COMMUNITY EYE CARE
Year : 1996 | Volume
: 44 | Issue : 3 | Page : 179--182
Surgical magnification for intracapsular cataract surgery in a rural hospital
Andrew Braganza1, Arthur C.K. Cheng2, Ravi Thomas1, Jayaprakash Muliyil3,
1 Schell Eye Hospital and Department of Ophthalmology, Vellore, India
2 Department of Ophthalmology, University of Sydney, Sydney, Australia
3 Department of Community Health, Christian Medical College, Vellore, India, India
Schell Eye Hospital, Arni Road Vellore 632 001
Intracapsular cataract extraction is still the most common type of operation performed in India, especially in eye camps, and most of these are done without magnification. To assess the surgical outcome of intracapsular cataract surgery in a rural hospital with various magnifying systems, 121 consecutive eyes (121 patients) with uncomplicated cataract were randomly allocated to surgery with the operating microscope, binocular loupe or unaided eye. The surgery was performed by either consultants or first year residents. The best corrected vision at least four weeks post-operatively was compared among the three groups. The performance between the consultants and the junior residents was also compared.
The improvement of surgical outcome with magnification was statistically significant (p=0.0045); and clinically important with a relative risk reduction of 60.6%. The comparison between microscope and loupe magnification did not show a significant difference (p=0.24). However, with an operating microscope, the consultants performed significantly better than the junior residents.
These findings suggest that the use of magnification in intracapsular cataract extraction provides a definite advantage over an unaided eye and that the binocular loupe is a good alternative to the operating microscope in this kind of surgery.
|How to cite this article:|
Braganza A, Cheng AC, Thomas R, Muliyil J. Surgical magnification for intracapsular cataract surgery in a rural hospital.Indian J Ophthalmol 1996;44:179-182
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Braganza A, Cheng AC, Thomas R, Muliyil J. Surgical magnification for intracapsular cataract surgery in a rural hospital. Indian J Ophthalmol [serial online] 1996 [cited 2019 Sep 20 ];44:179-182
Available from: http://www.ijo.in/text.asp?1996/44/3/179/24583
To tackle the 12 million cataract blind in India, many mobile units and permanent rural general hospitals have been established under the National Programme for Control of Blindness. A large volume of surgeries are performed in these centers with limited time and resources; intracapsular cataract extraction (ICCE) is still the treatment of choice. A survey of ophthalmologists in the country revealed that at least 57% of cataract surgery performed is ICCE. Most of these operations are also done without magnification.
The advantages of an operating microscope in precision surgery is well documented. However, no study has documented and quantified the improvement in visual outcome by using magnification in ICCE in a rural setting. We conducted a prospective randomized controlled trial in a peripheral surgical center to determine the visual outcome of ICCE performed with an operating microscope, binocular loupe or unaided eye. This study, however, was not designed to determine the causes of visual impairment post-operatively or to try to determine the mechanisms whereby magnification during surgery affected the vision postoperatively.
MATERIALS AND METHODS
All operations were performed in the ophthalmic department of a permanent rural hospital attached to a medical college. The permanent rural hospital offers a cataract screening programme and surgery to the nearby rural areas. Once a week, one consultant and one first year postgraduate trainee on rotation from the base hospital operate on the cataract patients identified during the week. Since all routine cataract surgeries performed in the base hospital are extracapsular cataract extraction (and phacoemulsification), the permanent rural hospital becomes an important center for junior residents to learn ICCE. Intermediately experienced trainees (those with 2 to 3 years of experience) do not attend surgery at the permanent rural hospital.
A total of 121 patients operated by six consultants (more than five years of experience) and seven junior residents (less than one year of experience) were included in the study. All the patients selected for surgery were above 42 years of age with uncomplicated cataract and best corrected vision before surgery was less than 3/60. While patients with controlled systemic hypertension were included in the study, patients with history of diabetes mellitus, patients who needed special care by a consultant due to anticipated surgical difficulties, or one-eyed individuals were excluded. Other ocular pathology such as evidence of active or past uveitis, glaucoma or ocular trauma was routinely excluded by the screening procedure. Pre- and postoperative slit lamp examinations using a Kowa portable slit-lamp were routinely performed. The pre-operative intraocular pressure (IOP) were less than 21 mmHg in either eye in all cases. Patients were randomly allocated on the basis of the last two digits of their hospital numbers to undergo surgery with a portable microscope (MENTOR CM III), binocular loupe (Keeler 4x) or unaided eye to obtain an allocation ratio of 1:1:2. The hospital numbers were considered equivalent to random numbers as they were allotted through the general OPD. Allotment into groups was done immediately prior to the start of the surgical session. The type of cataract was mature or hypermature in all cases and had no bearing on the randomization.
The surgical procedure adopted was a standard ICCE under local anesthesia (facial and retrobulbar block). After the insertion of superior rectus suture, a fornix-based conjunctival flap was made. An incision was then made to enter the anterior chamber and extended from 160 to 180 degrees of circumference with corneal scissors. This was followed by the insertion of a pre-placed 8/0 virgin silk suture at 12 o'clock position. A peripheral iridectomy was performed and cryo extraction of the lens was done. After the injection of sterile air (we used syringes with air autoclaved) into the anterior chamber, at least five corneal-scleral sutures (8/0 virgin silk) were placed. Subconjunctival injection of 20mg gentamicin and 2mg dexamethasone was also given at the end of the procedure. All intra-operative mplications were recorded and a standard postoperative management regimen with topical betamethasone 0.1% q6H, homatropine 1% q 12H, chloromphenicol 0.3% q 8H and oral acetazolamide 250mg q6H for 3 days was followed. Patients remained in the hospital for one week post-operatively and were then instructed to return for follow-up after a week and then every two weeks till six weeks after discharge. Best corrected vision recorded at least four weeks post-operatively was used to compare the visual outcome of surgery. Results were interpreted collectively and with reference to the surgeons' level of experience.
Analysis was aimed at comparing the level of visual acuity and the frequency of complications in the two groups. Absolute Risk Reduction (ARR) was calculated as a difference of the occurrence of poor vision between the two groups. The Number Needed to Treat (NNT) to avoid one case of poor vision was calculated as 1/ ARR. Chi-square test and test of proportions were used to analyze the results where appropriate.
In the final analysis only 116 patients (116 eyes) were considered since five patients were excluded from the analysis due to inadequate follow-up. Surgery with magnification was done in 59 eyes and without magnification in 57 eyes. The patients in each group were compared on a number of different variables.
The age, IOP and pre-operative visual acuities were not significantly different between the groups. There was no significant difference in the distribution of different magnifying systems between the consultant and junior resident group (p > 0.75).
The difference in best corrected vision measured at least 4 weeks post-operatively between the magnification and no magnification group is shown in [Table:1]. The follow up period varied from four weeks to twenty-six weeks, with only one patient whose final visual acuity was measured before suture removal. The difference between the groups was statistically significant (p=0.0045) and clinically important with a Relative Risk Reduction of 60.6%, the Number Needed to Treat was 4.3. Comparison of the post-operative visual acuity between the patients with microscope magnification and those with loupe magnification [Table:2] showed no statistically significant difference (p=0.24).
The post-operative vision of cases operated on by consultants and junior residents when different magnifying systems were used showed that a consultant could perform significantly better than a resident with a microscope (p=0.037). However, this finding did not apply to the binocular loupe (p=0.390) [Table:3].
There were 14 complications in the group with magnification of which 10 were unplanned extracapsular extraction (ECCE), 3 were vitreous loss (2 of which were associated with unplanned ECCE and 1 was cryo injury to the cornea and iris. In the group without magnification, there were 24 complications of which 18 were unplanned ECCE, 5 were vitreous loss (4 of which were associated with unplanned ECCE) and 1 was iridodialysis. The distribution of the cases of unplanned ECCE between magnification surgery and no magnification surgery is shown in [Table:4]. There was no significant difference in the complication rate between consultants and residents, but the numbers were too small for valid statistical interpretations.
Causes of visual loss included corneal oedema (one patient) and age related macular degeneration (one patient). No case of visual loss due to glaucoma, or optic nerve pathology was recorded. The remaining visual loss was attributed to operative technique. This aspect was not further investigated in the study.
Most ophthalmic surgeons intuitively believe that operations under magnification will provide better surgical results. However, no study has demonstrated the effect of magnification on post-operative vision in ICCE which is practiced widely in the type of mass surgery that is involved in blindness eradication programmes in India.
In our study, patients were randomly allocated to surgery with or without magnification. The comparison of a number of variables including age, IOP and pre-operative visual acuities showed no significant difference between the two groups. The difference of the distribution of each system between the consultants and junior residents was also not significant. The groups were similar on a number of variables suggesting that the comparison of post-operative visual acuities was a valid one.
The use of magnification significantly improved the outcome of surgery (p = 0.0045). The clinical significance of this result was assessed using the Number Needed.to Treat (NNT). The NNT tells us the number of patients we need to treat with the particular procedure, in order to prevent one complication (or achieve one benefit) as compared to an alternative approach. The NNT of 4.3 means that we only need to do approximately 5 operations with magnification to achieve one more postoperative vision - 6/12, compared to unaided eye surgery. (If we assume the five patients we lost in our follow-up all did badly - vision <6/12, the calculated NNT would still be 4.7) [Table:1]. Considering the number of ICCE performed in the country each year and the relatively low cost of a portable operating microscope or binocular loupe, magnification could improve surgical results cost-effectively.
The distribution of unplanned ECCE in each group also supports the thesis that magnification allows better surgical performance. Among those operations without the use of magnification, the frequency' of unplanned ECCE was 31.6%; with the use of magnification, the relative risk of this complication could be reduced by 46.5%. NNT was 6.8 [Table:4]. This means that for every 7 operations we do with magnification, one umplanned ECCE would be prevented.
Our findings also show that for ICCE, loupe magnification is just as effective as microscopic magnification. In fact, loupe magnification also provides a clinically important improvement in comparison to unaided eye surgery (Relative Risk Reduction of 46.4% and NNT of 5.6). Considering that a binocular loupe is only one-third the price of an operating microscope, it could be a good alternative in this kind of operation. It must be emphasized, however, that using a loupe is very different from using a microscope, and that most modern surgeons' preference would probably be the latter. This is to be encouraged as the country is moving towards ECCE and posterior chamber intraocular lens surgery. Using the microscope for ICCEwould seem to be appropriate in this background.
The improvement of performance with microscopic magnification in the consultant group can be partially explained by their experience. Because they have years of experience in operating under microscopes, they are able to maximize the performance of surgery. However, the same argument does not apply to loupe magnification. In fact, consultants only attend operations at the permanent rural hospital once every 2 to 3 months and may not necessarily use loupe magnification every time they operate. Therefore, even though they are trained and familiar with loupe operation, they may not reinforce this skill often enough. Though the power of the study to show a significant difference is small, nevertheless, our results may have important implications in the allocation of surgeons with various skill levels to different magnifying systems.
One recognized problem in the study is the uneven distribution of patients among the surgeons. While one may argue that some surgeons might have predominant effects on the result and confounded the results of this study, we believed that this is a true reflection of the real life situation in the country. Since time and resources are limited, those who are available and those who can operate effectively will have more surgeries. For the results of this study to be applicable in real life, we could not create an artificial situation where each surgeon only operated a fixed number of patients.
Although we were much impressed by the improvement of visual outcome with the use of magnification, we have not taken into account the time required for microscopic surgery as a measure of cost-effectiveness. While we did not feel that the time taken was different between magnification and no magnification operation, we cannot substantiate this impression with hard data. With a backlog of 12 millions cataracts, many would argue that it is more important to perform more surgeries under the given time constraints and sacrifice the visual outcome to a certain extent. Others, however, may prefer to perform quality surgery only. While our study shows that magnification is effective in terms of visual outcome, further studies are required to examine the question of quantity versus quality specifically. A larger study, perhaps a multi-center trial, would also be needed to eliminate any difficulties in analysis due to small sample size.
In summary, the use of magnification in ICCE in a rural setting can improve visual outcome compared to unaided eye surgery. A binocular loupe is a good alternative to the operating microscope and provides similar surgical result in terms of visual outcome.
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