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ROP

Retinopathy of prematurity (ROP) is a retinal disorder of low birth weight premature infants potentially leading to blindness in a small but significant percentage of those infants. The results of the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity Cooperative Group indicated that treatment is associated with a 41% decrease in the occurrence of posterior retinal traction folds or detachments and a 19% to 24% decrease in the incidence of blindness when evaluated 5 years later. Because of the sequential nature of the progression of ROP, the proven benefits of cryotherapy and, more recently, the acceptance of at least equivalent therapeutic benefit of laser therapy for the same indications,standards of practice now demand carefully timed retinal examinations of at-risk infants by an ophthalmologist experienced in the examination of preterm infants for ROP to minimize the risk of visual loss by those infants.

This statement outlines the principles on which a screening program to detect ROP in infants at risk might be based. The goal of an effective screening program must be to identify the relatively few preterm infants who require treatment for ROP from among the much larger number born each year while minimizing the number of stressful examinations required for these sick infants. Any screening program designed to implement an evolving standard of care has inherent defects, such as overreferral or underreferral, and cannot, by its very nature, duplicate the precision and rigor of a scientifically based clinical trial. With that in mind and on the basis of information published thus far, the sponsoring organizations of this statement suggest the following guidelines for the :

1. Infants with a birth weight of less than 1500 g or with a gestational age of 28 weeks or less, as well as selected infants between 1500 and 2000 g with an unstable clinical course who are believed to be at high risk by their attending pediatrician or neonatologist, should have at least 2 fundus examinations performed after pupillary dilation using binocular indirect ophthalmoscopy to detect ROP. One examination is sufficient only if it unequivocally shows the retina to be fully vascularized bilaterally.
2. Examination for ROP should be performed by an ophthalmologist with sufficient regular experience and knowledge in the examination of preterm infants for ROP to identify the location and sequential retinal changes in this disorder using binocular indirect ophthalmoscopy. The location and sequential retinal changes, if any, should be recorded using the International Classification of Retinopathy of Prematurity.
3. The first examination should normally be performed between 4 and 6 weeks of chronologic (postnatal) age or, alternatively, within the 31st to 33rd week of postconceptional or postmenstrual age (gestational age at birth plus chronologic age), whichever is later, as determined by the infant's attending pediatrician or neonatologist. If using the postconceptional age guideline, examinations are generally not needed in the first 4 weeks after birth. The timing of the initial screening examination may be adjusted appropriately on the basis of other reliable data, such as local incidence and onset of ROP or the presence of other recognized risk factors. The initial screening examination and subsequent examinations should be timed to permit sufficient time for treatment, including, any extra time required for transfer to another facility for treatment, if necessary. Treatment should generally be accomplished within 72 hours of determination of the presence of threshold 1 ROP to minimize the risk of retinal detachment before treatment.
4. Scheduling of follow-up examinations at the recommendation of the examining ophthalmologist is best determined by the findings at the first examination using the International Classification of Retinopathy of Prematurity. For example, if the retinal vasculature is immature and extends into zone II but no retinopathy is present, follow-up examination should be planned at approximately 2- to 3-week intervals until normal vascularization proceeds to zone III (ie, in the nasal periphery, there is no retinopathy and normal vessels are present within 1 disk diameter of the ora serrata).
5. Once an infant has been determined on first examination to be at risk for ROP, the following schedule is suggested:
   1. Infants with ROP that may soon progress to threshold ROP should be examined at least weekly. These include:
      1. Any infant with ROP less than threshold in zone I
      2. Infants with ROP in zone II, including:
         1. those with stage 3 ROP without plus disease (defined as posterior pole dilation and tortuosity of the retinal vessels)
         2. those with stage 2 ROP with plus disease; and
         3. those with stage 3 ROP with plus disease not yet extensive enough to justify ablative surgery.
   2. Infants with less severe ROP in zone II should be examined at 2-week intervals. Those without ROP but with incomplete vascularization in zone I should be seen at 1- to 2-week intervals until retinal vascularization has reached zone III or until threshold conditions are reached.
   3. If the retinal vascularization is incomplete in zone II but no ROP is detected, follow-up examination should be planned at approximately 2- to 3-week intervals until vascularization proceeds into zone III.
   4. Retinas with incomplete vascularization only in zone III usually mature completely; ROP in zone III normally regresses (involutes) without adverse consequences. However, the finding of normal vascularization in zone III is unusual in the initial examination of very low gestational age infants. In cases in which zone III vascular maturation seems to be present on initial examination of very low birth weight infants, this finding should be verified by at least 1 repeat examination within 2 to 3 weeks.
6. Infants reaching threshold 1 disease (stage 3 ROP in zone I or II in 5 or more continuous clock hours or 8 cumulative clock hours [30° sectors] with plus disease [posterior retinal vessel dilation and tortuosity]) should receive ablative therapy for at least 1 eye within 72 hours of diagnosis, generally before the onset of retinal detachment. Stage 3 ROP with vascularization in zone I or borderline zone I to II may appear different from purely zone II stage 3 disease in that proliferation may appear flat, only appearing to be significantly elevated when it has become extremely severe. In view of this difficulty in distinguishing between stages 2 and 3 in posterior regions, infants with suspected stage 3 ROP in zone I or border zone I to II with plus disease should be examined especially carefully to determine if they meet the threshold criteria noted above.
7. Parents of infants with ROP should be informed of the nature and possible consequences of this disorder throughout the infant's hospital stay, beginning at the time of first diagnosis and continuing on an ongoing basis with updates on its progression during hospitalization.
8. Responsibility for examination and follow-up of infants at risk for ROP must be carefully defined by each neonatal intensive care unit. Unit-specific criteria for examination for ROP should be established for each neonatal intensive care unit by consultation and agreement between neonatology and ophthalmology services. These criteria should be recorded and should automatically trigger scheduled ophthalmology examinations. If hospital discharge or transfer to another neonatal unit or hospital is contemplated before retinal maturation into zone III has taken place, the availability of appropriate follow-up ophthalmologic examination must be ensured, and specific arrangement for that examination must be made before such discharge or transfer occurs. The transferring primary physician should have the responsibility of communicating orally and in writing what eye examinations are needed and their required timing to the infant's new primary physician. The new primary physician should ascertain the current ocular examination status of the infant from the record and through communication with the transferring physician so that any necessary examinations by an ophthalmologist with regular experience and knowledge of the examination of preterm infants for ROP can be arranged promptly at the receiving facility. If responsibility for arranging follow-up after discharge is delegated to the parents, it must be clearly understood by the parents that blindness is a possible outcome, that there is a critical time window to be met if treatment is to be successful, and that timely follow-up examination is essential to successful treatment; this information should be transmitted to the parents orally and in writing. If such arrangements for follow-up after transfer or discharge cannot be made, the infant should not be transferred or discharged.

Infant Vision

The visual system begins to develop early in the human embryo, but the most critical period of development of the visual system occurs late in gestation, from 28 to 40 weeks. At 36 weeks of gestational age, the pupillary responses to light are just becoming consistent, the pho­toreceptor to ganglion cell connections are continuing to mature, the lateral geniculate nuclei are developing their characteristic 6 layers, and the ocular dominance columns of the visual cortex are halfway through their formation. Development of the retina (especially the fo­vea) and visual cortex continues after birth. Postnatal vi­sual stimulation is also essential for the development of normal vision, and this process takes place over the first 2 to 3 years of life. Early deprivation of visual stimula­tion secondary to severe ptosis, corneal opacity, cata­ract, or vitreous hemorrhage will hinder normal visual development.

NORMAL VISUAL BEHAVIOR IN AN INFANT

                        At birth, infants (defined as children from birth to 1 year of age) are able to see and blink in response to light. In the few weeks after birth, they are increasingly able to differentiate lines, patterns, movement, and finally, color.

                        At about 6 weeks of age, infants begin to make meaningful eye contact and display a social smile, both indicators of normal visual development. Smiling at this age is visually learned. The focal distance for infants is about 12 inches, and they are particularly attracted to faces and high-contrast visual targets. At this age, the infant has little regard for distance objects. It is estimated by sweep visual evoked potentials (VEP) that newborns have visual acuity of approximately 20/400. Infants at this age may fixate fairly well on a stationary object, but if the object is moved, the infant may not follow the target well. In addition, these infants often display decreased visual attention on monocular occlusion during the examination. Intermittent horizontal strabismus is very common and considered normal at this age.

                        At 3 months of age, the infant should be able to fixate and accurately follow a moving toy, tracking first horizontally and then vertically a few weeks later. At this age, the infant will fix and follow with an eye occluded.

                        By 6 months of age, infants will display more prolonged visual attention to near targets and will attend at greater distances. Stereovision is beginning to develop. At this age, all signs of intermittent strabismus should have resolved.

                        By 1 year of age, most infants will attend to objects at a 20‑foot distance.

ABNORMAL VISUAL BEHAVIOR IN AN INFANT

Abnormal vision in an infant ranges from no vision to decreased visual attention for age, presenting as a failure/delay in gaining the visual milestones noted ear­lier. The signs of abnormal vision may include:

                        poor eye contact with caregivers

                        poor fixation, and/or following, on a face, or later, toys

                        delayed onset of a social smile

                        nystagmus (if present, onset is typically between 1 to 4 months of age)

                        excessive light sensitivity (day blindness or hemeralopia)

                        staring at lights (ceiling lights, sun, sunny window)

                        pressing on the eye with a thumb, finger, or knuckle (oculodigital sign)

                        holding objects very close to the eyes

                        failure to develop attention to distant objects

Evaluation of the Visually Impaired Infant

Assessing the visually impaired infant may appear daunting, but employing knowledge of a few basic te­nets (sidebar) and obtaining specific key historical and clinical examination information will lead the practitio­ner to the correct diagnosis in an efficient manner.

HISTORY

After the history of poor vision has been obtained, other historical information often supplies clues as to the eti­ology of the abnormal vision, especially if no etiology is readily apparent on the eye examination.

NEUROLOGIC DISORDERS. Decreased vision in an infant may be caused by cerebral insults or congenital cerebral maldevelopment, which is typically associated with other neurologic abnormalities such as delay in development of milestones (head control, rolling over, truncal control, crawling and walking, speech), micro­cephaly, and seizures (especially infantile spasms). These neurologic signs imply that the infant’s abnormal vision may be brain-based.

PRETERM BIRTH. Premature infants, especially those born at the lowest gestational ages, are at high risk for anterior and posterior visual pathway insults, which cause retinal, optic nerve, and/or brain damage, leading to visual loss.

FAMILY HISTORY OF BLINDNESS. A family history of blindness or very poor vision even after refractive correction, or a family history of albinism, nystagmus, or retinal dystrophy/degeneration, are critical historical elements and may lead to the diagnosis. A family his­tory of consanguinity is important because it increases the likelihood of autosomal recessive disorders when the family history is negative.

UNUSUAL MANNERISMS. Light staring is a manner­ism that is very common in children with brain-based causes of visual impairment. These children will often stare at a bright light, bright window light, and occa­sionally wave their hand or fingers in front of their faces as they gaze at the light.

The oculodigital sign (Figure 1) is a mannerism that poorly sighted children may display. It occurs more commonly in patients with retinal disease, particularly retinal dystrophies. This sign consists of repeated and forceful pressing or poking of the globe(s) with a fin­gertip or knuckle, typically through a closed eyelid. It is presumed that the blind child is creating a visual sensa­tion by retinal phosphene production.

Day blindness, or hemeralopia, is the inability to see in bright light. This occurs in specific retinal diseases, namely cone retinal dystrophies such as achromatopsia. Affected patients are unable, or refuse, to open their eye­lids in strong lighting conditions, such as outdoors. It has also been termed photo-aversion. Night blindness, or nyctalopia, occurs in retinal dystrophies that primar­ily affect the rods, but these conditions typically do not present in infancy.