Retinopathy of Prematurity (ROP, Retrolental Fibroplasia)
What is retinopathy of prematurity?
Retrolental Fibroplasia (RLF), or Retinopathy of Prematurity (ROP) as it is also known, is a developmental eye disease in infants that can lead to blindness. It manifests as a developmental eye disorder in pre-term or prematurely-born babies, when retinal detachment and scarring occurs in one or both eyes. It has the potential to cause permanent visual impairment or blindness. In the UK about 16 percent of babies born prematurely and about 65 percent of babies born weighing 1250g or less have ROP.
How does ROP occur and who is affected?
As a baby grows in the womb the retinal blood vessels mature from the 16th week of gestation. These blood vessels grow outward to the borders of the retina, forming the optic nerve to the rear of the eye. Their function is to transport nutrients and oxygen to the eye. Usually retinal development is complete within a month after birth.
However, in premature or underweight babies the blood vessels have not completely formed to the rims of the retina, meaning insufficient oxygen supply to the retinal periphery (outer edges). Irregular blood vessel growth is stimulated by this lack of oxygen, resulting in leaking and causing fibroplasia or scarring. As the scars shrink, the retina is forced to detach from the vitreous and underlying optical tissue layers at the back of the eye. Babies born 31 weeks or less into their gestation period are at risk, as are babies weighing approximately 1250 grams (2¾ pounds) or less.
What causes ROP?
The main cause of ROP is irregular retinal blood vessel development or “fibrovascular proliferation” with scarring and retinal detachment, however, other factors may contribute to progression of ROP, such as:
- Low birth weight.
- Malnutrition or Anaemia.
- Respiratory and breathing difficulties, such as Asthma.
- Other health or eye development conditions.
- Supplemental oxygen exposure (hypoxic), such as in incubators or through blood transfusions.
How does ROP affect overall health?
ROP can lead to degrees of vision loss and blindness. Babies with ROP are at a greater risk of developing other eye conditions into adulthood, such as glaucoma, cataracts, amblyopia (lazy eye), myopia (near-sighted) or strabismus (cross-eyed). Those with ROP experiencing visual impairment may also have visual-related learning and functioning difficulties, which can affect mental health and confidence.
How is ROP diagnosed?
Usually diagnostic testing is performed on premature babies four to six weeks after birth, but may be assessed earlier. There are four parts to the diagnostic screening tests for ROP:
- First, pupillary dilating (mydriatic) eye drops are applied, so that the pupils of the eyes dilate one hour before the eyes are screened. Anaesthetic eye drops are applied if a speculum is used to part the eyelids.
- Second, a small speculum keeps the eyelids apart and an Indirect Ophthalmoscope is used to examine the retina and blood vessels.
- Third, a neonatal indentor may be used for scleral depression to make the peripheral parts of the retina visible for examination, to see how the blood vessels are growing towards the retinal borders.
- Fourth, the growth extent of the retinal blood vessels is assessed along the vascular-avascular border, and scarring is evaluated for retinal detachment.
ROP is diagnosed as an eye disease according to the International Classification of Retinopathy of Prematurity (ICROP). The ICROP stages and retinal responses are monitored for one to three weeks. If not ROP, other eye disorders such as familial exudative vitreoretinopathy and persistent foetal vascular syndrome may be explored for diagnosis.
Is ROP diagnostic screening safe for infants?
Overall ROP diagnostic screening is safe, however, it may cause distress and discomfort and the infant’s heart rate, blood pressure and breathing can be affected temporarily. Sometimes comforters or pacifiers are used to reduce distress, and the testing time is kept to a minimum. Diagnostic screening is done under experienced medical supervision with great care. The alternative to not having ROP screening is the progression of ROP and potential blindness.
How does ROP progress in ICROP stages?
ICROP uses a system of zoning and staging to identify the progression of ROP eye disease. The zoning is based on where the retinal blood vessel or fibrovascular proliferation is located in the retina. There are three zones:
- Zone 1: Retina posterior.
- Zone 2: Annulus and inner border; radius and outer border.
- Zone 3: Retina residual temporal crescent.
The stages refer to the severity of fibrovascular proliferation, as identified through the ophthalmoscopic diagnostic tests, of which there are five stages:
- Stage 1: Presence of demarcation line indicating mild irregular retinal blood vessel growth.
- Stage 2: Elevated ridge indicating a moderate irregular retinal blood vessel growth.
- Stage 3: Visible fibrovascular proliferation, indicating severe ROP onset causing scarring.
- Stage 4: Partial retinal detachment with leaking retinal blood vessels and scarring, which forces retinal detachment.
- Stage 5: Total retinal detachment, indicative of severe ROP and potential blindness.
Other parameters, such as clock hours and presence or absence of Plus Disease, may be included to gauge the extent of blood flow through the retina and ROP eye disease development.
What do the ICROP stages mean for visual impairment and treatment?
If caught in early stages ROP may be treated; however, as the disease progresses to full retinal detachment, the damage to visual impairment may be irreversible. Some infants with Stage 1 diagnosis may not require treatment and the condition may self-heal. Normal vision can also return during Stage 2 without further disease progression.
If Plus Disease is present with enlarged and twisted retinal blood vessels in Stage 3, treatment can be given to prevent retinal detachment. However, if retinal detachment progresses through Stage 4 and 5, severe visual harm and blindness may result. In most cases ROP eye disease in infants is treatable.
How is ROP treated?
Depending on the stage of ROP eye disease development different treatments may apply. ROP is commonly treated with:
- Peripheral retinal ablation, with laser photocoagulation to remove excess retinal blood vessels from the retinal periphery.
- Cryotherapy with probe freezing (largely replaced by laser treatment), which is also used to remove excess retinal blood vessels from the retinal periphery.
- Intravitreal injection with Avastin into Zones 1 and 2.
- Vitrectomy surgery for Stage 4 to remove the scar and replace the vitreous with saline solution.
- Scleral buckling for Stages 4 and 5 of retinal detachment; a silicone band holds the vitreous and prevents retinal detachment.
Both laser and freezing therapy are aimed at removing part of the peripheral retina containing the excess and irregular retinal blood vessels that usually lead to scarring and retinal detachment. Surgery may be required to re-attach the retina after detachment to prevent full central vision loss.
What are the side-effects or risks of ROP treatment?
Cryotherapy is largely replaced by laser treatment because of the resulting side-effects such as inflammation of the eyelids. Whether laser treatment or vitrectomy surgery is used, both surgeries are considered invasive and carry surgical risks, such as bleeding, rupturing and infection.
The treatments do have a risk of side vision loss with an uncertainty of side-effects in the long term. However, when weighed against the effects of Stage 5 retinal detachment, which causes blindness, treatment options may be beneficial in halting or slowing down ROP eye disease progression. Not all babies respond to ROP treatment, meaning that ROP eye disease may progress to blindness.
What is the prognosis for ROP and can it be prevented?
The condition is treatable and may have positive results for restoring vision during Stages 1, 2 and 3. However, not all infants respond to treatment during Stages 4 and 5, in which Plus Disease is present and the risk of blindness is greater. Early ROP screening, diagnosis and treatment in most cases prevents ROP disease from developing and causing visual degeneration. Other preventative measures include:
- Medical monitoring for prematurity, low weight, nutrition and anaemia.
- Avoiding excess oxygen exposure, such as through incubators and blood transfusions.