Man presents with visual complaints after laser peripheral iridotomy in left eye

The patient had narrow angles and was seeking a second opinion regarding laser iridotomy in his right eye.

Issue: May 25, 2011

ByLaurel N. Vuong, MD

ByCynthia G. Mattox, MD

Priti Batta

Namrata Nandakumar

A 61-year-old man diagnosed as a glaucoma suspect with narrow angles presented to the New England Eye Center.

The man had visual complaints of seeing horizontal streaks of light in his left eye since undergoing a laser peripheral iridotomy at an outside hospital. The streaks of light were seen in all types of lighting and were worse during nighttime driving. He was, however, asymptomatic in total darkness. The patient was also seeking a second opinion regarding management of his narrow angles and was hesitant to proceed with a laser iridotomy in his fellow eye.

History

The patient’s ocular history was significant for bilateral increased cup-to-disc ratios, for which he had been followed since 1987. Retinal nerve fiber layer measurements and Humphrey visual fields had been normal since his diagnosis. The patient was also found to have narrow angles in both eyes and underwent a laser peripheral iridotomy (LPI) in the left eye 1 month before his presentation. His medical history was significant for migraines, hypertension and borderline diabetes. The patient was taking Accupril (quinapril HCl tablets, Pfizer) for his blood pressure.

Examination

On exam, the patient’s best corrected visual acuity was 20/30 in the right eye and 20/25 in the left eye. Pupils were equal and reactive to light with no afferent pupillary defect. IOP was 19 mm Hg in the right eye and 17 mm Hg in the left eye, with a historical maximum of 23 mm Hg and 22 mm Hg, respectively. Pachymetry was thickened at 635 µm in the right eye and 632 µm in the left eye. Extraocular movements were full bilaterally. Slit lamp examination of the iris revealed deep anterior chambers centrally and no transillumination defects or pseudoexfoliation deposits. A peripheral iridotomy site was noted between the 11 and 12 o’clock position in the left eye (Figure 1). Trace nuclear sclerosis cataracts were seen bilaterally. Gonioscopy revealed a steep approach to the right angle with only anterior trabecular meshwork visible, and it was compressible to posterior trabecular meshwork throughout using dynamic gonioscopy. The angle was open to the scleral spur in the left eye. An undilated fundus exam showed a cup-to-disc ratio of about 0.75 and flat macula in both eyes.

Figure 1. Anterior segment photograph of the left eye showing laser peripheral iridotomy in the 11 to 12 o’clock position.

Images: Vuong LN and Mattox C

What is your diagnosis?

Patient with narrow angles

Based on the temporal relationship between the LPI and the streaks of light the patient was seeing, the LPI is the likely source of the visual disturbance. The actual iridotomy and LPI-related complications, including retinal detachment, posterior vitreous detachments, and refractive changes to the cornea or lens from the laser, are part of the differential. The patient’s history of migraines could also play a role.

Diagnosis and treatment

After observing the position of the LPI in the left eye and the patient’s natural lid position, it was determined that the iridotomy itself was the reason for the patient’s visual disturbance. A number of articles studying similar complaints and LPI position found that many superior LPIs near the lid margin form a tear film meniscus that causes a prismatic effect refracting light rays toward and through the LPI site. The effect is resolved when the lid is lifted away from the LPI, and this was true for our patient.

Many patients who experience this side effect after poorly positioned LPIs are reassured to understand that the dysphotopsia is not indicative of a serious condition. Patients can be offered a colored contact lens to block the passage of light through the LPI. However, over time, the lid position may naturally lower and cover the LPI. Our patient chose no further treatment.

Taking into account the patient’s lid position (Figure 2), an LPI was placed at the 9 o’clock position to treat the narrow angle in the right eye. At his 1 month follow-up visit, the patient had no visual complaints and had not developed any dysphotopsia associated with the LPI. However, repeat gonioscopy revealed a persistently narrow angle that opened only to the anterior trabecular meshwork inferiorly and nasally and barely to the posterior trabecular meshwork superiorly and temporally.

Figure 2. External photograph of both eyes, showing upper eyelid margin position.

Figure 3. Ultrasound biomicroscopy of the right eye revealing iridociliary contact consistent with plateau iris syndrome.

Persistent narrow angle after a successful LPI could indicate an incomplete LPI or a clot obscuring the opening. Peripheral anterior synechiae could be present. Structural or anatomical variations, such as plateau iris, ciliary body or iris cysts, could be pushing the peripheral iris anteriorly into the angle. Medications such as Topamax (topiramate, Ortho-McNeil-Janssen Pharmaceuticals), which can cause uveal effusion, should also be considered. Rare conditions such as aqueous misdirection or disruption of the lens capsule causing a rapidly progressive cataract could also cause narrow angles, although the anterior chamber depth would show progressive shallowing in these cases.

The iridotomy was found to be patent. The patient had neither mature cataracts nor was he taking any medications that could cause uveal effusion. Ultrasound biomicroscopy (UBM) was performed to assess any structural variation, and the patient was diagnosed with plateau iris based on the iridociliary contact that is typically seen with this condition (Figure 3).

Plateau iris is the cause of more than 50% of recurrent angle closure in younger patients, generally more women than men and in hyperopic patients. The diagnosis is suspected when the angle does not open after an LPI is placed. Anatomically, in plateau iris, the pars plicata is larger and anteriorly placed; thus, the iris root is inserted anteriorly on the ciliary face, and the ciliary sulcus is absent. This anatomy results in an iridociliary contact that pushes the peripheral iris anteriorly into the angle.

Although UBM is the best way to make the diagnosis, the slit lamp exam and gonioscopy can also be revealing. On the slit lamp exam, the anterior chamber depth is normal centrally, but there is a flat or convex iris surface peripherally. On gonioscopy, the angle appears narrowed or closed, but there is a sharp drop-off peripherally. With compression, a double hump configuration appears, with the peripheral hump corresponding to the ciliary body propping up the iris root and the central hump corresponding to the iris resting over the anterior lens surface. Plateau iris occurs in two subtypes: the complete syndrome, in which the angle becomes occluded to the upper trabecular meshwork or Schwalbe’s line and there is corresponding acute elevation of IOP, and the incomplete syndrome, which is more common and the angle is occludable to mid-level and the IOP is unchanged. These patients are more likely to develop peripheral anterior synechiae or damage to the trabecular meshwork from constant chafing and are at risk for eventually developing chronic angle closure glaucoma.

Untreated plateau iris has a component of pupillary block that should be treated with a peripheral iridotomy first. In some plateau iris patients, the angle will be sufficiently opened after LPI and they can simply be monitored with regular exams and gonioscopy. However, if the angle remains narrow where the posterior trabecular meshwork is mostly obscured, further treatment should be considered. Argon laser iridoplasty is often a successful treatment for plateau iris. Long-duration large spot size laser burns should be applied to the far peripheral iris. Properly applied, the laser applications cause stromal shrinkage, which widens the angle. Medical management with low-dose pilocarpine will induce miosis and thin the iris, allowing for the angle to open, and it is particularly useful in lightly colored irides that often do not absorb laser energy well. Cataract extraction will open the angle in plateau iris patients, and even clear lens extraction may be considered in select cases. In severe cases of plateau iris syndrome, ciliary process shrinkage with endoscopic cyclophotocoagulation at the time of lens removal can be effective. If angle closure glaucoma is persistent or develops after these treatments, surgical choices include goniosynechialysis, trabeculectomy or tube shunts.

In the case of our patient, he underwent argon laser iridoplasty in his right eye with successful widening of the angle. Because the angle in the left eye was open after LPI, he did not require additional treatment in that eye but will continue to be monitored.

Summary

Lid position should always be inspected before an LPI to prevent unwanted visual disturbances from lid margin-tear film meniscus, causing a prismatic effect refracting light rays through the LPI site. The lid position should be ascertained before apraclonidine pretreatment, as the drop causes lid retraction. LPI position at the 3 or 9 o’clock position is preferable in avoiding this visual complaint. If the patient experiences visual disturbance, a color contact lens may be placed to block light entering through the iridotomy.

All narrow angles should be treated with an LPI to prevent acute angle closure from pupillary block. If the angle, however, does not widen after an LPI, careful gonioscopy and UBM should be performed to determine any anatomical reasons for the narrow angle. Plateau iris is diagnosed on UBM when iridociliary contact is seen. Argon laser iridoplasty is typically performed to shrink the peripheral iris stroma and thus widen the angle.

References:

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Laurel N. Vuong, MD, and Cynthia Mattox, MD, can be reached at New England Eye Center, Tufts University School of Medicine, 750 Washington St., Box 450, Boston, MA 02111; 617-636-4219; fax: 617-636-4866; website: www.neec.com.

Edited by Priti Batta, MD, and Namrata Nandakumar, MD. Drs. Batta and Nandakumar can be reached at New England Eye Center, Tufts University School of Medicine, 750 Washington St., Box 450, Boston, MA 02111; 617-636-4219; fax: 617-636-4866; website: www.neec.com.

Disclosure: No products or companies are mentioned that would require financial disclosure.