Introduction

Since its introduction in 2005, trabectome surgery has become a well-accepted treatment for open-angle glaucoma [1]. Its decreases in intraocular pressure (IOP) have been shown in several studies [1–3]. Multiple authors have reported the possibility of combining trabectome surgery with cataract extraction [3–5]. Because the surgical approach through a single clear-cornea incision is the same for both procedures, and comorbidity of glaucoma with cataracts (especially in the older population) is common, combined surgery seems to be a reasonable option. It has recently been shown that combined trabectome and cataract surgery shows no significantly higher risks or postoperative complications than a solitary trabectome surgery. Additionally, this combination did not affect the mean decrease of IOP lowering [3, 6]. In pseudo-exfoliation glaucoma, the mean IOP has been shown to decrease more than after the solitary trabectome procedure [7].

To our knowledge, no study to date has examined the outcomes and possible side effects of the combined surgery, such as a lower precision in matching the targeted refraction, intra- or postoperative complications, including posterior capsule rupture, cystoid macular edema, or even endophthalmitis, in comparison with cataract surgery alone.

In this report, we will address these concerns and evaluate the complications and refractive outcomes of combined trabectome-cataract surgery compared to a cataract-alone procedure.

Methods and materials

Ethics statement: This retrospective observational study was approved by the local ethics committee (University of Freiburg Ethics Committee No. 235/10_160678) and followed the regulations of GCP and the Declaration of Helsinki.

We included 137 eyes of 121 patients from a total of 185 eyes and 153 patients who underwent combined cataract-trabectome surgery at the University Eye Hospital in Freiburg, Germany, by two experienced trabectome and cataract surgeons. A total of 48 eyes were excluded due to missing follow-up examinations. Biometry was performed using a partial coherence interferometer (IOL Master, Carl Zeiss AG, Oberkochen, Germany). An intraocular lens (IOL) power calculation was performed using the SRK/T formula for axial length in the range of 21 mm up to 26 mm (131 eyes). For six eyes, that exceeded 26 mm in length, the Haigis formula was used. No eye was shorter than 21 mm. The IOL types used were the Alcon SA60AT (n = 69), Alcon MA60AC (n = 2), Alcon SN60WF (n = 2), and Zeiss CT Asphina 409M (n = 64). Targeted refraction for 129 eyes was zero D (diopters), −2D for six eyes, and -1D for two eyes. Trabectome surgery was performed over 100 up to 120 degrees through a clear-cornea incision with a width of 1.8 mm which was then widened up to 2.2 mm for cataract surgery.

The refractive outcome was determined as the spherical equivalent calculated from subjective refraction following a basic autorefractive measurement at least 2 months after surgery. Herein, the best corrected visual acuity (BCVA) was determined. For all patients, intra- or postoperative complications were recorded during in-house follow-up examinations or were reported by external ophthalmologists who took care of the patients after surgery.

As a control group for patients who underwent cataract surgery alone, we compared our data to a quality control database of the postoperative results of our outpatient surgery department, as documented in the Augennetz Südbaden. In total, the data of 1,704 patients were available, including postoperative refraction, BCVA, and intra- or postoperative complications. All of these surgeries were performed by a total of ten surgeons through a clear-cornea incision with a width of 2.2 mm.

The difference of the target refraction and the spherical equivalent of the final refraction was calculated to determine the absolute biometry prediction error (BPE). IOL power calculation was performed the same way that it was done for combined surgery with the SRK/T formula for axial lengths within the range of 21 mm up to 26 mm. Shorter or longer eyes were calculated using the Haigis formula.

All calculations and statistics were performed using the R program (R Foundation for Statistical Computing).

Results

Refraction

Mean axial length for the 137 eyes that underwent combined surgery was 23.60 mm (SD 1.35; SE 0.11; range 21.12 – 29.91 mm).

The mean biometry prediction error (BPE), given as absolute value, for all 137 examined eyes was 0.53 D (standard deviation (SD) 0.44; standard error (SE) 0.04; range −1.47 to 2.23). In 18 eyes, the BPE was larger than the range of +/−1D (10 times with Alcon SA60AT, four times with Zeiss CT Asphina 409M, two times with Alcon MA60AC), whereas for three eyes, we found a biometry error exceeding +/−2D. (Alcon MA60AC, Alcon SA60AT, Zeiss CT Asphina 409M). The BPE was divided into subgroups of 0.5D, 1D, 1.5D, and 2D and is shown in Table 1.

Table 1 Biometry prediction error (BPE) for combined surgery
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BPEs for the different lens types that were implanted are shown in Table 2. Overall, there were no significant differences between the groups of SA60AT and CT Asphina 409M in the BPE (p = 0.36). The mean BPEs for SA60AT were 0.55 D (SD 0.44; SE 0.05; range −1.47 to 1.67), 0.48 D (SD 0.38; SE 0.04; range −1.47 to 2.23) for CT Asphina 409M and 0.98 D (SD 0.89; SE 0.44; range −0.25 to 2.16) for the group of other lens types (MA60AC, SN60WF). Both patients with an implanted sulcus-based MA60AC had a BPE higher than 1D (2.16 D and 1.19 D).

Table 2 Biometry prediction error (BPE) for different lens types in combined surgery
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BPEs for different types of glaucoma entities are shown in Table 3. There were no significant differences between the two large groups of primary open-angle glaucoma (POAG, n = 79) and pseudo-exfoliation glaucoma (PEX, n = 47) (p = 0.26). A two-sample t test power calculation was performed (data not shown); the power of the test (POAG vs. PEX) was 0.1. The mean BPE for POAG was 0.51 D (SD 0.42; SE 0.04; range −1.47 to 2.23); for PEX, 0.60 D (SD 0.47, SE 0.06; −1.3 to 2.16); and for the other glaucoma entities (myopic glaucoma, normal tension glaucoma, uveitis-associated glaucoma, and ocular hypertension), 0.41 D (SD 0.25; SE 0.07; range −0.39 to 0.69).

Table 3 Biometry prediction error (BPE) for different glaucoma entities (primary open-angle glaucoma (POAG), pseudo-exfoliation glaucoma (PEX))
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Corneal astigmatism pre- and postoperatively was compared within and between both groups and showed only partially statistical but no clinical relevance with differences at about 0.1 D (data not shown).

Visual acuity

To determine the visual acuity, patients with ocular comorbidities other than glaucoma were excluded. This group consisted mainly of patients with age-related macular disease and a history of retinal vessel occlusion or retinal detachment. The mean best corrected visual acuity (BCVA) over the 118 examined glaucoma-only eyes was 0.81 (SD 0.23; SE 0.02; range 0.02 to 1). Table 4 shows the outcomes of the BCVA.

Table 4 Best corrected visual outcome (BCVA) in combined surgery (n = 118)
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Complications

During two surgeries, a rupture of the posterior capsule occurred. Therefore, a sulcus-based IOL (MA60AC) had to be implanted.

A clinically significant postoperative cystoid macular edema (loss of visual acuity, edema in macular optical coherence tomography) was found in three patients (2.2 %). Two of these patients had pseudo-exfoliation glaucoma, and one had primary open-angle glaucoma. Local corticosteroid therapy, non-steroidal anti-inflammatory eyedrops, and systemic acetazolamide were prescribed over 6 weeks. Macular edema and visual acuity improved in all three cases. Cystoid macular edema was not associated with rupture of the posterior capsule.

In none of the above-described patients did postoperative infections or even a case of endophthalmitis occur. No expulsive bleeding was observed either. Slight bleeding into the anterior chamber occurred almost regularly and was not observed as a complication after surgery.

Comparison with cataract surgery

For the 1,704 eyes that underwent outpatient cataract surgery, complete follow-up data are available. Mean biometry prediction error for these eyes was 0.48 D (SD 0.51; SE 0.01; range −4 to 5.13). Best corrected visual acuities mean was 0.78 (SD 0.22; SE 0.01; range 0.01 to 1). Mean axial length for a sample of 837 eyes was 23.26 mm (SD 0.69; range 17.16 – 27.54 mm). Table 5 shows the comparison between the two groups. No significant difference was observed concerning BPE or BCVA.

Table 5 Comparison against cataract surgery for the biometry prediction error (BPE), best corrected visual acuity (BCVA), and macular edema
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Discussion

Prediction of refractive outcomes

Postoperative refraction is important for patients undergoing cataract surgery, regardless of whether they receive solitary cataract or combined procedures. It is possible that trabectome surgery puts patients at an increased risk of missing the target refraction.

Compared to other refractive outcome studies, our results match those in the current literature. A BPE within ±1D could be achieved in 86.9 % of our cases. The results in unselected groups of patients undergoing cataract surgery underlie some variations. Zadi et al. achieved 82.1 % within the range of ±1D in their study from 2007 [8] on 1,000 patients. A Swedish report from 2008 included more than 23,000 patients and found that 83.8 % of the patients were within ±1D of a biometric error [9]. In 2009, Gale et al. proposed benchmarks of 85 % of patients to achieve a final spherical equivalent within ±1D of the predicted figure and 55 % of the patients within a range of ±0.5D [10]. These benchmarks can be achieved within our data on combined surgeries. Another benchmark for comparison was the results of the European Registry of Quality Outcomes for Cataract and Refractive Surgery (EUREQUO) database. A benchmark of at least 87 % of surgeries having a refractive outcome of a spherical equivalent within ±1D of the targeted refraction and a mean biometric prediction error of 0.6D was recommended in this study [11]. Their figure of 87 % was nearly matched by our figures, and the mean biometric prediction error of 0.53D in our data also fell within these benchmarks. For all studies that we compared, a near-reality population was used, without any a priori selection for possible surgical complications or ophthalmological comorbidities.

Concerning the combination of glaucoma surgery and cataract extraction, only two studies have reported the influence of trabeculectomy ab externo trabeculotomy or drainage implants on the refractive outcome in combined surgery. Law et al. found no difference in refractive outcomes after combining cataract extraction with trabeculectomy [12], whereas Tzu et al. found the same results in a comparison of ab externo trabeculotomy or drainage-implant surgery combined with cataract extraction compared to mere cataract surgery [13]. Our findings appear to support these previous reports, although different types of glaucoma surgery were examined.

In comparison to our own in-house data on cataract-alone surgeries, we found no differences between the two groups. This is a valuable comparison because most of the influencing factors concerning the surgery are equal.

The comparison between pseudo-exfoliation glaucoma and open-angle glaucoma showed no difference in refractive outcomes between those two groups. As a limitation of this comparison the test power of 0.1 and so a reduced reliability has to be kept in mind. Ishikawa et al. reported earlier that mere cataract surgery in pseudo-exfoliated eyes showed no other refractive outcomes 1 month postoperatively compared to non-exfoliated eyes [14]. Our report supports these findings, as we found no difference between the group with pseudo-exfoliation glaucoma and other glaucoma entities regarding their refractive outcome.

Visual acuity

The final BCVA is biased by comorbidity. This complicates comparisons to other cataract-alone studies because of the effects of the given ocular comorbidity (glaucoma) on the results. In the EUREQUO study, 89.7 % of glaucoma patients who underwent cataract surgery achieved a visual acuity of 0.5 or better (47.2 % achieved 1.0 or better), whereas 98.2 % of patients without ocular comorbidity achieved a visual acuity of 0.5 or better (69.9 % achieved 1.0 or better) [15]. Compared to our in-house data, we achieved satisfying results, as there was no effect of visual outcomes because of the cataract surgery was combined with the trabectome procedure. The control group from our outpatient surgery department is a broad mixture of all types of ophthalmologic patients undergoing cataract surgery. This mix might result in a slightly less accurate visual acuity because ophthalmological comorbidities that could otherwise be excluded in the cataract-trabectome group play a role. However, most outpatient surgeries were performed on eyes that were preoperatively evaluated as requiring a less-complicated surgery or having fewer significant comorbidities, especially in comparison to the pseudo-exfoliation glaucoma group, which accounted for approximately 34 % of eyes that underwent the combined surgery.

Complications

No serious complications occurred intraoperatively in any of the 137 eyes that underwent combined surgery. It is well-accepted that cataract surgery in pseudo-exfoliation glaucoma eyes is more difficult than in non-pseudo-exfoliation eyes [16]. This might have resulted in the relatively high number of postoperative cystoid macular edema that occurred after the combined surgery (2.2 %). In our control group, this occurred in only 1.9 % of the surgeries. It has been shown that 20-30 % of patients showed a postoperative cystoid macular edema angiographically [17], whereas only 1-2 % of all patients after cataract surgery showed a clinically significant, defined as a visual acuity-influencing, edema [18]. Henderson et al. reported that 2.4 % of cataract patients developed clinically significant macular edema [19]. Our group of 134 patients might be underpowered to determine such low complication rates. The size of our group may also account for the non-existent incidence of complications, such as endophthalmitis. At the very least, there seemed to be no dramatic increase in serious complications.

Limitations of this study

Our retrospective study included only 137 eyes in total. This constitutes (compared to the group of cataract-alone surgeries) a rather small group. However, we were able to compare these combined surgeries to a control group from the same hospital and in the same setting, thereby excluding the majority of the confounders.

However, there are inhomogenities between these two groups, so the comparision has to be seen as what it is: a near-life group of different cataract surgeries being compared with another near-life group of cataract-glaucoma surgeries. For further detailed analysis of subgroups, more data on the quite small group of eyes that underwent combined surgery have to be recorded.

The retrospective nature of the study is another limitation of the study. As yet, there are no data at all on refractive and visual outcome after this combined surgery, thus we think that a retrospective approach to the topic is better than not addressing it.

It should be noted that the lowering of intraocular pressure is not the subject of this report. These results for the same cohort have been published elsewhere [6].

Conclusions

In conclusion, our data show no differences regarding visual acuity or refractive outcomes between combined or mere cataract surgery. This is important because patients desire a well-defined and achievable outcome after cataract surgery with respect to the quality of life. We observed a slightly higher rate of pseudophakic cystoid macular edema in the combined surgery group, which may have been due to the relatively small group of eyes that were examined.

Overall, we showed that a combination of trabectome and cataract surgery is as accurate as cataract-alone surgery and did not display a higher risk of complications. The separation of these two surgeries into two standalone procedures would be even more expensive and would entail risking a second surgery. Thus, a combination of trabectome and cataract surgery may be recommended if indications for both are present. However, a larger number of patients should be examined to determine the rate of severe, but rare complications in the future.