advertisement

Editors Selection IGR 17-4

Response

Comment by Hanna Maria Öhnell on:

67306 Structural and Functional Progression in the Early Manifest Glaucoma Trial, Öhnell H; Heijl A; Brenner L et al., Ophthalmology, 2016; 123: 1173-1180

Find related abstracts

We would like to thank Dr Weinreb and the IGR editorial board f or selecting our published work for discussion, and we appreciate that the three reviewers were willing to spend time on our paper.

Several comments emphasize that different results may have been obtained if photography had been replaced with, e.g., OCT. We agree with that and have discussed that in the paper stressing that our comparison is between standard automated perimetry and disc photography only. We also want to point out that OCT was not available when EMGT started in 1992. Indeed there are results suggesting that modern techniques, e.g., OCT, may be more sensitive for detecting structural change than disc photographs, but it is crucial to control for the amount of false positives for the different instruments and the applied criteria. Another reason to favour imaging might be the fact that identifying the minute changes in optic disc configuration that we are looking for is difficult and time-consuming. The readers are encouraged to look at the 12 randomly chosen pairs of disc photographs that were published with the paper. We believe that most will agree with our view that the observed changes are so small, that it is unrealistic that they would be regularly detected in ordinary clinical management. This is probably the reason that the earlier published results based on the EMGT Disc Photography Reading Centre indicate that less than one percent of study eyes showed disc progressed before field progression.

One reviewer remarked that it is likely that glaucomatous damage becomes visible first in structure and later in function. This may well be the case, but in our study we looked for structural and functional progression in study eyes where the vast majority had such damage at study inception. Also in the fellow eyes of these patients, 20% already had glaucomatous optic discs. If one aims to find out if structural or functional damage arises first, it would be necessary to perform a prospective study of normal appearing eyes, preferably population-based. It would require a very large study population even if one would narrow it down to those with an elevated risk. The alternative is experimental studies where results so far indicate that the processes are parallel with a substantial inter-individual variation in what type of deterioration that is detected first (Harwerth et al. Invest Ophthalmol Vis Sci 1999;40:2242-2250).

One reviewer suggested that the fact that fields were obtained every three months, but disc photographs only every six months may have created a bias in favour of visual fields. This is not the case, however, as we discussed in the paper. The EMGT visual field criterion required repeated deterioration at the same test locations in three consecutive field tests. For fields the date of the last test was defined as the date for progression, while the date of the first photograph when progression could be seen was defined as the date for disc progression, creating some bias in favour of discs. Still, in the study eyes with field defects at baseline visual field progression was detected first more than four times as often as optic disc progression. In the fellow eyes, a mix of seemingly normal eyes, eyes with preperimetric glaucoma, and eyes with ocular hypertension, fields and photographs revealed progression first with the same frequency.

Our results also raised the question whether the relationship of the type of changes over the course of the disease depended on the degree of damage. This is of course generally believed to be the case. We have studied this issue in a subsequent paper which has been accepted for publication in Acta Ophthalmologica, and believe that when reading the paper our colleagues will be just as surprised at the results as we were.

• ← Previous
• Next →