Slowly Progressive Retinal Arteriovenous Malformation and RelativeAmblyopia

Congenital retinal arteriovenous malformation¹ isa rare, unilateral, nonhereditary disorder with variable visual impairmentdepending on the severity of the vascular anomaly. Most cases do not showany anatomical progression.² Venous occlusion,intraretinal or vitreal hemorrhage,³ oroptic atrophy² are rare causes of suddenor gradual visual loss. We describe the case of a child with visual loss causedby slow progression of a foveal vascular loop and relative amblyopia.

A 6-year-old boy had deteriorating vision 1 year after the incidentaldetection of a retinal arteriovenous malformation in his right eye (Figure 1). At the time of the initial detection,his visual acuity was 20/20 OU. One year later, his visual acuity was 20/60OD and 20/20 OS. Multiple dilated and tortuous vessels emerged from the rightoptic disc (Figure 2) with 1 superotemporalloop reaching the fovea. No retinal thickening, exudates, bleeding, or relativeafferent pupillary defects were present. Scanning laser ophthalmoscope–fundusperimetry showed an absolute scotoma overlying the foveal vascular loop. Fixationwas unstable and 5° inferotemporal to the fovea (Figure 2). Comparison with the fundus photograph taken 1 year earliershowed some advancement of the loop.

The left eye was healthy. There was no strabismus, and stereopsis (Langtest) was normal. Cycloplegic refraction was +2.00 diopters spherical OU.The medical history, systemic history, and examination results were unremarkable.Recent magnetic resonance tomography results did not show any intracranialanomaly of Bonnet-Dechamp-Blanc or Wyburn–Mason syndrome.

Because the location of the loop itself did not account for the totalamount of visual acuity loss, we suspected relative amblyopia and recommendedocclusion of the left eye for 4 hours per day.

Eight months later, visual acuity had improved to 20/30 OD and scanninglaser ophthalmoscope– fundus perimetry showed a definite central shiftof the retinal fixation area (Figure 2).Esotropia of +10° without correction and +3° with correction was nowpresent.

Afterward, occlusion therapy was difficult and finally abandoned bythe parents. One year later, visual acuity was 20/400 OD. A further progressionof the vascular loop and a 13° temporal shift of the fixation area werepresent (Figure 2). Because of thatand the lack of success to maintain useful vision, we stopped any treatment.

The initial drop in visual acuity may have been due to 2 factors, aslow progression of the loop approaching the fovea and relative amblyopia.The progression of the loop toward the fovea was gradual and totaled 500 µmin 33 months (180 µm/y). Although most cases of arteriovenous malformationare thought to be stable,² anatomical changesof arteriovenous malformations have previously been described⁴ butnot linked to visual loss.

On the other hand, relative amblyopia is likely to have been a contributingfactor. It is defined as a reversible functional deficit superimposed on acongenital organic abnormality or pathologic changes acquired in early childhood.Our hypothesis was supported by the increase in visual acuity with patchingand the shift of fixation. When manifest esotropia was present, strabismicamblyopia may have contributed to the final visual loss.

Not all retinal AV malformations are stationary, and small changes caninduce a visual loss that may be amplified by relative amblyopia in patientsduring their sensitive period of visual development. Unlike this patient,most cases do not progress. A trial of occlusion therapy may be warrantedin young children if visual acuity is worse than expected from the locationof a central loop.

The author has no relevant financial interest in this article.

Corresponding author: Oliver Ehrt, MD, Department of Ophthalmology,Ludwig Maximilians University, Mathildenstr 8, D-80336 Munich, Germany (e-mail: oliver.ehrt@med.uni-muenchen.de)