RETINOPATHY OF PREMATURITY - DR. CHAHVEER SINGH BINDRA
INTRODUCTION: Originally designated as retrolental fibroplasias by Terry in 1952 who related it with premature birth. The term ROP was coined by Heath in 1951. It is potentially blinding condition typically affecting preterm neonates of low gestational age and low birth weight. In highly and moderately developed countries, the incidence of ROP is increasing with advancement in neonatal management. It is a disorder of development of retinal blood vessels in premature babies. Normal retinal vascularization happens centrifugally from optic disc to ora. Vascularization up to nasal ora is completed by 8 months (36 weeks) and temporal ora by 9-10 months (39–41 weeks). Out of 26 million annual live births in India, approximately 2 million are <2000 g in weight and are at risk of developing ROP. In India the incidence of ROP is between 38 and 51.9% in low-birth-weight infants. SCREENING: American Academy of Pediatrics guidelines - Infants with birth weight of ≤1500 g, Gestational age of 30 weeks or less, and Infants with birth weight between 1500 and 2000 g or gestational age of >30 weeks with unstable clinical course. Indian scenario - Birth weight <1700 g, Gestational age at birth <34–35 weeks, Exposed to oxygen >30 days, Infants born at<28 weeks and weighing <1200 g are particularly at high risk of developing severe form of ROP, Presence of other factors such as respiratory distress syndrome, sepsis, multiple blood transfusions, multiple births (twins/triplets), apneic episodes, intraventricular hemorrhage increase risk of ROP. In these cases screening should be considered even for babies>37 weeks gestation or >1700 g birth weight The first screening should be done within 4 weeks (30 days) of life in infants with age >28 weeks of gestational age. Screening should be done earlier (2–3 weeks after birth) if gestational age is <28 weeks or birth weight is<1200 g. Screening should be done by an ophthalmologist who is well versed with indirect ophthalmoscopy in ROP babies. Child should be fed 1 hour prior to examination. CLASSIFICATION: The International Classification of Retinopathy of Prematurity (ICROP) was devised by expert ophthalmologists in the field from 11 countries to help more suitably describe the observations of the disease. The original classification in 1984 describes 3 concentric zones of retinal involvement to define the antero-posterior location of the retinopathy. Each zone is centered on the optic disc rather than the macula, since normal retinal growth proceeds forward from the optic disc towards the ora serrata in a systematic fashion. Zone I(posterior pole or inner zone consists of a circle), the radius of which extends from the centre of the optic disc to twice the distance from the centreof the optic disc to the centre of the macula. The radius of this zone subtends an angle of 30 degrees. The limits of the zone are consequently defined as twice the disc-foveal distance in all directions from the optic disc; an arc of 60 degrees. Zone II is the area extending from the edge of zone I peripherally to a point tangential to the nasal ora serrata (at the 3 o clock position in the right eye and the 9 o clock position in the left eye. The temporal edge of zone II cannot be more accurately defined as the anatomic landmarks needed to identify the equator in premature infants are obscured. Zone III is the residual crescent of retina anterior to zone II. By convention zones I and II are considered mutually exclusive. Retinopathy of prematurity should be considered in zone II until it can be confirmed that the nasal most 2 clock hours are vascularised to the ora serrata. STAGING: Plus disease: It is an indicator of severity of the disease and is defined as venous dilation and arterial tortuosity of the posterior pole vessels Pre-plus disease: It is defined as posterior pole vascular dilation and tortuosity which is more than normal but less than plus disease Aggressive posterior ROP: This refers to an uncommon, rapidly progressive, form of ROP previously referred to as “rush disease” or “type 2”ROP. It is characterized by a posterior location, severe plus disease, and flat intraretinal neovascularization. It can progress very fast to stage 5 ROP and blindness, if not intervened early. EARLY TREATMENT OF ROP (ETROP)CLASSIFICATION: FOLLOWUP SCHEDULE: TREATMENT:A. ROLE OF LASER:Since the stimulus for abnormal vessels comes from the avascular retina therefore ablating the peripheral avascular retina is believed to cause regression of the ROP. Laser therapy significantly allows more precision of treatment as well as reduces the unfavorable side effects of the cryotherapy and has more than 90% successful results. The entire avascular retina up to the ora serrata should be ablated with near confluent burns (0.5–1 burn width apart) up to the ridge. Heart rate and apnea spells should be monitored throughout the laser. Follow-up visits after laser treatment are usually weekly till the ROP regresses and involution of all tractional elements is seen and vascularization reaches the temporal ora B. ROLE OF ANTI VEGF: VEGF is needed in premature babies for the normal organogenesis and vasculogenesis. Also systemic absorption may cause vascular development delay in other organs in these premature babies - not recommended as the first-line therapy. The follow-up period after mono therapy is unpredictable as there can be a recurrence of neovascularization even beyond 54 weeks of post gestational age. It is recommended that follow-up should be continued till there is no evidence of tractional elements and the vascularization reaches ora. In Zone 1 ROP, the Laser treatment outcomes are poorer. Treatment with anti-VEGF followed by a 4–5 days later with laser treatment in these cases has improved the efficacy of laser along with a reduced need for extensive laser especially at the posterior pole Present indications for anti-VEGF in ROP : Primary therapy for aggressive posterior zone 1 disease (APROP), Aggressive anterior ROP or media haze due to aggressive posterior disease to improve visualization for laser treatment, Failed laser treatment leading to persistent neovascularization, tractional elements or tractional retinal detachment prior to surgery C. ROLE OF SURGERY: Surgery is done for tractional retinal detachment (TRD) repair as seen in Stages 4 and 5 ROP. The aim for surgical intervention in Stage 4 ROP is to prevent progression of retinal detachment. Lens sparing vitrectomy has shown promising results in Stages 4A and 4B. CONCLUSION: Considering the poor outcome of surgery in end stage ROP timely intervention in the form of laser treatment is the best treatment option. There is need to increase the awareness of the disease to make sure these babies can be treated on time.