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CHAPTER 10

EVOLUTION PHASES OF GLAUCOMA

10.1 Introduction

In the same manner that Dr. Armarly [1] proposed a practical classification to evalu-ate the optic nerve condition by dividing the optic disc into 10 parts, and Dr. Raul Reca[2] proposed another one dividing the optic disc into 6 parts, the confocal tomography ofthe optic nerve suggests a further classification.

The previous classifications are based on an analysis of areas (relationship betweenoptic disc area, cup area and rim area) that can be correlated with the areas measured withby the HRT.

The tomographic classification is mainly based on the volumes of said structures andonly secondarily on areas and other parameters. This is due to the possibility of stere-ometric and three-dimensional analyses.

The advantage provided by volume measurements over area measurements, is thatthe former are raised to the third power, while the latter are only raised to the secondpower (whenever change occurs, no matter how slight, there is a greater variation if thevalue is raised to the cube than if it is raised to the square).

10.2 Parameters used in the classification of evolution

As already stated, the main parameters used for the classification were volumes,followed by areas, thickness and slopes.

The volumes taken into consideration are the neuroretinal rim volume (NRR) andthe cup volume. The most important one, in fact, is the neuroretinal rim volume, but thecup volume is also taken into account since a decrease of the neuroretinal rim volumeproduces an increase of the cup volume; it is a cause-effect relationship. The same occurswith areas: the cup area (red) increases as the rim area (green and blue) decreases (figure8.8, chapter 8).

The most important parameters used for the classification are listed in figure 10.1and illustrated in figure 10.2, where the parameters belonging to the optic disc are sepa-rated from those that are analyzed in the contour line graph. These latter parameters are:mean RNFL thickness, height variation of contour line, and the area enclosed by thecontour line and the reference plane in the contour line height variation diagram (RNFLcross sectional area). As we all know, the reference plane, far from being just anotherparameter, is the limit on which most parameters strictly depend and with which they

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have a close relationship. On this account, its position must always be verified, and in alongitudinal study, it must be checked to see that it always remains at the same level.

10.3 Concept and limits of normality

The concept of normality is based on the fact that all the optic disc parameters arenormal. Nevertheless in clinical practice, sometimes, for one reason or another, the factthat one or two parameters are not within the limits of normality or normal range does notindicate pathology. The concept and limit of normality are outlined in figure 10.3.

The limits of normality were obtained from a study on 108 normal volunteers [3].Figure 10.4 lists the most important limits. For example, for neuroretinal rim volume, thenormal inferior limit (0.32 mm3) and not the normal superior limit, is given, since this isused mainly to differentiate a large NRR from an optic disc edema.

In some patients a neuroretinal rim volume smaller than 0.32 mm3 may be found inthe first tomography, which makes them fall within the classification of borderline. Nev-ertheless, it must be taken into account that the evolution of these patients sometimes

Parameters used for classificationrim volumecup volumerim areacup areacup shape measuremean RNFL thicknessheight variation of contour lineRNFL cross sectional area

Fig. 10.1: Parameters used for classification

Fig. 10.2

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does not involve optic nerve damage but they remain stable for years, which indicates aphysiological or normal decrease of the neuroretinal rim in this group of patients.

10.4 Evolution Phases

The glaucomatous optic disc evolution was classified into the following groups:- Normal (N)- Borderline (BL)- Phase 1 (P1)- Phase 2 (P2)- Phase 3 (P3)- Phase 4 (P4)

With the exception of the borderline optic disc, the rest of the stages are separatedfrom one another by more than two standard deviations, rendering the separation intodifferent groups more significant. Only the parameters meeting this requirement arementioned, since most of the remaining ones bear no significant differences between thedifferent evolution stages.

Fig. 10.3: Concept of normality. The value of all parameters mentioned must be withintwo mean standard deviations of the normal values (normal range).

Limits of normality rim volume min. 0.32 mm3

cup volume max. 0.12 mm3

rim area min. 1.37 mm2

cup area max. 0.60 mm2

cup shape measure max. –0.15 mean RNFL thickness min. 0.17 mm height variation of contour line min. 0.27 mm RNFL cross sectional area min. 0.87 mm2

Fig. 10.4: Limits of normality

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Normal rim volume > 0.32 mm3

cup volume < 0.12 mm3

rim area > 1.37 mm2

cup area < 0.60 mm2

cup shape measure < –0.15 mean RNFL thickness > 0.17 mm height variation of contour line > 0.27 mm RNFL cross sectional area > 0.87 mm2

normal visual field

The normal optic disc is characterized by a slightly visible Elschnig's Ring, except inthe temporal area. Both poles have important fiber bundles, which correlate with the twocamel humps displayed by the contour line diagram (figure 10.5).

Borderline rim volume > 0.32 mm3

cup volume < 0.12 mm3

rim area > 1.37 mm2

cup area < 0.60 mm2

cup shape measure < –0.15 mean RNFL thickness > 0.17 mm height variation of contour line > 0.27 mm RNFL cross sectional area > 0.87 mm2

normal visual field

In the borderline optic disc, the neuroretinal rim volume is normal by measuring theentire disc, but if we analyze the rim volume by octants and quadrants, there is a de-creased value in one of these sectors. The decrease of the neuroretinal rim volume in thisphase does not affect the whole optic disc. It corresponds to Burk's pseudonormal opticdisc in which the humps remain unchanged and there is a slight neuroretinal rim loss.Except of the cup increase, no parameters are altered (this is less frequent; figure 10.6).

Phase 1 rim volume 0.32 - 0.30 mm3

cup volume 0.12 - 0.24 mm3

rim area 1.37 - 1.20 mm2

cup area 0.60 - 1.00 mm2

cup shape measure –0.15 - –0.12normal visual field

The optic disc in phase 1 is characterized by a generalized decrease of the retinalthickness that can be seen in the contour line diagram as a decreasing distance betweenthe contour line and the reference plane. At the same time a decrease in the height of thecamel humps, which correlates with the loss of fiber bundles and with the fact that El-schnig's Ring is more visible than before, can be observed (figure 10.7).

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Fig. 10.5

Fig. 10.6

Fig. 10.7

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Phase 2 rim volume 0.30 - 0.20 mm3

cup volume 0.24 - 0.48 mm3

rim area 1.20 - 0.80 mm2

cup area 1.00 - 1.50 mm2

cup shape measure –0.12 - –0.07beginning of visual field defects

The optic disc in phase 2 has already a loss of up to 50% of the total retinal nerve fi-bers. The disappearance of both humps, which correlates with a great cup increase thatinvades the superior and the inferior poles, can be seen. The mean RNFL thickness pre-venting the contour line from approaching the reference plane, remains unchanged (figure10.8).

phase 3 rim volume 0.20 - 0.10 mm3

cup volume 0.48 - 0.96 mm3

rim area 0.80 - 0.40 mm2

cup area 1.50 - 1.80 mm2

cup shape measure –0.07 - –0.02visual field defects

The optic disc in phase 3 is characterized by a great decrease of the mean RNFLthickness, which causes the approach of the contour line towards the reference plane.(When localized defects occur, the contour line reaches the reference plane in the dam-aged areas.) The summation image allows the bottom of the cup and Elschnig's Ring tobe clearly seen in their full extend. The cup surface covers almost the whole the opticdisc surface. The NRR persists like a thin hale around it (figure 10.9).

Phase 4 rim volume 0.10 - 0.00 mm3

cup volume > 0.96 mm3

rim area 0.40 - 0.00 mm2

cup area > 1.80 mm2

cup shape measure >= 0visual field in stage 3 (terminal)

The optic disc in phase 4 is characterized by a final decrease of the retinal thickness,where the contour line diagram is parallel to the reference plane, and in the places wherethere is no NRR left the contour line height variation diagram is below the referenceplane. This fact correlates with the appearance of white regions in the analysis of thesurfaces and with the presence of absolute visual field defects (figure 10.10).

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Fig. 10.8

Fig. 10.9

Fig. 10.10

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In figure 10.11, all six phases are summarized. In the normal optic disc, as well as inthe borderline disc, Elschnig’s Ring can only be seen in the temporal sector, whereas inall other phases it can almost be seen in its full extend, due to fiber atrophy. The bottomof the cup is more clearly seen from phase 2 on.

If the brightness of the retina in each section are observed, it is noticed that it de-creases steadily from normality to phase 4.

The cup shape measure changes rapidly. In phase 2 the cup slope is almost perpen-dicular, and in phases 3 and 4 bayonet-shaped vessels are revealed.

The small vessels become more and more evident and their contours are more visibleas they become more definite (this is due to the atrophy of the retinal nerve fibers).

Nevertheless, at first glance, the condition of the optic disc in phase 4 may seembetter than in phase 3. Also, the time elapsed between the normal and the borderline opticdisc, or between the borderline optic disc and the disc in phase 1 may seem the same.This is clearly solved with a stereometric analysis of the surfaces.

Figure 10.12 shows the six phases in the "Measure" menu, with the color codedanalysis of the surfaces. In the normal optic disc, the cup is seen surrounded by a largeNRR and not centered in the optic disc. This occurs in normal conditions due to the greatentrance of fibers at the superior and inferior poles. In the borderline optic disc, it is pos-sible to see how the cup area increases at the expense of a rim area decrease. Simultane-ously, the cup becomes central and its area invades the tilted neuroretinal rim area, thusreducing its separation from the flat neuroretinal rim. In the optic disc of phase 1, the cuparea continues to increase and the cup gets closer to the flat neuroretinal rim, leaving athin separation covered by the tilted neuroretinal rim. The total surface of the NRR de-creases markedly. In the optic disc in phase 2, the cup increases considerably and starts tobecome slightly eccentric, and the tilted rim disappears completely in these reagions.Consequently, the cup surface borders the flat rim surface. This fact can sometimes causelocalized defects and, together with the diffuse atrophy of the rest of the retina, it corre-lates with the onset of the visual field defects in this phase. In the optic disc in phase 3,the cup almost covers the complete optic disc region. The tilted rim has almost com-

Fig 10.11

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pletely disappeared. Only a thin flat rim margin separates the cup from the external opticdisc margin. This small volume of NRR keeps the visual function unchanged; this is cor-related with the rapid visual field loss produced when the remaining NRR is damaged. Inthe optic disc in stage 4, the cup has occupied almost all the optic disc surface and insome sectors, where the NRR has been completely destroyed, the cup touches the exter-nal optic disc margin, making the total absence of the NRR evident in that sector. Whiteregions can occur in stage 4 which are due to the fact that the retinal surface is below thelevel of the reference plane in the most badly damaged sectors. These lesions produceabsolute optic disc defects of bad prognosis.

Fig. 10.12

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10.5 Clinical Cases

Case 1: Male, 64 years of age, left eye. Visus with correction: sph -1, cyl -0.25 in 0degree, with diagnosis of open angle glaucoma, diagnosed 8 years ago. The intraocularpressure monitored with daily pressure curve during these 8 years, shows at 7 o’clock inthe morning 33 mm Hg. The other pressures taken at 9.00 a.m. and 13 , 15, 18 , 21 and 24hours were below 19 mm Hg. These figures where partially changed with medical ther-apy and the intraocular pressure at 7 o’clock in the morning changed to 24-28 mm Hg. Atthis moment the computerized perimetry with Octopus is normal and the HRT indicatesthat the optic nerve head is in phase 1 (figures 10.13 and 10.14).

Fig. 10.13

Fig. 10.14

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Case 2: Patient with 72 years of age (male), with diagnosis of chronic glaucomawith narrow angle. The patient was treated because of hypertension for 15 years. (Intra-ocular pressure without medication: 31 mm Hg, with medical therapy: 24 mm Hg.)Peripherical iridectomy with YAG laser was performed. Later, trabeculoplasty with Ar-gon laser. After these procedures, the monitoring of the intraocular pressure was donewith daily pressure curve: mean 17 mm Hg, variability 1.5. HRT presents in the left eyeoptic disc in phase 2, which is in correlation with a border-line visual field (figures 10.15and 10.16).

Fig. 10.15

Fig. 10.16

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Case 3: Patient with 57 years of age (female), left eye, with diagnosis of open angleglaucoma and myopia. Visus: 10/20 with sph. -5.00. The intraocular pressure measuredwith daily pressure curve shows a mean of 23 mm Hg, variability 1.6. The computerizedperimetry presents a visual field in stage III, with M.D. 18.9 and C.L.V. 96.4. The HRTshows an optic disc in phase 3 (figures 10.17 and 10.18).

Fig. 10.17

Fig. 10.18

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Case 4: Patient with 65 years of age (female), with diagnosis of open angle glau-coma, made 20 years ago. The trabeculoplasty was performed 5 years ago. The monitor-ing of intraocular pressure was made with spot check pressure and not with daily pressurecurve. The pressures taken by other ophthalmologists were 25 mm Hg. The actual visuswith a correction of sph. 0.75 is 18/20. Computerized perimetry shows a visual field instage III., with M.D. 23.2 and C.L.V. 60.5. The HRT shows an optic disc in phase 4,where the only retinal nerve fiber bundle present is the papillo-macular one (figures10.19 and 10.20).

Fig. 10.19

Fig. 10.20

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Bibliography

1. Armarly MF: Genetic determination of cup/disk ratio of the optic nerve. Arch.Ophthalmol 1967;78:35-43.

2. Reca R: In: Sampaolesi R (ed.): Glaucoma; Edit. Panamericana, Buenos Aires, Ar-gentina, 1991, pp. 305-306.

3. Sampaolesi JR, Sampaolesi R: Lecture: Study of normality in the optic nerve headwith HRT, in “Curso y Simposio Argentino de Glaucoma, July 1995, Buenos Aires,Argentina.

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