Exploring subtleties helps ophthalmologists understand postoperative surprises.
Reviewed by Dr Sayoko Moroi.
Plateau iris can be an uncommon diagnostic surprise in some patients with unexpected postoperative challenges and idiosyncratic drug reactions. Dr Sayoko Moroi, chair, and Dr William H. Havener, endowed professor at The Ohio State University Wexner Medical Center in Columbus, Ohio, United States, recently presented surprise cases to alert physicians to the possibilities of plateau iris and what she gleaned from these patients.
Plateau iris is a normal anatomical variant: it is a ciliary body positioned in such a way that it physically changes the anatomy angle. This can obstruct the trabecular meshwork as plateau iris syndrome (PIS), which is a form of primary angle-closure glaucoma (PACG).
According to the 2020 American Academy of Ophthalmology Preferred Practice Pattern for Primary Angle Closure (PAC), there are six PAC phenotypes: PAC suspect, PAC, PACG, acute angle-closure crisis, plateau iris configuration (PIC) and PIS. These differ depending on the degree (or absence) of iridotrabecular contact, presence or absence of anterior synechiae, and the intraocular pressure (IOP) and optic nerve status.
Plateau iris is also a relatively common disorder that occurs in patients with narrow angles treated with laser iridotomy and in patients without glaucoma. PIC occurs more often in hyperopic than myopic eyes.
Anterior chamber (AC) examination may show a shallow or moderate-depth AC, but the iris may “drape” the crystalline lens, with a narrow peripheral AC. Gonioscopy shows a flat central-mid iris, an iris root that has a steep approach into the angle and a double hump sign. High-resolution ultrasound or ultrasound biomicroscopy (UBM), Dr Moroi’s preference, has the advantage of visualising the entire lens and ciliary body compared with anterior-segment optical coherence tomography, which does not have this capability.
Case 1 was a 60-year-old man with healthy eyes with 20/15 bilateral uncorrected visual acuity (VA); the right and left eye IOPs were 14 and 11 mm Hg, respectively, and the angles were open with no sign of plateau iris. In the study in which the man participated as a healthy control, acetazolamide was administered orally.
The next day his VA was 20/25 bilaterally, IOPs were 36 and 35 mm Hg, respectively, and the angles were closed. UBM showed a shallow AC, iris draped over the lens and appositional angle closure.
A longitudinal view showed a ciliochoroidal effusion and a B-scan showed a shallow posterior choroidal effusion. The patient was diagnosed with an acetazolamide-induced ciliochoroidal effusion; the drug was withdrawn, and timolol, prednisolone and atropine were prescribed. Two weeks later the VA and IOPs returned to the baseline levels, according to Dr Moroi.1
In commenting on this case, she compared the appearance on UBM of typical plateau iris, in which there is a steep insertion of the iris into the peripheral angle with the ciliary processes rotated more forwards, with that of atypical plateau iris, in which the iris is inserted on top of the ciliary processes. Another form, PIS, is characterised by iridocorneal contact and no sulcus.
Case 2 was a 56-year-old woman who presented for an opinion about myopic refractive surprise after cataract surgery in her left eye. She received a diagnosis of malignant glaucoma aqueous misdirection. The VA in that eye was 20/25 with approximately 4 D of myopia and an IOP of 16 mm Hg.
Biomicroscopy showed a shallow AC, patent iridotomy and a posterior-chamber IOL with posterior synechiae on the optic. Gonioscopy showed peripheral synechiae to the scleral spur and a PIC.
The VA in the right eye was 20/20, with approximately 2 D of hyperopia and an IOP of 16 mm Hg. Biomicroscopy showed a deep, quiet AC, patent iridotomy and a clear lens. Gonioscopy showed the angle open to the trabecular meshwork and PIC.
A snapshot of the patient’s recent ocular history showed IOPs in both eyes that were uncontrolled; after attempts at control with various procedures, pars plana vitrectomy was performed bilaterally. Ultimately, Dr Moroi recognised the plateau iris, and she released the posterior synechiae on the optic, placed a capsular tension ring and performed endoscopic cyclophotocoagulation (ECP) in the patient’s left eye.
After this intervention, her refraction was plano, since the effective optic position was in the proper plane. The patient refused this treatment in the right eye in favour of corrective lenses.
Case 3 was a 71-year-old woman with open-angle glaucoma who had undergone an uncomplicated phacoemulsification with a single-piece IOL with square haptics implanted in the capsular bag of her right eye. Postoperatively, she had 5 months of ocular pain, blurred vision and elevated IOP, despite multiple attempts to taper corticosteroids. The VA in the right eye was 20/25 and the IOP was 29 mm Hg.
Slit-lamp evaluation showed trace cells, no transillumination defects and haptics within the capsular bag. Gonioscopy showed PIC and a fundus evaluation showed mild cystoid macular oedema.
UBM showed ciliary processes that were rotated forwards; the iris was directly on top of the ciliary process, and the angle was open – all consistent with a plateau iris. UBM also identified what Dr Moroi referred to as “haptic herniation”, by which the square haptic of the IOL compressed the ciliary processes.
The capsular bag over the haptic was seen to be fibrotic on endoscopy during surgery. Because an IOL exchange was considered too dangerous with this fibrosis, Dr Moroi performed ECP to shrink the ciliary processes away from the haptic.
Because of her experience with plateau iris, Dr Moroi observed that patients with a plateau iris may have a smaller interplicata diameter (IPD) compared with controls. In a study2 of 19 healthy control eyes and 37 eyes with plateau iris, 13 of which had angle-closure glaucoma, Dr Moroi and colleagues measured the horizontal and vertical interplicata diameters and found the mean of these to be much smaller in PIC and PAC compared with the controls.
“In eyes with PIC and PIS with smaller IPDs, a single-piece IOL with square haptics in the bag can theoretically touch the ciliary processes and cause uveitis-glaucoma-hyphaema (UGH) syndrome,” Dr Moroi concluded. “In contrast, multipiece IOLs with smaller, round haptics may not cause mechanical trauma on the ciliary processes.”
Dr Moroi’s presentation has several take-aways. She noted that the plateau iris can be missed if it has an atypical appearance, as in case 1. Moreover, the mechanism of acetazolamide-induced ciliochoroidal effusion may be similar to that of topiramate-induced ciliochoroidal effusion.
In a patient with a myopic shift as in case 2, plateau iris may be present. Dr Moroi also explained that a single-piece IOL may cause in-the-bag UGH syndrome. If PIC/PIS was identified previously, a multipiece IOL may be a better choice; if a high-power optic is needed, a single-piece IOL and a small capsular tension ring can be used to assure that the optic position is appropriate.
In addition, Dr Moroi noted that she considers the capsular tension ring places “horizontal tension” on the capsular bag and minimises potential touch between the square haptics of a single-piece IOL and the anteriorly rotated ciliary processes. Lastly, plateau iris is a normal anatomical variant (approximately 20–30% of eyes) and can have clinical consequences due to variation in the ocular biometry measurements.