Division on Visual Impairments

DVI Quarterly Volume 58(1)

A quarterly newsletter from the Council for Exceptional Children's Division on Visual Impairments containing practitioner tips for Teachers of Students with Visual Impairments, Certified Orientation and Mobility Specialists, and other professionals.

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(Vanderbilt Children's Hospital, 2009), so ROP will generally be more severe the earlier the child is born. Pathology of ROP 42 There are two stages in the progression of ROP. The first phase is the loss of blood vessels to the retina, and the second phase involves the abnormal, excessive growth of new blood vessels (neovascularization). The normal progression of the development of blood vessels begins at 4 months (about 16 weeks) of gestational age, beginning at the optic nerve, and completes at around 8 months (36 weeks), reaching the ora serrata. Thus, ROP generally progresses through the first stage at about 30-32 weeks. The first stage of ROP is when the area of the retina without blood supply due to the non-development of vessels becomes hypoxic, or deprived of oxygen. The second phase of neovascularization occurs at about 32-34 weeks, triggered by increased metabolic activity in the infant and in response to the under-oxygenated area of the retina. This new, abnormal growth of blood vessels can cause scarring, leakage, and tangles of vessels which can extend into the vitreous and lens causing retinal detachment (Chen & Smith, 2007). One theory for the cause of ROP is the exposure to oxygen after birth. In utero, the oxygen levels the fetus is exposed to are 1/2 to 1/3 the levels the infant will breathe in normal room air. If oxygen therapy is used, the level increases even more. Chen found that in mice models, once the mice were exposed to increased oxygen levels, normal vessel growth stopped and regressed. The resulting hypoxic area of the retina induced new, abnormal vessel growth. The specific molecular causes and progressions for vessel growth have been found to be related to levels

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