December 2018

RESIDENTS

EyeWorld journal club
Review of “Can preoperative anterior segment optical coherence tomography predict posterior capsule rupture during phacoemulsification in patients with posterior polar cataract?”


by Benjamin Young, MD, Venkatesh Brahma, MD, Emily Li, MD, Marez Megalla, MD, Andrew Pouw, MD, and Jessica Chow, MD


Jessica Chow, MD, residency director, Yale School of Medicine


Yale School of Medicine residents, from left: Venkatesh Brahma, MD, Emily Li, MD, Benjamin Young, MD, and Marez Megalla, MD
Source: Yale School of Medicine

The question of whether OCT can predict capsular rupture with posterior polar cataracts is answered in this very large series compiled at Aravind. I asked the Yale residents to review this important study that appears in the December issue of JCRS.

—David F. Chang, MD,
EyeWorld journal club editor

Aposterior polar cataract (PPC) is a rare congenital cataract with an incidence of approximately 3 to 5 in every 1000.1 PPCs usually form early in life, either during embryogenesis or during infancy, caused by abnormalities in normal lens development associated with remnants of the hyaloid system.1 Multiple case series have suggested a possible autosomal dominant pattern of inheritance.2–8 Noted to be bilateral in 60–85% of cases,1 they can be visually significant as they usually lie at the nodal point of the eye. PPCs are classically described as a dense, white, thick, discoid opacity in the central aspect of the posterior lens with a whorled appearance, likened to the layers of an onion or a bull’s eye target. Clinically, PPCs are classified into two types: stationary or progressive. Stationary PPCs account for approximately 65% of PPCs and stay stable in size and appearance over time, with minimal change in symptoms. Progressive PPCs account for 35% of PPCs and have enlarging circular radiations with time, thus leading to worsening symptoms. Symptoms include significant glare and halos, which usually improve with mydriasis. The treatment for a visually significant PPC is surgical; however, given the higher risk of posterior capsular (PC) rupture in PPC, cataract extraction poses a challenge for the surgeon.9
The incidence of PC rupture in PPC surgery ranges from 26% to 36% in older studies, which has improved to 4–7% in more recent reports.10 Independent risk factors for PC rupture include PPC >4 mm in diameter and age younger than 40 years.11 In the event of PC rupture, lens fragments can fall posteriorly into the vitreous cavity. Retained lens fragments result in sequelae such as persistent inflammation, vitreous loss, cystoid macular edema, and retinal detachment.
Successful surgical management of PPCs requires careful evaluation and planning at each stage of the process to minimize the risk of posterior capsular rupture and dropped lens. Preoperatively, surgeons should counsel patients in great detail about the risk of lens drop and potential need for additional vitreoretinal surgery. However, until now, there has not been an objective method with which to stratify the risk of this complication.
Kumar et al. assessed the utility of anterior optical coherence tomography (AS-OCT) in preoperatively identifying patients whose PCs are likely to rupture during removal of posterior polar cataracts. This prospective study evaluated 64 eyes from 62 patients of the Aravind Eye Hospital in Pondicherry, India, who carried a diagnosis of PPCs of a maximum of 4 mm diameter and who underwent phacoemulsification cataract surgery. The study excluded patients with factors that may complicate cataract surgery, such as posterior capsular tear identifiable at the slit lamp, pseudoexfoliation, dense, posterior subcapsular or cortical cataract, or previous ocular trauma.
AS-OCT images of the PPCs were obtained and the states of the PCs were assessed by a single observer. Capsules were deemed “intact” if the capsular margin was visualized below the PPC without any defects or discontinuities and “dehiscent” if the contrary was true. All patients had their cataracts removed by a single, experienced surgeon who was masked to the AS-OCT findings.
Of the 64 eyes enrolled in the study, eight eyes (12.5%) showed dehiscent PC on AS-OCT, of which five (7.8%) showed intraoperative PC dehiscence, one of which required pars plana vitrectomy. The three eyes that showed dehiscence on imaging but not intraoperatively were found on review to have a dense plaque causing artifact in one eye and multiple minute areas of PC deficits that caused an interpretation of dehiscence. No eyes had intraoperative PC dehiscence that were not detected on AS-OCT. Based on the above results, AS-OCT was determined to carry the following statistical markers for detecting posterior capsular dehiscence: sensitivity 100%, specificity 94.9%, positive predictive value 62.50%, and negative predictive value 100%.
This paper’s strengths include its prospective nature, large sample size, and use of a single surgeon who was masked to the imaging results. The determination of PC dehiscence was objective and reproducible, though only a single observer was used. In most cases, the authors were able to directly correlate the imaging findings (PC dehiscence) to their intraoperative findings. The high negative predictive value (100%) makes AS-OCT clinically useful in helping clinicians risk stratify their patients with PPC.
Interestingly, 27.5% of the eyes that showed PC dehiscence on AS-OCT did not show intraoperative PC dehiscence. While these numbers were low and still led to excellent specificity, two of the eyes that were falsely read as having PC dehiscence still likely had very thin posterior capsules, which the cataract surgeon may want to be aware of preoperatively.
Some factors may limit the generalizability of this study, which excluded both PPC less than 4 mm in diameter as well as denser cataracts. Older studies have demonstrated that PPCs larger than 4 mm were an independent risk factor.10 Further, increased optical density caused one false positive reading on AS-OCT; evaluating whether denser nuclear cataracts could also contribute to false negatives is therefore important. Additionally, a distinction between the different morphologies of PPC (such as stationary vs. progressive PPC) was not made in this study, nor whether their behavior is the same under AS-OCT.
In summary, this study effectively demonstrates the utility of AS-OCT in assessing the integrity of the posterior capsule in PPC with a high negative predictive value. Further areas of interest include exploring whether knowledge of PC dehiscence by AS-OCT preoperatively can significantly aid the surgeon in avoiding need for vitrectomy, as occurred in one case for the blinded study surgeon. Additionally, a future study could track whether PC dehiscence evolves over time in PPC. If that were the case, it could inform argument for early PPC extraction to prevent intraoperative complications. Regardless, using this study’s results, AS-OCT can more confidently be used to tailor risk counseling patients with PPC preoperatively.

References

1. Kalantan H. Posterior polar cataract: A review. Saudi J Ophthalmol. 2012;26:41–9.
2. Addison PK, et al. Posterior polar cataract is the predominant consequence of a recurrent mutation in the PITX3 gene. Br J Ophthalmol. 2005;89:138–41.
3. Yamada K, et al. Genetically distinct autosomal dominant posterior polar cataract in a four-generation Japanese family. Am J Ophthalmol. 2000;129:159–65.
4. Tulloh CG. Hereditary posterior polar cataract with report of a pedigree. Br J Ophthalmol. 1955;39:374–9.
5. Ionides AC, et al. A locus for autosomal dominant posterior polar cataract on chromosome 1p. Hum Mol Genet. 1997;6:47–51.
6. Bidinost C, et al. Heterozygous and homozygous mutations in PITX3 in a large Lebanese family with posterior polar cataracts and neurodevelopmental abnormalities. Invest Ophthalmol Vis Sci. 2006;47:1274–80.
7. Berry V, et al. Alpha-B crystallin gene (CRYAB) mutation causes dominant congenital posterior polar cataract in humans. Am J Hum Genet. 2001;69:1141–5.
8. Liu M, et al. Identification of a CRYAB mutation associated with autosomal dominant posterior polar cataract in a Chinese family. Invest Ophthalmol Vis Sci. 2006;47:3461–6.
9. Osher RH, et al. Posterior polar cataracts: a predisposition to intraoperative posterior capsular rupture. J Cataract Refractive Surg. 1990;16:157–62.
10. Ionides A, et al. Visual outcome following posterior capsule rupture during cataract surgery. Br J Ophthalmol. 2001;85:222–4.
11. Kapoor CG, et al. Posterior polar cataract: Minimizing risks. Med J Armed Forces India. 2016;72:242–6.

Contact information

Chow
: jessica.chow@yale.edu

Review of “Can preoperative anterior segment optical coherence tomography predict posterior capsule rupture during phacoemulsification in patients with posterior polar cataract?” Review of “Can preoperative anterior segment optical coherence tomography predict posterior capsule rupture
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