PLATEAU IRIS

Guest Author

SHIBRA FAROOQ

Ajmal Khan Tibbiya College

Aligarh, India

INTRODUCTION

Plateau Iris

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.

DISEASE ENTITY

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.

ETIOLOGY

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.

EPIDEMIOLOGY

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.

PATHOPHYSIOLOGY

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.

PRIMARY PREVENTION

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.

DIAGNOSIS

HISTORY

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.

PHYSICAL EXAMINATION

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.

"Double-hump sign"

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.

DIFFERENTIAL DIAGNOSIS

Other possible diagnoses include:

1. Pupillary block (relative or absolute)
2. Iridociliary cysts (“Pseudoplateau iris”)
3. Peripheral anterior synechiae
4. Lens-induced angle closure (“Phacomorphic glaucoma”)
5. Nanophthalmos

MANAGEMENT

MEDICAL THERAPY

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.

SURGERY

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.

PROGNOSIS

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.

PRIMARY CONGENITAL GLAUCOMA

Guest author

SABEEH

Ajmal Khan Tibbiya Colege

Aligarh, India

Introduction

Primary Congenital Glaucoma (PCG) is a potentially blinding disease of children, which if untreated, would result in a lifetime of blindness. It occurs due to obstruction of the drainage of the aqueous humor caused by a primary developmental anomaly at the angle of anterior chamber. Although PCG is the most common glaucoma seen in infancy, it is still an uncommon disease. The variable incidence in various ethnic groups points towards a genetic basis for the disease.

Epidemiology

• The disease varies sustainability in different ethnic groups from 1:1250 births in Slovakian Roms to 1:20,000 in Scandinavian regions.
• In the West, the average incidence is about 1:10,000 births, but appears to be higher in Asians.
• In Saudi Arabia, it is reported to be 1:2500, while Indian's have incidence of 1:3300.
• The disease was responsible for 4.2% of blindness in the pediatric population.

Inheritance

• Most cases of PCG are sporadic in occurrence.

• Recessive inheritance of some cases of PCG is proved by:

1. A high frequency of parental consanguinity.
2. The presence of disease in about 25% of sibs of probands.
3. The presence of the disease in all children of a marriage between 2 affected persons.
4. The occurrence of Glaucoma in collaterals of both parents some families.

Genetic defects

• According to Human Genome Organization (HUGO) Nomenclature Committee, loci for congenital glaucoma are designated by GLC3 and letters are added to distinguish specific loci in order of their discovery.
• Till date, 3 genetic loci have been linked to PCG:
• GLC3A at chromosome locus 2p21.
• GLC3B at chromosome locus 1p36.
• GLC3C at chromosome locus 14g24.3
• Of these only the GLC3A locus has been linked to a specific gene. This gene is called CYP1B1 and is the largest known enzyme of the human cytochrome p450 pathway.
• There are several known missense mutations within the CYP1B1 gene.
• Among these, the mutations identified are:
• G61E, Ter223, P193L, E229K, R390C, R368H.
• A study on the genotype-phenotype correlation of these patients identified the frame shift mutation and R390C homozygous mutation as being associated with very severe disease and poor prognosis regardless of any treatment.

Structural defects and clinical features

• The glaucomas are a heterogeneous group of insidious diseases associated with elevated IOP and optic nerve atrophy.
• Primary Congenital Glaucoma is a specific, inherited developmental defect in the trabecular meshwork and anterior chamber angle.
• The developmental anomalies of the anterior chamber angle prevent drainage of aqueous humor, thereby elevating IOP.
• Elevation of IOP in children younger than 3 years of age causes rapid enlargement of the globe, occurs primarily at the corneo-scleral junction.
• As the cornea and limbus enlarge, the endothelium of the cornea and Descemets membrane are stretched. This stretching can result in a linear rupture of Descemet's membrane known as Haab's striae.
• The Descemet's membrane ruptures may occur acutely causing an influx of aqueous into the stroma and epithelium resulting in sudden corneal edema.

Haab's striae

Clinical features of PCG typically include:

1. Tearing
2. Photophobia
3. Buphthalmos (enlargement of the globe)
4. Clouding of the cornea

More serious consequence of elevated IOP is that it can rapidly lead to axonal loss and permanent visual impairment in untreated children.

Buphthalmos

Management

The management of Congenital Glaucoma starts with parental counseling, which includes discussion for: need for surgery and possibilities of multiple surgeries; the need for lifelong follow up and the combination of problems to be tackled (IOP, amblyopia management, refractive correction, possible keratoplasty).

Panicker and associates have graded the severity of glaucoma depending upon the clinical features as given below in table.

SEVERITY INDEX FOR GRADING PCG

Clinical parameters used for grading	Normal	Mild	Moderate	Severe/Very severe
Corneal diameter	Upto 10.5mm	>10.5-12mm	>12-13mm	>13mm
IOP	Upto 16 mmHg	>16-20 mmHg	>2030 mmHg	>30mmHg
C/D ratio	0.3-0.4	>0.4-0.6	>0.6-0.8	>0.8
Last recorded VA	20/20			<20/400-NPL
Corneal opacity	No edema	Mild edema	Severe edema	Severe edema+Haab’s striae

Examination under anesthesia is an essential part of PCG management. It includes the following examinations:

EUA

Tonometry

General anesthesia usually lowers the IOP, except for ketamine.

The Tono-pen is convenient and easy to use.

The normal IOP in infants under anesthesia is usually in the low teens.

A pressure of 20 mmHg or more should be considered abnormal.

Corneal diameter

Using calipers the corneal diameter measurement should be taken from limbus to a similar point 180-degree away at the opposite limbus.

The 95% ranges of normal corneal diameters are: 9.4 mm to 11 mm at age 1 month, 10.5 mm to 11.7 mm at age 6 months, and 10.8 mm to 12 mm at age 12 months.

In PCG, the diameter of cornea may enlarge to as much as 17 mm.

Changes in the corneal diameter less than 0.5 mm in the follow up examination should be interpreted cautiously.

Gonioscopy

A 14 mm Koeppe lens provides a clear view of the angle of the eye and a hand held microscope with a Barkan light or any type of illuminator is necessary for gonioscopy during anesthesia.

In Congenital Glaucoma the Iris usually is inserted anterior to scleral spur and the angle recess is poorly formed.

Fundoscopy

Dilated fundus examination and disc evaluation are essential in diagnosing congenital glaucoma.

Optic nerve cupping larger than 30% of the disc diameter, especially if asymmetric between two eyes, is strong evidence that the disc is under pressure and may be glaucomatous.

Glaucomatous cupping in infants, unlike adults is usually reversible after normalization of IOP.

The younger the child, the faster is the reversibility.

Surgical treatment

The surgical options include:

Goniotomy

Trabeculectomy

Trabeculectomy with anti-fibrotic agents

Goniotomy

 

Trabeculotomy

A trabeculotomy-trabeculectomy combined surgery has been found to result in more favorable outcomes and many surgeons prefer that approach.

In case of refractory cases not responding to surgery, a repeat surgery is needed.