Visual field constriction has been demonstrated in children who have undergone cryotherapy for threshold retinopathy of prematurity (ROP) and in those with subthreshold ROP not requiring treatment.1,2 Laser photocoagulation has superseded cryotherapy as the established treatment modality for ROP in most centers. As with cryotherapy, laser treatment of threshold ROP involves ablation of the peripheral avascular retina. Therefore, the peripheral visual field in laser-treated patients may be affected in a manner similar to that shown in the CRYO-ROP study for cryotreated patients.1 There is little information in the literature on the effect of laser on the visual field of patients with severe ROP. Takayama et al. reported visual field restriction on Goldmann perimetry in 13 of 13 children treated with xenon laser or cryotherapy for severe ROP.3 However, they did not look at the two treatment modalities separately and did not attempt to quantify the extent of visual field loss. Ospina et al. reported a visual field reduction, judged to be of the order of 15° or less, in 24 eyes treated with argon laser and tested using the white-sphere kinetic perimetry method described by Van Hof-van Duin et al. for young children.4'5
The objective of this study was to evaluate the visual fields of a cohort of premature infants who were treated with 360° diode laser photocoagulation for threshold ROP at a single center and to compare them with the visual field findings in a group of children, also premature, with documented subthreshold ROP that had regressed spontaneously without laser treatment. Mean follow-up was 11 years.
PATIENTS AND METHODS
Fourteen patients who received 360° diode laser treatment for threshold ROP in zone H, 9 or more years previously, were identified from a register of treated children at the neonatal unit of the National Maternity Hospital, Dublin, Ireland. In all cases, laser treatment was administered, under sedation, anterior to the fibrovascular ridge, in accordance with the Royal College of Ophthalmologists' guidelines for ROP treatment.6 Three of these patients had cerebral palsy and were excluded from the study because they were unable to perform Goldmann perimetry. All of the remaining 1 1 children were recruited with informed parental consent.
Nine patients with subthreshold ROP (at least stage 2, zone II ROP with spontaneous regression), also with 9 or more years of follow-up, were identified from a log book of infants screened for ROP in the neonatal unit (screening criteria of gestational age of less than 31 weeks or birth weight of 1,500 g or less). These children were selected for inclusion in the study to provide a comparison group that closely matched the study population in terms of prematurity and severity of ROP.1'2
Visual Field Testing
Kinetic perimetry was performed by an experienced visual field tester who was masked to the ROP and treatment status of the patients. A Goldmann perimeter was used with a radius of 300 mm and a background luminance of 31.5 apostilb. Monocular visual fields were assessed, first in the right eye and then in the left eye, without spectacle correction, through an undilated pupil. Two stimuli of the same intensity (1,000 apostilb), but of different size (V4e = 64 mm2 and H4e = 1 mm2), were presented in a standardized fashion along eight meridians: 15°, 60°, 105°, 150°, 195°, 240°, 285°, and 330°. These meridians were chosen to avoid temporal artifact and upper dip, which can occur if testing is performed along the horizontal and vertical meridians using the Goldmann apparatus.2·7 The extent of the visual field in each meridian was estimated as the median value of three measurements taken in each meridian. The sum of the median values for all eight meridians was recorded as the total visual field extent for that eye.7,8
Visual acuity was recorded monocularly, by a single observer (EM), with the children wearing their normal spectacle correction, where applicable. Best-corrected distance visual acuity was recorded using a back-illuminated distance ETDRS chart (Lighthouse, New York, NY) at a test distance of 4 m. Visual acuity was estimated as the logMAR value of the last line on which the child could correctly identify three of the five available letters.
Structural Assessment and Refraction
After visual function testing, dilated fundal examination was performed (cyclopentolate 1%) to assess for ROP residua. Cycloplegic refraction was performed using a desktop autorefractometer (Model AR-630A, Nidek, Tokyo, Japan).
Analysis was performed using MATLAB 6.5 (Statistics Toolbox 4.0, The MathsWorks, Natick, MA). Because the data did not appear to be normally distributed, continuous outcomes were compared with the nonparametric Wilcoxon rank sum test, and categorical outcomes were compared using Fishers exact test. A P value of less than .05 was considered significant.
Of the 1 1 children in the laser group, 7 had bilateral treatment and 4 had unilateral treatment for 360° threshold ROP, yielding a total of 1 8 treated eyes. The comparison group included nine children (16 eyes). Two of the nine children had received laser treatment of the temporal fundus for threshold ROP in one eye; these two treated eyes were excluded from the study. The demographic characteristics of both groups are shown in Table 1 . The gestational age for the study population as a whole ranged from 24 to 29 weeks, and birth weight ranged from 620 to 1,398 g. The duration of follow-up for these children ranged from 8.9 to 12.8 years. The only statistically significant differences in the demographic characteristics between the right and left eyes of the two groups were in terms of gestational age (right eye, P = .03; left eye, P = .04) and best-corrected distance visual acuity (right eye, P =.004; left eye, P =.002).
All of the study patients had normal fundal structure, other than the peripheral laser photocoagulation scars in the laser-treated group. In particular, there was no evidence of macular or disk dragging.
The total visual field extent for the study eyes is shown in Table 2. For the H4e stimulus, the right eye median visual field extent of the laser-treated children did not differ significantly from that of the untreated comparison group (P = .11), but the left eyes showed a borderline significant reduction (P = .046). For the larger V4e stimulus, no significant differences were noted (right eye, P = .41; left eye, P = .30).
The percentage reduction in mean visual field extent in the laser-treated children compared with the untreated subthreshold group, for the H4e stimulus, was 6.9% in right eyes and 10.3% in left eyes. For the V4e stimulus, it was 2.6% in right eyes and 4.0% in left eyes. Mean values were used for comparison with the results of other studies.1'7
Diode laser photocoagulation has been demonstrated to be a safe and effective alternative to cryotherapy in the treatment of threshold ROP.9"11 Assessments of laser-treated children have shown a clear benefit of laser treatment in preserving distance visual acuity and retinal structure. 12~14 In this study, we chose to further evaluate the functional outcome of lasertreated eyes by assessing the peripheral visual fields of a cohort of premature children who had received diode laser photocoagulation for threshold ROP.
We found a small constriction in visual fields in children with threshold ROP who received laser treatment compared with children with subthreshold ROP that resolved spontaneously. The observed reduction in visual field extent in the laser group did not reach statistical significance. We performed peripheral visual field testing using the Goldmann perimeter in a manner similar to that used in the studies by Larsson et al. and the Cryotherapy for Retinopathy of Prematurity Cooperative Group.1'7 Our study showed a reduction in visual field extent of 3% to 4% with the V4e target and a reduction of 7% to 10% with the H4e target for patients treated with diode laser. This compares favorably with the findings by Larsson et al. of a reduction of 9% and 13% for the V4e and H4e targets, respectively, in cryotreated patients with threshold ROP compared with patients with subthreshold untreated ROP.7 The CRYO-ROP study group reported a small overall reduction of 5% to 7% in visual field extent at 10 years in cryotreated eyes compared with untreated eyes with threshold ROP in which vision was preserved.1
It is not clear whether the reduction in visual field extent observed in our study is attributable to a direct effect of the diode laser itself or to the fact that the control group had less severe ROP from the outset. However, this small decrease in peripheral visual field is unlikely to be of functional significance.7·15 With the recent report from the Early Treatment for Retinopathy of Prematurity Cooperative Group recommending treatment of high-risk prethreshold ROP, and consequently, the treatment of increased numbers of premature neonates, it is reassuring that diode laser treatment does not appear to be associated with a clinically significant reduction in the peripheral visual field.16
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