Ans is 'a' i.e. Laser Photocoagulation Threshold disease in ROP is defined as stage 3+ ROP in Zones 1 or 2 occupying at least five contiguous clock-hours or eight noncontiguous clock-hours of retina.Treatment of threshold disease is Laser Photocoagulation.'Laser therapy has largely replaced cryotherapy because visual and anatomical outcomes are superior and laser induces less myopia. " -Kanski 6/e p610Other options:Antioxidants like vit E and slow reduction in 02 has no role in established ROP (threshold disease in our patient); although both are mentioned in few texts for prevention of ROP and even that is not well proven.Retinal reattachment is required when retina is detached like in stage 4 and 5 while Threshold disease is Stage 3 + disease.Also know:"Low birth weight and decreased gestational age are now considered the primary causative factors for ROP. Supplemental oxygen administration which was for a long time considered as the important causative factor is now considered only a risk factor. " - Khuran Ophthalmology 4/e p264 "ROP is confined to those with a birth weight of under 1.5 kg and/or a gestational age of under 32 wks. "- Parson 21/e P310 The hallmark of retinopathy of prematurity (ROP) is abnormal retinal vasculature. Ophthalmologists diagnose and make decisions about the initial treatment of ROP based on the appearance of the retinal blood vessels. Dilatation and tortuosity of the retinal vessels at the posterior pole is termed 'plus' disease. It is a sign of rapidly progressive ROP and is an indication for early laser ablation of the peripheral avascular retina.Retinopathy of prematurity (ROP)ROP is a bilateral proliferative retinopathy that develops in premature infants due to incomplete vasculogenesis of retina at the time of birth.During normal retinal development, vessels migrate from the optic disc to the ora serrata beginning at 16weeks of gestation. Capillary network is formed differentiating into mature vessels which extend to nasal ora by 36 wks and tangential ora by 39-41 wks.The pathogenesis of ROP begins with premature birth. Exposure of extrauterine environment causes phases of hyperoxia-vasocessation (obliteration of retinal vessels) and hypoxia-Vaso proliferation (neovascularization). VEGF is thought to be the most important molecule involved in the neovascularization.Neovascularization leads to retinal and vitreous changes which ultimately lead to retinal detachment.Classification of ROP:ROP is described using a number of parameters. These are location of the disease into zones (1, 2, and 3), the circumferential extent of the disease based on the clock hours (1-12), the severity of the disease (stage 1-5) and the presence or absence of "Plus Disease".Classification on the basis of severity, ROP is divided into 5 stages:-Stage I- the first sign of ROP (stage 1) is the appearance of a thin, fiat, white structure (termed a demarcation line) at the junction of vascularized retina posteriorly and avascular retina anteriorly.Stage II- the demarcation line develops into a pink or white elevation (ridge) of thickened tissueStage III- proliferation of vessels over the ridge and into vitreous (extra vitreal fibrovascular proliferation)Stage IV- partial retinal detachmentIVa- partial detachment with macular sparing IVb- partial detachment with macula involvedStage V- total retinal detachmentClassification on basis of anatomical location:-Since there is a direct correlation between severity of disease and amount of avascular retina, the location of the border between vascularized and avascular retina is an important prognostic sign.3 zones are divided to describe the location of ROP. Location of the border in zone 1 is the most severe disease and in zone 3 least.Zone 1 is defined as a circle, the center of which is the disc, and the radius of which is twice the distance of the disc to the fovea.Zone 2 is a doughnut-shaped region that extends from the anterior border of Zone 1 to within one disc-diameter of the ora serrata nasally and to the anatomic equator temporally.Zone 3 encompasses the residual temporal retina.Plus disease:- As ROP progresses, more and more shunting occurs in the neovascular tissue at the retinal vascular- avascular junction. This increased retinal vascular blood flow results in dilation and tortuosity of the major retinal arteries and veins in the posterior pole - described as "plus disease". Plus disease is the hallmark of rapidly progressive ROP and is notated by adding a plus sign after the number of the ROP stage.Management:Most of the cases (approx. 80%) of ROP resolve spontaneously, hence intervention is chosen according to the below given protocol.ROP is divided into Threshold and Pre threshold disease.Threshold disease: It is defined as stage 3+ ROP in Zones 1 or 2 occupying at least five contiguous clock-hours or eight noncontiguous clock-hours of retina.Treatment of Threshold disease is - Laser photocoagulation.Pre threshold disease is divided into 2 types:High risk or Type I - treatment is Laser photocoagulationLow risk or Type II - treatment is Weekly or Twice weekly observationType 1 Pre thresholdType 2 Pre thresholdZone I ROP (any stage) + Zone I, Stage 3 Zone II, Stage 2/3 +Zone I, Stage 1/2 - Zone II, Stage 3 -Laser PhotocoagulationWeekly or Twice weekly observationROP diseases less severe than Pre threshold are followed up.In this question, the child with zone 1, stage II 'plus' ROP falls into Pre threshold disease- Type 1 or high risk type, hence Laser Photocoagulation would be the management of choice.