It is the impression of many ophthalmologists that primary open angle glaucoma may behave differently in black populations than in other populations.1-6 The disease may have a greater prevalence, present earlier, progress more rapidly, respond to medicines differently, and be associated with a higher percentage of blindness. In addition, numerous authors have suggested that filtration surgery in blacks has a lower rate of success. The purpose of this paper is to assess the early results of filtration surgery for primary open angle glaucoma in a West Indian black population and to compare the results of two different types of filtration procedures.
MATERIALS AND METHODS
Black patients with primary open angle glaucoma were included in this study. Congenital, angle closure, and secondary open angle glaucoma were excluded. All reoperative, combined cataract/nitration, and aphakic procedures were excluded. All patients were examined by one of the three authors and found to have an unacceptable intraocular pressure for optic nerve and/or visual field on maximal tolerated medical therapy. Medical therapy included pilocarpine 1-6%, epinephrine derivatives, timolol maléate, and carbonic anhydrase inhibitors. Eighty filtration procedures were reviewed. There were 39 scierai flap trabeculectomy (partial thickness) procedures and 41 posterior Hp sclerectomy (full thickness) procedures. The average follow-up for both groups was six months. All surgery was done by one of the authors or by a senior eye resident under our direct supervision.
Aqueous suppressants were stopped in all patients, and topical chloramphenicol drops were given to preoperative eyes the day prior to surgery. Surgery was performed at the Queen Victoria Hospital, Castries, St. Lucia, West Indies. Local anesthesia and an operating microscope were used for all cases. A 4-0 silk superior reclus bridle suture and a timbal anterior chamber paracentesis were performed initially in all 80 cases.
PARTIAL THICKNESS FILTRATION PROCEDURE: Trabeculectomy (Group 1) 1. Superior fornix-based conjunctival flap. 2. Tenons capsule excision. 3. Meticulous cautery. 4. Rectangular Vz partial thickness scierai flap, Iimbus based. Dissection into clear cornea. 5. 2 mm x 4 mm rectangular tissue excision at the base of dissection to create sclerostomy. 6. Wide basal iridectomy. 7. Loose closure of posterior corners of scierai flap with two 9-0 or 10-0 nylon sutures. 8. Closure of conjunctival flap at each corner with interrupted 9-0 or 10-0 nylon sutures . 9. Anterior chamber deepened with balanced salt solution through paracentesis to assure patency of sclerostomy, bleb elevation and absence of leakage. Additional conjunctival sutures placed if necessary.
FULL THICKNESS FILTRATION PROCEDURE: Posterior lip sclerectomy (Group 2). 1. Superonasal limbal-based conjunctival flap. 2. Tenons capsule excision. 3. Meticulous cautery. 4. Perpendicular superblade incision through cornea immediately posterior to the conjunctival reflection. 5. Posterior lip sclerectomy <2 mm x 2 mm) with punch or super-blade excision to create sclerostomy. 6. Wide basal iridectomy. 7. Conjunctival flap closure with interrupted 10-0 nylon sutures. 8. Anterior chamber deepened with balanced salt solution through paracentesis to assure patency of sclerostomy, bleb elevation and absence of leakage. Additional conjunctival sutures placed if necessary.
All postoperative cases received similar programs of topical atropine, steroids and antibiotics. No systemic steroids were used. Patients remained hospitalized until the anterior chamber depth stabilized (three to seven days). Topical atropine and steroids were gradually tapered over a period of two months as postoperative inflammation subsided. A single daily drop of topical chloramphenicol was maintained indefinitely.
The independent sample (2-tailed) t-test for population differences, and the chi-square with Yates correction test were used for analyzing group differences, with P < 0.05 accepted as significant.
PREOPERATIVE EVALUATION (Table 1): No statistically significant differences were noted between the two groups with regard to average age, vision, intraocular pressure, or preoperative medications. The intraocular pressures recorded in Table 1 were the average of those measured for each patient at their clinic visit just prior to surgery. The number of glaucoma medications recorded in Table 1 were based on each patient's maximally tolerated medical program.
Group 1 had significantly more males than Group 2 (P < 0.01), and these males had higher preoperative intraocular pressures (P < 0.05) and a younger average age than female Group 1 patients or all Group 2 patients. The male preponderance and younger age noted in Group 1 did not alter the statistical significance of the difference between postoperative pressures between Group 1 and Group 2.
POSTOPERATIVE EVALUATION (Table 2): Vision - Vision did not change significantly from preoperative levels over the course of observation for Group 2. Two patients in Group 1 with markedly advanced glaucomatous optic nerve damage went from light perception to no light perception postoperatively.
Intraocular Pressure - A statistically significant difference between Group 1 and Group 2 was noted for average postoperative intraocular pressures (P < 0.0001). Group 1 had an average postoperative intraocular pressure of 17 mmHg; Group 2 had an average postoperative intraocular pressure of 10 mmHg (Table 2).
The number of patients with postoperative intraocular pressure less than 20 mmHg was significantly different for the two groups (P < 0.001). Group 1 had 27/39 eyes with postoperative intraocular pressures less than 20 mmHg, whereas Group 2 had 39/41 eyes with pressures less than 20 mmHg. A greater number (P < .001) of Group 1 eyes required glaucoma medications to achieve pressure reduction in comparison to Group 2 eyes.
Filtration Bleb - Analysis of filtration bleb formation postoperatively found a significant difference between the two groups. Blebs were characterized as either scarred, cystic/local or cystic/diffuse. 22/39 Group 1 eyes had flat, scarred blebs compared to 5/41 Group 2 eyes. The majority of Group 2 patients had local, thin, cystic blebs, and the only diffuse, cystic blebs were found in Group 2 (Table 2, P < 0.001).
Complications - Anterior chamber inflammation controlled by topical steroids, cataract and choroidal effusion were the most common complications. They did not differ in number between the two groups. Drainage of choroidal effusion with chamber reformation (choroidal tap) was done for any eye with flat anterior chamber associated with corneal- lenticular touch. Posterior synechiae, retinal detachment and vitreous loss were uncommon and occurred more frequently in Group 2.
Grading of Success (Table 3) - In addition to the arbitrary characterization of number of eyes with intraocular pressure less than 20 mmHg, success was graded subjectively in terms of how well the goals of the operation were met. If the operation resulted in an intraocular pressure judged acceptable for the status of the optic nerve and there was no visual loss, the operation was given an "A" rating. If the intraocular pressure was judged acceptable for the optic nerve, but there was visual loss secondary to non-glaucomatous factors, such as cataract or retinal detachment, the operation was given a "B" rating. "C" ratings were given to an eye in which the intraocular pressure was not judged acceptable for the optic nerve with or without medications and/or there was progressive glaucomatous visual field loss. In summary, Group 2 had a tendency toward more "A" ratings, but also had more cases with non-glaucomatous visual loss secondary to cataract, retinal detachment and inflammation (0.05 < p < 0.10). Group 1 had a significantly greater number of patients judged to have unacceptably high postoperative intraocular pressures (P < 0.05). These "C" rated patients were considered to be candidates for reoperation to further lower their intraocular pressure given the severity of their optic nerve damage. Two eyes from Group 1 developed progressive glaucomatous visual loss prior to reoperative intervention.
Filtration surgery may be associated with a poorer prognosis in a black population than in a white population. Reports are difficult to compare because of varying criteria for success, diagnostic categories, success rates, follow-up periods, and microsurgical capability; however, success rates are reported from 22% to 95% for filtration surgery in blacks.7'20 Although not all authors find significant differences between success and failure in blacks versus whites,21·22 results in blacks are often poorer than those reported for similar procedures in a white population.23 The early followup data in this report suggest that significant and satisfactory intraocular pressure lowering can be achieved in a black population with primary open angle glaucoma.
Differences in results are also known to exist between specific types of glaucoma operations for black patients. In particular, results and complications differ between partial thickness (scierai flap) trabeculectomies and full thickness sclerectomies. Several retrospective and prospective studies21,26 comparing these two types of filtration procedures found lower pressures, increased cystic bleb formation, reduced anti-glaucoma medicine requirements and increased shallow chambers in full thickness sclerectomies. One study found trabeculectomies and sclerectomies to be equally successful in pressure reduction over five years.27 Two retrospective studies in black populations28,29 found equivalent pressure lowering in the two groups, but increased visual loss and endophthalmitis in the full thickness group. Another study found better pressure control in Caribbean blacks in Curacao with the use of trabeculectomy with cautery rather than cautery under a scierai flap.30
Our study shows that a full thickness procedure in combination with a limbal based conjunctival flap results in significantly lower intraocular pressures, reduced medication requirements and more cystic blebs when compared to a partial thickness procedure in combination with a fornix-based conjunctival flap. A lower intraocular pressure without the need for supplemental medical therapy is especially important in the West Indian population of Saint Lucia where access to glaucoma drugs and medical compliance are problems. This point is further emphasized by the fact that two patients with partial thickness procedures developed progressive glaucomatous visual loss prior to a time when reoperation could be performed. Complications, although not common, occurred more frequently in the full thickness sclerectomy group. The significant difference in intraocular pressure, medication requirements and bleb formation between the two groups as early as six months postoperatively, suggests that full thickness sclerectomies may warrant consideration as the surgical procedure of choice is selected black patients. Because of the difference in conjunctival flap mobilization, we do not present this as a strict comparison between full thickness and partial thickness techniques.
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