Ординатура / Офтальмология / Английские материалы / The Glaucomas Volume 1 Pediatric Glaucomas_Sampaolesi, Zarate_2009

The figure above shows the correlation between visual acuity and axial length in 90 cases of trabeculotomy and 38 cases of combined surgery. The limit at which visual acuity drops below 20/40 is 25.5 mm and 31 mm for the trabeculotomy and combined-surgery groups, respectively. In both groups, visual acuity of less than 20/40 is due to breakage of the central Descemet’s membrane, macular alterations, amblyopia, and corneal opacities.

To prevent myopia-related reduction of vision it is necessary to carry out frequent check-ups of the child’s vision from immediately after surgery, using the preferential looking test.

There has been a major change in the prognosis of congenital glaucoma over the past 40 years, so that nowadays, if a corrected, well-indicated surgery is carried out, the result is good or very good. If we look at the literature, 68 years ago J. Ringland Anderson [2], in his classic monograph “Hydrophthalmia or congenital glaucoma, its causes, treatment, and outlook,” described glaucoma as a disease with the worst prognosis that leads to blindness, but his son, Douglas R. Anderson [3], in his complete review published in Survey, shows us that this prognosis has since changed completely.

References

1.Meyer G, Schwenn O, Grehn F (2000) Trabekulotomie bei Kongenitalem Glaukom. Ein Vergleich zur Goniotomie. Ophthalmologe 97:623–628

2.Anderson R.J: Hydrophthalmia or congenital glaucoma (Cambridge University Press, London, 1939).

3.De Luise V.P and Anderson D.R: Primary infantile glaucoma (congenital glaucoma). Surv Ophthalmol 1983; 28: 1–19.

The Glaucomatous Optic Nerve Staging System with Confocal Tomography

History of the Optic Nerve Examination

Since the first images of the fundus were obtained with an ophthalmoscope, created by Helmholtz [1] in 1950, examination methods have continued to improve. First, examination with direct ophthalmoscopy was used, followed by examination with binocular indirect ophthalmoscopy, optic disc drawings, optic disc stereophotographs, planimetry, Takamoto and Schwartz’s stereophotogrammetry, neuroretinal rim measurements, Airaksinen and Tuulonen’s evaluation of the retinal nerve fiber layer, optic disc pallor measurements, angiofluoresceinography of the optic disc, image analyzer (Rodenstock Optic Nerve Head Analyzer, Topcon Analyzer), laser scanning ophthalmoscope, and Lotmar and Goldmann’s stereochronoscopy. All these methods are extensively explained in the useful book The Optic Nerve in Glaucoma, by Varma and Spaeth [2].

Of these methods, we still find retinofluoresceinography particularly useful. We no longer use stereoscopic photographs of the optic nerve in adults, because of the significant interobserver variation in interpretation of results, as reported in the literature [3–5]. However, ste-

reoscopic photographs are useful for optic nerve examinations in children under 2 years of age because, due to their flat corneas, we have failed to obtain good images with confocal tomography. In Boston, we learned about Schwartz and Takamoto’s stereophotogrammetry [6], a very reliable method whose results are consistent with those obtained with the Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany). However, it is a time-consuming method. We later performed neuroretinal rim measurements using Airaksinen et al.’s [7] method, which we were able to put into practice based on Dannheim and Airaksinen’s personal communications. This turned out to be the most useful method. We also tried Lotmar and Goldmann’s optic disc stereochronoscopy [8]. All these methods require pupil dilation.

The above-mentioned methods, and particularly the measurement of optic disc parameters (area, cup area, neuroretinal rim), required the formula introduced by Littman in 1982 [9] to obtain the dimensions (length, surface) of any observable object in the fundus (exudates, tumors, foreign bodies, optic discs, vessels, etc.). Images of these elements can be observed with considerable magnification produced by the ocular system.

This morphometric magnification was corrected to provide true values with the Littman formula. Littman was an engineer who worked for Zeiss whom we met in Buenos Aires. Since 1982, his formula has allowed us to obtain true measurements in millimeters or square millimeters of a body or structure on the retina. Corneal curvature, measured with an ophthalmometer, axial length, measured by echometry, and refraction are very important for this formula. Corneal thickness, its posterior curvature, lens face curvatures, the depth of the anterior chamber, and lens thickness are not required because even if they varied, their influence on the measurement is minimal. This formula does not apply for aphakia, pseudophakia, and refraction changes caused by lens opacity.

Finally, in 1990, the HRT was introduced by Heidelberg Engineering [10], and it was with this device that we started our extensive research in 1991, with more than 20,000 tomographies examined to date.

In this chapter, we cover what we believe is a very important topic: the HRT parameters used for optic

nerve staging in glaucoma, as well as the follow-up of optic nerve damage [11]. The tomographic classification is mainly based on the volumes of these structures, and only secondarily on surfaces and other parameters, because stereometric and three-dimensional analyses are now available. The advantage provided by volume measurements over area measurements is that the former are raised to the third power, while the latter are only raised to the second power (whenever a change occurs, no matter how slight, there is a greater variation if the value is raised to the cube than if it is raised to the square).

Table 17.1 Parameters used for classification Rim volume

Cup volume

Rim area

Cup area

Cup shape measure

Mean RNFL thickness

Height variation of contour line

Area between curve and plane

Parameters Used for Glaucoma Staging

As stated in the previous section, the main parameters used for the classification were volumes, followed by areas, thickness, and slope. The volumes taken into consideration are the neuroretinal rim volume and cup volume. The most important is neuroretinal rim volume; cup volume is also taken into account since a decrease in neuroretinal rim volume produces an increase in cup volume; this is a cause-effect relationship. The same occurs with area: the cup area (red) increases as the rim area (green and blue) decreases (Fig. 17.1).

The most important parameters used for the classification are listed in Table 17.1 and are illustrated in

Fig. 17.1, where the parameters belonging to the optic disc are separated from those analyzed in the contour line graph. These latter parameters are mean retinal nerve fiber layer (RNFL) thickness, height variation of the contour line and the area enclosed by the contour line, and the reference plane in the contour line height variation diagram (RNFL cross-sectional area). The reference plane is an important basis for and closely related to all other parameters. Therefore, its position must always be verified and, when performing a longitudinal study, one must check that it always remains at the same level.

Concept and Limits of Normality

The concept of normality is based on all the optic disc parameters being normal. Nevertheless, in clinical practice, one or two parameters may sometimes not be within the normal range, which does not indicate pathology. The concept and limit of normality are outlined in Fig. 17.2.

The limits of normality were obtained in a study of 108 normal volunteers [12]. Table 17.2 lists the most important limits, for example, for neuroretinal rim volume; the normal lower limit (3.20 mm3) and not the normal upper limit is given, since this is mainly used to differentiate a large neuroretinal rim from an optic disc edema.

In some patients, a neuroretinal rim smaller than 320 mm3 may be found during the first tomography, which is considered borderline in the classification. Nevertheless, the progression of these patients does not always involve optic nerve damage, but they remain stable for years, which indicates a physiological or normal decrease in the neuroretinal rim in this group of patients.

Progression Phases

Glaucomatous optic disc progression has been classi- -fied into the following groups:

- Normal

- Phase I

- Phase II

- Phase III

- Phase IV

Phase V

Phases are separated from one another by more than two standard deviations, rendering the separation into the various groups more significant. Only parameters meeting this requirement are mentioned, since most of those remaining parameters have no significant differences between the various progression phases.

Normal optic discs (Table 17.3) are characterized by a barely visible Elschnig ring, except in the temporal area. Both poles have important fiber bundles, which correlate with the two camel humps displayed by the contour line diagram (Fig. 17.3).

Fig. 17.4 HRT Phase I

In Phase I optic discs (Table 17.4), neuroretinal rim volume is normal on measuring the entire disc, but if the rim volume is analyzed by octants and quadrants, there is a decreased value in one of these sectors. The decrease in neuroretinal rim volume in this phase does not affect the entire optic disc. It corresponds with Burk’s pseudonormal optic disc, in which the humps remain unchanged and there is a slight neuroretinal rim loss. With the exception of the cup increase, no parameters are altered, which is seen less frequently (Fig. 17.4).

Fig. 17.5 HRT Phase II

Phase II optic discs (Table 17.5) are characterized by a generalized decrease in retinal thickness that can be seen in the contour line diagram as an approximation between the contour line proper and the reference plane. At the same time, a decrease in the height of the camel humps, which correlates with the loss of fiber bundles (see three-dimensional presentation) and with the fact that the Elschnig ring is more visible than before, can be seen (Fig. 17.5).

Table 17.5 Phase II

Rim volume

Cup volume

Rim area

Cup area

Cup shape measure

Normal visual field

0.32–0.30 mm3

0.12–0.24 mm3

1.37–1.20 mm2

0.60–1.00 mm2

0.15–0.12

Fig. 17.6 HRT Phase III

Phase III optic discs (Table 17.6) already have a loss of up to 50% of the total retinal nerve fibers. The disappearance of both humps, which correlates with a substantial cup increase that invades the superior and the inferior poles, can be seen. The mean RNFL thickness, preventing the contour line from approaching the reference plane, remains unchanged (Fig. 17.6).

Fig. 17.7 HRT Phase IV

Phase IV optic discs (Table 17.7) are characterized by a substantial decrease in mean RNFL thickness, which causes the contour line to approach the reference plane (when localized defects occur, the contour line reaches the reference plane in the damaged areas). The summation image allows the bottom of the cup and the Elschnig ring to be seen to their full extent. The cup surface covers almost the entire optic disc surface. The neuroretinal rim persists like a thin halo around it (Fig. 17.7).