Abstract
Purpose:
To determine the lens survival time following glaucoma drainage implant (GDI) surgery and identify the risk factors that may predict the time to cataract surgery.
Design:
Retrospective cross-sectional study.
Methods:
Phakic patients who underwent GDI surgery at a large tertiary referral center between January 1, 2016 and June 1, 2022 were included. Demographic and clinical data were collected and analyzed using multivariate and survival analyses, with statistical significance set at P < 0.05. The main outcome was time to cataract surgery (called lens survival time). Survival analyses were conducted using Kaplan–Meier and Cox regression methods.
Results:
Sixty-eight phakic subjects underwent GDI surgery, with a mean age of 56.4 ± 14.9 years. Of them, 36 subjects (53%) had primary glaucoma and 32 (47%) had secondary glaucoma. GDI 6-month success (intraocular pressure ≤21 mmHg) was achieved in 63 subjects (92%). Forty-three subjects had three or more years of follow-up data available and were included in the survival analysis. Median and mean lens survival time were 16 ± 2 and 20 ± 3 months, respectively. At 1, 2, and 5 years, the proportions of lenses that survived were 60.5% (26 lenses), 27.9% (12 lenses), and 2.3% (one lens), respectively. Timing of subsequent cataract surgery did not correlate significantly with subject demographics or type of glaucoma.
Conclusions:
Cataract progression occurred in nearly all patients following GDI surgery. None of the factors studied predicted the timing of cataract surgery, suggesting that cataract formation is primarily influenced by the surgery itself, with minimal impact from patient-specific risk factors.
Keywords: Cataract, glaucoma, glaucoma drainage implant, lens survival time, tube shunt
Cataract affects 56% of Americans aged 70 and above and is the leading cause of blindness globally.[1,2] Glaucoma is the leading cause of irreversible vision loss worldwide, impacting 3 million individuals in the USA with an estimated $2.5 billion annual cost to the US healthcare system.[3] Both conditions frequently coexist among elderly patients, exerting significant impacts on visual health when untreated.
The progression of cataract formation following glaucoma drainage implant (GDI) surgery has been observed in recent studies.[4,5,6] The Tube Versus Trabeculectomy (TVT) study revealed that cataract progression was observed in 80% of eyes that underwent tube shunt surgery, with 54% of eyes undergoing cataract extraction over a 5-year period.[4] Similarly, the Primary Tube Versus Trabeculectomy (PTVT) study showed that 32% (n = 43) of subjects with a GDI surgery underwent cataract extraction within the first 3 years.[5] The Ahmed Versus Baerveldt (AVB) study – which included subjects with primary open-angle as well as secondary glaucomas (e.g., uveitic, neovascular) – revealed that 26% of subjects in the Ahmed group and 38% of subjects in the Baerveldt group underwent cataract surgery over a 5-year follow-up period.[6]
The pathogenesis of cataract formation following tube shunt surgery is not well understood but is likely multifactorial, with risk factors including marked postoperative inflammation, poor intraocular pressure (IOP) control, and prolonged use of high-dose steroids in the postoperative period.[7]
While the TVT, PTVT, and AVB studies highlight the relationship between GDI surgery and cataract progression, both the TVT and the PTVT studies excluded secondary glaucomas. Although the AVB study did include secondary glaucomas, its primary focus was comparing the failure rates between the two devices, rather than tracking the time to cataract surgery following GDI surgery. Consequently, there is a knowledge gap in understanding the impact of GDI surgery on cataract formation in conditions like uveitis, trauma, and chronic steroid use. Therefore, discerning the timeline between GDI surgery and cataract extraction is beneficial in setting patient and provider expectations.
Our primary research objective is to determine the time to cataract extraction following GDI surgery. In addition, we seek to identify the risk factors that may accelerate cataract progression.
We hypothesize that patients with secondary forms of glaucoma (e.g., uveitic, neovascular, steroid induced) will undergo cataract surgery sooner than patients with primary forms of glaucoma following GDI surgery.
Methods
Study design and participants
This retrospective cross-sectional study was conducted in accordance with the Institutional Review Board guidelines of our institution, and it adhered to the principles outlined in the Declaration of Helsinki. Informed consent was waived as the study involved no more than minimal risk to the subjects.
We included phakic subjects who underwent GDI surgery between January 1, 2016 and June 1, 2022. The electronic health record was queried for all GDI surgeries in phakic subjects during the time interval specified.
We excluded subjects a) who underwent combined cataract extraction with intraocular lens implantation (CEIOL) and GDI surgery, b) who had a prior history of GDI, and c) who had no follow-up information after GDI surgery.
Data collection
Demographic information (age, race, gender), primary diagnosis, indications for surgery, history of uveitis, ocular trauma history, history of trabeculectomy, duration of initial surgery, and additional surgeries post-GDI surgery and during/after CEIOL surgery were extracted from the office notes. Records of IOP-lowering medications (topical and oral), topical steroid use, best-corrected visual acuity (BCVA) using the Snellen’s chart, and IOP measurements were documented. Goldmann’s applanation-based IOP measurements recorded by an ophthalmologist were given priority in cases of multiple IOP measurements during a visit.
Classification of glaucoma and surgical success
Glaucoma was classified as primary (e.g., primary open-angle and primary angle-closure) and secondary (e.g., neovascular, steroid-induced, uveitic, traumatic, other) glaucoma by the treating glaucoma physician. GDI 6-month success was defined as an IOP of 21 mmHg or lower at 6 months post-GDI surgery.[8]
Lens survival analysis
In addition, we assessed the duration from GDI surgery to cataract surgery, focusing on subjects with at least 3 years of follow-up data. Subjects with less than 3 years of follow-up data were still included in demographic and clinical presentation analyses for a better overall understanding of baseline characteristics and initial post-GDI surgical outcomes. Cataract surgery was decided based on shared decision-making between the ophthalmologist and the patient, with no specific criteria needed for surgery.
For the purposes of analysis, subjects were classified as visually impaired or legally blind as per the American Academy of Ophthalmology (AAO) guidelines, which defines visual impairment as 20/40 or worse in the better eye with best correction and legal blindness as 20/200 or worse in the better eye with best correction.[9]
Statistical analysis
Continuous variables (IOP, BCVA, etc.) were summarized using mean (standard deviation) and compared using t-tests or analysis of variance, while categorial variables (race, gender, etc.) were compared using Chi-squared or Fisher’s exact test. Survival analyses (for subjects with ≥3 years follow-up) were conducted using Kaplan–Meier and Cox regression methods. BCVA was converted to the logarithm of the minimum angle of resolution format for statistical analysis, and Statistical Package for the Social Sciences version: 29.0.0.0 (241) was employed for all calculations. Bonferroni correction was used for Chi-squared analyses involving categorical variables with multiple subgroups. Statistical significance was set at P < 0.05.
Multivariate analysis and outcome measures
Multivariate analysis assessed factors predicting the time from GDI to CEIOL surgery, and included demographics (age, race, eye, gender), uveitis history, prior trabeculectomy, trauma history, type of glaucoma, BCVA, interim surgery, frequency of topical steroid use, pre- or postoperative glaucoma medications, GDI type, and successful IOP control at 6 months following GDI. CEIOL outcomes were assessed by comparing BCVA and IOP measurements pre- and 6 months post-cataract surgery.
Results
Baseline characteristics
Sixty-eight subjects met the inclusion criteria. The mean age at GDI surgery was 56.4 ± 14.9 years [Table 1]. Among these, 42.6% (n = 29) were male and 57.4% (n = 39) were female. The cohort comprised 29% (n = 20) White people, 47% (n = 32) Black people, and 24% (n = 16) from other racial backgrounds. The mean follow-up duration in these 68 subjects was 42.0 ± 20.1 months.
Table 1.
Subject demographics and clinical characteristics categorized based on duration of follow-up after glaucoma drainage implant surgery
| >3 years of follow-up (n=43) | <3 years of follow-up (n=25) | Total (n=68) | |
|---|---|---|---|
| Age at GDI (years) | 59.6±13.2 | 50.9±16.1 | 56.4±14.9 |
| Follow-up duration (months) | 54.6±13.1 | 20.6±8.1 | 42.0±20.1 |
| Gender | |||
| Female, n (%) | 28 (65.1%) | 11 (44.0%) | 39 (57.4%) |
| Race | |||
| White, n (%) | 16 (37.2%) | 4 (16.0%) | 20 (29.4%) |
| Black, n (%) | 19 (44.2%) | 13 (52.0%) | 32 (47.1%) |
| Other, n (%) | 8 (18.6%) | 8 (32.0%) | 16 (23.5%) |
| Diagnosis | |||
| Open angle | 22 (51.2%) | 4 (16.0%) | 26 (38.2%) |
| Angle closure | 5 (11.6%) | 5 (20.0%) | 10 (14.7%) |
| Neovascular | 4 (9.3%) | 5 (20.0%) | 9 (13.2%) |
| Steroid/uveitic/traumatic | 12 (27.9%) | 9 (26.0%) | 21 (30.9%) |
| Other | 0 (0%) | 2 (8.0%) | 2 (2.9%) |
| Type of implant | |||
| Ahmed, n (%) | 37 (86.0%) | 25 (100%) | 62 (91.2%) |
| Baerveldt, n (%) | 6 (14.0%) | 0 (0%) | 6 (8.8%) |
| Prior history of | |||
| Uveitis (n, %) | 14, 32.6% | 11, 44.0% | 25, 36.8% |
| Trauma (n, %) | 1, 2.3% | 1, 4.0% | 2, 2.9% |
| Trabeculectomy (n, %) | 19, 44.2% | 4, 16.9% | 23, 33.8% |
GDI=glaucoma drainage implant
Glaucoma diagnoses included primary open-angle glaucoma (n = 26, 38%), primary angle-closure glaucoma (n = 10, 15%), and secondary forms (n = 32, 47%) such as neovascular (n = 9, 13%), steroid induced/uveitic/traumatic (n = 21, 31%), and other (n = 2, 3%). Uveitis history was present in 37% (n = 25) of subjects, while ocular trauma history was present in 3% (n = 2) of subjects. The discrepancy in the number of subjects with uveitic glaucoma and a history of uveitis is due to four participants whose uveitis resolved before GDI surgery. Prior trabeculectomy was reported in 34% (n = 23) of subjects.
An Ahmed valve implant was performed in 91.2% (n = 62) of cases, while a Baerveldt implant was performed in 8.8% (n = 6) of cases. GDI 6-month surgical success was achieved in 92% (n = 63) of patients at 6 months post-op. Mean IOP changed from 33.8 ± 10.7 preoperatively to 14.6 ± 6.6 at 6 months postoperatively (P < 0.001). In addition, a reduction in postoperative glaucoma medications from 4.1 ± 1.0 to 2.5 ± 1.3 medications (P < 0.001) was observed. Mean BCVA did not significantly change in 6 months after GDI surgery (P = 0.164) [Table 2]. The 6-month success of GDI surgery was not significantly correlated with subject demographics (age, race, gender, type of glaucoma) on a logistic regression analysis.
Table 2.
Visual acuity, intraocular pressure, and glaucoma medication use before and after GDI surgery and cataract extraction
| Before GDI | Six months after GDI | Before CEIOL | Six months After CEIOL |
P
|
||
|---|---|---|---|---|---|---|
| Pre- and post-GDI | Pre- and post-CEIOL | |||||
| BCVA (logMAR) | 0.80±0.92 | 0.95±0.92 | 1.28±0.87 | 0.55±0.71 | P=0.164 | P<0.001 |
| IOP (mmHg) | 33.8±10.7 | 14.6±6.6 | 14.8±7.7 | 12.6±4.7 | P<0.001 | P=0.025 |
| Glaucoma medications (n) | 4.1±1.0 | 2.5±1.3 | 2.9±1.5 | 2.0±1.4 | P<0.001 | P<0.001 |
BCVA=best-corrected visual acuity, CEIOL=cataract extraction with intraocular lens implantation, GDI=glaucoma drainage implant, IOP=intraocular pressure, logMAR=logarithm of the minimum angle of resolution
Of note, our dataset included one child with secondary glaucoma due to complications from congenital hereditary endothelial dystrophy. She had no history of uveitis, trauma, or trabeculectomy, and underwent GDI surgery at 6 years of age with an Ahmed valve implant. Six-month surgical success was achieved. However, due to having less than 3 years of follow-up data, this subject was excluded from lens survival analysis.
Lens survival analysis
Of the 68 subjects, 63% (n = 43) had three or more years of follow-up data available, and these were used in the survival analysis. The mean follow-up duration in these 43 subjects was 54.6 ± 13.1 months. Among them, 86% (n = 37) received an Ahmed valve implant, while 14% (n = 6) received a Baerveldt implant. Out of 43 subjects, 37% (n = 16) had cataract surgery within 1 year after GDI surgery, while 60% (n = 26) had cataract surgery in more than 1 year after GDI surgery. One subject did not undergo cataract surgery. The timing of cataract surgery in relation to GDI surgery did not correlate significantly with age, race, gender, history of uveitis, prior trabeculectomy, history of trauma, type of glaucoma, visual acuity, interim surgery, frequency of topical steroid use, pre- or postoperative glaucoma medications, type of GDI (valved vs. non-valved), and successful IOP control at 6 months following GDI surgery on using a Cox regression analysis.
The median lens survival time was 16 ± 2 months [Fig. 1]. Those with primary glaucomas had a median lens survival time of 15 ± 3 months, while those with secondary glaucomas had a median survival time of 16 ± 2 months [Fig. 2]. Using a log-rank test, no significant differences in lens survival were noted between primary and secondary glaucoma forms (P = 0.51).
Figure 1.
Lens survival time following GDI surgery. The lens survival time was defined as the time from GDI surgery to cataract extraction. The x-axis represents the lens survival time in months, while the y-axis represents the proportion of subjects who remained phakic. GDI = glaucoma drainage implant
Figure 2.
Lens survival time following GDI surgery, grouped by glaucoma type: primary (e.g., POAG, PACG) and secondary (e.g., steroid induced, traumatic, uveitic, neovascular, and other). No significant differences in lens survival were observed between primary and secondary glaucoma forms (P = 0.510). GDI = glaucoma drainage implant, PACG = primary angle-closure glaucoma, POAG = primary open-angle glaucoma
Cataract surgery after GDI procedure
Six months after GDI surgery, 40% (n = 17) of the 43 subjects met the AAO criteria for legal blindness, while 33% (n = 14) met the criteria for visual impairment. These values rose to 51% (n = 22) and 44% (n = 19), respectively, at the last visit before cataract extraction. In addition, significant reductions in visual acuity were observed between the post-GDI visit (0.95 ± 0.92) and the pre-CEIOL visit (1.28 ± 0.87), suggesting cataract development and/or progression occurred (P < 0.001).
Out of the 43 subjects, all but one underwent cataract extraction following GDI surgery. Mean BCVA 6 months after CEIOL was 0.55 ± 0.71, which was markedly higher compared to the visit before cataract surgery (P < 0.001). Notably, 55% of subjects (n = 23) improved by three lines or more, while 40% (n = 17) improved by five lines or more.
The change in IOP before and 6 months after CEIOL was statistically significant [14.8 (7.7) mmHg vs. 12.6 (4.7) mmHg; P = 0.025] [Table 2]. The mean number of glaucoma medications decreased significantly from 2.9 ± 1.5 before cataract surgery to 2.0 ± 1.4 six months after cataract surgery (P < 0.001). Of note, 9% (n = 4) of subjects were completely weaned off their glaucoma medications 6 months post-cataract surgery.
Discussion
Our study successfully demonstrates that GDI surgery effectively lowers IOP but poses a considerable risk for accelerating cataract progression in phakic patients. Therefore, careful monitoring of patients post-GDI surgery is essential to ensure optimal visual outcomes. Here, we present a single tertiary academic institution’s experience in tracking the interval between GDI surgery and subsequent cataract extraction to help guide physicians in their surgical planning for phakic patients who need GDIs.
Our subjects underwent GDI surgery without concurrent cataract surgery. Several studies have evaluated the efficacy of standalone glaucoma surgery (trabeculectomy or GDI) compared to combined glaucoma and cataract surgery. The results have been conflicting – some studies report worse long-term IOP outcomes with combined surgeries,[10,11] while others suggest that cataract surgery does not affect long-term GDI success.[12,13,14] In cases of secondary glaucoma, especially uveitic glaucoma, increased postoperative inflammation following cataract surgery may lead to a higher risk of GDI failure.
The median lens survival time following 6-month successful GDI surgery was 16 ± 2 months. We found no significant difference in lens survival the between primary and secondary forms of glaucoma, suggesting that secondary forms of glaucoma may not expedite the need for CEIOL compared to primary glaucomas. Moreover, we did not find any demographic or preoperative factors that predicted the time to cataract surgery following GDI surgery, including age, race, gender, history of uveitis, prior trabeculectomy, history of trauma, type of glaucoma, visual acuity, interim surgery, frequency of topical steroid use, pre- or postoperative glaucoma medications, type of GDI (valved vs. non-valved), and successful IOP control at 6 months following GDI surgery.
Cataract progression following glaucoma surgery is well documented,[15,16,17,18] yet the underlying mechanisms remain poorly understood. One hypothesis suggests that disruption of aqueous humor flow across the lens may impair nutrient delivery, leading to lens opacification.[18] Alternatively, postoperative inflammation and shallowing of the anterior lens may accelerate cataract formation due to physical irritation of the lens.[17,19] Factors such as diabetes, corticosteroid use, and prolonged inflammation are known to contribute to cataract formation,[20,21,22,23] implying that secondary causes of glaucoma (i.e., neovascular, uveitic, and steroid-induced glaucoma) may further accelerate cataract progression in conjunction with GDI surgery. However, our findings suggest otherwise. We observed that these risk factors do not significantly alter the timing of cataract surgery, suggesting that they may have a more indolent effect on cataract formation compared to the relatively accelerated progression seen post-GDI surgery. Moreover, visual acuities 6 months after GDI surgery were significantly higher compared to pre-CEIOL, further supporting this observation.
Although most subjects experienced cataract progression after GDI surgery, 55% showed significant improvement in vision following CEIOL of at least three lines or more. This underscores the critical need for patient education on accelerated cataract development, preventing misinterpretation of such occurrences as indicative of subpar GDI surgery outcomes and guarded prognosis after cataract surgery in patients with multifactorial causes for vision loss.
Cataract surgery is known to lower IOP; proposed theories include opening of the angles after cataract surgery, widening of the trabecular meshwork by increased mechanical tension on zonules, reversal of the aqueous pump failure by returning it to a younger state, and accounting for the phacomorphic factor in the wide spectrum of glaucomas.[24,25,26,27] Our study observed a significant reduction in IOP before and after cataract surgery, corroborating previous literature on the therapeutic benefits of cataract surgery in glaucoma patients.[27,28,29,30]
Limitations
Our study was limited by the presence of a relatively small sample size of phakic subjects undergoing GDI without concomitant cataract surgery. In addition, its single-institution context may limit the generalizability of our findings. Another limitation was the use of 6-month data to define GDI success. Our primary outcome was cataract surgery, and we used 6-month success merely as a covariate to understand how it impacts the need for cataract surgery. Moreover, the absence of cataract classification during the analysis, such as the Lens Opacities Classification System (LOCS), represents another limitation. This was a retrospective study, and we do not routinely use the LOCS classification in our clinic. Instead, we used visual acuity as an indirect measure of cataract progression. The significant reduction in visual acuity between the post-GDI and pre-CEIOL visits strongly suggests cataract development and/or progression occurred.
The lack of association between the timing of cataract extraction after GDI surgery and the type of glaucoma may be attributed to our small sample size and the high prevalence of prior trabeculectomy (44.2%) among subjects included in lens survival analysis. Glaucoma filtration surgery is a known risk factor for cataract formation,[31,32,33] which may mask potential differences in the timing of cataract extraction between primary and secondary glaucomas following GDI surgery in subjects with a history of trabeculectomy.
Conclusion
Despite its limitations, our study offers insight into real-world clinical experiences and re-emphasizes the importance of patient education pre- and post-GDI surgery. Moreover, it is the first study to examine cataract progression following tube shunt surgery in both primary and secondary forms of glaucoma. Future multicenter studies with larger sample sizes are needed to validate our results and provide a broader understanding of cataract progression timelines following GDI surgery.
Conflicts of interest:
There are no conflicts of interest.
Funding Statement
Nil.
References
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