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Temporal iridotomies may minimize visual side effects
Evidence is mounting in favor of temporal vs. superior iridotomies.
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Most practicing ophthalmologists were trained to position their laser peripheral iridotomies at or immediately adjacent to the 12 o’clock position, but recent evidence has been mounting that this may not be the optimal location to minimize visual side effects. I will summarize the existing literature and then present my experience and pearls for making the switch to temporal laser peripheral iridotomies.
Murphy and Trope first reported the uncommon “perception of a thin line or blurred area after laser iridotomy” and hypothesized that partial coverage of the laser peripheral iridotomy (LPI) by the upper lid was responsible for this complaint. In their response to this report, Weintrab and Berke suggested that the tear meniscus at the edge of the upper lid created a base-up prism effect when overlapping the position of the LPI and that placement of the LPI at the 3 or 9 o’clock position might better serve the patient. In both reports, the authors noted that symptoms appeared to resolve with complete exposure of the LPI by lifting the upper lid.
Ian Conner
Based on these observations, Spaeth and colleagues completed a retrospective review of 172 consecutive eyes that underwent LPIs at Wills Eye. This study systematically evaluated visual complaints at least 1 month after LPI, asking about the presence of “halos, lines, crescents, ghost images, glare, spots, shadows, or blurring,” and recording the location of the LPI in relation to the position of the upper lid. Indeed, these symptoms were reported most frequently in patients with partial coverage of the LPI by the upper lid, but were also reported in patients with either complete coverage or complete exposure of the LPI. Fortunately, overall incidence of symptoms was low, regardless of LPI location.
In 2012, a cohort of 230 eyes within the Zhongshan Angle-Closure Prevention Trial was studied using measurement of retinal straylight (C-Quant, Oculus) and questionnaires at 18 months after LPI. The authors found a correlation between visual disturbance and cataract severity, but did not find any measurable relationship with LPI location.
To this point, however, all published evidence fell in the category of either individual case reports or retrospective analyses. The only prospective study of the effect of LPI position randomized patients scheduled for consecutive LPI to have a superiorly positioned iridotomy in one eye and a temporally placed iridotomy in the other. In 169 patients, the authors found a significant effect of position on incidence of new-onset linear dysphotopsia at 1 month after LPI (10.7% for superior location vs. 2.4% for temporal location). Unfortunately, there was also a moderate effect toward a more painful procedure for the temporal location. There were no differences in other complications between the eyes.
How does this affect my clinical practice?
Based on the recent prospective study and the case reports from the early 1990s, I now perform nearly all of my iridotomies at the temporal location. I avoid performing the laser at exactly 3 or 9 o’clock in order to avoid damage to the long ciliary nerves, which could result in additional pain or pupillary dysfunction. I usually target a crypt just inferior to the 3 or 9 o’clock position, taking care to avoid superficial iris vessels, and have the patient adjust his gaze slightly in the nasal direction in order to place the LPI as peripherally as possible.
Pearls for performing temporal LPIs
It is possible to get really far peripheral with temporal placement of the LPI. It is quite common to directly visualize an elongated ciliary process behind a well-placed temporal iridotomy. It is important to note that the ciliary process will be separated from the posterior iris by a narrow space, it will have a whitish appearance, and it can be mistaken for a deep iris stromal beam. Be cautious about using the YAG laser deep within the temporal iridotomy. Inadvertent YAG of a ciliary process can be quite painful for the patient and will have a tendency to bleed.
Evaluating for patency
Unlike superior LPIs, temporal iridotomies often do not transilluminate well. Most often, this is directly related to the relative position of an elongated ciliary process as described above; the process can even completely obscure the transillumination phenomenon. Fortunately, careful inspection of the iridotomy using a highly magnified slit beam, as well as routine gonioscopy after the procedure, will confirm patency. I actually prefer this diminished transillumination effect; it is likely that it is at least partially responsible for reducing the incidence of dysphotopsia.
I have not noted any difference in perceived pain since making the switch to temporal iridotomies, but I also have not studied this in any detail. The procedure remains well-tolerated in my patient population.
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References:
Congdon N, et al. Ophthalmology. 2012;doi:10.1016/j.ophtha.2012.01.015.Murphy PH, et al. Ophthalmology. 1991;doi:10.1016/S0161-6420(91)32091-8.
Spaeth GL, et al. J Glaucoma. 2005;14(5):364-367.
Vera V, et al. Am J Ophthalmol. 2014;doi:10.1016/j.ajo.2014.02.010.
Weintraub J, et al. Ophthalmology. 1992;doi:10.1016/S0161-6420(92)38516-1.
For more information:
Ian Conner, MD, PhD, is an assistant professor of ophthalmology at UPMC and the University of Pittsburgh. He can be reached at University of Pittsburgh School of Medicine, Eye & Ear Institute, 203 Lothrop St., 8th floor, Pittsburgh, PA 15213; email: connerip@upmc.edu.Disclosure: Conner reports no relevant financial disclosures.