Retinopathy of Prematurity Ophthalmologic Approach

Retinopathy of prematurity (ROP) is a disease that affects immature vasculature in the eyes of premature babies. It can be mild with no visual defects, or it may become aggressive with new blood vessel formation (neovascularization) and progress to retinal detachment and blindness. As smaller and younger babies are surviving, the incidence of ROP has increased.

During the 1940s and 1950s, ROP, also known as retrolental fibroplasia, was the leading cause of blindness in children in the United States. In 1942, Terry first reported the disease that was published in a report on the histologic findings of end-stage cicatricial disease.[6] In 1951, Campbell first suggested that ROP was related to the introduction of oxygen therapy into the newborn nursery, and this was confirmed by Patz.[7] Today, after oxygen therapy has been studied and found not to be the single causative agent, the factors that play a role in the pathogenesis of ROP are still unknown.

The retinal vasculature begins in the 16th week of gestation. Retinal vessels grow out of the optic disc as a wave of mesenchymal spindle cells. As these mesenchymal spindle cells lead the shunt, endothelial proliferation and capillary formation follow. These new capillaries will form the mature retinal vessels. The choroidal vessels (that are vascularized by the 6th week of gestation) supply the rest of the avascularized retina. The nasal portion of the retina is completely vascularized to the ora serrata by the 32nd week of gestation. The larger temporal area usually is completed at 40-42 weeks (term).

Two theories exist on the pathogenesis of ROP. The mesenchymal spindle cells, exposed to hyperoxic extrauterine conditions, develop gap junctions. These gap junctions interfere with the normal vascular formation, triggering a neovascular response, as reported by Kretzer and Hittner.[8] Ashton theorizes that 2 phases exist.[9] The first phase, a hyperoxic phase, causes retinal vasoconstriction and irreversible capillary endothelial cell destruction. As the area becomes ischemic, angiogenic factors, such as vascular endothelial growth factor (VEGF), is made by the mesenchymal spindle cells and ischemic retina to provide new vascular channels. These new vascular channels are not mature and do not respond to proper regulation.

The most conspicuous question in the pathophysiology of ROP is why it progresses in some premature infants despite rigorous and timely intervention, whereas, in other infants with similar clinical characteristics, it regresses. Csak et al believe that perhaps the genetic differences between infants could be an explanation.[10] Although many causative factors, like low birth weight, low gestational age, and supplemental oxygen therapy, are associated with ROP, several indirect lines of evidence suggest the role of a genetic component in the pathogenesis of ROP. The incidence of ROP is more frequent in white infants than in black infants and in male infants than in female infants. Genetic polymorphism may alter the function of the genes that normally control retinal vascularization, such as VEGF, which may also be involved in the pathogenesis of ROP.

In the future, evaluation of candidate genetic polymorphism influencing the outcome of ROP may provide new information about the pathogenesis of the disease. Screening of genetic polymorphisms may also help to identify and treat those infants who are at high risk in a more timely manner.

A 2023 review of the pathophysiology of ROP was published in Survey of Ophthalmology.[1]

United States

The incidence of ROP in premature infants is inversely proportional to their birth weight. Fielder studied infants weighing less than 1700 g and noted development of ROP in 51%.[11]

In general, more than 50% of premature infants weighing less than 1250 g at birth show evidence of ROP, and about 10% of the infants develop stage 3 ROP.

International

In 1995, ROP accounted for 10.6% of cases of blindness in children in schools for the blind in South Africa.[12]

On average, 500-700 children become blind because of ROP in the United States each year. In terms of life years of blindness, this translates to 30,000 life years of vision.

Annually, 2100 infants will be affected with cicatricial sequelae, including myopia, strabismus, blindness, and late-onset retinal detachment.

The rule of thumb is that approximately 20% of all premature babies will develop some form of strabismus or refractive error by the time they are age 3 years. This is why babies who are younger than 32 weeks or less than 1500 g receive follow-up care every 6 months, whether or not ROP is present.

Race

Palmer and colleagues showed that African Caribbean infants are less likely to develop ROP than their Caucasian counterparts.[13]

Sex

The incidence is slightly greater in male infants than in female infants.

Age

ROP is a disease of premature infants. All babies less than 1500 g birth weight or younger than 32 weeks' gestational age at birth are at risk of developing ROP.

As younger and smaller infants are surviving, the screening protocols are changing to include earlier gestational age. In any neonatal intensive care unit (NICU), the timing of the first evaluation must be based on the gestational age at birth. (See the Gestational Age from Estimated Date of Delivery calculator.)

• If the baby is born at 23-24 weeks' gestational age, the first eye examination should be performed at 27-28 weeks gestational age.

• If the baby is born at or beyond 25-28 weeks' gestational age, the first examination should occur at the fourth to fifth week of life.

• Beyond 29 weeks, the first eye examination probably should occur before the infant is discharged.

The prognosis is guarded until zone 3 is reached.

Patients should be educated about the following:

• Awareness of the risk of potential visual loss from amblyopia, strabismus, retinal detachment, or glaucoma

• Possible need for repeated surgical procedures

• Possible patching for amblyopia, thick glasses for myopia, or possible strabismus surgery

In 1984, a committee consisting of 23 ophthalmologists from 11 countries formed the International Classification of Retinopathy of Prematurity (ICROP). This new classification system demarcated the location of the disease into zones of the retina (1, 2, and 3), the extent of the disease based on the clock hours (1-12), and the severity of the disease into stages (0-5).

In obtaining a history for a premature infant, note the following:

• Gestational age at birth, especially if younger than 32 weeks' gestation

• Birth weight of less than 1500 g, especially less than 1250 grams

• Other possible risk factors (eg, supplemental oxygen, hypoxemia, hypercarbia, concurrent illness)

The following is a sample consultation form for ROP.

Retinopathy of prematurity consultation form and fundus drawing.

ROP is categorized in zones, with stages depicting the severity of the disease. The smaller and younger the infant at birth, the more likely the disease will involve the central zones with advanced stages.

ROP is categorized by the lowest zone and the highest stage observed in each eye.

Zone 1

Zone 1 is the most labile.

The center of zone 1 is the optic nerve. It extends twice the distance from the optic nerve to the macula in a circle. Using a 28-diopter lens, if any portion of the optic nerve is in the same view as the ridge of ROP, that is considered zone 1

Any disease in zone 1 (even stage 0, immature) is critical and must be monitored closely. Zone 1 does not follow the ICROP rules. The area is very small and changes can occur very quickly, sometimes within days. The hallmark of the disease worsening is not the presence of neovascularization (as in other zones, as specified by the ICROP) but is by the increasing dilation and tortuosity of the vessels. The vascularized retina seems to rise (like a soufflé) probably because of the increased arteriovenous shunting. Many ROP experts feel that any disease in zone 1, and certainly any plus disease, requires treatment.

Zone 2

Zone 2 is a circle surrounding the zone 1 circle with the nasal ora serrata as its nasal border.

The disease may progress quickly but usually there are warning signs that predate the threshold by 1-2 weeks, as follows: (1) The ridge shows signs of vascular arcading (increased branching); this is usually a sign that the disease is starting to become aggressive. (2) Increasing vascular dilation and tortuosity is present. (3) A "hot dog" on the ridge is seen; this is a thickened vascular ridge that may not show the typical fronds of neovascularization. Rather, the demarcation of vascularized and nonvascular retina is a thickened red 3-dimensional roll. This usually is seen in posterior zone 2 (borders zone 1) and is a poor prognostic indicator. (4) The Cryotherapy for Retinopathy of Prematurity Cooperative Group (CRYO-ROP) study described threshold disease as 5 contiguous or 8 noncontiguous hours of neovascularization (stage 3) with plus disease in zone 1 or 2. Of threshold eyes left untreated, 50% would develop adverse structural outcomes (eg, retinal detachment) 12 months after randomization.

Zone 3

Zone 3 is the crescent that the circle of zone 2 did not encompass temporally.

Aggressive disease rarely is seen in this zone. Typically, this is slowly vascularizing and requires evaluations every few weeks.

Many infants show inactive disease in zone 3 with a demarcation line and nonvascularized retina. This has been noted in toddlers and can be considered cicatricial peripheral disease. No ill sequelae are known to occur from this ridge.

Stage 0

This is the mildest form of ROP. It is immature retinal vasculature. No clear demarcation of vascularized and nonvascularized retina is present. Only a suggestion of the border is noted on examination.

• In zone 1, this may appear as a vitreous haze, with the optic nerve as the only landmark. Weekly examinations should be performed.

• In zone 2, examinations should be performed every 2 weeks.

• In zone 3, an examination every 3-4 weeks should be sufficient.

Stage 1

A fine, thin demarcation line between the vascular and avascular region is present. This line has no height and no thickness.

• In zone 1, this should appear as a flat, thin line (usually nasally first). No elevation from the avascular retina should be present. The retinal vessels should be smooth, thin, and supple. Weekly examinations should be performed.

• In zone 2, examinations should be performed every 2 weeks.

• In zone 3, an examination every 2-3 weeks should be sufficient.

Stage 2

A broad, thick ridge clearly separates the vascular from the avascular retina.

• In zone 1, if there is any hint of pink or red in the ridge, this is an ominous sign. If there is any vessel engorgement, the disease should be considered threshold and treatment commenced within 72 hours.

• In zone 2, if there are no vascular changes and the ridge has no engorgement, the eye should be examined within 2 weeks. Prethreshold is defined as stage 2 with plus disease.

• In zone 3, examination every 2-3 weeks should be sufficient, unless of course there is any vascular tortuosity or straightening of the vascular arcades.

Stage 3

The extraretinal fibrovascular proliferation (neovascularization) may be present on the ridge, on the posterior surface of the ridge or anteriorly toward the vitreous cavity. The neovascularization gives the ridge a velvety appearance, a ragged border.

• In zone 1, if there is any neovascularization, it is serious and requires treatment.

• In zone 2, prethreshold is defined as stage 3 without plus disease, or stage 3 with less than 5 contiguous or 8 noncontiguous hours. Threshold is stage 3 with at least 5 contiguous or 8 noncontiguous hours and plus disease.

• In zone 3, examination every 2-3 weeks should be sufficient, unless there is any vascular tortuosity or straightening of the vascular arcades.

Stage 4

This stage is a subtotal retinal detachment beginning at the ridge. The retina is pulled anteriorly into the vitreous by the fibrovascular ridge.

• Stage 4A does not involve the fovea.

• Stage 4B involves the fovea.

Stage 5

This stage is a total retinal detachment in the shape of a funnel.

• Stage 5A is an open funnel.

• Stage 5B is a closed funnel.

Plus disease is defined as arteriolar tortuosity and venous engorgement of the posterior pole, iris vascular engorgement, pupillary rigidity, and vitreous haze, which are part of the subclassification given to the above stages. The presence of plus disease is an ominous sign.

Pre-plus disease is defined as vascular abnormalities of the posterior pole that are insufficient for the diagnosis of plus disease but that demonstrate more arteriolar tortuosity and more venular dilatation than normal. Signs of pre-plus disease early in the course of ROP were shown to be strongly associated with development of severe ROP that required laser treatment. The diagnosis of pre-plus disease adds prognostic value beyond that already known with birth weight, gestational age, ROP zone, and ROP stage.[14]

Other terms mentioned with ROP include the following:

• Popcorn: Regressed neovascularization seen anterior to the internal limiting membrane. This is a cicatricial change and usually regresses completely over several weeks.

• Hot dog: A "red hot" active ridge, probably the site of increasing vascular channels. This is a critical hot area of activity. If noted on zone 1 or 2, this is an ominous sign. This area may regress with cicatrix floating in the vitreous cavity and nonpatent ghost vessels still visibly attached to the retina (a second ridge would clearly be identified anterior to this cicatrix). In less fortunate eyes, this area may be the site of a true retinal detachment (no advancing ridge would be visible and the vessels would not be ghostly but engorged).

• Rush disease: A very rapidly progressive subtype of ROP is called rush disease. If plus disease is accompanied by vascularization ending in zone 1 or in very posterior zone 2, the risk for rush disease is significant.

ROP is a disease of premature infants. All babies less than 1500 g birth weight or younger than 32 weeks' gestational age at birth are at risk of developing ROP.

Tolsma et al found that late neonatal bacteremia appears to be an independent risk factor for prethreshold/threshold ROP and plus disease. The study also found that presumed late bacteremia was associated with prethreshold/threshold ROP.[15]

Potential complications include the following:

• Loss of vision even with aggressive surgical treatment

• Amblyopia due to high refractive errors

• Strabismus

• Glaucoma

• Retinal detachment

In a 2014 case series of 36 eyes in 18 neonates with ROP, Hariharan and colleagues found that fluorescein angiography was better than standard digital imaging for monitoring infants treated with intravitreal bevacizumab.[16, 17] Precisely detailed advanced vascular growth could be seen with fluorescein angiography for all eyes, whereas digital fundus photography and clinical examination did not reveal subtle changes in vasculature as clearly.

The angiography protocol involved administration of an intravenous bolus of a 10% solution of sodium fluorescein dye, followed by a saline flush.[16, 17] Clinical fundus photography and fluorescein angiography were performed at the time of injection and photography was repeated 2 to 3 weeks after the injection.

In 2008, a telemedicine study showed that single-image and multiple-image telemedicine examinations perform comparably in the determination of a recommended follow-up interval and in the detection of plus disease.[18] In the future, there will likely be an increase and development of screening protocols, particularly in areas with limited access to ophthalmic care.[18]

A dilated fundus examination with scleral depression is necessary. The instruments used are a Sauer speculum (to keep the eyes gently open), a Flynn scleral depressor (to rotate and depress small eyes), and a 28-diopter lens (for proper identification of zones).

The first part of the examination should be external, with identification of iris rubeosis, if present. The next part of the examination should be the posterior pole, with identification of any plus disease or straightening of the vascular arcades. The eye is rotated to identify the presence or absence of zone 1 disease (if the ridge and the optic nerve are present in the same view, this usually implies zone 1). If the nasal vessels are not at the nasal ora serrata, this is still zone 2. If the nasal vessels have reached the nasal ora serrata, the eye is in zone 3.

Although oxygen therapy has been blamed for ROP progression in the past, many physicians believe that maximizing the oxygen saturation in these critical babies will induce regression in prethreshold disease. STOP-ROP (Supplemental Therapeutic Oxygen for Prethreshold Retinopathy Of Prematurity), a multicentered national study, found that no benefit was achieved by keeping the oxygen saturation above 95%. However, higher oxygen saturation levels were not found to worsen the disease in prethreshold babies.

Because ROP progresses sequentially, and timely treatment can reduce the risk for visual loss, at-risk preterm infants must be examined at proper times and intervals. A January 2013 policy statement from the American Academy of Pediatrics on screening for ROP provides screening recommendations, including descriptions of the following[5] :

• Criteria for screening

• Equipment and methods for retinal examinations for ROP

• Examiner qualifications and reporting criteria

• Timing of the first retinal examination, based on the infant’s postmenstrual age (gestational age at birth plus chronologic age)

There appears to be a lower incidence of very high myopia (≥8.00 diopters) when ROP is treated with intravitreal bevacizumab compared with conventional lasers,[19, 20] on the basis of results from the Bevacizumab Eliminates the Angiogenic Threat for ROP (BEAT-ROP) Cooperative Group study, which randomized 109 children (211 eyes) as infants to intravitreal bevacizumab or conventional laser treatment and then compared refractive outcomes at age 2.5 years. Moreover, myopia in the laser group was linked to greater numbers of laser applications, with an increase of -0.14 D for every 100 laser applications.[20]

Among infants with zone I ROP, very high myopia developed in 2 of 52 eyes (3.8%) in the bevacizumab group and 18 of 35 eyes (51.4%) in the laser group (P  < .001); among those with zone II posterior ROP, very high myopia developed in 1 of 58 eyes (1.7%) in the bevacizumab group and in 24 of 66 eyes (36.4%) in the laser group (P  < .001).[19, 20]

Cryotherapy was the original mode of treatment (since the 1970s). The procedure may be completed with general or topical anesthesia. It involves approximately 50 applications of a freezing probe under direct visualization with cryo applications to the avascular retina anterior to the fibrovascular ridge. The stress of the procedure may require assisted ventilation after the procedure. The most common complications include intraocular hemorrhage, conjunctival hematoma, conjunctival laceration, and bradycardia.

Laser surgery (eg, xenon, argon, diode) has been shown to be as effective as cryotherapy for ROP. The systemic adverse effects are significantly less, the ocular tissues are less traumatized, posterior zone 1 disease is treated easily, general anesthesia is not necessary, and, as many studies show, there is less incidence of late complications. Complications include corneal haze, burns of the iris, cataracts, and intraocular hemorrhages.

The use of diode laser therapy in extremely preterm infants with ROP appears not only to halt disease progression but also leads to good visual outcomes for most of these infants, thereby apparently offering similar structural and visual outcomes to those of low and very low birth weight infants with this condition.[21, 22]

Scleral buckling surgery and/or vitrectomy is usually performed for stages 4 and 5. Some surgeons recommend surgery for stage 4A, while others do not think surgery should be performed because of the risks and unproven benefit. Although some surgeons advocate surgery for stage 5, the surgeon with the most experience (ST Charles, MD, personal communication) no longer recommends surgery because of the poor anatomical and visual prognosis.

According to the largest reported case series in the world, lens-sparing vitrectomy to correct early degrees of retinal detachment results in excellent lens clarity and vision in the majority of infants with retinopathy of prematurity. Success rates for retinal reattachment with a single surgery were approximately 89% for infants with stage 4A retinopathy. Success rates for stage 4B retinopathy were 60%. The procedure was less successful in infants with stage 5 retinopathy, with an 18% success rate.[23]

An ophthalmology consultation is essential in a premature infant born weighing less than 1500 g and/or younger than 32 weeks' gestation (as defined by the attending neonatologist). Also, selected infants with a birth weight of 1500-2000 g or a gestational age of more than 32 weeks with an unstable clinical course, including those requiring cardiorespiratory support and who are believed by their attending pediatrician or neonatologist to be at high risk, should have retinal screening 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 in each eye. The ophthalmologist chosen should be one with the most experience in screening or treating this disease. A review of two randomized crossover trials performed in single centers found that the application of topical proparacaine 30 seconds before the evaluation brings about a reduction in pain scores, particularly at the moment of speculum insertion.[24]

An ophthalmologist experienced in this modality should perform laser or cryotherapy surgery.

Scleral buckle surgery and vitrectomy techniques in these small eyes should be left in the hands of experienced surgeons.

Practitioners involved in the ophthalmologic care of premature infants should be aware that the retinal findings that require strong consideration of ablative treatment were revised according to the Early Treatment for Retinopathy of Prematurity Randomized Trial study. The finding of threshold ROP, as defined in the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity, may no longer be the preferred time of intervention.

Treatment may also be initiated for the following retinal findings:

• Zone 1 ROP - Any stage, with plus disease

• Zone 1 ROP - Stage 3, with no plus disease

• Zone 2 ROP - Stage 2 or 3, with plus disease

The number of clock hours of disease may no longer be the determining factor in recommending ablative treatment. Treatment should generally be accomplished, when possible, within 72 hours of determination of treatable disease to minimize the risk of retinal detachment.

Vitamin E is not recommended in infants who weigh less than 1500 g.

The Light-ROP study evaluated the role of light in stimulating the development of ROP. Patients were either exposed to normal light conditions in the nursery or shielded from ambient light conditions. There was no difference in the number of patients developing ROP in either group.

In infants at risk for ROP, early administration of high-dose intramuscular vitamin A improves retinal function at 36 weeks’ postmenstrual age.

Any premature infant should continue to be monitored until active disease has subsided.

Since 20% of premature babies develop strabismus and refractive errors, a pediatric ophthalmologist should screen them every 6 months, until age 3 years.

Up to 10% of premature babies may develop glaucoma in later years. Eye examinations should be a part of their annual examinations.

Transfer the infant to a NICU that can handle the disease and the required surgical intervention if necessary.

In a prospective study by Repka et al, surfactant has not been found to lower the incidence of ROP.[25]

A study by Wu et al examined the use of bevacizumab to treat ROP.[26] Among the 27 patients (18 male, 9 female) in the study, 49 eyes were included. The study found that bevacizumab was effective and well-tolerated in some cases of ROP, most notably in stage 3. However, the study did note that complications from bevacizumab were possible in pediatric patients.

A study by Mintz-Hittner et al examined the use of bevacizumab to treat ROP in 150 infants.[27] The study found that monotherapy with bevacizumab showed a significant treatment benefit in zone I ROP (P=0.003) but not in zone II ROP (P=0.27). However, the study size was too small to assess safety. Long-term studies are still necessary.

A 2022 study showed: "Laser was associated with a lower rate of retreatment than ranibizumab in type 1 ROP (Zones I and II combined), while bevacizumab was associated with a lower rate of retreatment than laser in Zone I ROP. Aflibercept and bevacizumab demonstrate longer duration of action than ranibizumab for ROP."[28]

Ranibizumab intravitreal injection (Byooviz, Cimerli, Lucentis)

Bevacizumab intravitreal (Bevacizumab-vikg, Lytenava)

Aflibercept intravitreal (Eylea, Eylea HD)