Tele-Ophthalmology - All India Ophthalmological Society

COMMUNITY / SOCIAL OPHTHALMOLOGY SESSION175Tele-Ophthalmology: Effect of Compression and SatelliteTransmission on Image ParametersDr. Nishant Vijay Radke, Dr. Tarun Sharma, Dr. Rajiv Raman,Dr. Swakshyar Saumya Paul, Dr. Tandava Krishnan(Presenting Author: Dr. Nishant Vijay Radke)Diabetic retinopathy (DR) is becoming theleading cause of visual impairment in theworking population today in the developedworld 1 and a similar trend has been noted inIndia. For such a common disease with effectivepreventive treatment, there is a critical need for asensitive, specific and cost-effective screeningmethod. One of the challenges in DR screeningin India is to take these measures to rural area.One of the emerging solutions to this problem isTele-ophthalmology. Digital cameras are usedmore often in Tele-ophthalmology. Withincreasing detail needed for proper diagnosis,however, the size of the digital file increases. Thishas the potential of making Tele-ophthalmologycost-ineffective. 2,3 The solution to overcome thisappears to be effective compression the file size.To the best of our knowledge, no study has beenperformed to test the effect of transmission ofretinal images via Tele-ophthalmology via VSAT(Very small aperture terminal) satellite link in theJPEG format.Materials and MethodsFundus images of 133 consecutive diabeticpatients aged > 30 years attending DR screeningcamps in rural Tamil Nadu were taken. Patientswith media opacities were excluded. A single,mydriatic digital 450 fundus photograph of botheyes centered on the macula was taken by atrained photographer inside the Teleophthalmologyvan using Topcon TRC NW 100non-mydriatic camera (Topcon, Tokyo, Japan).The digital fundus images of each patient wereconverted to DICOM (Digital Imaging andCommunications in Medicine) format by PACS(Picture archival and communication software)telemedicine software (Vipro InfoTech,Germany). These images were transferred to thehub at a tertiary eye care base hospital by satellitelink using VSAT hardware at a transmission rateof 384 Kbps. A retinal specialist sitting in the hubevaluated all the images using the Sony videoconferencingsystem. Image parameters werestudied before and after the tele-transmission.Image comparison software Picture Explorerversion 7.2 was used for comparison of theimages .The various parameters studied were:JPEG quality index, smoothness index, vesselbranching and overall picture quality. Numberof branch generations of vessels visualised wasused to quantify the image quality. It was gradedas excellent if the number was 4, good for 3,average for 2 and 1 if only one clear branch wasseen. The effect of transmission by satellite oncompressed images at various levels ofcompression was also assessed. Eightconsecutive images were chosen and compressedusing JPEG software at 1:10, 1:20, 1:30, 1:40, 1:50,1:60 and 1:70 ratios. Statistical analysis was doneusing the GraphPad InStat [GraphPad Software,CA, USA.]Results266 of 133 patients were studied. There was nodifference in any of the objective parameters orthe vessel branching index between the imagesat the camp and at the hub (p>0.999). Forthe images compressed at various levels, thechanges in the objective parameters showed alinear trend of decreasing quality with increasingcompression. There was a strong negativecorrelation between level of image compressionand JPEG quality index (r = -0.9221)(95% CI =-0.9861 to -0.6208), smoothness index(r =-0.9299)(95% CI =-0.9875 to -0.6531), and overallpicture quality(r = -0.9266)(95% CI =-0.9869 to -0.6394) and a strong positive correlation betweenlevel of image compression percent loss(r =0.9113)(95% CI =0.5772 to 0.9840). All of thesecorrelations were significant. The image qualitywas excellent in all the images according to thevessel branching index upto 1:30 compressionlevel, and good in all images at 1:40 compression

176 AIOC 2010 PROCEEDINGSlevels. The quality progressively decreased untilall images obtained were poor at 1:70compression. There was no difference in any ofthe objective parameters or the vessel branchingindex studied before and after transmission forthese compressed images.DiscussionTele-ophthalmology has the potential to greatlyexpand and simplify access to expert ophthalmiccare for diabetics. 4 At a resolution of 1024 x 768,each 24-bit image takes 2.5 megabytes. Thevarious connectivity options for telemedicineservices are VSAT, PSTN (Public SwitchedTelephone Network), ISDN (Integrated ServicesDigital Network), Leased Line, Wireless LAN(Local Area Network) /WAN (Wide AreaNetwork) 5 . The VSAT provides faster speed andis ideal for transmission over long distances 5.The time needed for transmission can bedramatically reduced by image compression.JPEG (Joint Photographic Experts Group)compression is standardized and generallycompatible with many different applications. Thedescribed telemedicine models reported earlierhave used the Internet to transmit images. 6,7 Weprefer satellite transmission because of poorinfrastructure in rural areas. The Technical1. National Society to prevent Blindness. Visionproblems in the U.S.A.: New York: National Societyto Prevent Blindness, Operational ResearchDepartment, 1980.2. Eikelboom RH, Yogesan K, Barry CJ, Constable IJ,Tay-Kearney ML, Jitskaia L et al. Methods andlimits of digital image compression of retinalimages for telemedicine. Invest Ophthalmol Vis Sci.2000;41(7):1916-24.3. R S B Newsom, A Clover, M T J Costen, J Sadler, JNewton, A J Luff, C R Canning. Effect of digitalimage compression on screening for diabeticretinopathy. Br J Ophthalmol 2001;85:799-802.4. Cavallerano J, Lawrence MG, Zimmer-Galler I,Bauman W, Gardner WK et al AmericanTelemedicine Association, Ocular TelehealthSpecial Interest Group; National Institute ofStandards and Technology Working Group.Telehealth practice recommendations for diabeticretinopathy. Telemed J E Health. 2004;10(4):469-82.5. Recommended Guidelines and Standards forPractice of Telemedicine in India and HealthUnITe: The Framework for Information TechnologyInfrastructure for Health ( ITIH) for India.ReferencesWorking Group for standardization ontelemedicine in India recommends a satellite linkto connect to a remote site with high bandwidthpipe in a short duration. 5 Earlier studies haveattempted to look at the effect of various levels ofcompression on the quality of the image withboth subjective and objective parameters. 2,3However, to the best of our knowledge, nonehave studied the effect of transmission losses viaVSAT. 2,3 The level of acceptable compressionranges from 1:28 to 1:52. 2,3,8 There were manydifferences in the procedural details andparameters of individual studies. We studiedmultiple objective parameters as well asparameters like vessel branching and concurredthat the optimum level of compression formaintaining quality is 1:40. Further developmentof compression and image processing softwareheralds a ‘clearer picture’ in the future. 9,10,11The optimum level of compression for screeningDR using the JPEG algorithm appears to be 1:40.There is no degrading effect of transmission viasatellite on either the compressed or theuncompressed image quality. Telescreeningusing 1:40 image compression and VSAT satellitelink for image transmission seems to be aneffective model for screening of DR in rural areas.http://www.mit.gov.in/telemedicine/home.asp.Last Updated on 18/9/2003. accessed 5/7/2005.6. Luzio S, Hatcher S, Zahlmann G, Mazik L, MorganM, Liesenfeld B, et al. Feasibility of using theTOSCA telescreening procedures for diabeticretinopathy. Diabet Med. 2004;21(10):1121-8.7. Aiello LM, Bursell SE, Cavallerano J, Gardner WK,Strong J. Joslin Vision Network Validation Study:pilot image stabilization phase. J Am Optom Assoc.1998;69(11):699-710.8. Telemedical evaluation and management ofretinopathy of prematurity using a fiberoptic digitalfundus camera. J Digit Imaging 1996;9:178-84.9. A protocol for screening for diabetic retinopathy inEurope. Retinopathy Working Party. Diabet Med.1991;8(3):263-7.10. Kivijarvi J, Ojala T, Kaukoranta T, et al. Acomparison of lossless compression methods formedical images. Comput Med Imaging Graph1988;22:323-39.11. George LD, Lusty J, Owens DR, Ollerton RL. Effectof software manipulation (Photoshop) of digitizedretinal images on the grading of diabeticretinopathy. Br J Ophthalmol. 1999; 83(8):911-3.