Ajmal Khan Tibbiya College
Plateau iris is a type of narrow angle more commonly seen in younger adults that can lead to chronic angle closure glaucoma. Plateau iris is caused by a narrowing of the anterior chamber angle due to insertion of the iris anteriorly on the ciliary body or displacement of the ciliary body anteriorly, which in turn alters the position of the peripheral iris in relation to the trabecular meshwork (i.e. placing them in apposition).
Plateau iris syndrome is defined as a persistently narrow angle capable of closure despite a patent iridotomy.
Plateau iris is an ocular condition that requires appropriate diagnosis and treatment in order to prevent vision loss.
The term plateau iris was first used in 1958 to describe a unique configuration of the iris.
In 1977, a study of 8 patients who presented with angle closure glaucoma after an iridotomy helped clarify the condition.
In order to avoid confusion, the term plateau iris configuration (PIC) and plateau iris syndrome (PIS) were distinguished.
PIC is a pre-operative condition in which appositional or narrow angle is confirmed by gonioscopy; however, the anterior chamber depth is normal and the iris is flat. In PIC, the iris root angulates forward peripherally and then centrally in a planar fashion.
PIS, on the other hand, is a post-operative condition in which a patent iridotomy has eliminated the relative pupillary block that is normally seen in an appositional angle or primary angle closure glaucoma, but evidence of angle-closure persists without shallowing of the anterior chamber. PIS most commonly occurs in the early postoperative period, however, it can also occur years after surgery.
PIC is characterized by an appositional angle with a flat iris configuration, in contrast to an anterior bowing of the iris seen in a “typical angle closure glaucoma” in which there is a more crowded anterior chamber due to a hyperopic eye (short axial length). In patients with PIC, the iris root is often short and inserted anteriorly on the ciliary face, causing a shallow and narrow angle. With plateau iris configuration, there is a relative pupillary block mechanism.
Plateau iris syndrome is due to an abnormal anterior position of ciliary body. This anterior ciliary body displacement in turn alters the position of the peripheral iris in relation to the trabecular meshwork resulting in obstruction to aqueous outflow. Therefore, the etiology of plateau iris syndrome is distinct from that of most cases of angle closure glaucoma, which is usually caused by a relative pupillary block. PIS may be triggered by spontaneous pupillary dilatation (for e.g. in conditions of darkness) or in response to mydriatic agents.
Plateau iris syndrome is well recognized as a common etiology of angle closure in relatively young patients.
The prevalence of PIS was found to be approximately 32% by UBM after laser peripheral iridotomy (LPI) in a Singapore study in eyes at risk for primary angle closure in individuals greater than 50 years.
In another review, the prevalence of PIS was 64% in individuals less than 60 years old with recurrent symptoms of angle closure despite a peripheral iridotomy or iridectomy.
Patients with PIS tend to be young, female and less hyperopic than those with angle closure glaucoma caused by relative pupillary block.
In a large retrospective analysis by Ritch et al, the mean age of diagnosis for patients with PIS was 35.
Other potential causes of angle closure in young patients include iridociliary cysts, lens-induced angle closure, nanophthalmos, retinopathy of prematurity, uveitis (posterior synechiae), lens subluxation and a variety of other rare clinical conditions.
If the flow is impeded in any way, IOP will rise. In a patient with plateau iris configuration, the iris root is short and the ciliary body processes may be larger and more anteriorly positioned than normal. This results in a mechanical repositioning of the peripheral iris (i.e. “bunching” or focal aggregation of the peripheral iris), thereby crowding the angle and obstructing flow through the trabecular meshwork.
In either case, this anatomic abnormality obstructs the flow of aqueous fluid through the trabecular meshwork causing an increase in IOP and angle-closure glaucoma.
Plateau iris -configuration/-syndrome are anatomical abnormalities that should be kept in the differential diagnosis of patients with narrow angles or appositional angle closure, as the condition has potential to cause permanent vision loss. This condition occurs in a relatively young patient population so screening for plateau iris in young patients with symptoms of angle closure should not be delayed.
The diagnosis of plateau iris is most commonly made in asymptomatic patients on routine examination of the eye.
Patients with plateau iris tend to be female, in their 30-50s, hyperopic and often have a family history of angle-closure glaucoma.
Symptomatic patients present with headaches, eye pain, nausea and vomiting: symptoms that are indicative of an acute rise in IOP.
The patient may also complain of seeing halos around lights or blurring of vision. Symptoms are more likely to occur after dilatation of the pupil.
Slit-lamp examination of patients with plateau iris configuration usually shows a normal anterior chamber depth and a flat iris plane.
A “double-hump sign” on indentation gonioscopy is characteristically seen in this condition. The peripheral “hump” on the iris is caused by the ciliary body propping up the iris root, whereas the central “hump” represents the central third of the iris resting over the surface of the lens.
Ultrasound biomicroscopy (UBM) plays a fundamental role in the diagnosis of PIC/PIS, as this modality can definitely confirm the anatomic abnormalities of the ciliary body. In patients with PIC or PIS, UBM will show anteriorly situated ciliary processes and in some cases a shortened, thickened iris root that is inserted in a more anterior position in the ciliary body.
Other possible diagnoses include:
- Pupillary block (relative or absolute)
- Iridociliary cysts (“Pseudoplateau iris”)
- Peripheral anterior synechiae
- Lens-induced angle closure (“Phacomorphic glaucoma”)
The primary treatment modality for many patients with plateau iris configuration is surgical.
Many clinicians, however, will first treat with miotic agents such as pilocarpine to prevent pupillary dilatation leading upto surgery. Low dose or dilute pilocarpine can produce thinning of iris and facilitate opening of the angle by pulling the iris away from the trabecular meshwork.
Since patients with PIC often have an element of pupillary block, peripheral laser iridotomy is the first surgical intervention performed. A peripheral iridotomy, however, does not change the anatomy of the anterior chamber, so some patients with PIC may still experience a glaucoma crisis (the patient should now be considered PIS, not PIC).
If a peripheral iridotomy is unsuccessful in controlling the IOP (i.e. confirmed PIS), the treatment of choice is argon-laser peripheral iridoplasty (ALPI). This procedure is highly effective in eliminating appositional residual closure caused by PIS.
|PI & ALPI in same eye|
If peripheral iridotomy, ALPI and additional miotic agents fail to adequately control IOP, then surgical procedures such as trabeculectomy, drainage implantation or goniosynechiolysis should be considered.
The prognosis for patients with PIC/PIS is generally good, provided the condition is recognized before vision loss occurs.
Regular follow-up with serial gonioscopy ensures that the proper interventions and treatment modalities are initiated when necessary because angle-closure may develop years after successful iridotomy or iridoplasty.
Routine screening for the development of glaucoma should also be performed.