Retinopathy of prematurity is a
complex disease process. Researchers and clinicians studying ROP need
a way to communicate with each other about the severity and extent of
this process, as well as a way to objectively measure the effect of
possible risk factors and treatment options. The International
Classification of Retinopathy of Prematurity (ICROP) was designed to
meet this need. It was developed by a group of experts from around the
world, and was published in the Archives of Ophthalmology in 1984
(Vol. 102, pp.1130-1134). The ICROP defines retinopathy by several
distinct criteria: location, extent, stage, and plus disease.
LOCATION
The location of ROP refers to the location relative to the optic
nerve. The retinal vessels normally start their growth at the optic
nerve and gradually move toward the edge of the retina. Vessels that
are farther from the optic nerve (or the closer to the edge of the
retina) are more mature and less concerning. This has been
standardized by dividing the retina into three zones. Zone I is an
area centered on the optic disc and extending from the disc to twice
the distance between the disc and the macula. Zone II is a ring
concentric to Zone I which extends to the nasal ora serrata (the edge
of the retina on the side of the eye toward the nose). Zone III is the
remaining crescent of retina on the temporal (toward the temple) side.
![[diagram of retinal zones]](icrop.jpeg)
This diagram shows the three
retinal zones used to specify location in the ICROP. The zones are
centered on the optic nerve rather than on the center of the retina
(the macula) because the retinal vessels usually grow concentrically
from the nerve head. The temporal crescent of Zone III is usually the
last part of the retina that becomes vascularized.
EXTENT
The extent of ROP is described by how many clock hours of the retina
are involved. For example, if there is retinopathy extending from 1:00
around to 5:00, the extent of ROP is 4 clock hours.
STAGE
Retinopathy of prematurity is a progressive disease. It begins with
some mild changes in the vessels, and may progress on to more severe
changes. The stage of ROP describes how far along in this progression
the vessels have reached.
STAGE 1 ROP
Stage 1 is characterized by a demarcation line between the normal
retina nearer the optic nerve and the non-vascularized retina more
peripherally. The photograph above shows the orange vascularized
retina on the left, and the gray peripheral non-vascularized retina on
the right. A white demarcation line can be seen between the two.
Multiple small abnormally branching vessels can sometimes be seen
leading into the demarcation line.
STAGE 2 ROP
Stage 2 ROP has a ridge of scar tissue and new vessels in place of the
demarcation line. The white line now has width and height, and
occupies some volume. It may take on a pink color as it becomes more
vascularized. Small tufts of new vessels ("popcorn vessels")
may appear posterior to the ridge. In the photograph above, the
neovascular ridge (R) can be seen, as well as a tuft of new vessels
posterior to the ridge (arrowhead).
STAGE 3 ROP
Stage 3 ROP shows an increased size of the vascular ridge (between the
arrowheads in the photograph above), with growth of fibrovascular
tissue on the ridge and extending out into the vitreous. Fibrous scar
tissue is beginning to form in this stage, with attachments between
the vitreous gel and the ridge.
Stage 4 refers to a partial retinal detachment. The scar tissue
associated with the fibrovascular ridge contracts, pulling the retina
away from the wall of the eye. There may also be an exudation of fluid
under the retina, contributing to the detachment. Stage 4 is further
categorized depending upon the location of the retinal detachment. In
Stage 4A, the detachment does not include the macula, and the vision
may be good. In Stage 4B, the macula is detached, and the visual
potential is markedly decreased.
Stage 5 ROP implies a complete retinal detachment, usually with the
retina pulled into a funnel-shaped configuration by the fibrovascular
scar tissue. Eyes with stage 5 ROP usually have no useful vision, even
if surgery is performed to repair the detachment.
PLUS DISEASE
In more florid or severe retinopathy of prematurity, other changes in
blood vessels may occur which are termed "plus disease".
PLUS DISEASE
Plus disease implies dilation and tortuosity of the blood vessels near
the optic nerve. It also includes the growth and dilation of abnormal
blood vessels on the surface of the iris, rigidity of the pupil, and
vitreous haze. The diagnosis of plus disease is usually made based on
the appearance of the vessels near the optic nerve, as compared with
standard retinal photographs. The presence of plus disease suggests a
more fulminant or rapidly progressive course.
Rush disease is a term used to describe ROP in zone I with plus
disease. This group of patients has a more rapid progression of their
ROP, with changes sometimes occurring in days rather than weeks. Eyes
with rush disease tend to have a poorer prognosis than other eyes with
ROP.
USING THE ICROP
Almost any eye with ROP can be described accurately and concisely
using the ICROP. For example, an eye with a slightly elevated
neovascular ridge without fibrovascular tissue growing into the
vitreous, which extends from 7:00 to 11:00 about 4 disc/macula
distances from the disc, and which has dilation and tortuosity of the
vessels near the disc would be described as "4 clock hours of
stage 2 zone 2 ROP with plus disease".
An ICROP description of a given eye also carries some implications
about the severity of disease, the need for treatment, and the
prognosis. For example, stage 3 zone 1 ROP is relatively severe, will
need to be followed closely, and will very likely require laser
treatment. On the other hand, stage 1 zone 3 ROP is much less
worrisome, since this level of ROP almost always regresses
spontaneously.
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Country Hills Eye Center phyician
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