Lecture: International Classification of ROP or ICROP (3rd Edition)

In this lecture, Dr. Chan looks back at the previous editions of ICROP and presents the 3rd Edition of the International Classification of ROP.

Lecturers: Dr. R.V. Paul Chan, Illinois Eye and Ear Infirmary, Illinois, United States


[Paul] I’d like to thank Orbis International for giving me the opportunity to present to you today the International Classification of ROP, third edition. I’m Paul Chan, I’m the chair of the department of ophthalmology and visual sciences at the Illinois Eye and Ear Infirmary at the University of Illinois at Chicago. I also serve as the chair for the ROP committee for IPOS, the International Pediatric Ophthalmology and Strabismus Council.

I want to thank the Knights Templar Eye Foundation and IPOS for their generous support for bringing us all together for this update.

First and foremost, I want to thank the incredible group of people who came together from around the world to bring us this ICROP Third Edition, really phenomenal.

Let’s look back, almost 30 years ago, in 1984 with the original ICROP are bringing us zone, stage, plus disease and then retinal detachment classification in 1987. And then in 2005, discussion around aggressive posterior ROP, pre-plus disease, and regression of ROP. Now 16 years later, actually 15 years later, bringing together this group to discuss an updated classification.

Why now? Over the years, there’s been a lot of progress and there’s been an evolution around treatment and also diagnosis. Especially with the advent of anti-VEGF therapy, which is being used around the world, in addition to laser, and also the many new imaging techniques such as OCT, OCTA, fluorescein angiography, and, of course, digital imaging that is being widely used.

There’s also been a lot that we’ve learned around aggressive posterior ROP and showing that there can be discrepancies around the disease based on expert diagnosis. In addition, APROP may look different in different populations. In resource-limited areas heavier and older babies may develop an aggressive type of disease that may not necessarily be so posterior. Our understanding of plus disease has also evolved with the advent of artificial intelligence algorithms and just our understanding around what plus disease is. I think there’s an important discussion around this as well.

Very importantly, the need to discuss what is reactivation, what is recurrence? As well as progression of the disease, especially with the use of anti-VEGF. When you look back at the literature and you see the reports around reactivation, especially after anti-VEGF treatment, many people have presented different definitions and I think it’s important going forward, especially for the management of children, to have some consensus or definitions around reactivation of disease.

Around 2019, the group came together, the group was chaired by Dr. Michael Chang who’s now director of the National Eye Institute. Excellent international representation, 34 ophthalmologists from six continents, 20 retina, 14 pediatric ophthalmology, 22 male and 12 female. These are the main topics that we discussed and worked through: APROP and AROP, ROP progression, reactivation, discussion around stage five disease, persisting avascular retina, vascular anomalies, description around posterior zone II and a notch, and of course, very importantly, plus disease.

When thinking about progressive posterior ROP, as we originally described, this would typically affect the smallest and most premature infants. But as I have mentioned earlier, we can see aggressive disease in older and heavier babies in certain areas of the world. And so we agreed on calling this aggressive ROP with the diagnostic features being the tempo of disease, the appearance of the vascular abnormalities, and not specifically tying this to location of disease.

Reactivation, very importantly, which can occur with laser, and also with anti-VEGF, but has become put in the forefront with the use of anti-VEGF therapy. How do we describe it as recurrent vascular dilation and tortuosity, and the presence of extratretinal vessels? And you can see here the descriptions around it.

Stage four, stage five classification. What is new in this update is the separation of stage five into three: 5A, 5B, and 5C. And this may have utility as we think through clinical trials going forward for surgical outcomes.

Persistent avascular retina and vascular anomalies can occur with or without treatment. And it’s very important to describe this and to document it. Avascular retina can be prone to retinal thinning, lattice-like changes, and may be associated with retinal detachments later in life. And I think, as many of the colleagues and partners in our field have described, after anti-VEGF therapy, you can develop some avascular anomalies in the periphery after anti-VEGF treatment.

Also presented is the discussion around documenting posterior zone II. You can see this new diagram that’s now being published describing what posterior zone II is. Describing the notch, if, for example, you have zone I secondary to a notch, you should document that. And also the recognition of plus disease and pre-plus as a continuous spectrum disease. Regarding the notch, you can see here describes an incursion by the ROP lesion of 1 to 2 clock hours along the horizontal meridian into a more posterior zone than the remainder of the retinopathy. And if that’s the case then you would document this as secondary to notch.

Plus disease, very importantly, we’ve often described it as just plus or no plus and then in 2005 as pre-plus. Here we’re acknowledging that it is a spectrum disease in that it’s determined from the vessels within zone I. Also a discussion around the vascular engorgement of the iris, poor pupillary dilation, poor peripheral retinal vascular engorgement with vitreous haze and so forth, not necessarily needed for plus disease diagnosis.

In summary, this is what is most relevant and new to this update. The discussion around APROP and AROP, details regarding regression and the reactivation of disease, further categorization of stage five ROP, descriptions around persistent avascular retina and vascular anomalies. Acknowledgment of the notch and describing the notch in posterior zone II, and, of course, very importantly, the plus disease spectrum. If you’re interested in reading the paper, you can scan this QR code here and you can download the paper, it’s open access. There’s also a very nice editorial by Dr. Michael Repka, which I think is very relevant and would be good to read as well.

Thank you for your attention and, again, I appreciate the opportunity by Orbis International to present the updates to the International Classification for ROP. Thank you.

November 23, 2021

Last Updated: October 31, 2022

1 thought on “Lecture: International Classification of ROP or ICROP (3rd Edition)”

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