Retinopathy of Prematurity
Diagnosis and Categorization
The diagnosis of ROP is made by an indirect ophthalmoscopic examination. The complete diagnosis also should have the description of the magnitude of the disease.
An International Classification of Retinopathy of Prematurity (ICROP) was presented in 1984 (and then revised in 2005), which describes the magnitude, in the form of ‘Zones’, ‘Extent’ and ‘Stages’ of the disease and whether ‘Plus disease’ is present or absent.(20). These descriptions help to define which neonates can be observed and which require treatment.


Zone 1 Zone 2 Zone 3
Lies within a circle centred on the disc of radius equal double the distance between the disc and the foveola. Lies outside zone1, bound externally by a circle concentric to that of zone 1, the radius of which is the distance from the disc to the nasal ora serrata It is the temporal crescent of retina which lies outside zone 2.

The extent is described in terms of number of clock hours involved(20).

The more premature the baby, the less of the retina is vascularised. The avascular hypoxic retina is opaque, while well vascularised retina is transparent and the junction between the two has a demarcation line. Branching vessels within the plane of the retina are often seen running till the demarcation line (Stage 1).
If it progresses the line acquires height and volume and now appears like a pink or white ridge (Stage 2).
Continued VEGF production causes extraretinal fibrovascular proliferation, which is recognized by vessels growing from the ridge into the vitreous (Stage3). The Fibrous tissue then begins to contract, exerting a pull on the retina (Stage 4). In advanced disease, the entire retina is detached (Stage 5).

Stage Description
Stage 0 Immature vascularisation, no ROP
Stage 1 Demarcation Line
Stage 2 Ridge ± tufts of fibrovascular proliferation
Stage 3 Extraretinalfibrovascular proliferation
• Mild
• Moderate
• Severe
Stage 4 Subtotal Retinal Detachment
• A. Extrafoveal
• B. Involving the fovea
Stage 5 Total Retinal Detachment

Plus Disease and Preplus Disease
Plus disease was described by International Classification of Retinopathy of Prematurity (ICROP) in 1984, as ROP in which there was engorgement of retinal veins and tortuosity of arterioles(20). It occurs due to vascular shunting through the neovascularisation and indicates severe disease. Other features include vitreous haze, dilated iris vessels, non dilating pupil.
In the 2005 modification of the ICROP the definition of Preplus disease was added, which described dilated tortuous veins, but to a lesser degree than that seen in plus disease(20).

Threshold disease & Prethreshold disease
The definitions of threshold and prethreshold disease are important for decision making regarding treatment.
The multicenter trial for cryotherapy for retinopathy of prematurity (CRYO ROP), defined threshold disease as ‘5 contiguous or 8 cumulative clock hours of stage 3 disease in Zone I or II, with Plus disease’ (21) . Neonates with threshold disease should be treated, as they have a 50% chance to progression to retinal detachment if left untreated.
The Early Treatment of Retinopathy of Prematurity trial (ETROP) explored the need for treatment even before threshold disease and defined Prethreshold disease which is further classified into types 1 & 2 (22).

Type 1 Zone I any stage with plus disease
Zone I any stage 3 without plus disease
Zone II stage 2 or 3 with plus disease
Type 2 ZoneI stage 1 or 2 without plus disease
Zone II stage 3 without plus disease

Aggressive Posterior ROP (APROP)
Along with preplus disease, the 2005 modification of the ICROP also described APROP also called as ‘Rush Disease’. The disease involves the posterior pole and progresses rapidly without necessarily going through the classic stages(20). This disease affects the lowest birth weight babies. The fundus shows ‘brush-like neovascularisation’ with shunting of blood from arterioles to venules such that both become tortuous and dilated and it becomes difficult to differentiate between the two. Since there is rapid progression to stage 5 disease, urgent treatment is warranted(20).

Natural History
80% of the time, ROP regresses spontaneously, with the fibrovascular structures becoming fibrotic. The more florid the disease at the time of involution, the more severe are the cicatricial sequelae(13). The stages of cicatrization are given as follows:-
Stage 1: Shows peripheral retinal disturbances
Stage 2: There is straightening out of the temporal retinal vascular arcades, with peripheral vitreo retinal fibrosis. There is ‘dragging’ of the macula temporally due to the fibrosis.
Stage 3: Excessive fibrosis results in a falciform retinal fold.
Stage 4: Partial retinal detachment.
Stage 5: Complete ring of retro lenticular fibrovascular tissue with total retinal detachment.


Contributor Information and Disclosures

Sasha Mansukhani
(MS – Ophthal) Assistant Lecturer in Ophthalmology, Kamathipura Eye Hospital, Mumbai

First Created : 11/5/2014


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