FP 314 : Clinical Outcome of Pars Plana versus Anterior Chamber Ahmed Glaucoma Valve for Refractory Glaucoma

Dr.MEENA MENON , 

Dr.Aditi Singh

Introduction :

Historically, glaucoma drainage devices (GDDs) have beenreserved for patients deemed to be poor candidates forpartial thickness guarded filtration procedures.¹ In recentdecades, GDDs have increasingly been incorporated into theroutine surgical management of glaucoma patients, due totheir favorable safety profile, promising long-term successrates, and less frequent need for follow-up¹.

Conventional anterior chamber (AC) placement ofGDDs has been associated with anterior segment complications,including corneal endothelial touch, corneal endothelialfailure, and corneal graft failure.² In addition, ACplacement may not be feasible in certain cases, such aspatients with inadequate anatomical space in the AC orthose with previously compromised corneas.³ Implantationof GDD tubes into the posterior segment through the parsplana (PP) has been described as an alternative surgical

strategy since 1991, as the more posterior location of thetube reduces the risk of corneal decompensation and tubeerosion.⁴ However, PP placement of GDD tubes has operativerisks as well, including vitreous incarceration of thetube, vitreous hemorrhage, and retinal detachment.⁵ Success

rates of intraocular pressure (IOP) control after PP placementof GDD tubes for the management of refractoryglaucoma and in the context of concurrent newer cornealprocedures have been variable but promising.^6-10

The purpose of the present study was to compare the clinical outcomes andcomplications of eyes undergoing Ahmed GDD implantation with PP tube placement witheyes which had conventional AC tube implantation.

Materials and Methods :

Study Design : This is a retrospective review of patients undergoing glaucoma tube implant surgery between 2014  and 2017.Because of the retrospective nature ofthe study, written informed consent was not required.

Study Population :

Inclusion criteria :

patients who underwent a PP or an AC tube placementof an Ahmed Glaucoma Valve (FP-7 or PC-7

model,New World Medical, Rancho Cucamonga, CA) between January 2014 and December 2017

at Sankara eye hospital ,  Bengaluru.  Clinical and surgicalrecords of patients were retrospectively reviewed.

Surgical Technique :

Ophthalmologic comorbidities were used as selectioncriteria for tube placement. A low corneal endothelial count,Fuchs’ dystrophy, and previous corneal transplant were the comorbidities used more frequently as justification for theposterior positioning of the tube. Valve model was selectedby surgeon discretion. For all GDD surgery, the plate wassecured to sclera in subtenon’s space, roughly 8mm behindthe limbus, with nonabsorbable suture. Ahmed plates wereplaced between adjacent recti  muscles. For AC tubes, a 22-gauge needle was used to makea sclerostomy into the AC. For PP tubes, the tube wasrouted directly into the posterior segment through either anexisting trochar port from the concurrent vitrectomy, orthrough a new sclerostomy created with a 23-gauge needleabout 3 to 3.5mm posterior to the limbus. All deviceimplantations were performed by a single glaucoma surgeon and vitrectomies were performedby 1 of 3  vitreoretinal surgeons between January 2014 and December2017.

Data Collection :

Demographic characteristics recorded for each patientincluded age, sex, glaucoma diagnosis, preoperativelens and cornea status, ocular surgical history, and concurrentintraocular surgeries.

Collected clinical data included Snellen best-corrected visualacuity (BCVA), IOP (by Goldmann applanation Tonometryor Tonopen or digitally in keratoprosthetic eyes), and number of IOP-lowering medications,and was extracted from medical reports written at baselineand at each postoperative visits until last date of follow-up. Complicationsincluding corneal decompensation, vitreous hemorrhage,tube erosion, diplopia (based on patient’s self-report), and hypotony (defined as IOP <6mmHg) were recorded.

Outcome Measures :

Criteria for success were defined as postoperative IOPbetween 6 and 21mmHg with ( qualified ) or without ( complete )  supplementalglaucoma medication, preservation of light perception orbetter vision, and no further glaucoma surgeries at the timeof the last follow-up visit. Cases that did not fulfill these criteria were defined as a failure.

Statistical Analysis :

RESULTS : Baseline characteristics of patients are described in Table 1. Sixteen eyes of 16 patients underwent PP placementof an Ahmed glaucoma implant, and twenty two eyes of 22 patients underwent AC placement of an Ahmed implant. Average age at the time of surgery was 45.7 yearsin the PP group and 33.6 years in the AC group . Mean preoperative best corrected visual acuity was log MAR 1.71  and log MAR 1.70 in AC and PP groups respectively

Glaucoma diagnoses from most common to leastcommon were  neovascular glaucoma (23.7 %), silicon oil induced glaucoma ( 21.05%) , post penetrating keratoplasty  ( 10.5%), congenital glaucoma ( 10.5%),aphakic (7.8%), combined mechanism ( 7.8%) , unspecified ( 5.2%),others ( POAG,PACG,steroid induced ,post uvietic, post traumatic)  2.6% each.( Table 2 ) Five  eyes in the AC entry group and 2 eyes in the PP group had undergone a prior glaucoma surgery. Mean follow up in AC entry group was 18.5 months and 13.4 months in PP group.Table 3 describes the postoperative data at last followup.Mean preoperative IOP in AC entry group was 34.9 mm of Hg and 35.13 in the PP group.Mean IOP in the last postoperative follow up  was 15.16 +3.9 mm of Hg  and  16.13 + 7.3 mm of Hg in AC and PP entry group respectively .In bothgroups, mean IOP at all follow-up time points was lower thanmean preoperative IOP.At last follow-up, mean IOP had decreased  by 19.7 mm of Hg in AC entry group  and 19 mm of  Hg in PP group.

Mean number of antiglaucoma medications decreased from 3.32  and  3.06  preoperatively  to 1.95 and 2.0 at last postoperative follow up in AC and PP entry  groups respectively.Mean postoperative BCVA was log MAR 1.19  and log MAR 1.63 in AC and PP groups respectively. In the AC entry group 9.1 % had complete success , 81.8% has qualified success , while 9.1 % were lost to follow up. None of the patients in this group had failure till last follow up. In the PP entry group 6.3 % had complete success , 56.3%  has qualified success , 12.5 % were lost to follow up, while 25% had failure till last follow up . Overall success rate of Ahmed implant in our study was 78.9% ( 7.9 % complete success , 71.1% qualified success) . 22.7 % eyes of AC group and 43.8% eyes in PP group  had complications. 18.2 %  eyes in the AC entry group and 25 % eyes in the PP group required revision surgeries.

Discussion :

This retrospective study examined the clinicaloutcomes of GDD AC versus PP tube placement.The

study found an overall success rate of 90.9% for the AC group and  62.6 % for the PP group.

Despite differences in baseline characteristicswith regard to their previous surgeries,sample size, this findingsuggests that PP placement of GDD tubes can provide comparable  IOP control as effectively as AC placement of tubes.Although direct comparison between previous studies is

difficult because of differing study populations, the successrates reported here slightly  differ  to those reported in otherstudies of PP placement of GDD tubes, which range from72% to 94%^7,11-16, . This can be due to small sample size and inclusion of all age groups.

Mean IOP and mean number of IOP-lowering medicationsdid not differ between PP and AC groups at baseline,last follow-up, or any interim time points and remained in that range .The Tube Versus Trabeculectomystudy reported a 43% reduction in IOP at 5 yearsafter AC placement of a GDD¹⁷. The decrease in meannumber of glaucoma medications required in both groups isan additional positive indicator that the surgery effectivelyreduced IOP.

Visual acuity can be affected by many ocular factors,and a wide range of VA outcomes have been reported afterplacement of GDDs^7,11,16, with stable or improved VAattributed to the higher proportion of concurrent VA-correcting  procedures performed, including secondary IOLplacements and corneal grafts. In our study there was an improvement of mean BCVA.

Limitations of this study include its retrospective nature,small sample size , variability in sample size between two groups,  variability of follow-up times, and inability to match cases andcontrols on characteristics such as age , previous ocular procedures.

Table 1 : Baseline characteristics

	AGV through AC entry	AGV through pars plana entry
No of eyes	22	16
Mean Age	33.6 years	45.7 years
Preoperative mean BCVA	logMAR 1.71	logMAR 1.70
Gender   Male                  Female	12 10	9 7
Preoperative mean IOP	34.9 mm Hg	35.13 mm Hg
Preoperative mean no. of antiglaucoma medications	3.32	3.06
No. of eyes with prior glaucoma surgery	5	2

Table 2 : Glaucoma diagnosis

Glaucoma Diagnosis	No. of eyes	Percentage
Neovascular Glaucoma	9	23.7
Silicone oil induced	8	21.05
Post penetrating keratoplasty	4	10.5
Congenital	4	10.5
Aphakic	3	7.8
Primary open angle	1	2.6
Primary angle closure	1	2.6
Steroid induced	1	2.6
Post traumatic	1	2.6
Post uveitic	1	2.6
Combined mechanism	3	7.8
Unspecified	2	5.2

Table 3 : Postoperative data at last followup 

	AGV through AC entry	AGV through pars plana entry
Mean follow up	18.5 months	13.4 months
Mean IOP at last followup	15.16 + 3.9 mm of Hg	16.13 + 7.3 mm of Hg
Mean decrease in IOP	19.7 mm of Hg	19.0 mm of Hg
Mean no of antiglaucoma medications at last followup	1.95	2.0
Mean postop BCVA at last followup	logMAR 1.19	logMAR 1.63
Complete success	9.1 %	6.3%
Qualified success	81.8 %	56.3%
Lost to followup	9.1%	12.5%
Failure	0%	25.0%
Revision surgeries	18.2%	25%

 Conclusion:

Insertion of AGV into the pars plana is safe and effective method for IOP control in selected cases.

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