP operating system, processor capabilities of 900 mhz with a 30 GB hard disc and 256 MB RAM, device integration with DICOM/JPEG/Twain protocols, a CD ROM with writer, USB port, backup system, and a monitor, with a 10/100 bps network card.
At the reading station, an Intel compatible computer with dual monitor support, a Windows XP operating system, processor capabilities of 900 mhz with a 30 GB hard disc and 512 MB RAM, 3Dlabs oxygen GVXI graphics card (for stereo viewing), a CD ROM with writer, USB port, backup system, used with a 17/21 inch, >100 mhz refresh rate monitor and 3D Revelator, IR version goggles (for stereo viewing) are required.
The file server requirements include a Windows XP operating system, processor capabilities of 900 mhz with a 30 GB hard disc and 512 MB RAM, a CD ROM with writer, USB port, and a monitor with disaster & recovery systems such as Backup & Network Attached Storage.
Connectivity requirements included a Dialup (PSTN/ISDN/Satellite) connection with DICOM transfer over the Internet.
The operating characteristics of the video camera are optimized for acquiring high quality retinal images in low-light-level conditions with the lowest available flash intensities, to ensure patient comfort, minimize pupil reaction to light, and to facilitate obtaining multiple images from the same eye at one sitting. The option of anterior segment photography is sometimes useful for evaluating ocular media clarity.
Images
The single stereoscopic pair of images centered on the macula and included the optic disc were acquired manually by horizontal translation of the fundus camera, as is standard for obtaining non-simultaneous stereoscopic retinal photographs; four equidistant images covering the peripheral areas of the retina were also taken(Figure 1). The stereoscopic pair of images were labeled as A1-A1’ and the four ‘peripheral’ images were labeled A2, A3, A4 and A5 respectively.
The acquisition protocol of this system (1+4, 5 field protocol) uses a modified protocol over Joslin Vision Network Team (1+2, 3 field protocol) 5 so as to provide better confidence for reading and grading retinopathy, especially for peripheral images.
Field Definitions
The 45° field size is approximately nine times the diameter of the optic disc. A description of the images and the processes followed for their acquisition are presented below:
A1, and A1': 45 degree field, focused centrally between the temporal margin of the optic disc and the centre of the macula, with the horizontal central line of the image passing through the center of the disc. Stereoscopic images are obtained by capturing one image through the left aspect of the pupillary opening and the second image through the right aspect of the pupil by shifting the camera laterally. A slight delay between the first and the second image may be necessary to allow for adequate pupil mydriasis.
A2: 45 degree field supero-temporal to the optic disc so that the lower edge of the field is at a tangent to the horizontal line passing through the centre of the optic disc and the nasal edge of the field is at a tangent to the vertical line passing through the center of the disc.
A3: 45 degree field infero-temporal to the optic disc so that the upper edge of the field is at a tangent to the horizontal line passing through the centre of the optic disc and the nasal edge of the field is at a tangent to the vertical line passing through the center of the disc.
A4: 45 degree field supero-nasal to the optic disc so that the lower edge of the field is at a tangent to the horizontal line passing through the centre of the optic disc and the temporal edge of the field is at a tangent to the vertical line passing through the center of the disc.
A5: 45 degree field infero-nasal to the optic disc so that the upper edge of the field is at a tangent to the horizontal line passing through the centre of the optic disc and the temporal edge of the field is at a tangent to the vertical line passing through the center of the disc.
Software
This software captures retinal images, and transmits them to a central reading center for interpretation and grading. It is DICOM compliant and HL7 ready for enterprise integration at sites. ADRES 3.0 also permits capture of structured and unstructured clinical data such as relevant patient demographics, medical histories, and related laboratory results using flexible templates which are linked uniquely to the related retinal images through patient study identification numbers in patient wise and visit wise folders. These are transmitted after being de-composed to form xml structures (eXtensible Markup Language). The images are compressed using the industry standard JPEG Lossless compression algorithm for optimized storage and transfer.
Grading Protocol for Diabetic Retinopathy
Readers grade the images of A1-A1’, A2, A3, A4 and A5 45° images in reference to the ETDRS seven standard 30° field stereoscopic fundus photographs. Two sets of images representing each eye are verified for quality (gradability) before commencing grading. The retinal findings for each eye of each patient are recorded on electronic medical grading templates by the grader, the results are compiled and appropriate advice is automatically generated. The advice is verified by the grader, who places his electronic signature; the diagnosis and therapeutic advice is sent back to the remote center and simultaneously filed in the database.
The graders enter clinical findings, which are converted to results according to a lesion grading matrix (Table 2), which is based on established standard practice guidelines such as those of ETDRS and AAO’s Preferred Practice Patterns.
Table 2: DR grading matrix for ADRES 3.0
| Lesions |
Images to be assessed |
Grading Inputs |
| Field not Readable |
A1, A1', A2, A3, A4, A5 |
|
| Microaneurysms |
A1, A1', A2, A3, A4, A5 |
Present / Absent |
| Hemorrhages |
A1, A1', A2, A3, A4, A5 |
HGE present. Compare with std 2A, noting whether they are less than in the standard photograph, or more than /equal to that seen in the standard photograph. |
| Hard exudates |
A1, A1', A2, A3, A4, A5 |
Present / Absent |
| Cotton Wool Spots |
A1, A1', A2, A3, A4, A5 |
Number of lesions |
| Retinal Thickening |
A1, A1' |
Number of areas present of size less than one disc area, and number equal to or more than one disc area in size.
Distance of the retinal thickening from center of macula in microns (<500, 500-1500, >1500 microns) |
| Venous beading |
A1, A1' |
Number present which are larger than that seen in standard photograph 6A; number of size less than one fourth of the disc area, and number equal to or more than one fourth of the disc area in size |
| IRMA |
A2, A3, A4, A5 |
Number present which are larger than that seen in standard photograph 8A; number of size less than half disc area, and number equal to or more than half the disc area in size |
| NVD |
A1, A1' |
Present / Absent |
| NVE |
A2, A3, A4, A5 |
Present / Absent |
| Disc Edema |
A1, A1' |
Present / Absent |
| PRH |
A1, A1', A2, A3, A4, A5 |
Present / Absent |
| VH |
A1, A1', A2, A3, A4, A5 |
Present / Absent |
| FPD |
A1, A1' |
Present / Absent |
| FPE |
A2, A3, A4, A5 |
Present / Absent |
| TRD |
A1, A1', A2, A3, A4, A5 |
Present / Absent |
| Occluded Vessels |
A1, A1', A2, A3, A4, A5 |
Present / Absent |
CSME on the images was assigned Grade 1 if there was retinal thickening within 500 microns from center of macula, as Grade 2 if hard exudates (HE) were present within 500 microns from center of macula with adjacent retinal thickening, and as Grade 3 if the area of retinal thickening was at least equal to one disc area, and any part of which was within 1500 microns from center of macula.
The presence or absence of associated lesions such as Asteroid Hyalosis, Central Vein Occlusions, Branch Vein Occlusions, Disciform Macular Degeneration, Macular Hole, ERM, Glaucoma, Diabetic Papillopathy, AION, Lipemic DR, et cetera can be entered in the electronic file if any such lesions are identified.
Clinical equipment
The comprehensive eye examination included measurement of Snellen’s visual acuity, slit-lamp biomicroscopic examination aided with the 3-mirror contact lens when required, dilated fundoscopy using a 60 or 90 Dioptre lens (VOLK) and indirect ophthalmoscopy.
Clinical grading of diabetic retinopathy and of clinically significant macular edema (CSME) was based on the Extension of the Airlie House Classification used in the ETDRS study. Additionally, presence of pre-retinal (PRH) or vitreous hemorrhage (VH), or neovascularization of a quarter or more of the disc area (NVD) was graded as high risk proliferative diabetic retinopathy, and presence of a tractional retinal detachment led to the retinopathy being graded as Advanced PDR. This was followed for the grading of fundus images as well.
Ethical issues:
Patients were counseled about the disease and their informed consent for participation in the validation study was obtained prior to allocation, despite the study protocol being the same as that followed for all diabetics attending the clinic. The study had been presented to and approved by the Research Committee of Aravind Eye Care System.
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