Dear Editor,

I can join the editorial appreciation of Axer-Siegel and coworker's recent article,1 as expressed by O'Keefe and Kirwan.2 In an experimental set-up the authors studied the effects of cryo- vs. diode laser application on the axial eye growth in 6-week-old rabbits. The induced eye wall trauma stimulated growth, of both anterior and posterior eye segment. This can be compared to the axial elongation as experimentally triggered by surgical lid-suture or corneal opacification in young monkeys.3,4

In their editorial conclusion O'Keefe & Kirwan took the experimental rabbit study as support for laser therapy as the present 'mainstay of therapy for (human) ROP'. Less myopia is recorded (by most clinical authors) after laser therapy as compared to cryotherapy in eyes with threshold ROP, and the present rabbit study inicates that cryo-treated eyes became longer than laser-treated eyes.

However, one should bear in mind what was learned from human clinical studies during the non-interventional period (up to about 1985), namely a) that myopia of prematurity (MOP, often with a reduced visual potential) mainly appeared after advanced retinopathy of prematurity (ROP), and b) that ex-prematures without observed ROP eventually also had more myopia than full-term controls. In accord, Axer-Siegel et al. were cautious in their interpretations, recalling that 'ROP in humans by itself alters ocular growth'.

In this context I shall refer to natural history preterm eye data. In apparently normal ex-prematures' eyes at school age, my thesis study of 1976 indicated that pre-term delivery seemed to be an impediment to the overall growth (axial eye length and corneal curvature radius; head circumference and body height).6 This was evident at the age of 10 years, and longitudinally assessed also at age 18-19.7 Anterior segment proportions remained shorter (more foetal) and axial elongation in cases of MOP (accordingly) was less than expected from degree of myopia. It was hypothesised that there is a continuum of relative growth arrest ranging from virtually zero in some prematures and up to high degrees, with a likely relation to the low-birth-weight and ROP status of the infant.8 Also, Conolly and coworkers at school-age follow up found shorter axial lengths, despite more myopia, where advanced ROP had been treated by cryo as compared to diode laser.9

All considered, though I cannot fully agree with the editorial, I do agree that laser therapy seems to be more gentle to the eye with advanced ROP than cryotherapy, at least as effective, and hopefully with better long-term functional outcomes.

Hans C Fledelius
Rigshospitalet University Eye Dept E 2061
DK 2100 Copenhagen Ø
Denmark
E-mail: rh03217@rh.dk

References

1. Axer-Siegel R, Bourla D, Kremer I, Weinberger D, Snir M. Effect of peripheral retinal laser ablation with cryotherapy versus diode laser photocoagulation on axial lenght in the growing rabbit eye. Brit J Ophthalmol 2006; 90: 491-495.

2. O'Keefe M, Kirwan C. Diode laser versus cryotherapy in treatment of ROP. Advantages of laser therapy. Editorial, Brit J Ophthalmol 2006; 90: 402-403.

3. Wiesel TN, Raviola E (1979). Myopia and eye elongation after neonatal lid fusion in monkeys. Nature 1979; 266: 66-68

4. Wiesel TN, Raviola E (1979). Increase in axial length of the macaque monkey eye after corneal opacificatin. IOVS 1979; 18: 1232-36

5. Cryotherapy for Retinopathy of Prematurity Cooperative Group. Multicenter trial of cryotherapy for retinopathy: preliminary results. Arch Ophthalmol 1988; 106: 471-479

6. Fledelius H. Prematurity and the Eye (thesis). Ophthalmic 10-year follow-up of children of low andnormal birth wright. Acta Ophthalmol 1976, Suppl 128.

7. Fledelius HC (1982). Ophthalmic changes from age 10 to 18 years. A longitudinal study of sequels to low birth weight, parts III and IV. Anterior eye segment; vitreous and axial length. Acta Ophthalmol 1982; 60: 393-402; 403-411.

8. Fledelius HC. Eye size, refraction, and ocular morbidity. An ultrasound oculometry review. Doc Ophthalmol Proc Ser 1995; 58: 39-46.

9. Conolly BP, Ng EYJ, Arch McNamara J, Regillo CD, Vander JF, Tasman William. A comparison of laser photocoagulation with cryotherapy for threshold retinopathy of prematurity at 10 years. Ophthalmology 2002; 109: 936-941