Trends in Rates of Adverse Events After Pars Plana Vitrectomy Among Medicare Beneficiaries

Abstract

Objective

To assess complication rates of pars plana vitrectomy (PPV) among older Americans and determine whether rates of adverse events and additional surgery have changed over the past decade.

Methods

Claims data were reviewed to identify all adults ≥ 68 years in the 5% Medicare sample undergoing a first PPV during 1994-1995, 1999-2000 and 2004-2005. One-year rates of severe complications (endophthalmitis, suprachoroidal hemorrhage, retinal detachment), less-severe complications, receipt of additional surgery, and blindness were calculated and compared among the 3 groups using Cox regression. Analyses were adjusted for prior adverse events (3-year run-up), demographic characteristics, and comorbid conditions.

Results

The 3 cohorts had 3,263, 5,064, and 5,263 patients, respectively. The 1-year severe complication rates did not differ among the 3 groups (range, 4.8–5.5%). The hazard of a less-severe complication or additional surgery was higher in the 2004-2005 cohort than in the earlier cohorts (p<0.05 for all comparisons). The hazard of endophthalmitis was higher among blacks (p=0.07) and other races, (p=0.02) than whites.

Conclusions

Over the past decade, rates of severe complications after PPV remained stable, but rates of less-severe complications and subsequent surgery increased. Future studies should explore the potential factors explaining these changes and the alarming elevated incidence of post-PPV endophthalmitis among nonwhites.

INTRODUCTION

Pars plana vitrectomy (PPV), introduced by Machemer in 1969,¹ is a common retinal procedure for treating such conditions as diabetic retinopathy, vitreous hemorrhage, macular holes, infectious and inflammatory conditions of the retina, trauma, and cataract surgery complications.^2,3 Numerous technological advances have recently been introduced, allowing for more-efficient vitrectomy and expanded surgical indications. Such advances include introduction of smaller (25- and 23-gauge) instrumentation, higher-frequency vitreous cutters, and adjunctive agents– e.g., heavy liquids, intraocular dyes, and intravitreal medications, including triamcinolone and antivascular endothelial growth-factor agents. As more retina specialists incorporate these newer techniques, determining whether these innovations have affected the safety profile of vitrectomy surgery becomes important. Recent studies have found increased rates of endophthalmitis with the smaller-gauge suture-less techniques,^4-9 while others have not ^10,11

Although studies have documented potential post-PPV complications, no large-scale study has assessed the frequency of these complications in a nationally representative sample or studied changes in complication rates over time. In this study, we analyzed rates of post-PPV complications among Medicare beneficiaries and assessed whether complications rates have changed from 1994–2006.

METHODS

The Medicare 5% database contains detailed claims records from a random sample consisting of 5% of the overall Medicare population obtained from the Centers for the Medicare and Medicaid Services. Medicare 5% inpatient, outpatient, Part-B, and durable medical equipment claims files were used to identify a nationally representative sample of Medicare beneficiaries aged ≥68 years undergoing PPV surgery during 1994–2006. The data contained information on beneficiaries’ demographic characteristics, and diagnostic (International Classification of Diseases, 9th Revision, Clinical Modification, ICD-9-CM)¹² and procedural codes (Current Procedural Terminology, CPT-4)¹³ submitted with claims. Durable medical equipment claims files, which contained Healthcare Common Procedure Coding System codes, were used to identify beneficiaries using low-vision aids. Data were linked by a unique identifier, permitting construction of longitudinal, person-specific data from January 1, 1991 through December 31, 2006.

Sample Selection

We identified all individuals undergoing PPV surgery based on these CPT codes: 67036, 67108, 67038-40, 65260, 65265, 67299, 66990, 66850. Using this sample, we created 3 cohorts consisting of those undergoing their first PPV during 1994-1995 (hereafter, the 1994 cohort), 1999-2000 (1999 cohort), and 2004-2005 (2004 cohort). A 3-year look-back period was performed to account for eye-related diagnoses and procedures before the index procedure (PPV). To ensure that the index procedure was the first PPV performed on a given beneficiary, we excluded individuals undergoing a PPV during the look-back period. We excluded individuals whose PPV occurred before age 68 because their pre-PPV Medicare coverage was insufficiently long for a complete 3-year look-back. Individuals in Medicare risk plans or living outside of the U.S. for ≥12 months during the look-back period were excluded.

We followed all individuals for 365 days after the PPV or until censoring. Patients were censored, meaning they could no longer be followed, when they joined a Medicare risk plan, moved outside the U.S., died, underwent another PPV or any subsequent intraocular surgery; this mitigated the possibility of misattributing complications to the original PPV.

Adverse Events

Adverse events were identified using ICD-9-CM and CPT codes. Complications were classified as (1) severe—endophthalmitis, suprachoroidal hemorrhage, rhegmatogenous, tractional retinal detachment; (2) less severe—choroidal detachment, vitreous hemorrhage, retinal edema, glaucoma, retinal tear, hypotony, corneal edema, recurrent corneal abrasions/erosions; (3) additional surgical procedures—another PPV, retinal detachment repair performed using another technique besides PPV, glaucoma surgery, enucleation/evisceration, vitreous tap, intravitreal injection, laser retinopexy, panretinal photocoagulation, focal laser; or (4) development of blindness or low vision (Table 1: Available on the Archives of Ophthalmology website at: www.archopthalmol.com).

Table 1.

List of Diagnosis and Procedure Codes

Pars plana vitrectomy	67036, 67108, 67038, 65260, 67039, 65265, 67040, 67299, 66990, 66850
Adverse events
Severe complications
Endophthalmitis	360.0x
Suprachoroidal hemorrhage	363.6x, 363.72
Tractional retinal detachment / includes PVR	361.81
Rhegmatogenous retinal detachment	361.0, 361.0x
Less severe complications
Choroidal detachment	363.7, 363.70, 363.71
Vitreous hemorrhage	362.81
Retinal edema	362.07, 362.53, 362.83
Glaucoma	365.x
Retinal tear	361.30, 361.31, 361.32, 361.33
Hypotony	360.3, 360.30, 363.31, 363.32, 360.34
Corneal edema	371.20, 371.21, 371.22, 371.23
Recurrent corneal abrasion / erosion	371.42
Receipt of additional surgery
Subsequent vitrectomy	67036, 67038, 67039, 67040, 66990, 66850, 67108, 65260, 65265, 67299
Repair retinal detachment	67101, 67105, 67107, 67110, 67112, 67115, 67120
Incisional glaucoma surgery (tube, trab)	66170, 66172, 66180
Enucleation / evisceration	65091, 65093, 65101, 65103, 65105
Vitreous Tap	67015
Intravitreal Injection	67028
Laser retinopexy	67141, 67145
Panretinal photocoagulation	67228
Focal laser	67210
Blindness / Use of low vision aids	360.41, 360.42, 369.xx, 92392, V26.00, V26.10, V26.15
Co-morbid ocular conditions
Diabetes mellitus	250.xx
Proliferative diabetic retinopathy	362.02
Age-related macular degeneration	362.5, 362.50, 362.51, 362.52, 362.57
Trauma (ruptured globe and intraocular foreign   body)	871.0, 871.1, 871.2, 871.5, 871.6
Panuveitis	360.12
Cataract	366.x
Macular hole	362.54
Epiretinal membrane	362.56
Intraocular procedures
Ruptured globe repair	65270-65290
Keratoplasty	65710-65755
Keratoprostesis	65770
Corneal surgery to correct surgically induced   astigmatism	65772-65775
Paracentesis of anterior chamber with removal   Vitreous, blood, etc.	65800-65805, 65810, 65815
Synechialysis (not including goniosynechialysis)	65870, 65875, 65880
Removal of epithelial downgrowth, implanted   Material, blood clot	65900, 65920, 65930
Injection of air, liquid, or meds into anterior chamber	66020, 66030
Trabeculectomy	66150, 66155, 66160, 66165
Wound revision major/minor	66250
Surgical peripheral iridotomy (PI)	66500-66505
Repair iris	66680, 66682
Intra-ocular lens (IOL) repositioning	66825
Cataract extraction	66830-66984
Insertion of IOL (not assoc with cataract surgery)	66985
IOL exchange	66986
Partial anterior vitrectomy	67005, 67010
Injection medication into vitreous	67025, 67027
Dissection of vitreous	67030, 67031

Analysis

We calculated the incidence of the above-listed conditions during the look-back period before the PPV surgery. T-tests assessed possible differences in adverse event rates between the 1994 and 2004 cohorts and the 1999 and 2004 cohorts. Individuals identified as having had an adverse event listed in Table 1 before the PPV were excluded from subsequent incidence calculations and regression analysis for that particular event. For example, for patients receiving an endophthalmitis diagnosis before the PPV, no post-PPV endophthalmitis diagnoses were coded as complications of the procedure. For these same patients, however, a new diagnosis of glaucoma after PPV would be considered a surgical complication. Incidence was calculated by dividing the number of individuals receiving a first diagnosis of the complication after PPV by the total number of individuals without prior diagnosis of the complication, accounting for censoring. Therefore, if an individual received an endophthalmitis diagnosis following PPV but was censored first, that complication was codes as 0. Alternatively, if the patient received the diagnosis within the 365-day follow-up period, before censoring or any subsequent intraocular surgery, the observation was coded as 1.

To calculate whether individuals in the different cohorts were more likely to develop study complications, we performed unadjusted and adjusted time-to-event analyses using Cox proportional hazards-model regression. Dependent variables were severe complications, less-severe complications, additional surgeries, blindness or low vision, and endophthalmitis. Individuals were coded as 1 if they developed these complications after vitrectomy and 0 otherwise. Regressions included cohort-identifying variables with the 2004 cohort the omitted referent.

In the multivariate analysis, we included a continuous variable for age and binary variables for gender, black race, other race (whites, the omitted referent), prior diagnosis of: severe complications, less severe complications, diabetes mellitus, proliferative diabetic retinopathy, age-related macular degeneration, eye trauma (open globe or intraocular foreign body), panuveitis, cataract, macular hole, or epiretinal membrane, prior retina surgery, prior intraocular procedure, or same-day procedure (retinal or other intraocular surgery with the PPV).

In sensitivity analysis, we extended the look back period from 3 years to 5 years for the 1999 and 2004 cohorts to determine whether an extended look back period would affect the results. Statistical analyses were performed using SAS 9.0; SAS Inc., Cary, NC. A p-value <0.05 was considered statistically significant. The Duke University and University of Michigan institutional review boards approved the study.

Results

The total number of beneficiaries undergoing PPV surgery in the 1994, 1999, and 2004 cohorts were 3,263, 5,064, and 5,263, respectively (0.24%, 0.40%, and 0.39%, respectively, of the overall samples). Mean ages of the cohorts ranged from 76.4 to 77.3 years. Compared with the other 2 cohorts, the 2004 cohort had higher proportions of males and other races. (p<0.001) (Table 2)

Table 2.

Descriptive Statistics at Baseline (%)

	1994		1999		2004
Beneficiaries in cohort	3263		5064		5263
Pre-existing diagnoses
Severe complications	33.5	***	26.1	***	29.6
Endophthalmitis	5.9	***	4.1		3.6
Suprachoroidal hemorrhage	1.4		1.3		1.6
Tractional retinal detachment / includes PVR	7.4		5.5	***	7.1
Rhegmatogenous retinal detachment	23.3		18.4	***	21.5
Less severe complications	53.0	***	51.8	***	60.1
Choroidal detachment	1.5	**	0.9		0.9
Vitreous Hemorrhage	8.4	*	10.1		9.7
Retinal edema	15.7	***	20.1	***	28.5
Glaucoma	31.2		26.9	***	31.3
Retinal tear	6.8	**	5.8	***	8.6
Hypotony	0.5		0.5		0.4
Corneal edema	4.9	***	2.8		2.6
Recurrent corneal abrasion / erosion	0.6		0.4		0.5
Previous ocular surgeries
Repair retinal detachment	10.5	***	6.6	**	5.4
Incisional glaucoma surgery#	0.6	*	0.9		1.1
Enucleation / evisceration	0.1		0.0		0.1
Vitreous tap	1.3		1.7	*	1.2
Intravitreal injection	2.1	***	1.9	***	9.3
Laser retinopexy	6.0	***	3.6		3.6
Panretinal photocoagulation	9.7		9.6		9.2
Focal laser	7.8		12.0	***	8.1
Blindness / use of low vision aids	7.0		6.7	*	7.9
Comorbid ocular conditions
Diabetes mellitus	31.6	***	35.1	***	43.5
Age-related macular degeneration	29.9	*	45.3	***	32.3
Proliferative diabetic retinopathy	11.2	***	11.8	***	14.1
Trauma	2.0	***	1.2		1.0
Panuveitis	0.4		0.3		0.3
Cataract	80.0		81.4		80.9
Macular Hole	15.9	***	14.6	***	18.9
Epiretinal membrane	25.0	***	26.0	***	39.7
Demographic characteristics
Age (years)	76.4		77.3	***	76.5
Male	42.3	***	41.2	***	46.6
White	89.0	**	91.1	***	86.8
Black	7.8		5.6	***	8.1
Other race	3.2	***	3.3	***	5.1

Notes:

^*p<0.05

^**p<0.01

^***p<0.001 compared with the 2004 cohort.

^#trabeculectomy, glaucoma drainage device implantation

Relatively common pre-PPV retinal diagnoses included age-related macular degeneration, epiretinal membrane, rhegmatogenous retinal detachment, and retinal edema. (Table 2) These conditions were not necessarily indications for the PPV (e.g., macular degeneration), but were included in the analyses to assess whether they could have influenced post-PPV complication rates. The 2004 cohort had significantly higher proportions of patients with histories of retinal tears, retinal edema, epiretinal membranes, and diabetes mellitus, than the 1994 and 1999 cohorts did.

Percentages of beneficiaries in the 1994, 1999, and 2004 cohorts with at least 1 severe adverse event diagnosed before the PPV were 33.5%, 26.1%, and 29.6%, respectively. Less-severe adverse events had occurred in 53.0%, 51.8%, and 60.1%, respectively. Furthermore, during the look-back period, nearly 25% of each cohort had undergone an intraocular surgery besides cataract surgery before the PPV.

Post-PPV incidences of severe adverse events were similar among the cohorts (Table 3), ranging from 4.8% to 5.5% (p>0.2). Post-PPV rates of endophthalmitis were 0.3% in 1994, 0.4% in 1999, and 0.4% in 2004 (p>0.2). The post-PPV incidence of blindness or use of low-vision aids ranged from 2.5% to 3.3% (p>0.2 for both comparisons).

Table 3.

Incidence of Post-Vitrectomy Adverse Events and Receipt of Additional Surgery (%)

	1994		1999		2004
Severe complications	5.5		4.8		4.9
Endophthalmitis	0.3		0.4		0.4
Suprachoroidal hemorrhage	0.6		0.5		0.4
Tractional retinal detachment (includes PVR)	1.4		1.3		1.8
Rhegmatogenous retinal detachment	4.6		4.3		4.0
Less severe complications	17.3	*	14.8	***	20.0
Choroidal detachment	0.5		0.4		0.4
Vitreous hemorrhage	1.5		2.0		1.5
Retinal edema	7.0	**	5.9	***	9.4
Glaucoma	7.8		6.1	*	7.5
Retinal tear	1.7		1.0	***	1.9
Hypotony	0.3		0.3		0.2
Corneal edema	1.4		1.1		1.4
Recurrent corneal abrasion / erosion	0.4		0.2		0.2
Need for additional surgery	22.3	***	30.2	*	32.3
Vitrectomy	12.5	***	22.8		22.8
Repair retinal detachment	4.3	*	3.2		3.2
Incisional glaucoma surgery#	0.5		0.5		0.8
Enucleation / evisceration	0.4		0.3		0.2
Vitreous tap	0.6	***	1.0		1.4
Intravitreal injection	0.6	***	0.6	***	6.6
Laser retinopexy	2.2	**	1.3		1.3
Panretinal photocoagulation	4.1	*	3.6		3.1
Focal laser	3.7		4.1	**	3.0
Blindness / use of low vision aids	2.6		3.3	*	2.5

Notes:

^*p<0.05

^**p<0.01

^***p<0.001

^#trabeculectomy, glaucoma drainage device implantation

The proportion of patients with new diagnoses of less-severe adverse events was lower in the 1994 (17.3%; p<0.05) and 1999 (14.8%; p<0.001) cohorts than in the 2004 cohort (20.0%) (Table 3). Rates of additional surgery also were lower in the 1994 (22.3%; p<0.001) and 1999 (30.2%; p<0.001) cohorts than the 2004 cohort (32.3%). Between the 1994 and 2004 cohorts, the proportions undergoing a second PPV increased from 12.5% to 22.8% (p<0.001). The rate of post-PPV intravitreal injections in the 2004 cohort was 11 times as high as the 1994 cohort (6.6% vs. 0.6% p<0.001), and the rate of post-PPV vitreous taps was twice as high in 2004 (1.4% vs. 0.6%; p<0.001).

In the multivariate analysis, the likelihood of a severe adverse event did not differ between the 2004 and the 1994 (adjusted¹ HR, 0.99, [95% CI, 0.78–1.25] or 1999 (adjusted HR, 0.95 [CI, 0.77–1.17]) cohort (Table 4). Compared to the 2004 cohort, the hazard of a less-severe adverse event was lower in the 1994 (adjusted HR, 0.78 [CI, 0.66–0.91]) and 1999 (adjusted HR, 0.75 [CI, 0.65–0.86]) cohorts. The likelihood of additional surgery was 40% lower in the 1994 cohort (adjusted HR, 0.60 [CI, 0.55-0.66]), and 11% lower in the 1999 cohort (adjusted HR, 0.89 [CI, 0.83–0.96]), than in the 2004 cohort.

Table 4.

Hazard Ratios (95% Confidence Intervals) From Cox Proportional Hazards Model

	Severe Complications		Less Severe Complications		Additional Surgery		Blindness/Low Vision		Endophthalmitis
	Unadjusted	Adjusted	Unadjusted	Adjusted	Unadjusted	Adjusted	Unadjusted	Adjusted	Unadjusted	Adjusted
1994 cohort	1.03 (0.82,1.30)	0.99 (0.78,1.25)	0.78 (0.67,0.91)	0.78 (0.66,0.91)	0.62 (0.57,0.68)	0.60 (0.55,0.66)	0.93 (0.71,1.23)	0.84 (0.63,1.12)	0.73 (0.35,1.55)	0.80 (0.37,1.71)
1999 cohort	0.93 (0.76,1.15)	0.95 (0.77,1.17)	0.70 (0.61,0.80)	0.75 (0.65,0.86)	0.90 (0.84,0.97)	0.89 (0.83,0.96)	1.28 (1.01,1.62)	1.04 (0.81,1.33)	0.86 (0.46,1.62)	0.88 (0.46,1.70)
Prior
Severe complication				1.21 (1.05,1.38)		1.23 (1.15,1.32)		1.71 (1.37,2.13)		0.99 (0.51,1.93)
Less severe complication		1.19 (0.99,1.44)				1.06 (0.99,1.14)		1.29 (1.04,1.61)		1.15 (0.64,2.06)
Retina surgery		0.96 (0.72,1.28)		1.00 (0.81,1.23)		1.53 (1.41,1.66)		1.47 (1.13,1.91)		0.87 (0.37,2.03)
Intraocular procedure		1.20 (0.92,1.57)		1.09 (0.90,1.30)		1.02 (0.92,1.13)		1.25 (0.89,1.75)		1.72 (0.77,3.86)
Diabetes mellitus		0.96 (0.78,1.19)		1.05 (0.91,1.21)		1.08 (1.00,1.17)		1.21 (0.95,1.53)		1.28 (0.69,2.36)
Proliferative diabetic   retinopathy		0.78 (0.54,1.13)		0.77 (0.59,1.01)		1.14 (1.02,1.27)		0.92 (0.62,1.35)		0.55 (0.17,1.80)
Age-related macular   degeneration		0.86 (0.71,1.05)		0.68 (0.59,0.79)		1.06 (0.99,1.14)		2.06 (1.65,2.59)		1.20(0.65,2.22)
Trauma		1.91 (1.01,3.60)		1.54 (0.98,2.44)		1.07 (0.80,1.43)		3.84 (2.42,6.11)		2.73 (0.64,11.64)
Panuveitis		3.64 (1.49,8.85)		2.14 (0.79,5.74)		1.40 (0.84,2.33)		0.97 (0.14,6.90)		10.58 (2.47,45.33)
Cataract		0.82 (0.66,1.02)		1.37 (1.15,1.62)		1.02 (0.94,1.11)		0.70 (0.56,0.89)		0.69 (0.35,1.34)
Macular hole		1.16 (0.93,1.46)		0.72 (0.60,0.86)		0.90 (0.82,0.99)		0.41 (0.26,0.65)		0.44 (0.15,1.26)
Epiretinal membrane		0.83 (0.67,1.01)		1.06 (0.92,1.22)		0.80 (0.75,0.87)		0.54 (0.41,0.71)		1.33 (0.72,2.47)
Same day surgical procedure		0.69 (0.51,0.92)		1.13 (0.94,1.36)		0.75 (0.67,0.84)		0.79 (0.54,1.14)		0.99 (0.42,2.32)
Demographic characteristics
Age		0.99 (0.98,1.01)		1.00 (0.99,1.01)		0.99 (0.99,1.00)		1.03 (1.02,1.05)		1.04 (0.99,1.09)
Male		1.31 (1.10,1.57)		1.07 (0.95,1.21)		1.06 (0.99,1.13)		0.92 (0.74,1.13)		1.20 (0.68,2.12)
Black		1.20 (0.86,1.67)		1.00 (0.78,1.29)		1.06 (0.94,1.20)		0.86 (0.53,1.39)		2.32 (0.94,5.68)
Other race		1.07 (0.68,1.69)		0.93 (0.66,1.29)		1.00 (0.85,1.17)		0.87 (0.47,1.59)		3.06 (1.18,7.95)

Covariates associated with an increased hazard of a severe adverse event were male gender (adjusted HR, 1.31 [CI, 1.10–1.57]), trauma (adjusted HR, 1.91 [CI, 1.01–3.60)], and panuveitis (adjusted HR, 3.64 [CI, 1.49–8.85]). In contrast, same-day surgery (PPV and another intraocular procedure simultaneously) was associated with a reduced hazard of a severe adverse outcome (adjusted HR, 0.69 [CI, 0.51–0.92]). Patients with a history of a severe adverse event had an increased hazard of a less-severe event after the PPV (adjusted HR, 1.21, [CI, 1.05–1.38]). Patients with previously diagnosed macular degeneration (adjusted HR 0.68, [CI, 0.59–0.79]) or macular holes (adjusted HR 0.72, [CI, 0.60–0.86]) had a reduced hazard of a less-severe adverse event (Table 4).

Covariates associated with undergoing additional surgery after PPV included having histories of a severe adverse event before the PPV (adjusted HR, 1.23, [CI, 1.15–1.32]) and of retinal surgery (adjusted HR, 1.53, [CI, 1.41–1.66]), or proliferative diabetic retinopathy (adjusted HR, 1.14 [CI, 1.02–1.27]). Patients who had another intraocular surgery and the PPV performed simultaneously had a 25%-reduced hazard of additional surgery (adjusted HR, 0.75, [CI, 0.67–0.84]) (Table 4).

Racial disparities in the likelihood of developing endophthalmitis were observed. Compared with whites, the hazard of endophthalmitis was nonsignificantly higher in blacks (adjusted HR, 2.32, [CI, 0.94–5.68]) and significantly higher in other races (adjusted HR, 3.06, [CI, 1.18–7.95]).

In sensitivity analysis, increasing the look back period from 3 years to 5 years did not materially affect our results (results not shown).

Discussion

To our knowledge, this is the first study of adverse events after PPV surgery using a nationally representative sample of Medicare beneficiaries. Rates of severe, sight-threatening complications were relatively low, and were unchanged from 1994 through 2006. After adjustment for covariates in the multivariate analysis, rates of severe complications did not differ between cohorts. Rates of less-severe adverse events and additional surgery were significantly higher in the 2004 cohort than in the 1994 or 1999 cohort.

Several clinical trials and limited-site observational studies have reported post-PPV complication rates^{6,8,10,11,14-39} (Table 5). At 0.3–0.4%, our rate of endophthalmitis is 10 times as high as the 0.039% reported from an analysis of 15,326 patients in 1984–2003.¹⁹ Studies of endophthalmitis after 20-guage PPV include one reporting a rate of just 0.018%,⁶ and another reporting 0.046%.¹⁴Two other such studies include a review of 20-gauge PPV surgeries performed at Moorfields Eye Hospital during 1986–1990, finding an endophthalmitis rate of 0.15%,⁴⁰ and an analysis of 1500 post-PPV eyes finding a rate of 0.2%.⁴¹ Methodologic differences may account for the considerably lower rates of endophthalmitis in some studies compared with ours. In most studies, the followup time fell in the 6–25 week range, compared with 1 year in our study. Furthermore, one study excluded all late-onset diagnoses of endophthalmitis.¹⁴ Limiting our follow-up to 6 weeks would reduce incident cases of endophthalmitis from 49 to 34, still yielding a higher rate (0.26%) than those from most studies. No study reported mean patient age at the time of PPV, making direct comparisons with our study difficult.

Table 5.

Published Rates of Adverse Outcomes Following Pars Plana Vitrectomy Surgery (%)

Study	Type of PPV	Eyes	Endophthalmitis	Choroidal Detachment	Retinal Detachment	Hypotony	Follow up (Mean)
Blankenship 197741	20-gauge PPV	1,500 eyes	0.2%				Unavailable
Kattan et al 1991 25	20-gauge PPV	1,974 eyes	0.051%				Unavailable
Bacon et al 199340	20-gauge PPV	3,900 eyes	0.15%				Unavailable
Cohen et al 1995 18	20-gauge PPV	12,216 eyes	0.07%				Unavailable
Park et al 1995 34	20-gauge PPV	98 eyes (MH repair) 43 eyes (MP surgery)	1% (MH repair) 0% (MP surgery)		14% (MH repair) 5% (MP surgery)		3 months minimum (3-40 months MH, 3- 37 months MP)
Aaberg et al 1998 14	20-gauge PPV	4,583 eyes (from July 1989 to Dec 1994) 6,557 eyes (from Jan 1984 to Dec 1994, included period from Kattan study)	0.044% 0.046% (for total 10- year period including Kattan study)				6 weeks
Campo et al 1999 16	PPV for primary pseudophakic RRD	294 eyes	0%	0%	NA		6-80 months (19 months)
Eifrig at al 2004 19	All PPV at BP January 1, 1984 and December 31, 2003	15,326 eyes	0.039% (No endophthalmitis with 25-gauge)	0%			6 weeks
Brazitikos et al 2005 15	PPV for primary pseudophakic RRD	150 eyes	0%	0%	NA	0%	12 months minimum (includes referring ophthalmologist)
Ahmadieh et al 2005 10	PPV for RRD in phakic and aphakic patients	225 eyes	0%	0%	NA	0%	6 months minimum
Ibarra et al 2005 23	25-gauge PPV for less complex retinal pathology	45 eyes	0%	0%	2.22%	0%	6-25 months (13 months)
Joondeph et al 2005 24	PPV from January 1993 to December 2002	10,397 eyes	0.048%				Unavailable
Lakhanpal et al 2005 28	25-gauge PPV	140 eyes	0%	3.57%	0%	0%	(34 weeks)
Oshima et al 2006 33	25-gauge PPV combined with CE/IOL	150 eyes	0%	0.72%	0.67%	13%	6-26 months (9.7 months)
Weichel et al 2006 37	20-gauge for primary pseudophakic RRD	68 eyes (PPV) 84 eyes (PPV/SB)	0%	1.4% PPV 2.3% PPV/SB	NA	0%	3-34 months (10 months)
Heimann et al 2007 22	PPV for RRD in phakic and pseudophakic patients	681 eyes	0%	0%	NA	0%	1 year
Kim et al 2007 26	23-gauge PPV	40 eyes	0%			2.5%	3-13 months (8.4 months)
Kunimoto and Kaiser 2007 6	20-gauge PPV vs 25-gauge PPV	5498 eyes (20- gauge) 3103 eyes (25- gauge)	0.018% (20-gauge) 0.23% (25-gauge)	0%			8-41 weeks (25 weeks)
Valmaggia 2007 36	20- and 25-gauge PPV for ERM	64 eyes (20- gauge) 75 eyes (25- gauge)	0% (20-gauge) 1.33% (25-gauge)	0% (20-gauge) 4% (25-gauge)	4.69% (20- gauge) 0% (25-gauge)	0% (20-gauge) 12% (25-gauge)	Unavailable
Yamakiri et al 2007 39	Triamcinolone acetonide assisted PPV vs. conventional PPV	774 eyes	0%				3 months
Chen et al 2008 17	20-gauge PPV vs. 25-gauge PPV	3046 eyes (20- gauge) 431 eyes (25- gauge)	0.03% (20-gauge) 0.23% (25-gauge) (case combined with CE/IOL)				14 days
Gupta et al 2008 20	23-gauge PPV	92 eyes	0%		0%	6.50%	12 weeks minimum
Guyomarch et al 2008 21	25-gauge PPV	110 eyes	0.909%		0.909%	6.363%	Unavailable
Lai et al 2008 27	25-gauge for primary RRD	53 eyes	0%	6%	NA	0%	Minimum 1 month
Lommatzsch et al 2008 29	25-gauge PPV for ERM	625 eyes	0%	2.7%	2.10%	2.70%	Unavailable
Mason et al 2008 30	20-gauge PPV vs. 25-gauge PPV	2,642 eyes (20- gauge) 1,906 eyes (25- gauge)	0.076% (20-gauge) 0.053% (25-gauge)				Minimum 3 months
Miller et al 2008 31	25-gauge for primary RRD	42 eyes	0%	0%	NA	0%	Minimum 3 months
Mollan et al 2008 32	20-gauge PPV	5,278 eyes	0.038%				Unavailable
Scott et al 2008 8	20-gauge PPV vs 25-gauge PPV	6,375 eyes (20- gauge) 1,307 eyes (25- gauge)	0.03% (20-gauge) 0.84% (25-gauge)				Unavailable
Shimada et al 2008 11	20-gauge PPV vs 25-gauge PPV	3,592 eyes (20- gauge) 3,343 eyes (25- gauge) (542 straight incision, 2801 angled incision)	0.0278% (20-gauge) 0.0299% (25-gauge) (occurred in straight incision)				Unavailable
Tewari et al 2008 35	23-gauge PPV	81 eyes	0%	0%	0%		6.5 months (3-9 months)
Wimpissinger et al 2008 38	20-gauge PPV vs 23-gauge PPV	60 eyes	0%	3.33% total (occurred in 23- gauge)	0%	0%	3 months

BP = Bascom Palmer Eye Institute; CE/ IOL = cataract extraction with intraocular lens insertion; ERM = epiretinal membrane; MH = macular hole; MP = macular pucker; PPV = pars plana vitrectomy; RRD = rhegmatogenous retinal detachment; SB = scleral buckle

Reported rates in the literature of endophthalmitis after 25-gauge PPV have ranged from 0.03% to 0.84%, a range into which our observed rates, 0.3–0.4%, fall.^{6,8,11,14,17-19,24,25,30,32} Since smaller-gauge PPV is often a suture-less procedure, some investigators have expressed concern that inadequate closure of the sclerotomies may increase patients’ risk for adverse outcomes, e.g.–postoperative hypotony and endophthalmitis.⁴ While some studies have demonstrated elevated incidence rates of endophthalmitis with smaller-gauge vitrectomy,^6,8 Shimada and colleagues found no difference in endophthalmitis rates between conventional 20G PPV and smaller-gauge PPV.¹¹ Unfortunately, the claims data we used did not specify whether cases used smaller- or larger-gauge instrumentation. Therefore, we cannot know with certainty what percentage of cases performed in 2004–2005 used the newer, smaller-gauge technology. While no study has reported trends in use of smaller-gauge PPV, a survey by the American Society of Retina Specialists estimated that in 2004–2005, approximately 30% of retina surgeons used mostly smaller-gauge (25G) vitrectomy.⁴² If we assume that a similar percentage of cases in our 2004 cohort were performed by using smaller-gauge vitrectomy, and that the risk of endophthalmitis is roughly 10-fold higher with smaller-gauge instruments, as some researchers have suggested, our sample size would have had ample power to detect differences in endophthalmitis rates between the 2004 cohort and the 1994 and 1999 cohorts.

After adjustment for other potential factors, the rates of postoperative endophthalmitis did not differ among the cohorts. Although these rates did not differ on the basis of ICD-9 codes, the incidence of post-PPV vitreous tap (CPT code 67015)—a procedure done almost exclusively to confirm an endophthalmitis diagnosis—was higher in the 2004 cohort than in the 1994 cohort. The proportion of patients from all cohorts undergoing postoperative vitreous taps was more than double the proportion receiving a diagnosis of endophthalmitis, however; therefore, some providers may have used the code for vitreous tap to bill for diagnoses other than endophthalmitis.

There are several possible explanations for the increase in rates of less-severe complications and additional surgery from the earlier cohorts to the 2004 cohort. First, the ability to detect certain retinal conditions increased over time. Due to improvements in imaging technology and quality, coupled with a reduction in the price of imaging modalities, the use of diagnostic imaging devices (e.g., optical coherence tomography) to identify retinal diseases has risen dramatically.⁴³ The elevated incidence of less-severe complications(e.g., epiretinal membranes and retinal edema) in the 2004 cohort may partly reflect more widespread use of optical coherence tomography and other imaging devices.⁴⁴ Moreover, it is unsurprising that compared with the 2 other groups, the 2004 group had a 10-fold higher incidence of postoperative intravitreal injections (CPT code 67028)–a common treatment for retinal edema–more easily identified using these imaging devices. Intravitreal injections of triamcinolone acetonide and antivascular endothelial growth-factor agents have also become increasingly popular recently to treat many ocular conditions– e.g., diabetes-mellitus complications and age-related macular degeneration.^44-48

Another possible explanation for the increased incidence rates over time is expanded indications for PPV and the emergence of various alternative interventions for residual pathology after PPV surgery. Perhaps cases deemed untreatable after 1 PPV surgery in 1994 were being treated with repeated or other surgeries in the 2004 cohort.

Despite the apparent improvement in access to PPV over the past decade among older nonwhite patients, rates of post-PPV endophthalmitis among nonwhites in our study were higher than those for whites. After adjustment for covariates, the rate of post-PPV endophthalmitis was more than twice as high for blacks, and more than 3 times as high for other races, as for whites. Although the difference in endophthalmitis rates between blacks and whites was statistically insignificant (p=0.07), given the devastating vision loss associated with endophthalmitis, this finding may be clinically significant. Similar findings of elevated endophthalmitis rates among nonwhites have been observed after cataract and glaucoma surgeries.^49,50

The use of large administrative health-care databases to study adverse outcomes after intraocular surgery was first described by Javitt and colleagues, who assessed rates of endophthalmitis after cataract surgery among Medicare beneficiaries.⁵¹ Others have used Medicare-claims databases to study complications after glaucoma surgery.⁵² Unlike single-center observational studies, which can be influenced by case mix, surgical technique, or surgeon experience, national health-care claims databases capture care provided by many different surgeons, and therefore may better represent the surgical experience of patients in the community. Furthermore, unlike observational studies and clinical trials, these databases are often large enough to allow study of rates of infrequent adverse events, such as endophthalmitis. Finally, the longitudinal nature of Medicare claims data enables longer and more-uniform follow-up to monitor for postoperative complications.

Use of administrative databases for research purposes limits our study in several ways.⁵³ First, Medicare claims exist to collect payment, not to capture details of clinical encounters. Thus, capturing an adverse event using this database requires that the clinician has both identified and billed for the complication. Second, we cannot confirm whether any given event resulted from a particular surgical procedure. Third, because claims data do not specify which eye has undergone surgery or experienced the adverse event, some adverse events in this series could have occurred in the nonsurgical eye. Finally, because only Medicare beneficiaries were studied, our findings may not reflect complication rates of patients who are younger, have another insurance type, receive care through the Veterans Administration system, or reside outside of the U.S.

In summary, among Medicare beneficiaries undergoing PPV, rates of severe complications, including endophthalmitis, were unchanged over the past decade, although rates of less-severe complications and subsequent intraocular surgeries increased significantly. Given the aging population, rising prevalence of proliferative diabetic retinopathy⁵⁴ and other indications for PPV surgery, and the increasing influence of imaging techniques to identify potential PPV candidates it is important that recently implemented technological advancements designed to improve the efficiency of PPV surgery are not compromising patient safety. Unchanged rates of severe complications suggest that technological advances have not adversely affected patients risk. However, additional studies should further explore the factors contributing to elevated rates of less-severe complications and subsequent intraocular surgeries, including vitreous taps, and disparities in outcomes among racial minorities undergoing PPV surgery.