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<ul><li><p>British Journal of Ophthalmology 1995; 79: 892-899</p><p>Fundus imaging in patients with cataract: role fora variable wavelength scanning laserophthalmoscope</p><p>J N P Kirkpatrick, A Manivannan, A K Gupta, J Hipwell, J V Forrester, P F Sharp</p><p>AbstractAims-An investigation was carried out tocompare the image quality of the ocularfundus obtained clinically, photographi-cally, and with the scanning laser ophthal-moscope (SLO) at visible and infraredwavelengths in patients with significantcataract.Methods-Nineteen patients admittedfor routine cataract extraction wereexamined clinically by two independentobservers to ascertain cataract type andclarity of fundus view with an indirectophthalmoscope. Fundus photographyand both confocal and direct (non-con-focal) SLO imaging at 590 nm, 670 nm,and 830 nm were carried out after pupil-lary dilatation. Images obtained weregraded independently using a recognisedgrading system.Results-Quality ofSLO images appearedto be superior to indirect ophthalmos-copy (p</p></li><li><p>Fundus imaging in patients with cataract: role for a variable wavelength scanning laser ophthalmoscope</p><p>Table 1 Grading system for optic disc image clarity(adaptedfrom Nussenblatt et a110)</p><p>Gradingscore Optic disc features</p><p>0 Fundus detail clear1 Slight blurring of optic disc margin and fine vessels2 Fine vessels on optic disc visible but blurred3 Only large disc vessels discernible. Disc margin</p><p>blurred4 Optic disc margins just discernible. Major vessels</p><p>not seen5 Red reflux present but optic disc not seen</p><p>estimated using a modification of a scoringsystem developed for grading of severity ofvitreous opacities in posterior uveitis.10 Inparticular the observers were concerned withthe appearance and-clarity of the optic disc andadjacent vessels (Table 1). Observers' resultsof clinical examination, including grading ofoptic disc clarity, were noted independentlyand no discussion between observers regardingtheir clinical assessments took place.</p><p>IMAGING PHOTOGRAPHYFundus photography and scanning laserophthalmoscopy were carried out at the samesitting within a few minutes of one another.From each patient a minimum of four fundusphotographs was taken by one operator(JNPK) using a Nikon Retinapan-45 funduscamera using Fujichrome 100 film with theflash setting at maximum intensity and 1/60second exposure. A 35 degree field centred onthe optic disc was used. Colour transparencieswere graded independently by both observersby viewing on a light box with a X 10 loupe.The same grading system was used as forindirect ophthalmoscopy (Table 1).</p><p>For quantitative analysis the transparencywhich was adjudged to be ofbest image qualityfor each patient was digitised by projectionthrough a 550 nm interference filter using ahighly collimated light source and a 25 degreefield of the frame centred on the optic discwas focused onto an optically aligned, mono-chrome Kodak MegaPlus charge coupleddevice (CCD) camera (1320X 1024 elements).Digital output from the camera was fed to theframe grabber of a Series 151 image processingsystem (Imaging Technology Inc, USA) per-mitting capture of each frame at a resolution of1024X 1024 pixels. The grey level for eachgrabbed transparency was adjusted so that themaximum intensity within the image was set ata level of 255. The system was controlled by aSUN IPX workstation (Sun Microsystems,USA) through the VISILOG image processingsoftware (Noesis, France).</p><p>IMAGING - SCANNING LASEROPHTHALMOSCOPYScanning laser ophthalmoscopy was carriedout using the custom built Aberdeen scanninglaser ophthalmoscope."1 12 This instrument issimilar to commercially available instrumentsbut permits a greater degree of flexibility withrespect to confocal aperture size and wave-length source. All images were of a 25 degree</p><p>field centred on the optic disc and consistedof 740X511 pixels. Patients were imaged at830 nm, 670 nm, and 590 nm using diodelaser sources for 830 nm and 670 nm while atunable rhodamine-6-G dye laser (SpectraPhysics-375, USA), pumped by a 1 W argonlaser (Spectra Physics Stabilitic-2017, USA)was used for the 590 nm image. The entranceand exit pupil sizes of this SLO were 1 mm and6 mm in diameter respectively and the incidentpower at the cornea for all laser sources wasset at 200 puW/cm2. Patients were imagedboth with and without a confocal aperture of400 ,um diameter and the gain control for thedetector was adjusted to provide an imagecentred on the optic disc with the optimumcontrast. A minimum of two images for eachaperture size and wavelength setting weregrabbed and transferred to the SUN IPXworkstation for subsequent grading (Table 1)and image analysis.</p><p>IMAGE PROCESSING AND QUANTITATIVEANALYSISFor convenience of image handling andstorage digitised fundus photographic imageswere reduced to 512X512 pixels. SLO imageswere converted to a similar format by cutfingunwanted pixels from the sides of the imagesand adding a row of pixels of zero value to thetop of the image. Despite attempts to registerthe images to allow automated processing theimage quality in many of the images was poorand both automated and manual registrationtechniques were considered impractical.A quantitative comparison of digitised</p><p>fundus photographs and SLO images wascarried out as follows. From the availableimages of each patient the best quality imagesfrom fundus photography, and SLO imaging at830 nm, 670 nm, and 590 nm, with and with-out the confocal aperture, were selected forprocessing. Using binary image drawing toolswithin the software program it was possible tocreate a series of binary 'mask' images whichcould select out a small portion of the originalimage for analysis. For each image a first orderbranch retinal arteriole and venule with animmediately adjacent area of backgroundfundus close to the optic disc was selected.Three separate masks of approximately 1000pixels in area were created to overlap arteriole,venule, and background respectively. For eachpatient studied the same portion of arteriole,venule, and background fundus was selectedmanually from all of the images, both photo-graphic and SLO images, and subjected toquantitative analysis. A typical SLO imagewith overlying image masks is shown inFigure 1. The statistical data concerning thegrey levels of the pixels in the original imagecovered by each mask could then be calcu-lated and transferred to a spreadsheet. Thedata recorded were the number of pixels,minimum and maximum grey levels, meangrey level, and standard deviation of the greylevels. Using these data a simple measure ofimage quality, object contrast, could bedefined as follows:</p><p>893</p><p> on 10 July 2018 by guest. Protected by copyright.</p><p>http://bjo.bmj.com</p><p>/B</p><p>r J Ophthalm</p><p>ol: first published as 10.1136/bjo.79.10.892 on 1 October 1995. D</p><p>ownloaded from</p><p>http://bjo.bmj.com/</p></li><li><p>Kirkpatrick, Manivannan, Gupta, Hipwell, Forrester, Sharp</p><p>Figure 1 Four scanning laser ophthalmoscope images ofoptic disc imaged at 590 nm withconfocal aperture. Overlying areas marked in green are the binary masks used to comparecontrast ofbackgroundfundus reflectance (top left) with adjacent arteriole (top right) andvenule (bottom left). Note image noise accentuated by photographic reproduction.</p><p>Mean grey level below 'background mask'Arteriole contrast=</p><p>Mean grey level below 'arteriole mask'</p><p>andMean grey level below 'background mask'</p><p>Venule contrast=</p><p>Mean grey level below 'venule mask'</p><p>where a value of 1 implies no contrast - that is,no discrimination between object and back-ground.</p><p>In addition, the ability to discriminatebetween two structures depends not only onthe ratio of mean grey level but also on thenoise or random variation in the two structuresbeing compared. Using data concerningvariance of pixel distributions, 95% confidencelimits for each mask area were calculated todetermine whether the two adjacent regionswere significantly different in grey level charac-teristics.</p><p>STATISTICAL ANALYSISInterobserver variability for grading of cataracttype was analysed by use of a weighted kappa(K) score. Interobserver variation for thegrading of image quality of indirect ophthal-moscopy, fundus photography, and SLOimaging was also calculated. Intraobservervariation for grading of image quality wascarried out on all of the SLO images arrangedin random order 4 weeks after the initialgrading process.</p><p>For subsequent comparison of subjectivegrading between image groups the meanobserver score from the two observers was usedand groups were compared using a non-para-metric Wilcoxon matched pairs analysis.</p><p>Correlation between cataract type gradingand subjective image quality scores wasanalysed using Kendall's rank correlation.</p><p>Comparison between arteriole and back-ground 'masks' and between venule and back-ground 'masks' for individual images wascarried out using 5% and 95% confidencelimits as these image regions were assumed tohave a normal distribution. For comparison ofcontrast ratios between digitised fundusphotographs and SLO images the Wilcoxonmatched pairs test was applied.</p><p>For all statistical tests significance wasassumed if the value of p was less than 0 05.</p><p>Results</p><p>QUALITATIVE DATAThe mean age of the patients included in thestudy was 76x3 (SD 9 1) years and there werefour males and 15 females. Details of thecataract type grading according to the LOCS IIsystem are shown in Table 2. Weighted kappascores for interobserver variability ofgrading ofcortical cataract, nuclear opacity, and posteriorsubcapsular cataract were 084, 0-76, and 0-83respectively, showing good agreement betweenobservers.From the 19 patients included in the study</p><p>at the time of clinical examination, 17 under-went satisfactory fundus photography with acamera failure leading to loss of fundus photo-graphs in two patients (patient numbers 17and 19). All patients underwent SLO imagingbut attempts were not successful in all patientsat all wavelengths. In one patient (patientnumber 8) non-confocal images at all threewavelengths were not recorded. This patient'sdata were excluded from any comparison ofconfocal and non-confocal imaging. For SLOimaging in general, it was more difficult toachieve a recordable image with confocal imag-ing compared with non-confocal techniquesand, furthermore, imaging at 590 nm and670 nm was found to be more difficult than at830 nm. For this reason the SLO image seriesis not complete for patient numbers, 4, 7, 12,13, 15, 16, and 17 (see Table 3).</p><p>Table 2 Grading of cataract type for 19 patientsaccording to LOCS II system9</p><p>Image grading score</p><p>Patient Cortical Nudear Posterior subcapsularNo (grade 0-4) (grade 0-3) (grade 0-3)</p><p>1 3 1 22 3 3 33 1-5 1 14 2-5 1 25 2-5 3 0-56 2-5 1 37 4 3 08 3 2 2-59 1 2-5 310 1 3 211 1 2 312 2 3 313 1 3 314 1 2-5 0-515 3 3 016 1 25 317 4 2 318 3 3 319 1 1-5 05</p><p>894</p><p> on 10 July 2018 by guest. Protected by copyright.</p><p>http://bjo.bmj.com</p><p>/B</p><p>r J Ophthalm</p><p>ol: first published as 10.1136/bjo.79.10.892 on 1 October 1995. D</p><p>ownloaded from</p><p>http://bjo.bmj.com/</p></li><li><p>Fundus imcaging in patients with cataract: role for a variable wavelength scanning laser ophthalmoscope</p><p>Table 3 Mean image grading score for 19 patients from clinical examination, fundusphotography, and scanning laser ophthalmoscope imaging at 590, 670, and 830 nm withand without confocal aperture</p><p>Scanning laser ophthalmoscopy</p><p>590 nm 670 nm 830 nmPatientNo Clinical Photo Confocal Direct Confocal Direct Confocal Direct</p><p>1 15 1 1 2 2 2 2 22 2 3 2 2 2 2 2 2-53 2 25 2 2 2 3 2 24 3 3 NR 1-5 NR 3 NR 35 1 3 3 1-5 2 2 1 5 26 3 3-5 3 2 2-5 2 2 27 4 5 NR NR NR NR NR 58 1 1-5 2 * 2 * 2 *9 1-5 2 2 1-5 2 2 2 210 2 3 2 2 2 3 2 311 1-5 2 1 1 1-5 1-5 2 212 4 4 NR 3 NR 4 NR 2-513 4 4 NR 2 NR 3 2 314 1 2-5 1 1 1-5 1-5 1 1-515 4 4 NR NR NR 3 NR 316 3 3 NR 2 2-5 2 2 217 3 * NR 5 2-5 2-5 1-5 218 4 3 2 1 2 2 1-5 219 1 * 3-5 1 2 1 1-5 2</p><p>NR=image not recordable; *=image recordable but not stored.</p><p>Mean values for clarity of optic disc detailgraded by the two observers for indirect oph-thalmoscopy, fundus photography, and SLOimaging with and without confocal aperture at590 nm, 670 nm, and 830 nm are shown inTable 3. For fundus photography the gradingscore is applied to the best of four images whilefor SLO images the grading score is that for thebetter of two images at each wavelength, withand without confocal aperture. Interobservervariation for indirect ophthalmoscopy, fundusphotograph, and SLO image grading was cal-culated to be 0-82, 0 77, and 0 55 respectivelywhich shows an acceptable level of agreement.Intraobserver variation for observer one forSLO images was found to be 0-62 which alsoshows a good degree of reproducibility.Taking the SLO images for each patient as a</p><p>group the lowest grading score (best quality)for any image is shown in Table 4 and com-pared with the scores for indirect ophthal-moscopy and fundus photography taken fromTable 3. In general the quality of fundus</p><p>Table 4 Summary of image grading score for 19 patientswith optimum scanning laser ophthalmoscopy (SLO)imaging wavelength recorded</p><p>Image quality grading score</p><p>Patient Optimum Wavelength details ofNo Clinical Photo SLO optimum SLO image</p><p>1 1-5 1 1 590c2 2 3 2 590c+d, 670c+d, 830c3 2 2-5 2 590c+d, 670c, 830c+d4 3 3 1-5 590d5 1 3 1-5 590d,830c6 3 3-5 2 590d, 670d, 830c+d7 4 5 5 N/A8 1 1-5 1-5 830d9 1-5 2 1-5 590d10 2 3 2 590c+d. 670c, 830c11 1-5 2 1 590c+d12 4 4 2-5 830d13 4 4 2 590d,830c14 1 2-5 1 590c+d, 830c15 4 4 3 670d,830d16 3 3 2 590d, 670d, 830c+d17 3 N/A 1-5 830c18 4 3 1 590d19 1 N/A 1 590d,670d</p><p>'c'=confocal; 'd'=non-confocal.</p><p>photographic detail is less than that seen witheither the indirect ophthalmoscope or SLO. Atypical example of a fundus photograph andSLO image (590 nm confocal) is shown inFigure 2. Using the Wilcoxon matched pairstest to compare groups, with the exclusion ofdata from patients 17 and 19 for photography,it is seen that SLO imaging shows a significantimprovement over indirect ophthalmoscopy(p</p></li><li><p>Kirkpatrick, Manivannan, Gupta, Hipwell, Forrester, Sharp</p><p>aL)</p><p>Cocn</p><p>0)</p><p>co</p><p>0)</p><p>coa)</p><p>E</p><p>5</p><p>4</p><p>0</p><p>MENE</p><p>3 _</p><p>2</p><p>1</p><p>n</p><p>MEN</p><p>_ Em</p><p>A 7</p><p>*00</p><p>0</p><p>00000 A cac</p><p>00 A -0</p><p>4-S* AAAAAAco</p><p>* AAA (u</p><p>0</p><p>6</p><p>5</p><p>4</p><p>3</p><p>2AAAA</p><p>vIndirect Photography SL(</p><p>ophthalmoscopyFigure 3 Scatter diagram showing qualitative gradingscores for indirect ophthalmoscopy, fundus photography,and scanning laser ophthalmoscopy (SLO). Best imagequality is given lowest grading score.</p><p>remaining five patients it was seen that imagingat 830 nm yielded best results in four patientswhile one patient had no useful SLO imagedata (patient 7). In no patient was 670 nmexclusively the optimum wavelength for fun-dus imaging.</p><p>Correlation of image quality with cataracttype has been performed using Kendall's rankcorrelation coefficient, T. By adding the scoresfor cortical, nuclear, and posterior subcapsularcataract an overall cataract score with apossible maximum of 10 can be assigned to agiven patient. Correlation of this score withimage quality is significant for indirectophthalmoscopy only (p=0-025). If the scorefor posterior subcapsular cataract is notincluded in this total then both indirect oph-thalmoscopy and fundus photography showsig...</p></li></ul>


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