Anterior Proliferative Vitreoretinopathy in the Silicone Study

Anterior Proliferative Vitreoretinopathy in the Silicone Study Silicone Study Report Number 10 Kenneth R. Diddie, MD,1 Stanley P. Azen, PhD,2 Hal M. Freeman, MD,3 Donna C. Boone, MS,2 Thomas M. Aaberg, MD,4 Hilel Lewis, MD,1 Norman D. Radtke, MD,5 Stephen]. Ryan, MD,6 for the Silicone Study G roup7 Background: As part of the design of the Silicone Study, a new classification of proliferative vitreoretinopathy (PVR) was developed that distinguishes the different types of contraction found in PVA. In contrast to the original Retina Society system that emphasized the post-equatorial retinal pathology (posterior PVR), the Silicone Study classification system included the characteristic types of contraction found in both the equatorial region and the pre-equatorial retina and vitreous base (anterior PVR). Methods: The authors contrast (1) preoperative and intraoperative findings and (2) vision and anatomic outcomes in the cohort of anterior PVR eyes with the cohort of posterior-only PVR eyes. For the cohort of eyes randomized to perfluoropropane gas (CsFs) or silicone oil, the authors carry out univariate and multivariate analyses to assess the predictive value of baseline and intraoperative parameters on vision and anatomic outcome. Results: Anterior PVR was present in 321 eyes (79%) and was more prevalent in eyes that had undergone an unsuccessful vitrectomy before study entry than in eyes that underwent a primary vitrectomy for PVR (88% versus 73%; P < 0.001). Compared with eyes that had posterior PVR at the preoperative examination, eyes that had anterior PVR tended to (1) be graded (Retina Society classification system) as D-1 or worse (86% versus 49%; P < 0.0001), (2) have worse «2/200) visual acuity (93% versus 86%; P = 0.003), (3) have more hypotony (24% versus 11%; P = 0.03), more edema (8% versus 2%; P = 0.04), more aqueous flare (P = 0.02), more macular pucker (69% versus 52%; P = 0.005), and more intravitreal contraction (21% versus 6%; P = 0.002). When compared with eyes that had anterior PVR, eyes with posterior PVR had a better outcome at the 6-month postoperative examination: complete attachment of the retina (76% versus 62%; P = 0.04), visual acuity of 5/200 or better (64% versus 45%; P = 0.006), and normal intraocular pressure (86% versus 71 %; P = 0.04). For eyes with anterior PVR, significant predictors of poor «5/200) visual acuity were a preoperative PVR grade D-1 or worse and the use of CsFs gas as the intraocular tamponade. Conclusion: The Silicone Study classification of anterior PVR permits greater specificity in characterizing PVR and is prognostic of anatomic and vision outcome. Eyes with anterior PVR and clinically significant posterior PVR changes had a better ~isual prognosis if silicone oil was used. With the current understanding of the pathoanatomy of anterior PVR and the recent development of new surgical techniques, the incidence of anterior PVR in eyes that previously underwent vitrectomy may decline, and the prognosis in eyes with anterior PVR may improve. Ophthalmology 1996; 103: 1092-1099

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Diddie et al . Anterior PVR in the Silicone Study The Silicone Study confirmed the superiority of silicone oil over sulfur hexafluoride (SF 6 ) gas as an intraocular tamponade in the management of retinal detachment complicated by severe proliferative vitreoretinopathy (PVR).l Eyes randomized to silicone oil were more likely to be re-attached successfully, to achieve a visu~l acuity of 5/200 or greater, and to have fewer complications than eyes randomized to SF 6 gas. In contrast, the semipermanent tamponade of silicone oil offered little or no advantage over the prolonged but relatively short-term tamponade with perfluoropropane (C 3Fg ) gas.? The Silicone Study also has shown t~~t for t~e cohort of eyes randomized to C 3Fs gas and silicone 011, there were few advantages in outcomes between eyes that underwent a primary vitrectomy for PVR and eyes that already had undergone at least one unsuccessful vitrectomy with gas tamponade before entry into the study." In addition, we have reported on the prognostic association of preoperative diffuse contraction of the retina anterior to the equator and postoperative chronic hypotony," on outcome differences due to retinotorny," on the risks and benefits of discretionary silicone oil removal," and on factors affecting the occurrence of postoperative corneal abnormalities." As part of the study, a Silicone Study classification system for PVR was developed that is based on the characteristic patterns of retinal distortion produced by the contraction of proliferative membranes on the retina or within the vitreous base.s This classification was designed to document the extent and anatomic distribution of PVR present preoperatively and to standardize surgical treatment. In this study, we report on the prevalence of anterior and posterior PVR for the 404 eyes randomized and followed in the Silicone Study. We contrast preoperative and intraoperative findings, and vision and anatomic outcomes and complications, in the cohort of eyes with anterior PVR with the cohort ofeyes with posterior PVR. Finally, we evaluate the benefit ofC3Fg gas versus silicone oil on vision and anatomic outcome within the subgroup

Originally received: May 26, 1995. Revision accepted: March 15, 1996. I Jules Stein Eye Institute, University of California, Los Angeles. 2 Department of Preventive Medicine, University of Southern California, Los Angeles. 3 Retina Associates, Boston. 4 Department of Ophthalmology, Emory University. Atlanta. Kentucky Retina Group, Louisville. Doheny Eye Institute, University of Southern California, Los Angeles. * A list of the Silicone Study Group members appears in Arch Ophtha/mo/ 1992;100:770-9. Presented at the American Academy of Ophthalmology Annual Meeting, August 1992. Supported in part by Public Health research grant NEI EY-05571 and the core grant for Vision Research NEI EY-03040, Bethesda, Maryland, and the Dow Corning Corporation, Midland, Michigan. Reprint requests to Stanley Azen, PhD, Department of Preventive Medicine, University of Southern California, 1540 Alcazar St, CRP 218, Los Angeles, CA 90033. 5

6

of eyes with anterior PVR and also within the subgroup of eyes with posterior PVR.

Methods The overall study design has been reported in detail? and is summarized in the Silicone Study Report Number 1.2 Informed consent and institutional review board approval were obtained for all patients and study centers. For the prevalence study, we report on all 404 eyes recruited and randomized to silicone oil or long-acting gas (either SF6 or C3Fg) , regardless of whether they underwent a primary vitrectomy for PVR or had already undergone at least one unsuccessful vitrectomy with gas tamponade before entry into the study. As part of the Silicone Study protocol, we characterized the distributions of PVR in these eyes at baseline using both the Retina Society and Silicone Study classification systems. The intraoperative and baseline determinations ofPVR were in agreement in 99% of the patients, and the intraoperative and baseline classifications of anterior and posterior PVR were in agreement in 89% of the patients. The Retina Society classification system was designed to grade the type and severity of posterior contraction in PVR. 1O This classification system defined PVR as a continuum of increasing pathology beginning with simple retinal pigment epithelial proliferation and clumping in the vitreous (grade A), to partial-thickness retinal wrinkling produced by contraction of scar tissue (grade B), to full-thickness fixed retinal folds (grades C and D). Grade C was subdivided further according to the number of total clock hours of the retina involved by fixed folds (C-l = 1-3 clock hours, i.e., ::;;90°; C-2 = 4-6 clock hours; and C-3 = 7-9 clock hours). To be classified as grade D, more than 9 clock hours of the retina must be involved by fixed folds. Grade D was further divided according to the narrowness of the funnel configuration of the detached retina: D-l is a wide-open funnel (opening, ~45 0), D-2 is a more narrow funnel (opening, <45°), and D-3 is a closed funnel. The Silicone Study classification system was designed to distinguish the different types of contraction found in PVR. 8 It provides a standardized retinal diagram to depict the various types of traction and a quantitative assessment to record the number of clock hours of the retinal circumference involved with each type of contraction. The contraction is described both in relation to its location relative to the equator of the eye (anterior, posterior, or subretinal), and also in relation to the type of contraction (focal, diffuse posterior, circumferential, perpendicular, and/or anterior). Details are as follows: Eyes with posterior PVR are characterized by one or more of the following two types of contractions: type 1, focal; and type 2, diffuse posterior. Type 1: Focal Contraction. Focal contraction is caused by an epicenter or multiple isolated epicenters of contraction in the posterior zone of the retina. Because there is a focal point toward which the resulting traction is directed, folds radiate away from each epicenter in a characteristic starfold configuration. Because it is local-

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ized, focal contraction has little effect on the overall configuration of the retinal detachment. Type 2: Diffuse Posterior Contraction. Diffuse posterior contraction is caused by linked adjacent epicenters of contraction that produce a diffuse area of irregular retinal folds in the posterior portion of the retina. Contraction in an anterior-posterior direction tends to flatten the normally bullous contours of the more anterior retina. Contraction in the circumferential direction creates a funneled configuration of the posterior retina, with folds radiating anteriorly toward the ora . Eyes with subretinal P VR are characterized by type 3 subretinal contraction. Type 3: Subretinal Contraction. An annular constriction around the optic disc or a linear fold are characteristic patterns of contraction caused by a strand of subretinal membrane. Contraction is mainly in a circumferential direction. Eyes with anterior PVR were characterized by one or more of the following three types of contraction: type 4, circumferential; type 5 perpendicular; or type 6, anterior. Type 4: Circumferential Contraction. Circumferential contraction is caused by diffuse preretinal membrane contraction within or immediately behind the insertion of the posterior hyaloid , which produces an area of irregular folds in this region of the retina. The retina is contracted in a circumferential direction and therefore a series of radial folds tends to form in the redundant retina on either side of the area of irregular folds. Type 5: Perpendicular Contraction. Perpendicular contraction is caused by contraction along an intact posterior hyaloid face. This produces a smooth circumferential fold at the insertion of the posterior hyaloid. Type 6: Anterior Contraction. Anterior contraction occurs most commonly in eyes that have either undergone a previous pars plana vitrectomy or incurred penetrating trauma. Proliferative membranes, which are variably opacified, are present on the remnants of the posterior hyaloid, the anterior hyaloid, and the surface of the residual vitreous base. Using the baseline examination, we classified eyes as having only posterior PVR (i.e., having only types I and/ or 2 contraction) or as having anterior PVR (i.e., having types 4, 5, and/or 6 contraction with or without types I, 2, or 3 contraction). Chi-square and Wilcoxon rank-sum tests were used to compare the differences in preoperative and intraoperative factors between eyes with anterior PVR and eyes with posterior PVR. Logistic regression analysis was used to evaluate the benefit ofC3Fg gas versus silicone oil on vision and anatomic outcome within the subgroup of eyes with anterior PVR and also within the subgroup of eyes with posterior PVR.

Results Prevalence of Anterior and Posterior Proliferative Vitreoretinopathy At the preoperative examination, anterior PVR was found in 321 (79%) of the 404 eyes randomized in the

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Silicone Study. Of these 321 eyes, only 10 (3%) were evaluated as having only anterior PVR, with no posterior PVR present. At the preoperative examination, posterior PVR without anterior PVR was found in 83 (21%) of the 404 eyes. Anterior PVR was more prevalent in eyes that had undergone at least one unsuccessful vitrectomy with gas tamponade before entry into the study than it was in eyes that underwent a primary vitrectomy for PVR: 151 (88%) of 172 eyes versus 170 (73%) of 232 eyes (P < 0.00 I). Table I contrasts the demographic and ophthalmologic characteristics for the 321 anterior PVR eyes with these characteristics for the 83 posterior PVR eyes. Compared with posterior PVR eyes, anterior PVR eyes tended to have a higher grade than C-3 according to the Retina Society classification system (76% versus 49%; P < 0.000 I), had worse (hand motions or light perception) preoperative visual acuity (92% versus 85%; P = 0.003), had more hypotony (24% versus II %; P = 0.03), more edema or corneal opacities (13% versus 2%; P = 0.04), and more aqueous flare (73% versus 60%; P = 0.02). Equal numbers of eyes were aphakic or pseudophakic. No other significant differences were found .

Intraoperative Evaluation Table 2 contrasts the prevalence of traction and breaks between the anterior PVR and posterior PVR eyes. Anterior loop contraction was present in 200 eyes with anterior PVR (62%), was more prevalent in eyes that had undergone at least one unsuccessful vitrectomy before entry into the stud y than it was in eyes that underwent a primary vitrectomy for PVR (82% versus 45%; P < 0.0001), and involved the following factors: three quadrants or more in 109 eyes; 7 to 12 hours in 109 eyes; the superior fundus in 9 eyes, the inferior fundus in 67 eyes, and both the superior and inferior fundi in 123 eyes. Diffuse anterior traction was present in 222 eyes (73%) with anterior PVR, was more prevalent in eyes that had undergone at least one unsuccessful vitrectomy than it was in eyes that underwent a primary vitrectomy for PVR (81% versus 59%; P < 0.003), and involved the following factors: three quadrants or more in 152 eyes and extended over 7 hours in 148 eyes; the inferior fundus in 36 eyes, the superior fundus in 7 eyes, and both superior and inferior fundi in 159 eyes. Posterior hyaloid contraction was present in 151 eyes (47%) with anterior PVR, was less prevalent in eyes that had undergone at least one unsuccessful vitrectomy than it was in eyes that underwent a primary vitrectomy for PVR (15% versus 75%; P < 0.0001), and involved the following factors: two quadrants or more in 148 eyes; the superior fundus in 1 eye, the inferior fundus in 30 eyes, and both the superior and inferior fundi in 120 eyes. Compared with posterior PVR eyes, anterior PVR eyes had significantly more macular pucker (69% versus 52%; P = 0.005) and intravitreal contraction (21% versus 6%; P = 0.002). There were no differences in the numbers and locations of breaks.

Diddie et al . Anterior PVR in the Silicone Study Table 1. Demographic Characteristics, Ocular History and Baseline Ocular Findings for Eyes with Anterior or Posterior-only Proliferative Vitreoretinopathy (all randomized eyes) Characteristic

Anterior PVR (n = 321)

Posterior PVR (n = 83)

21-88

64

64 20-85

0.81

94 (29) 227 (71)

26 (31) 57 (69)

0.72

76 (24) 84 (26) 87 (27) 74 (23)

42 (51) 14 (17) 15 (18) 12 (14)

<0.0001

11 (3) 13 (4) 184 (57) 113 (35)

6 (7) 6 (7) 54 (65) 17 (20)

0.003

117 (36) 204 (64)

31 (37) 52 (63)

0.88

77 (24) 236 (74) 5 (2)

9 (11) 73 (88) 1 (1)

0.03

279 (87) 25 (8) 14 (4) 3 (1)

81 (98) 2 (2) 0(0) 0(0)

0.04

201 (63)

50 (52)

0.D7

234 (73)

50 (60)

0.02

23 (7) 14 (5)

2 (2) 1 (1)

0.11 0.21

Age (yrs) Median Range Sex(%) Female Male Retina Society Classification (%) C-3 D-1 D-2 D-3 Visual acuity (%) ~5/200

2/200 Hand motions Light perception Refractive status (%) Phakic Aphakic/pseudophakic IOPt (mmHg) (%) :0:;5 (hypotony) 6-29 (normal) ~30 (elevated lOP) Corneal status (%) Clear Edema Opacity Both Aqueous cells (%) Present (1+ to 4+) Aqueous flare (%) Present (1+ to 4+) Neovascularization (%) Present Angle PVR

=

proliferative vitreoretmopathv; lOP

=

P*

intraocular pressure.

• Wilcoxon rank-sum test performed for age, PVR grade, and visual acuity; other variables were tested using the chi-square test or Fisher's exact test.

t

The following parameter had reduced sample size due to missing data: lOP (3 anterior).

Surgical Technique in Eyes with Anterior Posterior Proliferative Vitreoretinopathy Membrane dissection was carried out in three or more quadrants in 316 eyes (99%). Dissection was limited to the inferior fundus in 23 eyes (7%), and dissection was performed in both inferior and superior fundi in 293 eyes (92%). Membrane dissection was classified as "easy" in 73 eyes (23%), "difficult" in 223 eyes (69%), and "impossible" in 22 eyes (7%). Relaxing retinotomy was performed outside the posterior pole in 98 eyes (31%). The retinotomy was oriented in a circumferential direction in 85 eyes (87%), extending less than 6 hours in 69 eyes (98%). The retinotomy involved the inferior fundus in only 33 eyes (39%), the su-

perior fundus only in 4 eyes (5%) and both inferior and superior fundi in 48 eyes (56%). Radial retinotomy was performed in 18 eyes (6%), extended less than 6 hours in 16 eyes (89%), involving the superior fundus only in 7 eyes (39%), the inferior fundus in 5 eyes (28%), and both superior and inferior fundi in 6 eyes (33%). A relaxing retinotomy in the posterior pole was made in 12 eyes (4%). Relaxing retinotomy was performed less frequently in eyes that had undergone at least one unsuccessful vitrectomy (36 eyes, 37%) than it was in eyes that underwent a primary vitrectomy for PVR (62 eyes, 63%). Subretinal fluid was drained through a retinotomy in 200 eyes (62%), through a pre-existing retinal break in 130 eyes (40%), and through a sclerotomy in 4 eyes (1%). Drainage was done more frequently through a pre-existing

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Table 2. Intraoperative Evaluation of Eyes" with Anterior or Posterior-only Proliferative Vitreoretinopathy (all randomized eyes) Variable Type of traction (%) Anterior loop Diffuse anterior Posterior hyaloid Focal contraction Macular pucker Diffuse posterior Intravitreal Subretinal fibrosis Breaks (%) STQ

SNQ STQ+ SNQ ITQ INQ ITQ + INQ

Randomized treatment (%) Gas Silicone oil

Anterior PVR (n = 321)

Posterior PVR (n = 83)

Pt

200 (62) 222 (73) 151 (51) 271 (84) 219 (69) 240 (79) 67 (21) 63 (21)

72(88) 43 (52) 43 (78) 5 (6) 17 (21)

0.44 0.005 0.86 0.002 0.95

137 (44) 82 (26) 36 (11) 179(58) 111 (36) 70 (22)

28 (34) 18 (22) 6 (7) 40(49) 30 (37) 11 (13)

0.11 0.39 0.29 0.14 0.84 0.08

162 (50) 159(50)

40(48) 43 (52)

0.94

PVR = proliferative vitreoretinopathy; STQ = superotemporal quadrant; SNQ = superonasal quadrant; ITQ = inferotemporal quadrant; INQ = inferonasal quadrant. • Eyes classified as "cannot determine" are not included in the calculation of the percentages.

t

Variables tested using the chi-square test or Fisher's exact test.

retinal break that had undergone at least one unsuccessful vitrectomy (77 eyes, 59%) than it was in eyes that underwent a primary vitrectomy for PVR (53 eyes, 41%). Drainage was made most often in the superior nasal quadrant in 135 eyes (42%) and in the inferior quadrant in 83 eyes (26%). A scleral buckle was added in 30 eyes (9%), revised in 83 eyes (26%), and removed in 6 eyes (2%). Mechanical fixation devices were used in 15 eyes (16%). Equal numbers of eyes were randomized to long-acting gas (162 eyes, 50%) or silicone oil (159 eyes, 50%). Intraoperative complications occurred in 64 eyes (20%), retinal hemorrhage in 25 eyes (8%), choroidal hemorrhage in 13 eyes (4%), vitreoretinal incarceration in 4 eyes (2%), and subretinal air or gas in 10 eyes (3%). The duration of surgery ranged from 1 to 9 hours (median, 3 hours).

Surgical Technique in Eyes with Posterior Proliferative Vitreoretinopathy Membrane dissection was carried out in three or more quadrants in 83 eyes (99%). Dissection was limited to the inferior fundus in 6 eyes (7%), and dissection was performed in both inferior and superior fundi in 76 eyes (92%). Membrane dissection was classified as "easy" in 26 eyes (31%), "difficult" in 55 eyes (66%), and "impossible" in 2 eyes (7%). Relaxing retinotomy was performed outside the posterior pole in 19 eyes (22%). The retinotomy was oriented in a circumferential direction in 16 eyes (84%), extending

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less than 6 hours in 12 eyes (75%). The retinotomy involved the inferior fundus in only ten eyes (63%), the superior fundus only in one eye (6%), and both inferior and superior fundi in seven eyes (43%). Radial retinotomy was performed in seven eyes (8%), extending less than 6 hours in six eyes (85%), involving the superior fundus only in one eye (16%),the inferior fundus in six eyes(85%), and both superior and inferior fundi in one eye (16%). Relaxing retinotomy was less frequently performed in eyes that had undergone at least one unsuccessful vitrectomy (10 eyes, 53%) than it was in eyes that underwent a primary vitrectomy for PVR (9 eyes, 47%). Subretinal fluid was drained through a retinotomy in 50 eyes (60%), through a pre-existing retinal break in 32 eyes (38%), and through a sclerotomy in 2 eyes (2%). Drainage was done more frequently through a pre-existing retinal break in eyes that had undergone at least one unsuccessful vitrectomy (17 eyes, 53%) than it was in eyes that underwent a primary vitrectomy for PVR (15 eyes, 47%). Drainage was made most often in the superior nasal quadrant in 40 eyes (48%) and in the inferior quadrant in 19 eyes (23%). A scleral buckle was added in 11 eyes (13%), revised in 19 eyes (23%), and removed in 3 eyes (4%). Mechanical fixation devices were used in 11 eyes (13%). Equal numbers of eyes were randomized to long-acting gas (40 eyes, 48%) or silicone oil (43 eyes, 52%). Intraoperative complications occurred in 22 eyes (27%), retinal hemorrhage in 10 eyes (12%), choroidal hemorrhage in 2 eyes (2%), vitreoretinal incarceration in 3 eyes (4%), and subretinal

Diddie et al . Anterior PVR in the Silicone Study Table 3. Outcome of the Follow-up Examination for Eyes with Anterior or Posterior-only Proliferative Vitreoretinopathy (excludes eyes randomized to sulfur hexafluoride gas) Parameter

Anterior PVR (n = 272)

Posterior PVR (n = 66)

p.

Anterior PVR (n = 266)

6-mo Follow-upt

Retina (%) Completely attached Detached Visual acuity (%) ~5/200

<5/200

lOP (mmHg) (%) ~5 (hypotony) 6-29 (normal) ~30 (elevated lOP) Corneal status (%) Clear Edema Opacity Both Aqueous cells (%) Present (1+ to 4+) Aqueous flare (%) Present (1+ to 4+) Neovascularization (%) Present PVR

=

Posterior PVR (n = 62)

p.

12-mo Follow-upi'

164 (62) 100 (38)

48 (76) 15 (24)

0.04

158 (65) 85 (35)

44 (79) 12 (21)

0.04

122 (45) 150 (55)

42 (64) 24 (36)

0.006

117 (44) 149 (56)

24 (61) 24 (39)

0.01

68 (26) 190 (71) 8 (3)

9 (14) 55 (86) 0(0)

0.04

62 (25) 183 (73) 6 (2)

6 (11) 49 (88) 1 (2)

0.07

194(72) 43 (16) 27 (10) 4 (1)

47 (73) 11 (17) 5 (8) 1 (2)

0.95

174 (69) 41 (16) 29 (11) 10 (4)

43 (74) 7 (12) 5 (9) 3 (5)

0.74

89 (36)

22 (38)

0.80

62 (28)

19 (35)

0.54

112(46)

25 (43)

0.70

89 (40)

19 (35)

0.54

13 (5)

1 (2)

0.32

4 (2)

0(0)

0.32

proliferative vitreoretinopathy; lOP

=

intraocular pressure.

• Variables tested using the chi-square test or Fisher's exact test.

t The following parameters had reduced sample sizes due to missing data: retinal status (8 anterior, 3 posterior), lOP (6, 2), corneal status (4, 2), aqueous cells (6, 8), and aqueous flare (5, 7). t The following parameters had reduced sample sizes due to missing data: retinal status (23 anterior, 6 posterior), lOP (15, 6), corneal status (12, 4), aqueous cells (43,8), and aqueous flare (38,8).

air or gas in 1 eye (3%). The duration of surgery ranged from 1 to 9 hours (median, 4 hours). Outcome at the 6- and 12-month Follow-up Visit Because of their poor prognosis, eyes randomized to SF6 gas were excluded from the analysis of outcome. However, silicone oil eyes randomized during the SF6 versus silicone phase of the study are included. Two-hundred seventy-two eyes with anterior PVR and 66 eyes with posterior PVR randomized to silicone oil or C3Fs gas were examined at 6 months. The rates of postoperative procedures and repeat surgeries were similar between eyes with anterior PVR and eyes with posterior PVR: fluid-gas exchanges (15% versus 11%; P = 0.38); silicone oil removals (14% versus 20%; P = 0.28); and repeat surgeries (26% versus 35%; P = 0.14). Table 3 contrasts the outcome at 6 months for these eyes. In general, eyes with posterior PVR had significantly better outcomes than eyes with anterior PVR. Significantly more posterior PVR eyes were completely attached (76% versus 62%; P = 0.04), had visual acuity of 5/200 or greater (64% versus 45%; P = 0.006), and had less hypotony (14% versus 26%; P = 0.04).

Table 3 also contrasts the outcome for 266 anterior PVR eyes and 62 posterior PVR eyes examined at 12 months. Significantly more posterior PVR eyes were attached completely (79% versus 65%; P = 0.04) and had better visual acuity (61 % versus 44%; P = 0.01). Although nonsignificant, there was a trend for less hypotony in the group of eyes with posterior PVR (11% versus 25%; P = 0.07). A logistic regression analysis was conducted to evaluate the effect of treatment (C3Fs gas versus silicone) on outcome in eyes with anterior PVR and also in eyes with posterior PVR. Because we have demonstrated previously that the Retina Society grading is significantly associated with outcome, all analyses were adjusted for whether the grade was C-3 or greater than C_3.11 For eyes with anterior PVR, significant predictors of poor «5/200) visual acuity were a preoperative PVR grade greater than C-3 and the use of C 3F s gas as the intraocular tamponade (Table 4). For eyes with anterior PVR, the risk of poor visual acuity outcome is 2.1 times greater in grade D-1 eyes or worse than in grade C-3 eyes. An anterior PVR eye graded as D-1 or worse was two times more at risk for poor visual acuity if treated with long-acting gas than if treated with silicone oil. A

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preoperative PVR classification greater than C-3 also was predictive of postoperative retinal detachment. Compared with anterior PVR eyes graded as C-3 , anterior PVR eyes graded as D-I or worse were two times more at risk for anatomic failure. The choice of intraocular tamponade was not prognostic of anatomic outcome at 6 months. For eyes with posterior PVR, neither the PVR grade nor the intraocular tamponade was prognostic of visual acuity or anatomic outcomes at 6 months (Table 4).

Discussion The Silicone Study was designed to evaluate the risks and benefits of silicone oil and long-acting gas in treating PVR, the most common reason for unsuccessful retinal detachment repair. Using the original Retina Society classification system, 10 an eye had to have at least grade C-3 PVR to be eligible for the Silicone Study. During the Silicone Study, investigators observed that much of the clinically significant PVR was located anterior to the equator. 12, 13 Consequently, the in vestigators developed and reported on an alternative classification system for PVR to take this into account." The resulting Silicone Study classification system included the characteristic types of contraction found in both the equatorial region and the pre-equatorial retina and vitreous base (anterior PVR). The Silicone Study classification system provided a description ofPVR relevant to modem vitreoretinal surgery,

which involved the identification and dissection of both posterior and anterior PVR. The addition of these anterior categories allows for greater specificity in characterizing PVR . For example, using the Retina Society classification system, an eye with a grade D-3 (closed funnel) retinal detachment has the most severe stage of PVR. However, this eye may have little PVR anterior to the equator; therefore, this could be considered an exaggerated macular pucker, with a relatively good prognosis. Anterior PVR was more prevalent than posterior PVR in eyes treated and followed in the Silicone Study. The prevalence of anterior PVR was 79%, emphasizing that eyes randomized, treated, and followed in the Silicone Study had severe PVR. The prevalence of anterior PVR was significantly greater in eyes with vitrectomy before study entry than in eyes without a prior vitrectomy (88% versus 73%; P < 0.001). Anterior PVR may be promoted by a failed vitrectomy, or these eyes may have had more severe PVR initially, which precipitated their failed prerandomization vitrectomy. These data confirm that the classification of anterior PVR has prognostic use (Table 3). At both the 6- and 12month follow-up examinations, eyes with anterior PVR were less likely to have a completely attached retina (P < 0.05), less likely to have visual acuity of 5/200 or greater (P < 0.0 I), and more likely to have hypotony (P < 0.05 at 6 months only). Eyes with anterior PVR had a particularly poor prognosis with advanced grades of PVR according to the Retina Society classification system (Table 4). The Silicone Study found that silicone oil and C3Fs were, in general, equall y effective in treating PVR.2 On

Table 4. Benefit of Perfluoropropane Gas Relative to Silicone Oil at 6 Months in Eyes with Anterior and Posterior Proliferative Vitreoretinopathy (excludes eyes randomized to sulfur hexafluoride gas) Significant Predictor

Odds Ratio" (95% confidence interval)

p

Anterior PVR

Poor visual acuity « 5/ 200) PVR grade > C-3 Use of C 3F8 gas Retina detached PVR grade> C-3 Use of C 3FB gas

2.1 (1.2, 3.8) 2.0 (1.2, 3.3)

0.008 0.006

2.0 (1.1, 3.8) 0.8 (0.5, 1.4)

0.03 0.43

Posterior PVR

Poor visual acuity « 5/2 00) PVR grade> C- 3 Use of C 3F8 gas Ret ina detached PVR grade> C-3 Use of C 3F8 gas

1.7 (0.6, 4.8) 0.9 (0.3, 2.5)

0.28 0.79

1.6 (0.5, 5.1) 0.6 (0.2, 2.1)

0.40

0.43

ClFs = perfluoropropane; PVR = proliferative vitreoretinop ath y. • The odds ratios represent the risk of a poor outcome for each of the prognostic factor s. For exampl e, compared with anterior eyes graded as C-3, the risk of poor visual acuity outcome is 2.1 times greater in eyes with a Dvl grading or worse at the preoperative examination.

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Diddie et al . Anterior PVR in the Silicone Study the other hand, data from this subgroup analysis indicate that eyes with anterior PVR and clinically significant posterior PVR changes had a better visual prognosis if silicone oil rather than C3Fg gas was used. However, because there was a high incidence of relaxing retinotomies (31 % in eyes with anterior PVR, 22% in eyes with posterior PVR) , these data must be interpreted with caution. Modem surgical techniques allow the vitreoretinal surgeon to approach the anterior PVR directly and to avoid relaxing retinotomies in the majority of patients, yielding a better visual and anatomic outcome. 14.15 Therefore, the observed beneficial effect of silicone oil found in this study may be attenuated with more peripheral dissection and fewer retinotomies. A better understanding of the pathoanatomy of anterior PVR combined with modem surgical techniques are likely to decrease the incidence of anterior PVR and to improve the anatomic and visual outcome in these eyes.

References I. The Silicone Study Group. Vitrectomy with silicone oil or sulfur hexafluoride gas in eyes with severe proliferative vitreoretinopathy: Results of a randomized clinical trial. Silicone Study Report I. Arch Ophthalmol 1992;110:770-9. 2. The Silicone Study Group. Vitrectomy with silicone oil or perfluoropropane gas in eyes with severe proliferative vitreoretinopathy: Results of a randomized clinical trial. Silicone Stud y Report 2. Arch Ophthalmol 1992;110:780-92. 3. McCuen BW, Azen SP, Stern W, et al. Vitrectomy with silicone oil or perfluoropropane gas in eyes with severe proliverative vitreoretinopathy: results in group I versus group 2 (Silicone Stud y Report no. 3). Retina 1993;13:279-84.

4. Barr CC, Lai MY, Lean JS, et at. Postoperative intraocular pressure abnormalities in the Silicone Study (Silicone Stud y Report #4). Ophthalmology 1993;100:1629-35. 5. Blumenkranz MS, Azen SP, Aaberg TM, et al. Relaxing retinotomy with silicone oil or long acting gas in eyes with severe proliferative vitreoretinopathy (Silicone Study Report 5). Am J Ophthalmol 1993;116:557-64. 6. Hutton WL, Azen SP, Blumenkranz MS, et al. The Effects of silicone oil remo val in the Silicone Study (Silicone Stud y Report 6). Arch Ophthalmol 1994;112:778-85. 7. Abrams GW , Azen SP, Barr CC, et al. The incidence of corneal abnormalities in the Silicone Study (Silicone Stud y Report 7). Arch Ophthalmol 1995; 113:764-9. 8. Lean JS, Stern WH, Irvine AR, Azen SP for the Silicone Study Group. Classification of proliferative vitreoretinopathy used in the Silicone Study. Ophthalmology 1989;96: 765-71. 9. Azen SP, Boone DC, Barlow W, et at. Methods, statistical features and baseline results of a standardized, multicentered ophthalmologic surgical trial: the Silicone Study. Control Clin Trials 1991;12:438-55. 10. The Retina Society Terminology Committee. The classification of retinal detachment with proliferative vitreoretinopathy. Ophthalmology 1983;90:121-5. II. Lean J, Azen SP, Lopez P, et at. The prognostic utility of the Silicone Study classification system. (Silicone Stud y Report 9). Arch Ophthalmol 1996;114:286-92. 12. Lewis H, Aaberg TM . Anterior proliferative vitreoretinopathy . Am J Ophthalmol 1988;105:277-84. 13. Aaberg TM . Management of anterior and posterior proliferative vitreoretinopathy. XLV Edward Jackson Memorial Lecture. Am J Ophthalmol 1988;106:519-32. 14. Lewis H, Aaberg TM, Abrams GW. Causes of failure after initial vitreoretinal surgery for severe proliferative vitreoretinopathy. Am J Ophthalmol 1991; III :8-14. 15. Lewis H, Aaberg TM. Causes of failure after repeat vitreoretinal surgery for recurrent proliferative vitreoretinopathy. Am J Ophthalmol 1991;111:15-9.

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