Persistent Pupillary Membrane
Persistent pupillary membrane(PPM) is a frequently encountered congenital anomaly. It represents remnants of anterior tunica vasculosa lentis and appears as strands of connective tissue bridging the pupillary area. They are usually asymptomatic and of no functional significance. In rare cases, dense membranes can persist and obscure the pupil, causing amblyopia.
Although familial forms have been reported, most cases are sporadic in nature.
Persistent pupillary membrane represents remnants of anterior tunica vasculosa lentis. Embryologically, the iris forms as a solid sheet of mesodermal tissue known as the pupillary membrane. It is composed of vessels derived from anterior ciliary arteries and mesenchyme and lies ventral to the lens. The dorsal posterior hyaloid vessels anastomose with the network of vessels in the pupillary membrane to form tunica vasculosa lentis which provides nutrition to the lens. The pupillary membrane undergoes regression aided by macrophage phagocytosis in the sixth month and disappears completely by the eighth month of gestation. A failure of resorption of pupillary membrane leads to Persistent pupillary membrane. There is evidence that intrauterine stress, particularly from chronic maternal hypertension, may accelerate the disappearance of these membranes. Postnatal PPM undergoes considerable atrophy in the first year of life.
The remnants of pupillary membrane are seen in about 95% of neonates and 20% of adults. They are more common in premature babies. There is no sex predilection and may present unilaterally or bilaterally.
Duke-Elder has Classified PPM into several variants
- Type 1 membranes that are attached solely to the iris
- Type 2 membranes are Iridolenticular adhesions. In a sub-variant of type 2, pigmented dendritic iris stromal melanocytes, singly and in clumps, are situated aberrantly on the anterior lens capsule. These pigmented stars of the anterior lens capsule are often called “chicken tracks”.
- Type 3 membranes, which are attached to the cornea, typically occur in Axenfeld-Rieger syndrome. Pure capsular opacities associated with persistent pupillary membranes or epicapsular stars are very rare. They are congenital in origin, do not affect vision and may be nonaxial.
PPMs are usually asymptomatic except for cases with a pupillary opening of <1.5 mm in which decreased retinal illumination and diffraction results in impaired vision.
Slit lamp appearance of PPM can be variable. Most of the times, it can be seen as single or several lacy strands that partially bridge the pupil. The peripheral portion always inserts into the iris collarette. The central portion may attach to the anterior lens capsule or float with free edges. Iris melanocytes may be observed on the anterior lens capsule forming "pigment stars" or "chicken tracks". Infrequently, extensive sheet of iris membrane occluding the pupil may occur.Rare cases of hyphaema from a strand of PPM have been reported.Rarely, progressive pupillary occlusion may be seen with late angle closure glaucoma.
Diagnosis is clinical. Other tests to be performed are:
Retinoscopy- Lenticular astigmatism if focal lens opacity is present
High frequency ultrasound in extensive membranes may be helpful to evaluate relationship of membranes to lens capsule
Iris angiography- Only 0.3% demonstrate vascular perfusion. Most membranes do not justify assessment with fluorescein angiography.
Associations with PPM include amblyopia, coloboma, anterior polar cataract, strabismus, and anterior segment abnormalities like microcornea, microphthalmos and corneal opacity.
- Post inflammatory synechie
- Accessory Iris membrane (AIM)- also called iris duplication, closely resembles the normal iris tissue in color and thickness and presents a virtual second pseudopupil aperture in the centre.
- Congenital idiopathic microcoria
- Axenfeld–Rieger syndrome
- Peters anomaly
- Iridocorneal endothelium syndrome (ICE)
During the first year of life, most PPMs undergo atrophy and require no treatment. Membranes persisting after one year are less likely to regress spontaneously, increasing the risk of deprivational amblyopia. A 1.5-mm pupillary opening is necessary for adequate retinal stimulation and visual cortex development. Management of PPMs depends on the extent of the membrane, and consequently the size of the pupillary opening.
Small PPMs can be managed conservatively. Mydriatics, refractive correction, and patching for amblyopia have been used successfully in such cases.
Thick, fibrotic membranes may require surgical excision.  Surgery is generally performed in the first weeks or months of life, with good visual prognosis and consists of excision of the pupillary membrane using Vannas or vitreous scissors. However, surgical management is fraught with risks of anesthesia, intraoperative bleeding, intraocular infection, and cataract formation.
Older patients with thin, sparse membranes may be candidates for Nd:YAG laser membrane lysis. Photodisruption of membrane can rarely lead to hyphaema. The procedure also carries the risk of cataract formation, iritis, and pigment dispersion.
- AAO, Basic and Clinical Science Course. Section 6: Pediatric Ophthalmology and Strabismus, 2021-2022.
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