The effect of cataract extraction on intraocular pressure

Transcription

1 REVIEW C URRENT OPINION The effect of cataract extraction on intraocular pressure Mark A. Slabaugh and Philip P. Chen Purpose of review To examine the current literature covering the long-term effect of cataract extraction on intraocular pressure (IOP). Recent findings As a result of the high rate of cataract surgery, the impact on IOP continues to be the subject of multiple studies in different populations. Recent publications include those that distinguish patients with open angles from those with more narrow angles, as well as prospective analyses that address the impact of regression to the mean and other types of bias on the effect of postoperative IOP lowering. Summary There are sufficient data to suggest that cataract surgery provides a lowering effect on IOP in the long term. This effect appears to be proportional to preoperative IOP. Eyes with higher preoperative IOP have the greatest average lowering, whereas eyes with IOP in the lower range of statistically normal tend to have an IOP that is unchanged from baseline or even higher following cataract surgery. In patients with narrow angles, the IOP-lowering effect appears to also be proportional to the degree of anterior chamber deepening induced by cataract surgery. Keywords cataract surgery, glaucoma, intraocular pressure, narrow angles INTRODUCTION Intraocular pressure (IOP) remains the only known modifiable risk factor in the management of glaucoma and is well recognized as a primary risk factor for the development and progression of glaucoma. Long-term beneficial effects of cataract surgery on IOP have been reported for many years, and this subject has particular relevance for patients who have glaucoma or are considered to be at risk for developing glaucoma. Cataract surgery remains one of the most common surgical procedures performed, with approximately 3 million per year in the USA alone [1]. Even a small effect on IOP from cataract surgery could potentially modify the population glaucoma risk in a significant way. At the individual patient level, the effect of cataract extraction or lensectomy on IOP might result from a number of factors, as recent publications have attempted to identify. Preoperative IOP, ocular biometry, angle configuration, lens position and anterior segment pathologies such as pseudoexfoliation or pigment dispersion should guide patient counseling and surgical planning. CATARACT SURGERY IN EYES WITH OPEN ANGLES The evolution from intracapsular cataract extraction (ICCE) to extracapsular cataract extraction (ECCE) and later to scleral tunnel and clear corneal phacoemulsification makes it difficult to pinpoint when the long-term effect of surgery on IOP was first noted. Bigger and Becker [2] reported lower IOP after uncomplicated cataract extraction in glaucoma patients using ICCE in the early 1970s. Hansen et al. [3] later published the effects of ECCE with posterior chamber intraocular lens (PCIOL), a procedure with postoperative anatomic resemblance to current cataract surgery, and noted a significant decrease in IOP 4 months after surgery. In 1992, Department of Ophthalmology, University of Washington, Seattle, Washington, USA Correspondence to Mark Slabaugh, MD, Box , 325 Ninth Ave, Seattle, WA , USA. Tel: ; fax: ; mas12@uw.edu Curr Opin Ophthalmol 2014, 25: DOI: /ICU Volume 25 Number 2 March 2014

2 Cataract extraction effect on intraocular pressure Slabaugh and Chen KEY POINTS IOP prior to cataract surgery is the strongest predictor of postoperative IOP-lowering. In patients with narrow angles, cataract surgery is likely to lower IOP in proportion to the change in anterior chamber volume and depth. In patients with low IOP prior to cataract surgery, additional lowering should not be expected and some of these patients may have a higher IOP after cataract surgery. Steuhl et al. [4] noted a similar outcome in patients with and without glaucoma undergoing ECCE/ PCIOL and hypothesized that this effect was due to a widening of the angle, which they measured using laser tomography. Suzuki et al. [5] described the effects of cataract extraction by phacoemulsification with PCIOL on IOP in 1994 and also noted that this effect appeared to be proportional to the level of preoperative IOP. A later publication by the same authors described the 10-year IOP results of the same procedure and noted that there was a proportional effect on IOP: those having the highest preoperative IOP experienced the most postoperative lowering, whereas those with a low preoperative IOP frequently had a higher postoperative IOP [6]. These early studies recognized several key findings that have been reproduced in more recent studies. First, the effect on IOP in patients with open angles appears to be proportional to the level of preoperative IOP. This proportional effect on IOP has led to some confusion as to whether this finding might in fact be due to regression to the mean [7]. However, several recent studies suggest that the IOP effect is a true finding and not due to statistical error. A report derived from a post-hoc analysis of patients in the Ocular Hypertension Treatment Study (OHTS) demonstrated that the patients who underwent cataract extraction had proportional IOP-lowering [8 && ]. The OHTS had several measures in place to prevent regression to the mean such as multiple preoperative and postoperative IOP measurements performed according to strict guidelines using calibrated equipment. A recent randomized prospective trial designed to evaluate the effect of a trabecular bypass stent placed at the time of phacoemulsification versus phacoemulsification alone provides additional evidence for this finding [9,10]. Enrolled patients underwent medication washout prior to surgery, and the subsequent mean preoperative IOP of 25 mmhg was similar in both groups. At 1-year postoperatively, the cataract extraction-alone group had a mean IOP reduction of 8.5 mmhg, with 35% of patients having restarted ocular hypotensive medications. At 2 years postoperatively, the cataract extraction-alone arm had a sustained mean IOP reduction of 7.4 mmhg, whereas the mean number of medications increased slightly [10]. The absolute IOP reduction in this study was somewhat greater than that seen by other authors, but was confounded by the fact that patients were allowed to restart medications to maintain an IOP less than 21 mmhg. A publication by Yang et al. [11 && ] reported on a trial which prospectively evaluated 999 patients who underwent uncomplicated phacoemulsification and had statistically normal preoperative IOP with postoperative IOP measured at 3 months. They found a proportional effect to the IOP-lowering after cataract surgery when they stratified into five groups based on preoperative IOP. They also reported on the IOP of the fellow nonoperative eyes and showed that the IOP in those eyes was unchanged after surgery, which suggests that the IOP-lowering detected was not due to a statistical phenomenon. The biological basis for a proportional IOP-lowering effect from cataract surgery in patients with open angles is not clear. Poley et al. [12] proposed phacomorphic ocular hypertension as a new term to describe a continuum of lens-induced elevated IOP which may be reversed by lensectomy. A possible mechanism for this phenomenon, as proposed by Johnstone [13], is that the anterior lens zonules are unable to maintain posterior traction on the scleral spur as the lens increases in anteroposterior dimensions throughout life, thus resulting in decreased outflow facility. The strength of this hypothesis is that it does not require iris interference with the trabecular meshwork in these patients with open angles. Rather, it suggests a mechanical effect modulated through scleral spur position and zonular tension: small anatomic changes that may go undetected even with sophisticated anterior segment imaging. The relationship between cataract surgery and IOP appears complex when preoperative IOP is in the statistically normal range. Poley et al. demonstrated that whereas approximately 55% of patients with preoperative IOP between 15 and 17 mmhg had a lower IOP after cataract surgery, 30% had a higher postoperative IOP, and the remainder were unchanged. In the group with preoperative IOP below 15 mmhg, this proportion switched, with approximately 55% of patients having a higher postoperative IOP and 35% having a lower IOP [11 && ]. This finding was replicated in the study by Yang et al. [11 && ], although the point of reversal at which ß 2014 Wolters Kluwer Health Lippincott Williams & Wilkins 123

3 Glaucoma IOP became higher after phacoemulsification occurred at a lower IOP [10]. One might expect that if the IOP-lowering effect of cataract surgery was due solely to an anatomical and mechanical change, patients with low IOP preoperatively would be expected to have a less robust IOP effect or no change rather than an elevation. An alternatively proposed mechanism for the IOP-lowering after cataract extraction in patients with open angles is that trabecular endothelium is remodeled in response to stress from ultrasonic vibrations during phacoemulsification [14]. A related hypothesis that has not been investigated is that the trabecular endothelium undergoes stressinduced remodeling in response to the supraphysiologic IOP that is experienced by the anterior segment during routine phacoemulsification [15,16]. These hypotheses are inadequate as a comprehensive explanation, given that the first studies to report IOPlowering after cataract surgery were on patients undergoing ICCE or ECCE rather than phacoemulsification [2 4]. More work is required to elucidate the pathophysiology of this frequently observed phenomenon. The patients who arguably stand to benefit the most from lensectomy as an IOP-lowering procedure are also those who are most difficult to study, namely those with known glaucomatous optic neuropathy. As previously mentioned, most of these patients are already taking IOP-lowering medications. In the trabecular micro-bypass stent studies, patients underwent medication washout and showed a large subsequent decrease in IOP after phacoemulsification alone. However, applying this methodology clinically to obtain the maximum IOP-lowering effect of cataract surgery in glaucoma patient would be inadvisable. A recent study evaluating open angle glaucoma patients considered to be medically controlled prior to cataract extraction found that the preoperative IOP was the strongest predictor of postoperative IOP change [17]. Notably, 38% of patients had worsened IOP control after phacoemulsification, which is in line with the findings of Poley et al. in untreated patients with statistically normal preoperative IOP. Interestingly, patients with increased preoperative anterior chamber depth received the greatest benefit in IOP reduction from phacoemulsification. CATARACT SURGERY IN EYES WITH NARROW ANGLES The IOP effect of cataract surgery in patients with narrow angles is a subject of recent clinical research and interest. Early reports have suggested that in patients with narrow angles with or without elevated IOP, the level of IOP-lowering after cataract surgery is proportional both to the preoperative IOP and to the resultant angle widening [18 20]. Thus, patients with the narrowest angles preoperatively might be expected to benefit the most from cataract extraction as a single procedure, provided the angle has not become permanently closed with peripheral anterior synechiae. A recent publication by Huang et al. [21 & ] showed that preoperative lens vault as measured by anterior segment optical coherence tomography (AS-OCT) was correlated with IOP reduction, although lens thickness was not evaluated. The previously noted publication by Yang et al. [11 && ] showed that in addition to preoperative IOP, change in IOP after cataract surgery was proportional to lens thickness as well as changes in anterior chamber area and in degree of angle opening as evaluated by AS-OCT. Although that study did not specifically evaluate or stratify patients by angle anatomy, other researchers have shown in an Asian cohort that the increase in anterior chamber depth following cataract surgery is inversely proportional to preoperative anterior chamber depth in patients with occludable angles prior to surgery [22]. Investigators use of anterior segment imaging to describe several properties of the iris, angle anatomy and lens characteristics (vault and thickness) could assist in predicting which patients are the most likely to benefit from cataract surgery in terms of IOP-lowering [11 &&,20,23]. It is important to note that although these studies evaluated patients with narrow angles, they did not include patients with primary angle closure or angle closure glaucoma. Gonioscopy remains indispensable in successfully identifying these patients, whereas AS-OCT may provide additional objective data about angle morphology. Two recently published randomized trials comparing surgical approaches in patients with chronic angle closure have clarified treatment guidelines for eyes that do have synechial closure of the angle or eyes with appositional closure in the presence of a patent laser iridotomy [24 &,25]. In the first group, patients whose IOP was controlled to 21 mmhg or less with medical therapy were randomized to phacoemulsification or combined phacotrabeculectomy. The authors found that patients undergoing combined surgery had a decreased requirement for IOP-lowering medication postoperatively, but concluded that the marginal improvement in IOP control did not warrant the additional surgical risk of a trabeculectomy. Of note, only 1 out of 35 patients (2.9%) in the phacoemulsification-alone group went on to require trabeculectomy during the follow-up period of 2 years Volume 25 Number 2 March 2014

4 Cataract extraction effect on intraocular pressure Slabaugh and Chen In the second trial, patients whose IOP could not be medically controlled were randomized to phacoemulsification alone or trabeculectomy alone. The authors demonstrated that there was significant IOP-lowering after phacoemulsification alone, but that 73% of patients in that arm of the study required medications or trabeculectomy by 2 years. These authors concluded that there was significant benefit from phacoemulsification alone, but that trabeculectomy, despite having relatively more surgical complications, was more effective at controlling IOP. Five patients of 26 (19%) in the phacoemulsification-alone group went on to require trabeculectomy during the follow-up period of 2 years [25]. As these studies demonstrate, the proportional effect of IOP-lowering after cataract surgery does not necessarily extend to patients with closed angles. A plausible biological explanation for this is that only a proportion of the trabecular meshwork may be functionally available postoperatively to mediate the potential IOP-lowering effects of cataract surgery. They also highlight the importance of meticulous static and dynamic gonioscopy to evaluate what proportion of the angle has been permanently closed by peripheral anterior synechiae. CONCLUSION There are many reasons to consider cataract extraction in patients with elevated IOP or glaucoma. First, glaucoma patients derive an excellent visual benefit from the increased acuity and improved contrast sensitivity provided by an artificial lens [26]. The improved vision also allows more accurate visual field monitoring, and a clear optical pathway enhances the quality and reproducibility of any optic nerve imaging. The effect of cataract extraction on IOP is more complex and requires additional preoperative evaluation in order to best predict who is likely to benefit the most. Patients with narrow angles and patients with a high preoperative IOP will often see a lowering of their IOP after cataract surgery performed as a single procedure. This lowering effect is likely to be proportional to the level of preoperative IOP as well as the increase in anterior chamber depth. If the preoperative IOP is already low prior to cataract surgery, additional lowering should not be expected from surgery alone, and patients should be counseled about the risk of a higher postoperative IOP. Acknowledgements None. Conflicts of interest Financial support: Unrestricted departmental grant from Research to Prevent Blindness. No conflicting relationship exists for any author. REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Gollogly HE, Hodge DO, St. Sauver JL, Erie JC. Increasing incidence of cataract surgery: population-based study. J Cataract Refract Surg 2013; 39: Bigger JF, Becker B. Cataracts and primary open-angle glaucoma: the effect of uncomplicated cataract extraction on glaucoma control. Trans Am Acad Ophthalmol Otolaryngol 1971; 75: Hansen TE, Naeser K, Rask KL. A prospective study of intraocular pressure four months after extracapsular cataract extraction with implantation of posterior chamber lenses. J Cataract Refract Surg 1987; 13: Steuhl KP, Marahrens P, Frohn C, Frohn A. Intraocular pressure and anterior chamber depth before and after extracapsular cataract extraction with posterior chamber lens implantation. Ophthalmic Surg 1992; 23: Suzuki R, Tanaka K, Sagara T, Fujiwara N. Reduction of intraocular pressure after phacoemulsification and aspiration with intraocular lens implantation. Ophthalmologica 1994; 208: Suzuki R, Kuroki S, Fujiwara N. Ten-year follow-up of intraocular pressure after phacoemulsification and aspiration with intraocular lens implantation performed by the same surgeon. Ophthalmologica 1997; 211: Shrivastava A, Singh K. The effect of cataract extraction on intraocular pressure. Curr Opin Ophthalmol 2010; 21: && Mansberger SL, Gordon MO, Jampel H, et al. Reduction in intraocular pressure after cataract extraction: The Ocular Hypertension Treatment Study. Ophthalmology 2012; 119: A post-hoc analysis of the patients enrolled in the Ocular Hypertension Treatment Study who underwent cataract surgery during the study period versus those who did not. Patients undergoing cataract surgery (63 eyes of 42 patients) had their IOP reduced from a mean of 23.9 mmhg to a mean of 19.8 mmhg, and this effect was sustained for at least 1 year, and to a lesser extent over 3 years of follow-up. IOP was measured in a controlled, prospective fashion. 9. Samuelson TW, Katz LJ, Wells JM, et al. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology 2011; 118: Craven ER, Katz LJ, Wells JM, Giamporcaro JE, istent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mildto-moderate open-angle glaucoma and cataract: two-year follow-up. J Cat Refract Surg 2012; 38: && Yang HS, Lee J, Choi S. Ocular biometric parameters associated with intraocular pressure reduction after cataract surgery in normal eyes. Am J Ophthalmol 2013; 156: A prospective, observational trial of 999 otherwise normal individuals undergoing cataract extraction in one eye as a single procedure. The mean IOP decreased from 13.5 to 11.9 mmhg, whereas the unoperated fellow eyes were used as a control and showed an insignificant change from 13.6 to 13.4 mmhg in the 3-month follow-up period. The authors found that IOP reduction was correlated to preoperative IOP as well as anterior chamber area change. 12. Poley BJ, Lindstrom RL, Samuelson TW, Schulze R. Intraocular pressure reduction after phacoemulsification with intraocular lens implantation in glaucomatous and nonglaucomatous eyes: evaluation of a causal relationship between the natural lens and open-angle glaucoma. J Cataract Refract Surg 2009; 35: Johnstone MA. The aqueous outflow system as a mechanical pump; evidence from examination of tissue and aqueous movement in human and nonhuman primates. J Glaucoma 2004; 13: Wang N, Chintala SK, Fini ME, Schuman JS. Ultrasound activates the TM ELAM-1/IL-1/NF-kB response: a potential mechanism for intraocular pressure reduction after phacoemulsification. Invest Ophthalmol Vis Sci 2003; 44: Wilbrandt HR, Wilbrandt TH. Evaluation of intraocular pressure fluctuations with differing phacoemulsification approaches. J Cataract Refractive Surg 1993; 19: Tumminia SJ, Mitton KP, Arora J, et al. Mechanical stretch alters the actin cytoskeletal network and signal transduction in human trabecular meshwork cells. Invest Ophthalmol Vis Sci 1998; 39: Slabaugh MA, Bojikian BK, Moore DB, Chen PP. The effect of phacoemulsification on intraocular pressure in medically controlled open angle glaucoma patients. Am J Ophthalmol 2014; 157: ß 2014 Wolters Kluwer Health Lippincott Williams & Wilkins 125

5 Glaucoma 18. Mierzejewski A. Cataract phacoemulsification and intraocular pressure in glaucoma patients. Klin Oczna 2008; 110: Euswas A, Warrasak S. Intraocular pressure control following phacoemulsification in patients with chronic angle closure glaucoma. J Med Assoc Thai 2005; 88 (Suppl 9):S121 S Shin HC, Subrayan V, Tajunisah I. Changes in anterior chamber depth and intraocular pressure after phacoemulsification in eyes with occludable angles. J Cataract Refract Surg 2010; 36: & Huang G, Gonzalez E, Lee R, et al. Association of biometric factors with anterior chamber angle widening and intraocular pressure reduction after uneventful phacoemulsification for cataract. J Cataract Refract Surg 2012; 38: A prospective observational case series of 73 eyes of 73 patients undergoing phacoemulsification. IOP-lowering was related to preoperative lens vault as measured by AS-OCT. 22. Shin HC, Subrayan V, Tajunisah I. Changes in anterior chamber depth and intraocular pressure after phacoemulsification in eyes with occludable angles. J Cataract Refract Surg 2010; 36: Huang G, Gonzalez E, Peng PH, et al. Anterior chamber depth, iridocorneal angle width, and intraocular pressure changes after phacoemulsification: narrow vs. open iridocorneal angles. Arch Ophthalmol 2011; 129: & Tham CC, Kwong YY, Baig N, et al. Phacoemulsification versus trabeculectomy in medically uncontrolled chronic angle-closure glaucoma without cataract. Ophthalmology 2013; 120: Randomized, prospective trial of phacoemulsification (26 eyes) versus trabeculectomy (24eyes) forpatientswith uncontrolledchronicangleclosure. IOP was reduced by 8.4 mmhg in the phacoemulsification arm and 8.9 mmhg in the trabeculectomy arm; five patients in the phacoemulsification arm went on to require trabeculectomy. 25. Tham CC, Kwong YY, Leung DY, et al. Phacoemulsification versus combined phacotrabeculectomy in medically controlled chronic angle closure glaucoma with cataract. Ophthalmology 2008; 115: Musch DC, Gillespie BW, Niziol LM, et al., Collaborative Initial Glaucoma Treatment Study Group. Cataract extraction in the collaborative initial glaucoma treatment study: incidence, risk factors, and the effect of cataract progression and extraction on clinical and quality-of-life outcomes. Arch Ophthalmol 2006; 124: Volume 25 Number 2 March 2014