Safety and Efficacy of the Transition from Extracapsular Cataract Extraction to Manual Small Incision Cataract Surgery in Prevention of Blindness Campaigns.

PURPOSE: To compare the safety and the visual outcomes of two experienced cataract surgeons who converted from extracapsular cataract extraction (ECCE) to manual small incision cataract surgery (MSICS) during a campaign for the prevention of blindness.
METHODS: Two surgeons used the ECCE technique (ECCE group) during a campaign in Burkina Faso on 93 consecutive cataract patients with a corrected distance visual acuity (CDVA) <20/80 in the best eye. Both surgeons used MSICS for the first time on 98 consecutive cases in another campaign in Kenya after theoretical instructional courses.
RESULTS: There were no significant differences in CDVA at 3 months postoperatively. There were 69% of eyes with uncorrected distance visual acuity ≥20/60 in the MSICS group and 49% eyes in the ECCE group. Spherical equivalents ranged between -1D and +1D in 55% of the MSICS group versus 43% in the ECCE group. There were significant differences in the changes in the vertical component of astigmatism (J45) but not the horizontal (J0) component. There were no significant differences in the intraoperative complications. The most common postoperative complication was corneal edema on the first day in 40.86% and 19.38% of the ECCE and MSICS groups, respectively.
CONCLUSION: Transitioning from ECCE to MSICS for experienced cataract surgeons in surgical campaigns is safe. The rate of complications is similar for both techniques. Slightly better visual and refractive outcomes can be achieved due to the decreased induction of corneal astigmatism.

INTRODUCTION

The World Health Organization (WHO) estimates that 90% of the 285 million visually impaired people in the world live in low-income countries.1 The major causes of visual impairment are uncorrected refractive errors (43%) followed by cataract (33%), but the main cause of blindness is due to lens opacities (51%).23 In West Africa, the prevalence of cataract in adults is 40 years and older range from 21% to 62.1%.4

The difficulties for national governments to effectively reduce the backlog in cataract surgery has led to the organization of mass surgical campaigns by nongovernmental organizations and charity foundations.5

Phacoemulsification is accepted as the technique of choice for cataract surgery in developed countries. However, the ideal procedure for surgical campaigns in low-income countries remains controversial. The high cost of equipment and supplies, the dependence on technical assistance, and the complexity of the cases (hypermature cataracts with poor pupil dilation, zonular instability, and corneal opacities) are arguments against phacoemulsification as the best or at least the only technique for the majority of cases.6

Intracapsular cataract extraction (ICCE) has been used for many years in mass campaigns because it is a fast, cheap and easy technique that is sometimes carried out by trained local health agents (doctors or specialized nurses).47 However, the rate of postoperative complications and in general, the optical problems derived from aphakia, with a total dependence on spectacles and difficulties related to anisometropia represent serious limitations in broad application of ICCE.

Extracapsular cataract extraction (ECCE) replaced the “in toto” removal of the cataract for more than two decades in most developed countries. This technique is inexpensive, requires few technologic resources and many ophthalmic surgeons over 40 years are trained to perform this technique. Alternately, corneal or corneoscleral incisions of 8-10 mm expose the eye to surgical complications (e.g., expulsive hemorrhage, capsular ruptures, etc.,) that require suturing and induce considerable astigmatism with slow visual rehabilitation.

Manual small incision cataract surgery (MSICS) was first described by Kansas in 1990. In this technique, the nucleus is dislodged through a 6-6.5 mm scleral tunnel using several of the advantages of phacoemulsification (closed chamber procedure, no sutures needed, satisfactory control of astigmatism), avoiding use of advanced technology, and is relatively inexpensive. Hence, MSICS is becoming the technique of choice in mass surgical campaigns in low-income countries.8910 In addition, MSICS has been proposed as a technique of choice for advanced cataracts even in developed countries because the outcomes are comparable to phacoemulsification in almost all aspects except postoperative astigmatism.111213

As many of the surgeons who participate in charity programs are trained in ECCE but usually perform phacoemulsification in their home countries, the learning curve for MSICS has to be acquired during the campaigns. Although the outcomes of MSICS and phacoemulsification performed by ophthalmology trainees have been compared;14 there are no references in the literature comparing the results obtained by surgeons who change their technique from ECCE to MSICS in special circumstances such as surgical campaigns for charity or humanitarian purposes.

The goal of the present study is to compare the safety and visual outcomes obtained by two experienced surgeons who changed the cataract extraction technique from ECCE to MSICS during an international campaign for the prevention of blindness in two low income countries.

METHODS

This was a retrospective comparative cohort study of consecutive patients who underwent two different surgical settings in tertiary hospitals in Kenya and Burkina Faso.

Two surgeons - with over 15 years of experience in cataract surgery and who had been trained in the ECCE technique in Spanish hospitals between 1993 and 1998 - used this technique during the first week of December 2008 in Bobo-Diulasso (Burkina Faso) on one eye of 93 consecutive cataract patients (ECCE group). Inclusion criteria for the surgical campaign were: Corrected distance visual acuity (CDVA) <20/80 (0.6 logarithm of the minimum angle of resolution [logMAR]) in the best eye due to cataract and low income (checked by a local partner who helped arrange the surgical camps). Patients were excluded from the surgery if they had any other ophthalmic disease thought to be the main cause of blindness. Patients were excluded from the present study if they did not attend any of the postoperative visits. There was no limitation in age.

Both surgeons used the same criteria to include 98 consecutive cases in the campaign in Thika (Kenya) during the last week of May 2013 using the MSICS technique (MSICS group) for the first time after theoretical instructional courses in cataract and refractive surgery meetings.

The outcome measures of this study were the rate of complications related to surgery and visual outcomes including uncorrected distance visual acuity (UDVA), CDVA, spherical equivalent, and vector analysis of corneal astigmatism.

Study subjects were recruited by qualified local staff (nurses specialized in ophthalmology) in the Bobo-Dioulasso and Thika areas before the arrival of the surgical team. This study adhered to the tenets of Declaration of Helsinki and informed consent of the surgical procedures and participation in the study was obtained from each patient before surgery. The Local Ethical Committee approved the analysis of the data for this retrospective study.

Postoperative visual acuities were classified into good outcomes (VA ≥20/60), borderline outcomes (VA between 20/80 and 20/200), or poor outcomes (VA <20/200) according to the WHO's Prevention of Blindness Program guidelines.

Baseline examination

Patients for inclusion in the study were selected by qualified local staff in a screening exam which included, UDVA measurement, in daylight, using a Snellen Tumbling-E chart at 6 m and torchlight anterior segment examination before surgery. As the great majority of cases were hypermature white cataracts where refraction could not be obtained, the same mean values were considered for CDVA.

Preoperative examinations were subsequently performed were performed by our team at the hospital on the operative day. Preoperative examination included a slit lamp examination (91102242 by Bobes®, Spain), rebound tonometry ICare® (Tiolat Oy, Helsinki, Finland), keratometry (Helmholtz by Bobes®, Spain), A scan biometry (A-scan® by OTITM, Spain). Topical and peribulbar anesthesia were administered.

Cataract surgeries

All surgeries were performed by two Spanish surgeons (JJE and TMC) in the operating rooms of the district 22 hospitals at Bobo-Dioulasso and in the hospital at Thika.

For the ECCE group, ECCE with intraocular lens (IOL) power calculations were performed and rigid polymethylmethacrylate (PMMA) IOLs were implanted. A limbal incision of 8-9 mm at the 12 o’clock position was performed. A circular continuous capsulotomy (CCC) was attempted, in many cases under trypan blue staining of the anterior capsule (in white hypermature cataracts). Z-hyalin 1% sodium hyaluronate (Carl Zeiss™, Jena, Germany) was used as an ocular viscoelastic device. If capsular calcification or other anterior segment anomalies prevented this manoeuvre, a discontinuous anterior capsulotomy was performed using a cystotome or scissors. After extraction of the nucleus and cortical cleaning, an IOL was implanted in the posterior chamber. The IOLs were donated by laboratories to the campaign. Constants recommended by the IOL manufacturer were used for IOL calculation. All cases were targeted for emmetropia. If an exact power was not available for a case, we the residual myopic value closest to myopia. Continuous sutures were performed using 10/00 black monofilament after injecting 0.1 ml (1 mg) of cefuroxime solution in the anterior chamber.

For the MSICS group, two 1.5 mm limbal paracenteses were created at 2 and 10 o’clock to create a CCC using the same methods as described above. Subsequently, a superior fornix-based conjunctival dissection was created followed by thermal coagulation of bleeding vessels. A stainless 2.5 mm bevel down crescent knife (Beaver-Visitec International, Inc., Waltham, USA) was used to create a 7 mm × 2.5 mm superior scleral tunnel which was to remove the nucleus and for implanting the same rigid PMMA IOL model as the ECCE group. After removing the ophthalmic viscoelastic device, a tight self-sealing incision was verified and no sutures were applied in any of the cases. Conjunctival flaps were sutured with a single VICRYL® (polyglactin 910) suture (Ethicon, Inc., Somerville, New Jersey, USA).

After each procedure, a surgical report was created, recording the possible incidences following the criteria defined in the Oxford Cataract Treatment and Evaluation Team (OCTET) protocol.15 CTET was also used for the evaluation of the postoperative complications.

All cases were performed as a same-day surgery, with the patients leaving the clinic after compressive occlusion of the operated eye and with a postoperative appointment for the following day. Topical medication was given to the patients, and they were instructed on postoperative ocular care.

Follow-up

Sutures, corneas, IOLs, and pupils were assessed at 1 day postoperatively with a handheld slit lamp. A rebound tonometer was used to measure IOP, with hypotensive treatment as warranted.

Examination at the 3 months postoperative visit included measurement of UDVA CDVA, slit lamp examination, rebound tonometry, keratometry, retinoscopy, and refraction. Near distance visual acuities were not recorded. Objective refraction was done with a Retinoscope (3.5v Halogen HPX™ Streak Retinoscope, Model 18200; Welch Allyn, Skaneateles Falls, NY, USA), followed by a subjective examination with a trial box and glasses. All examinations and refractions were performed by two Spanish optometrists and one local ophthalmic nurse. The incidence and type of intraoperative and postoperative complications were also noted.

Intermediate examinations at 1 week and 2 weeks postoperatively were performed by local health workers affiliated with the program. The data corresponding to this visit have been omitted because visual acuity data were not collected.

Arithmetic means, medians, standard deviations (SDs), and standard errors were calculated for UDVA and CDVA (after converting the values to logMAR), sphere, cylinder, spherical equivalent, and defocus equivalent were calculated for each eye at every visit.

Based on these data, refractive efficacy and safety indexes were calculated using the following formula:

Equation 1: Efficacy = UDVA at 3 months postoperatively/preoperative CDVA

Equation 2: Safety = CDVA at 3 months postoperatively/preoperative CDVA.

These results were plotted based on previous refractive literature.161718 The refractive efficacy index expresses the ability of the procedure to provide a good UDVA. The safety index indicates the capability of the surgery to preserve or improve the best spectacle CDVA.

Visual acuity was recorded on a decimal scale and converted into logMAR for mathematical and statistical analysis. As efficacy and safety indexes are calculated using a mean value usually expressed on a decimal scale, the data were calculated after the conversion of the arithmetical means of spontaneous and UDVAs (UDVA and CDVA, respectively) expressed in the logMAR scale.

Vector analysis

The changes in corneal astigmatism after cataract extraction was evaluated using the vector method proposed by Thibos and Horner (Power vector).19 An advantage of this mathematical approach is that astigmatism is represented in rectangular vector form. Hence, conventional scalar methods can be applied to each vector component, and this allows the application of standard multivariate statistics in order to compute population means and variances, define confidence intervals and test hypotheses. Another characteristic of this vector methodology is the mathematical independence of each power vector component, called orthogonality. Given orthogonality, statistical analysis can be applied to each component separately. With this method, after decomposing each corneal cylinder in a horizontal (J0) component and vertical (J45) component, they can estimate “mean corneal astigmatism vector” before and 3 months after each type of surgical procedure.

A graph of polar representation of the mean corneal astigmatism vectors calculated before and 3 months after surgery was designed to provide a more intuitive representation of the impact of surgery on the corneal cylinder.

Data management and analysis

Data were tabulated using a spreadsheet (Microsoft Excel, Windows XP Professional, Microsoft Corp., Redmond, WA, USA). This was also used to perform the calculations for spherical equivalent and the equivalent defocus for each case. Statistical analysis was performed using the SigmaPlot 11.0 for Windows (SYSTAT Software, Inc., San Jose, CA, USA) for descriptive statistics of continuous variables for the description of the samples such as mean, SD, median, minimum, maximum, and range; descriptive statistics for categorical variables, obtaining frequencies, and percentages of the categories. Comparison tests of means or ranges (t-test or Mann-Whitney test) after using the Kolmogorov-Smirnov test on the samples for determining if continuous data were normally distributed. Categorical variables were compared with the Chi-square or Fisher's exact test. A P < 0.05 was considered statistically significant.

RESULTS

There were 93 patients (53.7% male) in the ECCE group. Mean age was 61.00 ± 5.65 years. The right eye was operated in 47.30% of cases. There were 98 patients in the MSICS group (34.69% females). The right eye underwent surgery in 43.96% of cases.

Visual acuities and refractive outcomes

There were no significant between-group differences in preoperative UDVA or CDVA 3 months postoperatively. Table 1 presents the refractive and visual acuity data for both groups. The mean refractive efficacy/safety indexes at 3 months postoperatively were 22/48, respectively, for the ECCE group and 20/37 for the MSICS group.

Table 1

Preoperative and 3 months postoperative data of patients who underwent extracapsular cataract extraction with intraocular lens implantation or manual small incision cataract surgery with intraocular lens implantation

Good UDVA was achieved in 69% of eyes in the MSICS group and 49% of eyes in the ECCE group [Figure 1a]. Three eyes lost one line of CDVA in the ECCE group, and 88% of eyes gained three or more lines. In the MSICS group, two eyes lost two lines of CDVA, one eye lost one line, and 87.5% gaining three or more lines [Figure 1b].

Figure 1

(a) The efficacy (top); (b) safety (middle) and (c) predictability (bottom) over the time of the surgical procedures 3 months after surgeries are shown in standardized graphs for reporting refractive surgery data

The spherical equivalent at 3 months postoperatively ranged between −1 and +1 Din 55% versus 43% of eyes in the MSICS and ECCE groups, respectively [Figure 1c].

Vector analysis of corneal astigmatism

There were statistically significant differences in the changes in J0 and J45 from baseline to three postoperatively in the ECCE group (Mann-Whitney P = 0.001 and P ≤ 0.001, respectively). There were no statistically significant changes in J0 and J45 from baseline to 3 months postoperatively in the MSICS group (Mann-Whitney P > 0.05 in both cases). The incision for ECCE had a greater impact on astigmatism than MSICS.

There were greater changes in mean corneal cylinder vectors from baseline to 3 months postoperatively in the ECCE group [Figure 2].

Figure 2

Polar representation of the mean corneal astigmatism vectors (being the vector's length the magnitude of corneal astigmatism in diopters as seen in the horizontal and vertical axes of the graph) calculated before and 3 months after procedures for both series

Complications

Eighty-seven (93.5%) ECCE surgeries and 91 (92.8%) MSICS procedures were performed uneventfully. Posterior capsule rupture was the most common intraoperative complication [Table 2]. One eye in the ECCE group developed an expulsive hemorrhage intraoperatively. One eye in the MSICS group had iridodialysis. intraoperatively. There were no significant differences in intraoperative complications between groups.

Table 2

Moderate to severe intraoperative complications of patients who underwent extracapsular cataract extraction with intraocular lens implantation or manual small incision cataract surgery with intraocular lens implantation

The most common postoperative complication was transient corneal edema on the first day after surgery in 38 (40.86%) eyes and 19 (19.38%) eyes in the ECCE and MSICS groups, respectively [Table 3]. This difference was statistically significant (P < 0.05). Hyphema occurred in one eye in the ECCE group and two eyes in the MSICS group. In these eyes, there was residual cortex in one eye for each group.

Table 3

Moderate to severe postoperative complications in patients who underwent extracapsular cataract extraction with intraocular lens implantation or manual small incision cataract surgery with intraocular lens implantation

There were no other preexisting pathologies that could cause poor vision postoperatively.

DISCUSSION

MSICS is becoming more common in cases when phacoemulsification is unavailable due to technical or financial reasons. MSICS has almost the same efficacy and is more efficient than phacoemulsification in some high volume eye care hospitals.620

Similarly, some studies have reported that MSICS can be more effective8 and more economical than ECCE.921 These studies support the use of MSICS for international prevention of blindness campaigns when technology is unavailable and financial resources are limited.

MSICS involves different surgical steps than ECCE. Hence, in our study, the surgeons trained in ECCE who wanted to transition to MSICS faced a learning curve in the special conditions of a mass campaign. Applying the stringent conditions of scientific research is sometimes difficult during charity programs as geographic accessibility may be limited and hence, the study sample may be limited. Therefore, designing a prospective, randomized, and controlled trials in the setting of prevention of blindness campaign is tenuous at best. However, despite the limitations of a retrospective cohort study performed over different populations, the aim of the present study was to analyze, as reliably as possible, a practical concern of surgeons who try to improve their skills and practice in these special conditions.

There were no statistically significant differences between groups in UDVA or CDVA at 3 months postoperatively. However, 69% of eyes in the MSICS group had good UDVA (VA ≥20/60) postoperatively, compared to 49% in the ECCE group. This could indicate that the refractive efficacy of MSICS was similar or slightly higher than ECCE in our study. In a high volume eye hospital setting, Gogate et al. found that both, MSICS and ECCE were safe and effective techniques requiring similar equipment but with MSICS providing better uncorrected vision.8

Although the WHO recommendations for visual improvement after cataract surgery implies higher levels of CDVA, it has been reported that the circumstances which affect the patients (including cultural level) in mass campaigns developed in low-income countries may affect the visual records.4

Although postoperative spherical equivalent with both procedures was similar, a better refractive efficacy of MSICS in our series can be explained by a smaller amount of induced astigmatism when compared to ECCE. Our observations concur with studies that have reported a smaller impact on corneal astigmatism with MSICS compared to ECCE.2223

The inability of obtaining subjective refraction in patients with hypermature cataracts led us to use corneal cylinder as a more reliable parameter to evaluate the changes in astigmatism. The need to suture 8-10 mm incisions caused higher astigmatism with ECCE. The instability of the corneal cylinder produced by the loss of tension of the sutures can induce refractive changes in the operated eye. This refractive change is especially undesirable for patients with economic difficulties who need to buy spectacles.

Almost identical postoperative CDVA was recorded for both groups. In addition, very similar percentages of eyes gained lines of CDVA in both groups. Taken together, these observations indicate similar refractive safety of both techniques. Similar refractive safety between ECCE and MSICS has been previously reported.8

The OCTET grading system was created to compare the outcomes and complications of different cataract surgery techniques. The systematic approach and the grading system and scoring depending on the consequences of the possible incidences make OCTET, especially pertinent for our study.2425262728

Notably, both surgeons had been trained for ECCE in the past and not MSICS, but the rate of intraoperative and postoperative complications were similar. Taking into account ethical considerations, it must be emphasized that these surgeons were well experienced having performed more than 5000 anterior segment procedures each. Expulsive hemorrhage is a severe and very uncommon intraoperative complication and the risk of it increases the longer the difference between pressures in the vitreous and anterior chamber is maintained. As MSICS is a “more closed procedure” because of the self-sealing tunnel incision, the risk of this complication seems to be greater in ECCE. Similar and relatively low percentages of posterior capsule rents were found for both series. Previous comparisons of MSICS and ECCE performed by trained surgeons have reported lower rates of vitreous loss for MSICS despite disruption of the posterior capsule.8 This observation was likely due to better maintenance of an adequate pressure in the anterior chamber8 contrary to our experience. However, the rare occurrence of a collapsed anterior chamber could explain the significantly smaller incidence of transient corneal edema seen at the early postoperative period in the MSICS group in our study.

CONCLUSION

The learning curve for the transition from ECCE to MSICS in experienced surgeons who operate in cooperation programs is safe, as the rate of complications is similar for both techniques even during the early learning phase. Slightly better visual and refractive outcomes can be achieved from the beginning due to the lower induction of corneal astigmatism.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.