Dear Editor

We thank Pushpoth and Sandramouli for their wide-ranging critique of our paper discussing previous isotretinoin use in potential military aviator recruits.[1] We cannot agree with their comment that the finding of 2 of 47 candidates, with clinically abnormal dark adaptation (DA) and 11 with electroretinogram (ERG) abnormalities does not justify further screening of this population. Aircrew recruits are a selected population, to a large degree without any significant history of systemic or ocular abnormalities. In balance of probability this selection makes it more likely that the retinal function of these individuals falls within the age-matched normal population, not less. The candidates had, for the most part, applied for a career in aviation long after taking isotretinoin, though we agree that it would have been desirable to prospectively follow the ERG and DA changes before and after treatment.

Pushpoth's and Sandramouli's assumption that isotreinoin-related retinal toxicity is dose-related cannot be made from our retrospective report; largely for the reasons outlined in their comments on incomplete dosage information. We do know that none of the individuals had a history, or family history of retinal abnormality and that clinical retinal and visual field measurements were normal. Colour vision tested normal in all cases with an Ishihara Pseudoisochromic Plate Test and Lanthony 15 hue colour vision test.

Our reference to Oner et al.[2] was not to compare the papers results but to disagree with the finding that all side-effects of isotretinoin were short-lived. Had they performed electrophysiology they might have found a different result.

In this paper we lend support to the findings of other studies that rod function can be adversely affected by previous isotretinoin use[3,4]. As aviation is a night-vision critical profession; we consider it justified at present to check the night vision of aircrew candidates with a history of isotretinoin by dark adaptometry, from a flight-safety point of view. We agree with Pushpoth and Sandramouli that a prospective study of the retinal effects of isotretinoin would shed more light on the problem as much remains to be learnt about the safety of isoretinoin.

Sincerely yours,

Susan P Mollan, Malcolm Woodcock, Peter Good and Robert AH Scott

References

1. Mollan SP, Woodcock M, Siddiqi R, Huntbach J, Good P, Scott RAH. Does use of isotretinoin rule out a career in flying? Br J Ophthalmol 2006;90:957-959

2. Oner A, Ferahbas A, Karakucuk S, et al. Ocular side-effects associated with systemic isotretinoin. J Toxicol 2004; 23:189-195

3. Brown RD, Grattan CEH. Visual toxicity of synthetic retinoids. Br J Ophthalmol. 1989;73:286-288

4. Weleber RG, Denman ST, Hanifin JM, Cunningham WJ. Abnormal retinal function associated with Isotretinoin therapy for acne. Arch Ophthalmol. 1986;104: 831-837

Dear Editor,

We read Mollen et al's (1) article with interest where they have concluded that previous isotretinoin use does not cause a clinically significant reduction in night vision in most people and that the retinal toxic effects of isotretinoin may be measurable by electroretinography (ERG) and dark adaptation (DA). While the authors have successfully highlighted the importance of counselling patients for potential irreversible loss of dark adaptation following isotretinoin use, their report, in our opinion, has failed to substantiate the need for routine screening of potential military and civilian commercial aviators.

In their study, 2 out of 47 patients had both abnormal ERG and DA while 11 others had certain abnormal ERG parameters which may or may not be of practical significance. The interpretation of this finding is debatable in the context of this study being a retrospective analysis, where we cannot assess the electrodiagnostic status of the patients in the study group prior to treatment. Only two patients in the study had abnormalities in both ERG and dark adaptation. Those two patients, X and Y, received treatment for a comparatively shorter period of time (8 and 12 weeks respectively) with respect to others (treatment range of 6 weeks to 6 months). Whether these patients had a higher dose of isotretinoin or they had any predisposing retinal problems are not adequately explained in the report. It would have been informative if the authors had compared the dose effect relations among those patients in whom the dose of treatment was known (8 patients with abnormal ERG and 23 patients with normal ERG in the isotretinoin group).

In this particular study, the authors have mentioned a patient who continued to show signs of retinal toxicity 8 years after cessation of treatment, presumably changes in ERG, but there is no description of this patient either in Table 1 or elsewhere in the article. Further, the authors have compared the persistence of retinal toxicity in this particular patient with the study conducted by Oner et al (2). In their study, Oner et al have looked into the visual acuity, anterior segment changes, intraocular pressure, Schirmer's test, tear film break up time, colour vision and changes in microbial flora. They specifically mention in their article that they did not perform any electrodiagnostic studies in their patients. Perhaps it is inappropriate to compare the two studies which have looked at entirely different aspects of side effects of isotretinoin.

Though Mollen et al have mentioned in their methodology that colour vision was tested in their patients, they have not elaborated on the relevant results in the article.

It is interesting to note that the authors have not justified in their main report their recommendation for routine electrophysiological screening for professions that are night vision critical, except in their abstract. It would be appropriate to conduct a prospective study, to look into the electrodiagnostic and other described ocular changes following the use of isotretinoin, to precisely address their question.

S. Pushpoth, S. Sandramouli

Wolverhampton and Midland Counties Eye Infirmary

Wolverhampton, United Kingdom

References

1.S P Mollan, M Woodcock, R Siddiqi, J Huntbach, P Good and R A H Scott; Does use of isotretinoin rule out a career in flying? Br J Ophthalmology 2006; 90: 957-959.

2.Oner A, Ferahbas A, Karakucuk S, et al. Ocular side-effects associated with systemic isotretinoin. J Toxicol 2004; 23:189-95.