Modified small-incision cataract surgery for combined extraction – A comparative study of two techniques

Abstract

Purpose:

To explore straight incision technique in terms of efficacy for intraocular pressure (IOP) lowering by small-incision cataract surgery (SICS) trab versus modified “frown” incision with triangular scleral flap technique.

Methods:

This study was done at a tertiary health center. It included 44 eyes diagnosed with cataract and coexisting primary glaucoma that underwent SICS with trabeculectomy using modified “frown” incision with triangular scleral flap technique and straight incision in group A (n = 22) and B (n = 22), respectively. Postoperative evaluation was done at first postoperative day, then at the end of first week, third week, and 6 weeks; at the end of third month and finally at the end of sixth months. Data were entered and analyzed via Microsoft Excel sheet and SPSS software using Mann–Whitney U test for averages and Chi-square test for categorical values.

Results:

Mean preoperative IOP in groups A and B were 38.6 and 29.1 mm Hg respectively, by applanation tonometry. After 6-month follow-up, mean of difference in IOP (preoperative – postoperative) for group A was 20.8 ± 8.3 mm Hg and that for group B was 17.2 ± 13.5 mm Hg.

Conclusion:

Capacity of IOP reduction of both techniques was found to be comparable and did not show much difference up to the end of 6 months. Mastering technique of group A (modified “frown” incision with triangular scleral flap technique) requires more expertise; the simpler straight incision technique provided in group B may be effectively used by the novice and current era Ophthalmologists to combat glaucoma coexistant with cataract.

Glaucoma and cataract follow a silent and highly variable natural course and are the most common causes of visual handicap in senescence. An ideal treatment can be planned by clinical examination aided by psychophysical and imaging tests after monitoring the baseline damage and checking progression. Long-term intraocular pressure (IOP) is controlled more by combined cataract and glaucoma procedures than by cataract extraction alone.[1] Nevertheless, factors such as extent of damage on diagnosis, compliance to medication, socioeconomic status, and life expectancy of patient demand specifically tailored management. It is quite common to notice that patients seek first consultation only because of visually significant cataract, when glaucoma is found to be coexistant. Majority of these cases have advanced glaucoma; thus, trabeculectomy is justifiable, hence, combined extraction with intraocular lens (IOL) implantation is the chosen option.[2] However, a surgeon’s skills, experience, and armamentarium play eminent role to deliver the best.

First surgical management for glaucoma was devised in 1856 by VonGrafe. De Wecker in 1858 performed iridectomy, followed by sclerostomy for chronic glaucoma.[3,4] Two basic principles for lowering IOP are either to increase outflow by creating an artificial passage or to decrease secretion by medical means.

Since 1960, trabeculectomy has been the most successful in lowering IOP in most types of glaucoma. First described by Cairns in 1968,[5] with some modifications, it is continued till date delivering variable results and efficacy.

Studies that stratified patients[1,6] based on preoperative IOP clearly demonstrated that patients with higher preoperative IOP enjoy the greatest reduction of IOP after cataract surgery.

Poley et al. published that greater IOP reduction could be expected in patients with higher preoperative IOPs. They showed a 6.5-mm reduction in the 23–31 mmHg preoperative group, a 4.8 mmHg reduction in 20–22 mmHg preoperative group, and 2.5 mm reduction in 18–19 mmHg preoperative group.

In a retrospective study[7] on long term outcome of trabeculectomy with and without small-incision cataract surgery (SICS) at a tertiary eye hospital in northern Nigeria, successful outcome was defined as IOP less than 21 mm Hg at fifteen months after surgery. Whereas in 97.4% cases success was achieved by trabeculectomy alone, in 94.1% cases SICS with trabeculectomy gave successful outcome.

Treating patients with cataract and glaucoma by conventional sutureless SICS and trabeculectomy has successfully fulfilled the aim of improving visual acuity and reducing IOP by means of one single procedure during the past two decades.[8]

The Indian Glaucoma Outcomes and Treatment randomized trial pioneered by Congdon et al. validated better IOP lowering by trabeculectomy groups (36% drop) than with medication groups (23% drop). Regression model revealed 45.3% drop in IOP by trabeculectomy alone being superior to trabeculectomy using 5-fluorouracil combined with cataract surgery that brought a drop of 30.4%, at 1-year follow-up.[9]

In the Indian scenario, because of continuing financial constraints or refractory nature of the disease to medical therapy with time, there is limitation on part of the patient to follow medical management. The cost of medical therapy for an year is approximately higher than that of trabeculectomy. In such tough call, combined extraction has been a more efficacious alternative for controlling IOP,[10] stabilizing visual field changes and optic disc damage in one session.

The authors modified combined SICS trabeculectomy for faster learning by omitting flap construction, thus, minimizing bleb-related complications, aiming for comparable postoperative outcome and IOP control.

Methods

The study was conducted after approval by the institutional ethics committee of a medical college hospital in central India. Informed written consent was obtained from all patients before their enrollment in this study.

A prospective comparative cohort study was performed in a tertiary health center, in accordance with the tenets of Declaration of Helsinki, included two groups of 22 patients each, aged more than 40 years, diagnosed and operated for primary glaucoma in last 9 years, with informed written consent taken from all 44 patients. All types of primary glaucoma with variable angle anatomy, anterior chamber depth, visual field changes, and IOP were included. Those with any other disorders (of cornea, vitreous, and retina) and secondary glaucoma were excluded.

Out of 44 eyes, 16 were on anti-glaucoma medication during a range of 2–21 months, whereas the rest were managed surgically as primary treatment. From records, preoperative workup, including history, best corrected visual acuity (BCVA), applanation tonometry, corrected IOP after central corneal thickness, slit lamp examination, fundoscopy, perimetry (in case BCVA >1/60) using Humphry’s field analyzer (HFA Carl Zeiss Meditech Model 720i), and gonioscopy for angle grading based on Scheie’s system (to evaluate anatomical and functional status of each patient) were followed. According to Scheie’s classification, when all structures are visible, it is labeled as wide open or 0. If iris root, ciliary body, posterior trabecular meshwork, and all structures are obscured, the grading is noted as I, II, III, and IV, respectively. Further cataract grading was done according to the Lens Opacities Classification system II (LOCS II) cataract grading system after dilating the pupil along with fundus examination. The eye to be operated was decided as per patient’s choice post counseling.

Group A were those managed by SICS (using modified “frown” incision with triangular scleral flap centered on incision) operated by the senior consultant heading the unit who had expertise of more than 10 years, whereas group B were operated by SICS (using straight incision) by a junior consultant of the same unit under supervision.

Procedure

1. Surgeries were performed under local peribulbar anesthesia. Intraoperatively, IOP was maintained between 15 and 21 mmHg, managed with intravenous fast infusion of 20% mannitol, if required.

2. A fornix based conjunctival flap was constructed, incising along the limbus between 10 and 2 O’clock, 6–8 mm in length, and 3–4 mm superoinferiorly.

3. After dissecting Tenon’s capsule along with conjunctiva and attaining haemostasis by wet field electrocautery, a limbus based triangular flap (4 mm on all sides) was incised in sclera centered at 12 O’clock such that base of triangle coincided with posterior limit of limbal blue zone, far edges were extended in a curvilinear manner 1.5–2 mm on both sides, resulting in a partial (one-third to half) thickness scleral groove of 6.2-mm cord length in group A [see Fig. 1].

   In group B, 6-mm long straight incision was made up to one-third to half the depth of scleral thickness, 2 mm away from limbus with No. 15 Bard Parker knife [Fig. 1].

4. Sub-scleral tunnel was made with crescent knife keeping side walls parallel, up to 2 mm of clear cornea without entering anterior chamber.

   An ophthalmologist trained in SICS has skill to modify the tunnel for sub-scleral trabeculectomy readily [Fig. 1].

5. After making a side port at 9 O’clock position, standard steps of SICS were followed for extra capsular cataract extraction and posterior chamber intraocular lens (PCIOL) implantation.

6. In group A, after IOL implantation, a block of deep sclera (1 mm × 4 mm) was excised using 15 degree side port blade and Vannas scissors from the limbal blue zone under direct visualization. This was facilitated by holding the preplaced apical suture to lift the central triangular flap, followed by peripheral iridectomy. The triangular scleral flap was sutured by one 10-0 nylon suture at the apex of the flap and one each at the side arms of the triangle.

   In group B, by visualizing limbal blue zone, trabecular window (3 mm horizontally × 1 mm) was removed by the side port knife. Sharp vertical cuts made by tip of 15 degree angulated side port blade provided non-ragged ends of Schlemm’s canal that opened in the scleral lake, formed by steps above. Thereafter, this area was irrigated. Scleral flap was sutured with interrupted 10-0 monofilament nylon suture 1 mm inside the farthest extent of scleral tunnel on both sides, taking care that suture bite was full thickness in anterior lip of scleral incision and partially from scleral bed [Fig. 2]. The needle traverses from sclera adjacent to clear cornea to emerge just inside the external incision at scleral bed.

7. Conjunctiva was repositioned by single 7-0 vicryl suture on each edge.

Figure 1.

Comparison of incision in group A versus group B

Figure 2.

Comparison of aqueous drainage in group A and group B

Results were evaluated in terms of IOP control, preservation of vision, and any bleb-related complications at day 1, then eighth, and 21^st postoperative day then at the end of 6 weeks, further at the end of three months postoperatively. Success was defined as postoperative IOP of 10–18 mmHg without medication for period of 6 months, without any major complications.[11] Comfort level while making trabecular window was low in initial few cases because done under limited visualization by holding upper lip of external incision at its center, gradually ease increased with progression of number of subjects. Also, preoperative analysis was done whether the distribution in two groups with respect to age, sex, laterality, type of glaucoma, and grading of cataract was comparable. P value less than 0.05 was considered as significant.

Data were entered in Microsoft Excel sheet individually for each case (pre and postoperative IOP), difference in IOP and percentage lowering and mean values were calculated therefrom for both groups, and statistically analyzed by statistical package for the social sciences (SPSS) software. Mann–Whitney and Chi-square tests were applied. Intra and postoperative complications were noted.

Results

In the present study, the range of age of group A patients was 45–67 years (mean being 58.1 year), whereas for group B, the range was 40–80 years (mean 64.1 year), which did not vary significantly. With 10 and 12 males and 12 and 10 females in group A and B respectively, no gender bias was seen. By Chi-square test, preference of laterality was not found. The two groups had similar distribution of types of glaucoma (P value = 0.741) and grades of cataract (P = 0.729) operated by either of the two procedures. The mean preoperative IOP was 38.6 and 29.1mmHg in group A and B respectively. While deciding the normality, we found that the data were skewed, hence, non parametric tests were applied for analysis [Table 1]. It was also noted that mean preoperative IOP was higher in group A compared to group B.

Table 1.

Demographic profile of the patients

	Group A	Group B	P
Age (Years)
Mean	58.1	64.1	0.135*
SD	5.0	11.5
Min	45.0	40.0
Max	67.0	80.0
Sex
Men	10 (45.45%)	12 (54.54%)	0.447#
Women	12 (54.54%)	10 (45.45%)
Laterality
Right	15 (68.18%)	14 (63.64%)	0.750#
Left	7 (31.82%)	8 (36.36%)
Type of glaucoma
Open angle	7 (31.82%)	6 (27.27%)	0.741#
Closed angle	15 (68.18%)	16 (72.73%)
Grade of cataract
NS I	5 (22.73%)	3 (13.64%)	0.729#
NS II	14 (63.64%)	16 (72.73%)
NS III	3 (13.64%)	3 (13.64%)

NS I – Nuclear Sclerosis Grade I, NS II - Nuclear Sclerosis Grade II, NS III - Nuclear Sclerosis Grade III. *Mann Whitney test between averages. ^#Chi-square test between categorical values

The groups’ statistical demographic data did not differ significantly. For analyzing the efficacy of both procedures, extent of lowering of IOP was noted. The two groups showed lowering of IOP with the mean of difference in IOP in group A (20.8 ± 8.3 mmHg) and that in group B (17.2 ± 13.5 mmHg) by Mann–Whitney U test. As shown in Table 2, clearly the drop in IOP is associated with type of surgical procedure as the former group exhibited the better of both successful outcomes. Nevertheless, “P” being 0.159 the difference between the pressure lowering for groups A and B was statistically not significant. In terms of percentage lowering of IOP, whereas it was 46.7 mean percentage lowering in IOP for group A, as much as 49.97 mean percentage lowering occurred for group B.

Table 2.

Mean, SD, minimum, maximum of preoperative, postoperative, and difference of IOP

	Pre op IOP	Post op IOP	Difference (Pre-Post)
Group A
Mean	38.6	17.9	20.8
Standard deviation	8.2	4.7	8.3
Minimum	20.6	12.2	3.3
Maximum	54.4	29.0	39.80
Group B
Mean	29.1	11.87	17.2
Standard deviation	13.8	3.5	13.5
Minimum	14.0	7.0	0.00
Maximum	69.0	18.0	55.00

IOP=intraocular pressure

Discussion

The cost of maximally tolerated medical therapy is much higher than combined surgery or trabeculectomy alone. Recipients having visually significant cataract with glaucoma may have the benefit of combined surgery under Indian government’s National Program for Control of Blindness policy that caters to cataract surgery free of cost.

In our study with age- and sex-matched groups, as per Chi-square test, there were no significant differences concerning type of glaucoma, preoperative IOP and grades of cataracts in groups A and B. Satisfactory IOP control was achieved in both groups without any IOP lowering drugs needed postoperatively.

Mann–Whitney U test revealed that the type of procedures and resultant lowering of IOP had an association: more lowering occurred with group A (frown with triangular flap at the centre), however, not significant statistically. Group A exhibited mean reduction in IOP of 20.8 ± 8.3 mmHg, which was greater than that of 17.2 ± 13.5 mmHg in group B at the end of 6 months. In a similar study conducted by Khurana et al. (2011) comparing the results and complications of combined manual SICS and PCIOL implantation with group A (trabeculectomy by sutureless) versus group B (inverted “W” shaped incision technique) showed a mean reduction in IOP of 12.52 ± 3.59 and 16.47 ± 3.79 mmHg in group A and B, respectively, after 8 weeks of follow-up (P < 0.001).[10]

In our study in group B, scleral wound was sutured resulting in better healing with a diffuse but functional bleb. This modification of suturing not only stabilized the wound and channelized required outflow of aqueous but also protected patients from bleb-related endophthalmitis.

In a study by Mittal et al. (2008), the IOP decreased from a baseline of 19.9 ± 7.47 to 13.9 ± 3.81 mm Hg in the manual SICS group and from 18.0 ± 6.45 to 13.9 ± 3.54 mm Hg in the phacotrabeculectomy group (P < 0.05) after average 39.8 ± 18.5 months follow-up.[12] Hence, it is of assurance for a novice surgeon that modified SICS trabeculectomy was found equally efficacious as phacotrabeculectomy, of which the latter proves costlier and requires experience. Although in the present study cohort was small, nevertheless, it can form basis for a larger cohort in future.

Shortcomings and complications

Our study does not include comparison of IOP lowering at each postoperative follow-up sequentially. The groups have been segregated and studied only as open- and closed-angle glaucoma to simplify for the purpose. In majority of group B patients, shallowing of anterior chamber was found with a negative Siedel’s test. This was managed by pressure patching with 1% atropine sulphate ointment overnight. In contradistinction, in group A, in a single case, hyphema occurred as during slit lamp examination done on first postoperative day, owing to a flat bleb lower lid massage was done gently to aid commencing functioning of the bleb resulting in hyphema. In yet another patient in group A, bleb revision had to be done using bent 26G needle under topical anesthesia as subtenon cyst-like formation was noticed in third postoperative week. Fibrinoid reaction in one patient in the same group was more a complication of cataract rather than glaucoma surgery.

Conclusion

Capacity of IOP reduction of both techniques was found to be comparable and did not show much difference up to the end of 6 months.

Efficacy of pressure lowering by combined extraction using both techniques is optimal; however, technique in group A mandates apt dissection of a triangular scleral flap merging with “frown” incision in sclera in same plane, which requires expertise. Our country’s surgeons who are skilled to do so are outnumbered by the backlog of cataract with glaucoma. In the present scenario of Indian health care system, combined SICS via straight incision with IOL implantation and trabeculectomy is a boon, because the novice surgeons are familiar with corneoscleral tunnel for cataract surgery. Thus, they can readily join hands with more skilled surgeons in the crusade against blindness. Outcome being comparable; they can gradually adapt to modified “frown” incision with triangular flap at the center of incision, minimizing flap related complications.

Consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.