Article Text

Retinal nerve fibre layer thickness
  1. 1st Department of Ophthalmology
  2. Semmelweis University Medical School
  3. 1083, Budapest
  4. Tömo u 25-29, Hungary
    1. A ASSI,
    2. P WATTS
    1. Moorfields Eye Hospital, London

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      Editor,—I read with interest the article by Assiet al on the measurement of the papillomacular retinal nerve fibre layer thickness in long standing stage IV macular holes.1 Using the nerve fibre analyser the authors found no difference in papillomacular retinal nerve fibre layer thickness variables between healthy eyes and eyes suffering from stage IV macular holes. In their discussion the authors interpret their results as a tendency for higher readings in the macular hole group, and try to explain this unexpected finding with the potential effects of intraretinal fluid movement from the edge of the hole towards the optic disc or with mechanical deformation of the Henle's fibre layer by vitreous traction.

      The authors' data, however, do not show a tendency for thickness being higher in the macular hole group. The differences between the groups are so minimal that they clearly do not represent any clinically meaningful differences (as clearly shown by the statistical analysis). Though the mean values of the total and temporal retinal nerve fibre layer thickness in the diseased group are minimally higher than those of the healthy eyes, the corresponding standard deviations are also considerably higher than in the normal group. This point suggests that the macular hole group was more heterogeneous than the control individuals. Since, unfortunately, the age of the control subjects is not shown in the article, one may speculate that the “tendency for difference” or better to say the relative inhomogeneity of the thickness values among the eyes with macular holes is a consequence of a age difference between the groups or a wider age range among the patients than in the control group. This possibility seems to provide a very simple explanation for the authors' finding, since retinal nerve fibre layer thickness was shown to decrease with age.2 3It would have been useful if the age of the control subjects had been provided by the authors, since excluding age related differences would support the fact that the inhomogeneity of the thickness values (and not a tendency for being higher than in the controls) is disease related, which seems to be realistic.



      Editor,—We thank Dr Hollo for his interest and comments. Our results do show a higher value for the mean total thickness of the retinal nerve fibre layer (RNFL) in the macular hole group but we did not suggest in any way a statistical or clinically significant difference between the two groups. We attempted to explain the apparently thicker peripapillary nerve fibre layer in macular holes on the basis of previous and relevant observations made by different authors. These include the presence of intraretinal fluid around the hole and vitreous traction on Henle's fibre layer. On the other hand, we have stated very clearly that our controls were matched to the macular hole patients for age, sex, and side of the affected eye. The mean age (73.1 years) and the standard deviation (7.92) are exactly the same for both groups. Dr Hollo's suggestion that the macular hole group is more heterogeneous on the basis of a different standard deviation value is therefore not valid. Although the number of subjects in our study is small, our data seem to suggest that the higher standard deviation value in the macular hole group might be related to alterations associated with long standing macular holes.