Retinopathy of Prematurity
Rupal H. Trivedi
M. Edward Wilson
Retinopathy of prematurity (ROP), formerly known as retrolental fibroplasia, is a proliferative disease of premature infants characterized by abnormal blood vessel development in the retina. With the continued improvement in survival of low birth weight and early gestational age infants, ROP remains a significant cause of childhood blindness. Cataract can occur as a complication of the disease or the treatment. Cataract can be an associated ocular pathology in eyes with ROP, as low birth weight and prematurity are risk factors for both entities.1,2 Alden et al.3 reported transient lens opacities in 3% of low-birth weight infants. These opacities, which are reversible in nature, are characterized by clear fluid vacuoles just anterior to the posterior capsule of the lens. Marcus et al.4 reported hereditary cataract developing in a premature infant after birth. The authors noted that very early cataract extraction may be necessary in premature infants to allow ROP evaluation. However, the occurrence of secondary cataract (secondary to treatment of ROP) has been reported more frequently in the literature and is our focus in this chapter.
Mild ROP has a negligible incidence of cataract. In more advanced disease, cataract is a known association. The Early Treatment for ROP study reported that for pre-threshold ROP patients 2 years of age, cataract or aphakia was found in 4% of the treated eyes (with peripheral retinal ablation applied at prethreshold) and 6% of the conventionally managed (observed at prethreshold and only treated if threshold was reached) eyes.5 Patients with retinal detachment (RD) associated with ROP, that is, stage 5 ROP, have as high as a 50% risk of developing cataracts.6
Laser photocoagulation has long ago supplanted cryotherapy as the standard treatment for threshold ROP. Compared with cryotherapy, laser is associated with a lower rate of RD and less myopia. However, laser retinal photoablation in eyes with ROP may be associated with an increased risk of cataract formation. Laser therapy in ROP patients can be applied with an argon, diode, or frequency-doubled YAG laser. Argon laser-treated eyes for ROP are at a somewhat higher risk of developing secondary cataract; however, the occurrence of cataract has also been reported in diode laser-treated eyes and less so with cryotherapy. A survey performed by Gold7 reported that 62% of the reported cataracts were associated with argon laser, 31% with diode laser, and 7% with cryotherapy. Sanghi et al.8 noted no cataracts in eyes treated with either frequency-doubled Nd:YAG laser or diode laser. Salgado et al.9 reported three eyes with cataracts (two requiring surgery) in a consecutive series of 259 eyes of 184 children treated for threshold or prethreshold ROP with transpupillary diode laser photocoagulation. A study of Bevacizumab in the treatment of patients with prethreshold ROP study reported cataract development in one eye (1%).10
TYPES OF SECONDARY CATARACTS
Transient
Focal opacities (either punctate or vacuolated) may occur at the capsular or subcapsular level. These are generally visually insignificant and often resolve spontaneously.11
Progressive and Visually Significant Lens Opacity without Retinal Detachment
Progressive lens opacification generally leads to total cataract and complete obstruction of the visual axis.12 Most of these eyes have had transpupillary laser treatment or “lens-sparing” vitrectomy. The latent period before cataract develops is reported as 1 to 4 weeks after laser treatment, but it can be as long as 6 months.13 Associated findings may include corneal edema, shallow anterior chamber, pupillary membrane, pigment on the anterior lens surface, iris atrophy, hyphema, posterior synechia, and iris neovascularization.13
Secondary to Retinal Detachment
A cataract develops frequently in eyes with ROP stage 4 or 5 (i.e., partial or total RD). These cataracts differ from the two types of cataracts described above in that their
onset is later. They occur months or years after RD or vitreoretinal surgery, rather than in the early posttreatment time frame. Approximately 15% of children treated by lens-sparing vitrectomy for ROP-related RD develop this type of delayed-onset cataract.14 Associated findings may include angle-closure glaucoma, shallow anterior chamber, corneal opacification, and posterior synechia.13 Knight-Nanan et al.6 reported cataracts in 55% of eyes treated for advanced cicatricial ROP.
onset is later. They occur months or years after RD or vitreoretinal surgery, rather than in the early posttreatment time frame. Approximately 15% of children treated by lens-sparing vitrectomy for ROP-related RD develop this type of delayed-onset cataract.14 Associated findings may include angle-closure glaucoma, shallow anterior chamber, corneal opacification, and posterior synechia.13 Knight-Nanan et al.6 reported cataracts in 55% of eyes treated for advanced cicatricial ROP.
ETIOPATHOGENESIS
Cataract formation after laser photocoagulation has been noted immediately, during the laser treatment, to as long as 99 days after the laser treatment, with most occurring in the first few postoperative weeks.
Anterior Segment Ischemia
Associated clinical findings such as iris and ciliary process atrophy13,15 suggest an ischemic etiology. Lambert et al.13 suggested that thermal injury to the long posterior ciliary arteries had resulted in anterior segment ischemia. This led to total cataract formation and often to eventual phthisis bulbi. We have seen children after photocoagulation for ROP where the entire eye appeared to have suffered an ischemic event. These eyes presented with corneal edema, iris ischemia, and cataract within 24 hours of laser therapy. In our experience, these rare cases are not associated with overly heavy treatment. They occur without warning in eyes with reportedly uneventful laser sessions. The cornea often improves in clarity but remains thickened. The cataract may also appear improved somewhat in appearance. In a few of these eyes, however, severe corneal thickening and opacity, total cataract, hypotony, and retinal ischemia have persisted. In these cases, the prognosis for visual recovery after cataract surgery is poor.
Thermal Injury
Premature infants have much of the tunica vasculosa lentis intact, which may allow for absorption of energy on the lens surface. Hazy vitreous and miosis in these infants may also necessitate higher-power settings. Paysse et al.16 theorized that postlaser cataracts are, in most cases, the result of thermal injury. This results from absorption of laser energy by lens proteins or hemoglobin in the blood circulating through a persistent anterior tunica vasculosa lentis. Thermal cataracts, for the most part, occur in the first postoperative weeks after laser treatment. This hypothesis is further supported by the lower incidence of cataract formation with diode laser compare to argon laser, as this phenomenon of laser energy absorption is likely to be less frequent because of the reduced absorption of diode laser energy by hemoglobin.
Uveal Effusion
Diode laser application in nanophthalmic eyes has been reported to cause uveal effusion that resulted in anterior rotation of the ciliary body and shallowing of the already narrow anterior chamber. The resulting corneolenticular apposition can lead to cataract formation in these eyes.17
Vitreoretinal Pathology
Cataract may be associated with chronic RD even when no intraocular surgery has been performed. In other eyes, the posterior lens capsule may have been breached at the time of vitreoretinal surgery. This can lead to lens hydration and complete cataract.
Phacoantigenic Uveitis
Lambert et al.13 noted iridocyclitis and posterior synechia in eyes with cataract after laser photocoagulation for ROP and theorized that phacoantigenic uveitis could have caused the cataract. They reported one patient with a rent in the posterior lens capsule at the time of cataract surgery when the only prior treatment had been laser therapy. The authors noted that the lens material was liquefied and theorized that microperforations may occur in some eyes during laser therapy.
RISK FACTORS
Argon laser-treated eyes for ROP may be at higher risk of developing secondary cataract compared with diode laser-treated eyes.
Transpupillary laser administration of laser may increase the cataract risk as opposed to a transscleral approach.
Prominent anterior tunica vasculosa lentis may increase the cataract risk. Sufficient laser energy may be absorbed by the persistent lens vasculature to cause thermal injury to the lens.
Inadvertent burns placed on the iris. Energy absorption caused by the iris pigment epithelium can cause heating of the anterior lens.
Confluent laser therapy or heavy laser treatment over the posterior ciliary vessels. A confluent laser pattern may have a higher success rate for regression of ROP than a less confluent laser pattern. However, cataract has been identified as a possible complication of confluent treatment.15 Also, extensive use of laser energy over the posterior ciliary vessels at the 3 o’clock and 9 o’clock positions may add to the risk of anterior segment ischemia and secondary cataract formation.
Vitreoretinal surgery. Cataracts occur more commonly after intraocular surgery.
REVIEW OF THE LITERATURE
Argon Laser Therapy
1992. Drack et al.11 reported transient punctate and comma-shaped opacities at the level of the anterior cortex/lens capsule, associated with a few posterior synechia.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
