The aim of this paper is to compare the glaucoma diagnostic reliability of two optic disc parameters: the relative cup area size determined by the Heidelberg retina tomography and the relative pallor area size determined by the proposed algorithm of the optic disc image analysis. Both parameters were measured for 240 normal healthy eyes and 240 glaucomatous eyes. The diagnostic reliability of studied parameters were compared using normalized distance d of their statistical distributions obtained for normal healthy and glaucomatous eyes and by comparison of area sizes under their ROC
(Receiver Operating Characteristic) curves. The normalized distances were 2.19 or 1.73 and the area sizes under ROC curves were 0.95 or 0.89 for relative cup or pallor area size. Both considered relative parameters are significantly influenced by the glaucoma and can be used in its diagnostics. The designed pallor analysis is less diagnostic reliable than the analysis of the cup

František Pluháček

Jaroslav Wagner

English

Hrčak - Portal of scientific journals of Croatia

Coll. Antropol. 37 (2013) Suppl. 1: 59–63Original scientific paperComparison of Reliability of the Eye Optic DiscCup and Pallor Areas in Glaucoma DiagnosticsFranti{ek Pluhá~ek and Jaroslav WagnerPalacký University Olomouc, Faculty of Science, Department of Optics, Olomouc, Czech RepublicA B S T R A C TThe aim of this paper is to compare the glaucoma diagnostic reliability of two optic disc parameters: the relative cuparea size determined by the Heidelberg retina tomography and the relative pallor area size determined by the proposedalgorithm of the optic disc image analysis. Both parameters were measured for 240 normal healthy eyes and 240 glauco-matous eyes. The diagnostic reliability of studied parameters were compared using normalized distance d of their statis-tical distributions obtained for normal healthy and glaucomatous eyes and by comparison of area sizes under their ROC(Receiver Operating Characteristic) curves. The normalized distances were 2.19 or 1.73 and the area sizes under ROCcurves were 0.95 or 0.89 for relative cup or pallor area size. Both considered relative parameters are significantly influ-enced by the glaucoma and can be used in its diagnostics. The designed pallor analysis is less diagnostic reliable thanthe analysis of the cup.Key words: Cup, pallor, glaucoma, laser scanning tomography, image analysisIntroductionEarly detection of glaucoma is necessary for effectivetreatment of this disease. One of effective methods ofglaucoma detection is the determination and analysis ofthe color and shape of the optic nerve head (i.e. optic disc,OD). Especially, the typical symptoms of glaucoma arethe enlargement of the optic disc cup and the rise of thepallor area of the cup1,2. The cup area can be exactly de-tected and subsequently numerically represented by thelaser scanning tomography method3–5. For the pallor de-tection, a suitable computer algorithm of digital colorphotography analysis of the optic disc can be used. We de-signed and verified the new image analysis method ofpallor detection and its numerical representation. For di-agnostic evaluation of the proposed relevant pallor nu-merical parameters, the suitable automatic evaluationalgorithms were designed and discussed6. In this paper,the diagnostic reliability of the above-mentioned numeri-cal parameters of the pallor were compared with the di-agnostic reliability of the common parameters obtainedby the laser scanning tomography.Subjects and MethodsSubjectsThe chosen numbers of 240 eyes of 120 normalhealthy subjects and 240 eyes of 120 subjects with theopen-angle glaucoma were considered in our investiga-tion. The examined normal healthy subjects had the agerange from 14 to 76 years with the average of 46 yearsand with the standard deviation of 13 years. The glauco-matous subjects under examination had the age rangefrom 10 to 82 years with the average of 51 years and withthe standard deviation of 16 years. The reported medicaldiagnoses were carried out on the basis of the subjectiveevaluation of independent measurement of the intra-ocular tension, visual field, enlargement of the cup usingthe laser scanning tomography and of subjective observa-tion of the thickness of the retina nerve fibre layer. All di-agnostic examinations were performed by the same oph-thalmologist.Method for the cup analysisThe cup area was represented by the relative quantityC/D, which means the ratio of the representative cuparea and the representative area of the total optic disc.The required representative areas were determined bythe common laser scanning tomography method, espe-cially using Heidelberg retina tomograph4,5.The used laser tomographic scanner (LTS) is based ona sequential point-by-point imaging and a confocal laserscanning microscopy. In the LTS device, a suitable diode59Received for publication June 20, 2012U:\coll-antropolo\coll-antro-(Suppl 1)-2013\11 Pluhacek.vp2. travanj 2013 13:15:35Color profile: Generic CMYK printer profileComposite  150 lpi at 45 degreeslaser source of the dominant wavelength 670 nm was fo-cused by the optical system of the LTS and of the eye tothe focal point situated on the optic disc. The laser beamscans point-by-point the optic disc by moving the focalpoint in the perpendicular direction to the optical axis ofthe scanning device at the constant position of the focalplane. The scanned area was divided into 384x384 scan-ning points. The angular size of the scanned area was15°. The light reflected from each single scanned pointwas separated from the incident beam and deflected to adetector, where it was registered and thereafter digitizedand stored by a computer as a two-dimensional sectionimage. During one investigation, the images were scan-ned up to 64 sections at different axial locations z of thefocal plane. The axial location z is the location in the di-rection of the optical axis of the scanning device and itwas measured according to a suitably selected referenceplane. The typical distance between two successive axiallocations of the focal plane was 62 mm. In the used confo-cal optical system shown in Figure 1, two pinholes are lo-cated differently: behind the laser source and in front ofthe detector, both optically conjugated to the focal pointof the laser source. By this arrangement, the light re-flected by the optic disc point placed outside the focalplane is not focused to the detector. Its detected opticalintensity is markedly smaller than the detected opticalintensity of the light reflected from the focal plane. Thus,an axial position z of each scanned point can be deter-mined in virtue of analysis of the experimental depend-ence of the detected optical intensity of the section imageson the focal plane position. Its maximum corresponds tothe searched axial position z of the considered scannedpoint. Finally, the required three-dimensional map, whichdescribes the dependence of z on the point position (x, y)in the above-mentioned reference plane, was construc-ted.The plane representative margin of the optic disc inthe reference plane was commonly approximated by asuitable smooth plane curve. Such a curve was found bythe automated perpendicular projections to the referenceplane of several points of the three-dimensional map se-lected by the operator. The cup is defined as a part of theoptic disc, that in the three-dimensional optic disc mapcorresponds to the area located in the depth equal orgreater than the conventional value h – 50 mm below thereference plane. The introduced value h expresses themean depth of the subsidiary area of the angular size 4°in the nasal part of the representative optic disc margin.Method for the pallor analysisIn the case of the numerical description of the pallor,the ratio P/D of the representative pallor area and therepresentative total optic disc area were utilized. Theserepresentative areas were obtained using the suitableimage analysis procedure of digital color optic disc im-ages. Such images were found by the digital color video--camera of resolution 576768 pixels connected with theadapted photographic system Retinofot Carl Zeiss Jena2016. The actual size of the scanned area was approxi-mately 5.84.4 mm. During every measurement, the pho-tographic system mentioned above was located so thatthe rows of the acquired image matrix correspond to thehorizontal direction. The brightness values of each of thecorresponding three image color channels (i.e. red, greenand blue) were standardly quantized to 256 discrete lev-els and represented by integers from 0 to 255. Value 0represents the minimum (zero) brightness and value 255represents the maximum brightness of each color chan-nel.The representative optic disc area of an image wasmanually demarcated by a convenient little excentricrepresentative boundary ellipse, which connects five au-xiliary points selected by the operator’s experience in theused color digitized image of the optic disc OD. It was as-certained experimentally that the brightness G of thegreen color channel is optimal for the pallor determi-nation6. The brightness G of the OD image generally un-desirably depends on illumination of the OD during itsphotography and often inconveniently changes along theOD periphery. Hence, every considered brightness valueG(u, v) of the image point (u, v), located in the intersec-tion of the u-th row and the v-th column of the imagepixel array, was suitably normalized to the new valueG'n(u, v) by the acceptable relationG u vG u vG GGG Gn' ( , )( , )( )=+− − −−−2A BAnBn AnB AAν νν ν (1)whereG u vG u vG GG u vG u vG GAnAA BBnBA B( , )( , ), ( , )( , )=+=+2 2(2)The introduced values GA and GB were defined as thegreen image channel brightness values of the largest oc-currence in pixels of the referential areas A and B. Theareas A and B mean the temporally and nasally locatedboundary parts of the representative OD area of the an-gle width 30° and of the thickness equal to the one fifth ofthe major semi-axis size a of the boundary ellipse (FigureF. Pluhá~ek and J. Wagner: Reliability of Cup and Pallor Areas in Diagnostics, Coll. Antropol. 37 (2013) Suppl. 1: 59–6360Fig. 1. Optical system of the LTS.U:\coll-antropolo\coll-antro-(Suppl 1)-2013\11 Pluhacek.vp2. travanj 2013 13:15:35Color profile: Generic CMYK printer profileComposite  150 lpi at 45 degrees2). In this manner, the defined areas A, B are advanta-geously influenced minimally by the glaucoma progres-sion. The also exploited quantities nA and nB representthe average values of column index n of pixels in the ar-eas A and B.The simultaneously considered representative pallorarea of the optic disc image is defined standardly as theimage area within the representative boundary ellipse,where the normalized value G'n is greater than or equalto the selected suitable threshold value p. The empiri-cally established optimum value p=0.2 was accepted inour investigation. Figure 3 shows an example of healthy(left) and glaucomatous (right) OD image with the corre-sponding negligible small and expressive large brightpallor area. The outlined boundary ellipses define therepresentative OD areas.Results and DiscussionAll the considered 240 normal healthy and 240 glau-comatous eyes were investigated using both above-de-scribed methods. The C/D and P/D ratios were computedfor the total optic disc of each investigated eye. Next, thehistograms of obtained statistical occurrences (absolutefrequencies) of C/D and P/D ratios were constructed inthe case of normal healthy eyes and glaucomatous eyes(Figure 4 and Figure 5). The corresponding mean C/Dvalues of normal healthy and glaucomatous eyes were0.23 and 0.50 with the relevant standard deviation 0.12.In the case of statistical distributions of P/D, the meanvalue and standard deviation of normal healthy, respec-tively glaucomatous eyes were 0.10 and 0.07, respectively0.24 and 0.09. The present results confirm the glaucomainfluence on the considered P/D and C/D ratios. The di-agnostic reliability of both introduced numerical param-eters C/D and P/D can be determined and compared bythe suitable normalized characteristic distance d of therelevant statistical distributions (histograms) for normalhealthy and glaucomatous eyes, or using the relevant re-ceiver operating characteristic (ROC) curves.The required normalized distance d of statistical dis-tribution of C/D or P/D is defined by the relation6–8dt t=−−h gh2g2σ σ21 2/(3)F. Pluhá~ek and J. Wagner: Reliability of Cup and Pallor Areas in Diagnostics, Coll. Antropol. 37 (2013) Suppl. 1: 59–6361Fig. 2. The eye optic disc boundary ellipse and the referential areasA and B.Fig. 3. Example of the healthy (left) and glaucomatous (right)OD image with the corresponding negligible small and expres-sive large bright pallor area. The boundary ellipses define therepresentative OD areas.Fig. 4. The histograms of statistical distribution of C/D ratios in the case of normal healthy (left) and glaucomatous (right) eyes.U:\coll-antropolo\coll-antro-(Suppl 1)-2013\11 Pluhacek.vp2. travanj 2013 13:15:36Color profile: Generic CMYK printer profileComposite  150 lpi at 45 degreesThe introduced characteristic quantities th, tg and sh,sh represent the mean values and standard deviations ofthe statistical distributions of C/D or P/D, relating tohealthy and glaucomatous eyes. The higher value of d in-dicates the higher diagnostic reliability. The values d =2.19 and d = 1.73 were obtained for the C/D and the P/Dratios by our investigation.An examined eye can be also diagnostically tested onthe basis of comparison of its C/D or P/D ratio with asuitably chosen testing so-called cut-off value tC/D of C/Dor tP/D of P/D. In such cases, the eye with the obtained nu-merical parameter C/D or P/D which is below, respec-tively over the chosen cut-off value is classified as healthy,respectively glaucomatous. For each value of tC/D or tP/D,the described test also gives the relevant sensitivity (truepositivity) and specificity9. The sensitivity is defined bythe probability, that a real glaucomatous eye can be clas-sified as glaucomatous. On the other hand, the specificityis equal to the probability, that a real healthy eye isclassified as healthy. Moreover, the value of denotation(1-specificity) (perceived as false positivity) representsthe probability of classification of a real healthy eye asglaucomatous. The dependence of sensitivity on (1-speci-ficity) is known as the ROC curve9. The smoothed ROCcurves (solid lines) relating to experimentally obtaineddata (dots) are plotted in Figure 6 for C/D and in Figure 7for P/D. Their numerical comparison was conventionallycarried out on the basis of area sizes under the relevantROC curves. The larger area size means the better diag-nostic reliability. The ascertained area sizes were 0.95 forC/D and 0.89 for P/D.ConclusionTwo different methods of eye optic disc analysis weredescribed and compared in this article with regard toF. Pluhá~ek and J. Wagner: Reliability of Cup and Pallor Areas in Diagnostics, Coll. Antropol. 37 (2013) Suppl. 1: 59–6362Fig. 5. The histograms of statistical distribution of P/D ratios in the case of normal healthy (left) and glaucomatous (right) eyes.Fig. 6. The ROC curve in the case of C/D ratio approximated bythe smooth curve (solid line) obtained using experimental data(dots).Fig. 7. The ROC curve in the case of P/D ratio approximated bythe smooth curve (solid line) obtained using experimental data(dots).U:\coll-antropolo\coll-antro-(Suppl 1)-2013\11 Pluhacek.vp2. travanj 2013 13:15:37Color profile: Generic CMYK printer profileComposite  150 lpi at 45 degreesglaucoma diagnostic. They relate to the analysis methodof the cup of the optic disc using common laser scanningtomography and to the image analysis method of the op-tic disc pallor. The present cup analysis is based on cre-ation and evaluation of the relevant three-dimensionalmap. Such a map was acquired by the laser scanning to-mography. For the diagnostic purposes, the cup was nu-merically represented by the relative quantity (ratio)C/D. In the case of the pallor analysis, the color digitalimage of the optic disc was utilized. This image was pro-cessed using the proposed image analysis algorithm,which determines the relative numerical representationof the pallor area in the form of the P/D ratio. The verifi-cation and comparison of the diagnostic reliability ofboth C/D and P/D ratios were performed using the de-fined normalized distance of their statistical distribu-tions and ROC curves. The present results show, thatboth ratios are significantly influenced by the glaucomaand can be effectively used in its diagnostics. It was alsoratified that the designed pallor diagnostic analysis isless reliable than the diagnostic analysis of the cup. How-ever, the advantage of the pallor analysis method consistsin the possibility of its application to the color digitizedcomputer images of the optic disc, which are obtainableby any currently available color fundus camera con-nected with a computer. In comparison with the laserscanning tomography, the designed pallor analysis me-thod requires no other special devices.AcknowledgementsAll the investigated optic disc images were kindly sup-plied by the physician MUDr. Tomá{ Kubìna. The au-thors would like to express their gratitude to him.This study was realised with the support of the inter-nal projects Optometry and its applications no. PrF_2012_014 of Faculty of Science of Palacký UniversityOlomouc.R E F E R E N C E S1. SHIELDS B, Textbook of Glaucoma (Williams & Wilkins, Baltimo-re, 1992). — 2. NESTEROV AP, Primary Glaucoma. In Czech. (Avicenum,Praha, 1991). — 3. BARTZ-SCHMIDT K, SENGERSDORF A, ESSER P,WALTER P, HILGERS RD, KRIEGLSTEIN GK, Greafe’s Archive forClinical and Experimental Ophthalmology, 234 (1995) 227. — 4. ZINSERG, HARBARTH U, SCHRÖDER H, Formation and analysis of three-di-mensional data with the laser tomographic scanner (LST). In: NASE-MANN JE, BURK ROW (Eds) Scanning Laser Ophthalmoscopy and To-mography (Quintessenz Velrlag, München, 1990). — 5. VERDONCK N,ZEYEN T, VAN MALDEREN L, SPILEERS W, Bull Soc Belge Ophthal-mol, 286 (2002) 51. — 6. PLUHÁ^EK F, POSPÍ[IL J, Optik, 116 (2005)133. — 7. MACHALA L, POSPÍ[IL J, Optik, 112 (2001) 335. — 8. DAUG-MAN JG, Biometric Decision Landscapes. Technical Report No. TR482(University of Cambridge Computer Laboratory, 1999). — 9. ZWEIG MH,CAMPBELL G, Clinical Chemistry, 39 (1993) 561.F. Pluhá~ekPalacký University Olomouc, Faculty of Science, Department of Optics, 17. listopadu 12, 771 46 Olomouc, Czech Republice-mail: pluhacek@prfnw.upol.czUSPOREDBA POUZDANOSTI OPTI^KOG DISKA OKA I PODRU^JA BLJEDILA U DIJAGNOSTICIGLAUKOMAS A @ E T A KSvrha ovoga rada bila je u dijagnostici glaukoma utvrditi pouzdanost dvaju parametara: veli~inu relativne povr{ineopti~kog diska i relativnih podru~ja bljedila. Oba parametra su mjerena na 240 zdravih o~iju i 240 o~iju s glaukomom.Rezultati su potvrdili da se oba parametra mogu upotrijebiti za dijagnosticiranje glaukoma. U dijagnostici glaukoma jeanaliza veli~ine relativnih podru~ja bljedila manje pouzdana od analize veli~ine relativne povr{ine opti~kog diska.F. Pluhá~ek and J. Wagner: Reliability of Cup and Pallor Areas in Diagnostics, Coll. Antropol. 37 (2013) Suppl. 1: 59–6363U:\coll-antropolo\coll-antro-(Suppl 1)-2013\11 Pluhacek.vp2. travanj 2013 13:15:37Color profile: Generic CMYK printer profileComposite  150 lpi at 45 degrees

Comparison of Reliability of the Eye Optic Disc Cup and Pallor Areas in Glaucoma Diagnostics

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia