Description of the condition
Cataract, or opacification of the lens, is the most common cause of visual impairment worldwide, and poses one of the greatest public health challenges of the 21st century (Asbell 2005; Resnikoff 2004). The opacified lens reduces the light reaching the retina, finally resulting in defective vision. No gender, racial, or ethnic group is immune to age-related opacification of the lens (age-related cataract (ARC)). ARC, constituting 90% of all cataracts, usually presents in the eyes of people older than 40 years (Schlote 2006). On the basis of slit-lamp examination, ARC is divided into three major types: nuclear, cortical, and posterior subcapsular (PSC) cataracts. Each of the three can occur alone or in combination, and all of them can progress to total opacification of the lens (Shiels 2010). Density and location of the lens opacity are the two main factors that determine the extent of vision affected. To date, no method has been confirmed to halt the formation of a cataractous lens.
The World Health Organization (WHO) conducted a global review of surveys in 2004, demonstrating that ARC remains the leading cause of blindness globally (accounting for 48% of world blindness), and that it has affected both developed and developing countries (Resnikoff 2004). Without extra intervention, the global blind population will increase to 76 million in 2020 (Frick 2003). The number of cataract operations per million population per annum (cataract surgery rate (CSR)) is a useful measurement of eye care delivery in different settings; it differs between developed and developing countries. In Sweden, the CSR was between 8000 and 9000 operations per million population per year from 2000 to 2009 (Behndig 2011), but in Africa the rate was only about 200 operations per million population per year (www.who.int/mediacentre/factsheets/fs214/en/). It is envisaged that under VISION 2020 (the global initiative for the elimination of avoidable blindness), a remarkable increase in the number of cataract surgeries will be noted, particularly in developing countries (Foster 2005). For example, about 0.5 million cataract surgeries were performed in India from 1981 to 1982, but the number had increased to 4.8 million by the year 2006 (Aravind 2008). Despite the increasing number of cataract surgeries, ARC continues to be a leading public health issue because of aging populations and increased life expectancies.
Description of the intervention
Currently, surgery remains the primary and only treatment available to cure ARC. Cataract surgery has dramatically changed over the past 50 years. Among various surgical techniques for cataract management, phacoemulsification using a clear corneal incision has evolved to become the gold standard (Kelman 1967). In phacoemulsification an ultrasonic handpiece is used to emulsify the opacified lens and aspirate the consequent small fragments. Compared with earlier cataract surgeries with large invasive incisions and a large astigmatic error postoperatively, phacoemulsification requires a small incision and thus improves surgical outcomes, including fewer intraoperative and postoperative complications and rapid visual rehabilitation. Continuous advancement in instrumentation, techniques, and intraocular lenses (IOLs) has allowed surgeons to achieve much smaller incision sizes.
The incision of standard coaxial phacoemulsifications measures about 3.0 mm in length. This incision size allows the silicone sleeve-covered phacoemulsification handpiece to fit snugly through the corneal wound. The covered silicone sleeve is intended to prevent thermal injury to the cornea. To improve effectiveness and safety in phacoemulsification surgery, two other approaches (microcoaxial phacoemulsification (C-MICS) and biaxial microincision cataract surgery (B-MICS)) were developed (Osher 2007a; Osher 2007b). These procedures allow surgeons to operate through even smaller incisions (Paul 2005). C-MICS allows surgeons to perform irrigation, ultrasound, and aspiration through one incision about 2 mm in length. B-MICS accomplishes irrigation and aspiration separately through two corneal incisions less than 1.5 mm in length (Lam 2009; Weikert 2006). These two approaches may result in intraoperative changes including use of cumulative dissipated energy (CDE), total use of balanced salt solution (BSS), surgical time, etc. To date, Infiniti Vision System (Alcon Laboratories) and Stellaris Vision Enhancement System (Bausch & Lomb) are the two main surgical systems used in the phacoemulsification cataract surgery already described.
How the intervention might work
The goal of cataract surgery is to improve vision by replacing the opacified lens with an artificial lens called the IOL. After the cataractous lens is removed, an IOL is required to be implanted inside the "bag" of the lens capsule to correct the measured refractive error. The very small incisions achieved with modern techniques (B-MICS and C-MICS) are expected to lower surgically induced astigmatism (SIA) and allow more rapid visual rehabilitation postoperatively, when compared with current phacoemulsification.
Why it is important to do this review
As phacoemulsification techniques and foldable IOLs developed rapidly in recent decades, the incision size for phacoemulsification was reduced from around 3.0 mm (standard coaxial phacoemulsification) to around 2.0 mm (C-MICS) and even smaller－measuring less than 1.5 mm (B-MICS) (Cavallini 2007; Luo 2012). Smaller clear corneal cataract surgical incisions are associated with better postoperative visual acuity (VA), less SIA, improved wound healing, earlier stabilization of refractive error resulting in shorter recovery time, more stable corneal biomechanical properties, and lower risk of endophthalmitis (intraocular inflammation) (Chee 2005). However, B-MICS and C-MICS require more advanced equipment and may result in longer surgical time, increased use of CDE, and consequently greater endothelial cell loss (ECL). Nowadays, phacoemulsification is widely used for cataract surgery, but the lower size-limits of the corneal incision should be understood, like other components of phacoemulsification such as the optimal size for continuous circular capsulorhexis (CCC). Therefore, an active area of study involves determining the optimal incision size for performance of phacoemulsification. To date, no systematic review of randomized trials has been conducted to assess the effectiveness and safety of incisions of different sizes for phacoemulsification surgery in age-related cataract.
The aim of this systematic review is to assess the effectiveness and safety of different sized incisions for phacoemulsification surgery in ARC.
Criteria for considering studies for this review
Types of studies
We will include only randomized controlled trials in this review.
Types of participants
We will include trials of participants affected by ARC with no ocular pathologic features other than cataract. We will not impose restrictions with regard to participants' gender or ethnicity.
Types of interventions
We will include trials that have compared at least two of the following four interventions (major systems included but not limited to Infiniti Vision System and Stellaris Vision Enhancement System):
1, Standard coaxial phacoemulsification (around 3.0 mm).
2. Microcoaxial phacoemulsification (2.2 mm).
3. Microcoaxial phacoemulsification (1.8 mm).
4. Biaxial microincision cataract surgery (under 1.5 mm).
Types of outcome measures
Mean SIA at one month after surgery, measured with corneal topography and assessed by the vector method. We will analyze SIA measured on day one, days five to seven, and six weeks to two months, as data are available.
1. Postoperative best corrected visual acuity (BCVA) measured by the Early Treatment Diabetic Retinopathy Study (ETDRS) or Snellen chart (transformed to the LogMAR scale) at one month. We will analyze preoperative BCVA and mean change in BCVA as data are available.
2. Postoperative changes, from measurements made preoperatively and at one month after surgery (we will also consider other times: day one, days five to seven, six weeks to two months), including the following:
- Mean ECL measured with noncontact specular microscopy (or percentage decrease as data are available).
- Mean central corneal thickness (CCT) measured with ultrasonic pachymeter (or percentage increase as data are available).
3. Intraoperative parameters recorded at the end of surgery, including:
- Use of CDE.
- Total use of BSS.
- Surgical time.
4. Surgical complications, including endophthalmitis, posterior capsule rupture (PCR), etc.
5. Quality of life as represented by any validated measures.
Search methods for identification of studies
We will search the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE, EMBASE, Latin American and Caribbean Literature on Health Sciences (LILACS), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We will not use any date or language restrictions in the electronic search for trials.
See: Appendices for details of search strategies for CENTRAL (Appendix 1), MEDLINE (Appendix 2), EMBASE (Appendix 3), LILACS (Appendix 4), mRCT (Appendix 5), ClinicalTrials.gov (Appendix 6) and the ICTRP (Appendix 7).
Searching other resources
We will search the references of included studies for additional relevant studies, without restriction in terms of language or date of publication.
Data collection and analysis
Selection of studies
Two authors independently will review the titles and abstracts identified through the electronic and manual searches. We will classify the titles and abstracts as 'definitely include'," 'unsure', or 'definitely exclude'. We will retrieve full text articles for those classified as 'definitely include' or 'unsure', and we will re-assess them according to the inclusion criteria of the review. If any disagreements on assessments arise, we will consult a third review author. For non-English and non-Chinese articles, we will use Cochrane worldwide resources to identify translators for specific languages. All publications from studies meeting the inclusion criteria will then undergo assessment of risk of bias and data extraction. When necessary, we will contact authors of articles to obtain further information. We will exclude studies classified as 'definitely exclude', and we will record the reason for exclusion in the 'Characteristics of excluded studies' table.
Data extraction and management
Two review authors independently will extract the data for the primary and secondary outcomes onto paper data collection forms developed in collaboration with the Cochrane Eyes and Vision Group. We will resolve discrepancies by discussion. If consensus is not reached, we will consult a third review author. One review author will enter data into RevMan 5.2 (RevMan 2012), and a second review author will verify the data.
Assessment of risk of bias in included studies
Two review authors independently will assess the risk of bias of included studies as part of the data extraction process. We will follow the tools for assessing risk of bias set forth in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011a).
The studies will be examined according to the following quality criteria: sequence generation; allocation concealment; masking of participants, personnel, and outcome assessors; incomplete outcome data; selective outcome reporting; funding source; and other sources of bias. Each quality criterion will be labeled as high risk of bias, low risk of bias, or unclear risk of bias (lack of information or uncertainty over the potential for bias). The assessments will be recorded in the 'Risk of bias' table.
Measures of treatment effect
For continuous outcomes, we plan to analyze the treatment effect as mean difference with 95% confidence intervals. We will calculate standardized mean differences (SMDs) if continuous outcomes are measured using different scales. Continuous outcomes include SIA, BCVA, ECL, CCT, CDE use, amount of BSS, and surgical time.
For dichotomous outcomes, we plan to analyze the treatment effect as a risk ratio (RR) or an odds ratio (OR) when the outcome occurs rarely (10% or less). Dichotomous outcomes include surgical complications.
Unit of analysis issues
The unit of analysis will be the eye. If any trial randomly assigned eyes of participants to any two of the types of interventions (standard coaxial phacoemulsification, microcoaxial phacoemulsification, and biaxial microincision cataract surgery), we will refer to Chapter 16 of the Cochrane Handbook for Systematic Reviews of Interventions as a guide for intra-person correlation between eyes (Higgins 2011b).
Dealing with missing data
We will contact study investigators for any missing data. If the investigators do not respond within six weeks or three attempts at contact, we will extract data as available from the published report and will impute the missing data using statistical methods. We will record any assumptions that we make during data imputation. We also will refer to guidelines in Chapter 16 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011b) for information on handling missing data.
Assessment of heterogeneity
We will use the I
Assessment of reporting biases
We will use funnel plots to identify any publication reporting biases if we have 10 or more included studies.
We will determine whether data synthesis can be done depending on the heterogeneity calculated. If the I
We will conduct sensitivity analyses to determine the impact of excluding studies with lower methodological quality, including exclusion of industry-funded studies and unpublished studies.
We acknowledge the Cochrane Eyes and Vision Group (CEVG) Trials Search Co-ordinators for developing the search strategy and executing the electronic searches. We also acknowledge Ann Ervin and the CEVG editorial team, and the peer reviewers, for their support and comments during preparation of this protocol.
Appendix 1. CENTRAL Search Strategy
#1 MeSH descriptor Cataract explode all trees
#2 MeSH descriptor Cataract Extraction explode all trees
#3 MeSH descriptor Phacoemulsification explode all trees
#4 MeSH descriptor Capsulorhexis explode all trees
#5 (Cataract* near/4 (extract* OR aspirat* OR operat* OR remov* OR surg* OR excis* OR implant*))
#6 (lens* near/4 (extract* OR aspirat* OR operat* OR remov* OR surg* OR excis* OR implant* OR emulsif*))
#7 (Cataract Extraction* OR Phakectom* OR Zonulolys* OR catarectomy)
#8 (pha?oemulsif* OR pha?o) OR Capsulor?hexis OR lensectomy
#9 Microphaco* OR miniphaco*
#10 Coaxial OR co-axial OR biaxial OR bimanual OR Microcoaxial OR micro-coaxial OR MICS OR C-MICS OR B-MICS OR MISICS OR SICS
#11 (#1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10)
#12 Incision* OR microincision*
#13 MeSH descriptor Microsurgery, this term only with qualifier: MT
#14 MeSH descriptor Surgical Procedures, Minimally Invasive, this term only
#15 (#12 OR #13 OR #14)
#16 (#11 AND #15)
Appendix 2. MEDLINE (OvidSP)search strategy
1. Randomized Controlled Trial.pt.
2. Controlled Clinical Trial.pt.
3. (randomized or randomised).ab,ti.
5. drug therapy.fs.
9. 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8
10. exp animals/ not humans.sh.
11. 9 not 10
12. exp Cataract/
13. exp cataract extraction/
14. exp Phacoemulsification/
15. exp Capsulorhexis/
16. (Cataract* adj3 (extract* or aspirat* or operat* or remov* or surg*or excis* or implant*)).tw.
17. (lens* adj3 (extract* or aspirat* or operat* or remov* or surg* or excis* or implant* or emulsif*)).tw.
18. (Phakectom* or Zonulolys* or catarectomy).tw.
19. (pha?oemulsif* or pha?o or Capsulor?hexis or lensectomy).tw.
20. (Microphaco* or micro-phaco or miniphaco* or mini-phaco*).tw.
21. (Coaxial or co-axial or biaxial or bimanual or Microcoaxial or micro-coaxial).tw.
22. (C-MICS or B-MICS or MISICS or SICS or MICS).tw.
23. 12 or 13 or 14 or 15 or 16 or 17 or 18 or 19 or 20 or 21 or 22
24. (Incision* or microincision*).tw.
25. Microsurgery/mt [Methods]
26. Surgical Procedures, Minimally Invasive/
27. 24 or 25 or 26
28. 11 and 23 and 27
The search filter for trials at the beginning of the MEDLINE strategy is from the published paper by Glanville et al (Glanville 2006).
Appendix 3. EMBASE.com search strategy
#1 'randomized controlled trial'/exp
#3 'double blind procedure'/exp
#4 'single blind procedure'/exp
#6 #1 OR #2 OR #3 OR #4 OR #5
#7 'animal'/exp OR 'animal experiment'/exp
#9 #7 AND #8
#10 #7 NOT #9
#11 #6 NOT #10
#12 'clinical trial'/exp
#13 (clin* NEAR/3 trial*):ab,ti
#14 ((singl* OR doubl* OR trebl* OR tripl*) NEAR/3 (blind* OR mask*)):ab,ti
#18 'experimental design'/exp
#19 'crossover procedure'/exp
#20 'control group'/exp
#21 'latin square design'/exp
#22 #12 OR #13 OR #14 OR #15 OR #16 OR #17 OR #18 OR #19 OR #20 OR #21
#23 #22 NOT #10
#24 #23 NOT #11
#25 'comparative study'/exp
#27 'prospective study'/exp
#28 control*:ab,ti OR prospectiv*:ab,ti OR volunteer*:ab,ti
#29 #25 OR #26 OR #27 OR #28
#30 #29 NOT #10
#31 #30 NOT (#11 OR #23)
#32 #11 OR #24 OR #31
#34 (cataract* NEAR/3 (extract* OR aspirat* OR operat* OR remov* OR surg* OR excis* OR implant*)):ab,ti
#35 (lens* NEAR/3 (extract* OR aspirat* OR operat* OR remov* OR surg* OR excis* OR implant* OR emulsif*)):ab,ti
#36 'cataract extraction'/exp
#37 'cataract extraction':ab,ti OR 'cataract extractions':ab,ti OR phakectom*:ab,ti OR zonulolys*:ab,ti OR catarectomy:ab,ti
#39 pha?oemulsif*:ab,ti OR pha?o:ab,ti OR capsulor?hexis:ab,ti OR lensectomy:ab,ti
#41 microphaco*:ab,ti OR miniphaco*:ab,ti
#42 coaxial:ab,ti OR 'co axial':ab,ti OR biaxial:ab,ti OR bimanual:ab,ti OR microcoaxial:ab,ti OR 'micro coaxial':ab,ti
#43 'c mics':ab,ti OR 'b mics':ab,ti OR misics:ab,ti OR sics:ab,ti OR mics:ab,ti
#44 #33 OR #34 OR #35 OR #36 OR #37 OR #38 OR #39 OR #40 OR #41 OR #42 OR #43
#46 incision*:ab,ti OR microincision*:ab,ti
#48 #45 OR #46 OR #47
#49 #32 AND #44 AND #48
Appendix 4. LILACS search strategy
( ((catarata$ or Cataract$) AND (extract$ or aspirat$ or operat$ or remov$ or surg$ or excis$ or implant$)) or (lens$ AND (extract$ or aspirat$ or operat$ or remov$ or surg$ or excis$ or implant$ or emulsify$)) or facoemulsif$ or Phacoemulsif$ or Phakectom$ or Zonulolys$ or catarectomy or Phaco$ or Phako$ or Capsulorhexis or Capsulorrhexis or lensectomy or Microphaco$ or miniphaco$ or Coaxial or co-axial or biaxial or bimanual or Microcoaxial or micro-coaxial or C-MICS or B-MICS or MISICS or SICS or MICS) and (Incision$ or microincision$ or microsurgery)
Appendix 5. metaRegister of Controlled Trials search strategy
(cataract OR Phacoemulsification OR Capsulorhexis OR phaco* OR phako* OR microphaco* OR Coaxial OR co-axial OR biaxial OR bimanual OR Microcoaxial OR C-MICS OR B-MICS OR MISICS OR SICS OR MICS) AND (incision* OR microincision* OR microsurgery)
Appendix 6. ClinicalTrials.gov search strategy
(cataract* OR Phacoemulsification OR phaco* OR phako* OR Capsulorhexis OR Coaxial OR co-axial OR biaxial OR bimanual OR Microcoaxial OR C-MICS OR B-MICS OR MISICS OR SICS OR MICS) AND (incision OR microincision OR microsurgery)
Appendix 7. ICTRP search strategy
Cataract = Condition AND Phacoemulsification OR Phakoemulsification OR Phaco OR Phako OR Phakectomy OR Zonulolyses OR Zonulolysis OR Catarectomy OR Capsulorhexis OR Capsulorrhexis OR Lensectomy OR Coaxial OR co-axial OR biaxial OR bimanual OR Microcoaxial OR C-MICS OR B-MICS OR MISICS OR SICS OR MICS OR incision OR microincision OR microsurgery = Intervention
Contributions of authors
CJ, XW, WX, and KY conceived and designed the review. CJ, XW, and WX wrote the protocol.
Declarations of interest
Sources of support
- No sources of support supplied
- National Eye Institute, National Institutes of Health, USA.Xue Wang is funded by the Cochrane Eyes and Vision - US Project through the National Eye Institute Grant 1 U01 EY020522-01
- Chongfei Jin is funded by Specialized Research Fund for the Doctoral Program of Higher Education of China (20100101120127), China.