Recent advances in customising cataract surgery
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《英国医生杂志》
1 Birmingham and Midland Eye Centre, City Hospital, Dudley Road, Birmingham B18 7QH, 2 Jules Stein Eye Institute, 100 Stein Plaza, University of California Los Angeles, CA 90095-7000, USA
Correspondence to: S Shah sunilshah@doctors.org.uk
Cataract surgery has advanced a lot over the years. This review describes the latest techniques and how they are used to customise the surgery to the needs of the individual patient
Introduction
Most of the information used in this review came from our day to day experience as surgeons doing cataract extractions. We identified the papers used in the review by a computerised literature search of the PubMed database with the keywords phacoemulsification, extracapsular cataract extraction, intraocular lens, and biometry. We gathered other information from lens manufacturers' data sheets.
Summary points
Cataract extraction is one of the most common elective procedures in the United Kingdom
Around 30% of people aged over 65 have visually impairing cataract
Every patient's eye is unique, and surgery must be tailored to the individual
Surgery can now be customised to reduce dependence on glasses for both distance vision and reading
Discussion of expectations and risks
Most cataract extractions can be done under local anaesthetic, injected or applied topically as drops, and as a day case. However, attention still needs to be paid to the patient's general medical condition, and this requires multidisciplinary cooperation.
Cardiovascular considerations
Uncontrolled hypertension presents an increased risk of orbital haemorrhage during injection of local anaesthetic and potentially of peroperative suprachoroidal expulsive haemorrhage (a catastrophic complication). Another risk factor for suprachoroidal expulsive haemorrhage is a pulse rate greater than 85 beats/min, so special consideration must be given to highly anxious patients (perhaps sedation) or those with poorly controlled atrial fibrillation.4
Glossary of terms
Astigmatism
A condition in which the surface of the cornea is not spherical but is irregularly shaped like the back of a spoon. An astigmatic cornea prevents light images from being focused to a single point, causing image distortion
Extracapsular cataract extraction (ECCE)
A surgical procedure that removes the cataractous lens of the eye but leaves the posterior lens capsule intact, enabling an intraocular lens to be positioned in its place. Technically this term also applies to phacoemulsification, but ECCE is now widely used in ophthalmic circles to mean a large incision cataract extraction in which the nucleus is expressed whole
Intracapsular cataract extraction (ICCE)
A surgical procedure in which the cataractous lens is removed completely within its capsule, leaving no support structures for an intraocular lens posterior to the pupil. In this procedure intraocular lenses were either sutured to the iris in the plane of the pupil or placed in the anterior chamber of the eye (anterior to the iris)
Optical aberrations
Chromatic—Failure of a lens to bring light of different wavelengths to a common focus. This can be compensated for by using an achromatic lens
Spherical—Failure of a lens system to image the central and peripheral rays at the same focal point
Coma—Blurring in the image plane (surface) of off-axis object points, caused by different parts of spherical lens surfaces exhibiting different degrees of magnification. An off-axis object point is not a sharp image point but appears as a characteristic comet-like flare
Phacoemulsification
A surgical procedure that uses an ultrasonic vibration to shatter and break up a cataractous lens, allowing it to be removed through a small sutureless incision
Anticoagulation
Anticoagulant levels must be checked before surgery, as the risk of orbital haemorrhage during injection of local anaesthetic is increased. However, for most cataract surgery anticoagulant levels within the recommended therapeutic ratio are acceptable.
Posture
Cataract surgery is done with patients supine. The patient needs to be able to lie flat and still for 20-30 minutes. This can be difficult for people with orthopnoea or kyphoscoliosis. Positioning of the patient can therefore increase the surgical difficulty and hence the risks of the procedure.
Ocular considerations
The eyes need to have been assessed for concurrent ocular conditions that may increase the risk of the surgery (for example, lid disease or conjunctivitis) or that may prevent the patient from getting a useful visual improvement (for example, age related macular degeneration or diabetic retinopathy).
Ophthalmologists are under ever increasing pressure to achieve "20/20" vision for their patients. Achieving this requires careful preoperative measurements and the use of the appropriate formula to calculate the power of the replacement intraocular lens. In order to decide this we need two basic pieces of information: the length of the eye and the degree of focusing power afforded by the cornea (box 1).
Box 1: Optimising results of biometry
Axial length—measurement by laser
Topography—keratometry
Formulas—SRK-T or Holladay-II, depending on axial length
Axial length—An ultrasound scan is routinely used to measure the axial length of the eye (generally about 24 mm). However, 54% of the errors in predicted postoperative correction by glasses after intraocular lens implantation are caused by errors in measurement of length.5 A 200 μm error in axial length measurement drops the visual acuity by one line on a Snellen chart. More recently, measurement of axial length by laser has started to come into use and has been shown to yield substantially better prediction of the intraocular lens power in cataract surgery than has biometry using ultrasonography.6
Corneal curvature—The refractive or focusing power of the cornea can be measured with a keratometer. Most corneas are not perfectly spherical but tend to have a steep axis and a flatter axis. The difference between the focusing powers of these two axes, measured in dioptres, is the astigmatism. An average of these two readings is used in working out the power of intraocular lens to be used.
Lens power formulas—After the eye's length and corneal curvature have been measured, the information is used to predict (calculate) the power of the intraocular lens implant that will be used to replace the patient's cataractous lens. Many different formulas have been developed to calculate this, but considerable variation can still occur in intraocular lens power predicted with different formulas (table B on bmj.com). The various regression formulas of Sanders, Retzlaff, and Kraff have become very popular because they are simple to derive and use.7-10 However, some of the other formulas are more accurate in patients with unusually long or short eyes—for example, Holladay-II.
Operative considerations
Patients often notice a useful improvement in their vision the day after phacoemulsification, compared with several weeks in those having large incision surgery. However, before the final outcome can be ascertained the eye must be allowed to settle down for three to four weeks. An optometrist in the community usually obtains the final correction with glasses, but this information is vital to monitor outcomes. The postoperative assessment is also vital for the diagnosis and management of potential complications resulting from the surgery (table C on bmj.com).
Box 4: Fine tuning results
Intraocular lens exchange
Piggyback intraocular lens:
"in the bag"
in the sulcus
anterior chamber
Laser refractive surgery
Astigmatic keratotomies
Fine tuning
Postoperative data must be constantly audited to ensure that appropriate standards are maintained and also to identify areas for potential improvement. Computerised databases can be of great use in this sort of audit, especially when integrated into the day to day running of a unit. For example, we can identify whether the preoperative measurements are continuing to be taken accurately enough and whether our incisions are causing excessive flattening of the corneas.
What is next?
The treatment of cataracts has progressed enormously since the days when the "couchers" used to roam from town to town dislocating cataractous lenses with needles, and it continues to evolve in the 21st century with an increasing trend towards customisation to the individual patient's needs (fig 4). What is clear, however, is that the provision of cataract surgery customised to the individual patient relies on far more than just the skill of the surgeon removing the cataract. Customised cataract surgery needs a multidisciplinary approach at several levels. Industry has a vital role in the development of new technologies, as do health services in the provision of appropriate eye care to populations. At the level of the individual patient such surgery involves the close cooperation of several professional groups, including physicians, anaesthetists, surgeons, opticians, and nurses, sharing information to carefully plan, carry out, and assess the results of every procedure. The future for people with cataracts is bright.
Fig 4 Customised cataract surgery
Three extra tables and extra references appear on bmj.com
Contributors: MW did most of the background research, wrote the text and tables, referenced the paper, and created or sourced the figures. SS had the idea of writing the paper, helped to plan the content, and did much of the editing. RJS provided most of the information on the new developments in cataract surgery, helped to plan the preoperative assessment section, and edited the final paper. MW and SS accept full responsibility for the content of the paper and controlled the decision to publish.
Funding: None.
Competing interests: None declared.
References
Reidy A, Minassian DC, Vafidis G, Joseph J, Farrow S, Wu J, et al. Prevalence of serious eye disease and visual impairment in a north London population: population based, cross sectional study. BMJ 1998;316: 1643-6.
Owsley C, McGwin G Jr, Sloane M, Wells J, Stalvey BT, Gauthreaux S. Impact of cataract surgery on motor vehicle crash involvement by older adults. JAMA. 2002;288: 841-9.
Royal College of Ophthalmologists. Cataract surgery: guidelines, February 2001. London: Royal College of Ophthalmologists, 2001:7. Available at www.rcophth.ac.uk/publications/guidelines/cataract_surgery.html
Speaker MJ, Guerriero PN, Met JA, Coad CT, Berger A, Marmor M. A case-control study of risk factors for intraoperative suprachoroidal haemorrhage. Ophthalmology 1991;98: 202-10.
Olsen T. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 1992;18: 125-9.
Findl O, Drexler W, Menapace R, Heinzl H, Hitzenberger CK, Fercher AF. Improved prediction of intraocular lens power using partial coherence interferometry. J Cataract Refract Surg 2001;27: 861-7.
Sanders DR, Kraff MC. Improvement of intraocular lens power calculation using empirical data .Am Intra-Ocular Implant Soc J 1980;6: 263-7.
Retzlaff J. A new intraocular lens calculation formula. Am Intra-Ocular Implant Soc J 1980;6: 148-52.
Sanders DR, Retzlaff J, Kraff MC. Comparison of the accuracy of the Binkhorst, Colenbrander, and SRKTM implant power prediction formulas. Am Intra-Ocular Implant Soc J 1981;7: 337-40.
Sanders DR, Retzlaff J, Kraff MC. Comparison of empirically derived and theoretical aphakic refraction formulas. Arch Ophthalmol 1983;101: 965-7.
Ernest P, Tipperman R, Eagle R, Kardasis C, Lavery K, Sensoli A, et al. Is there a difference in incision healing based on location? J Cataract Refract Surg 1998;24: 482-6.
Nielsen PJ. Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incisions. J Cataract Refract Surg 1995;21: 43-8.(Malcolm Woodcock, ophthal)
Correspondence to: S Shah sunilshah@doctors.org.uk
Cataract surgery has advanced a lot over the years. This review describes the latest techniques and how they are used to customise the surgery to the needs of the individual patient
Introduction
Most of the information used in this review came from our day to day experience as surgeons doing cataract extractions. We identified the papers used in the review by a computerised literature search of the PubMed database with the keywords phacoemulsification, extracapsular cataract extraction, intraocular lens, and biometry. We gathered other information from lens manufacturers' data sheets.
Summary points
Cataract extraction is one of the most common elective procedures in the United Kingdom
Around 30% of people aged over 65 have visually impairing cataract
Every patient's eye is unique, and surgery must be tailored to the individual
Surgery can now be customised to reduce dependence on glasses for both distance vision and reading
Discussion of expectations and risks
Most cataract extractions can be done under local anaesthetic, injected or applied topically as drops, and as a day case. However, attention still needs to be paid to the patient's general medical condition, and this requires multidisciplinary cooperation.
Cardiovascular considerations
Uncontrolled hypertension presents an increased risk of orbital haemorrhage during injection of local anaesthetic and potentially of peroperative suprachoroidal expulsive haemorrhage (a catastrophic complication). Another risk factor for suprachoroidal expulsive haemorrhage is a pulse rate greater than 85 beats/min, so special consideration must be given to highly anxious patients (perhaps sedation) or those with poorly controlled atrial fibrillation.4
Glossary of terms
Astigmatism
A condition in which the surface of the cornea is not spherical but is irregularly shaped like the back of a spoon. An astigmatic cornea prevents light images from being focused to a single point, causing image distortion
Extracapsular cataract extraction (ECCE)
A surgical procedure that removes the cataractous lens of the eye but leaves the posterior lens capsule intact, enabling an intraocular lens to be positioned in its place. Technically this term also applies to phacoemulsification, but ECCE is now widely used in ophthalmic circles to mean a large incision cataract extraction in which the nucleus is expressed whole
Intracapsular cataract extraction (ICCE)
A surgical procedure in which the cataractous lens is removed completely within its capsule, leaving no support structures for an intraocular lens posterior to the pupil. In this procedure intraocular lenses were either sutured to the iris in the plane of the pupil or placed in the anterior chamber of the eye (anterior to the iris)
Optical aberrations
Chromatic—Failure of a lens to bring light of different wavelengths to a common focus. This can be compensated for by using an achromatic lens
Spherical—Failure of a lens system to image the central and peripheral rays at the same focal point
Coma—Blurring in the image plane (surface) of off-axis object points, caused by different parts of spherical lens surfaces exhibiting different degrees of magnification. An off-axis object point is not a sharp image point but appears as a characteristic comet-like flare
Phacoemulsification
A surgical procedure that uses an ultrasonic vibration to shatter and break up a cataractous lens, allowing it to be removed through a small sutureless incision
Anticoagulation
Anticoagulant levels must be checked before surgery, as the risk of orbital haemorrhage during injection of local anaesthetic is increased. However, for most cataract surgery anticoagulant levels within the recommended therapeutic ratio are acceptable.
Posture
Cataract surgery is done with patients supine. The patient needs to be able to lie flat and still for 20-30 minutes. This can be difficult for people with orthopnoea or kyphoscoliosis. Positioning of the patient can therefore increase the surgical difficulty and hence the risks of the procedure.
Ocular considerations
The eyes need to have been assessed for concurrent ocular conditions that may increase the risk of the surgery (for example, lid disease or conjunctivitis) or that may prevent the patient from getting a useful visual improvement (for example, age related macular degeneration or diabetic retinopathy).
Ophthalmologists are under ever increasing pressure to achieve "20/20" vision for their patients. Achieving this requires careful preoperative measurements and the use of the appropriate formula to calculate the power of the replacement intraocular lens. In order to decide this we need two basic pieces of information: the length of the eye and the degree of focusing power afforded by the cornea (box 1).
Box 1: Optimising results of biometry
Axial length—measurement by laser
Topography—keratometry
Formulas—SRK-T or Holladay-II, depending on axial length
Axial length—An ultrasound scan is routinely used to measure the axial length of the eye (generally about 24 mm). However, 54% of the errors in predicted postoperative correction by glasses after intraocular lens implantation are caused by errors in measurement of length.5 A 200 μm error in axial length measurement drops the visual acuity by one line on a Snellen chart. More recently, measurement of axial length by laser has started to come into use and has been shown to yield substantially better prediction of the intraocular lens power in cataract surgery than has biometry using ultrasonography.6
Corneal curvature—The refractive or focusing power of the cornea can be measured with a keratometer. Most corneas are not perfectly spherical but tend to have a steep axis and a flatter axis. The difference between the focusing powers of these two axes, measured in dioptres, is the astigmatism. An average of these two readings is used in working out the power of intraocular lens to be used.
Lens power formulas—After the eye's length and corneal curvature have been measured, the information is used to predict (calculate) the power of the intraocular lens implant that will be used to replace the patient's cataractous lens. Many different formulas have been developed to calculate this, but considerable variation can still occur in intraocular lens power predicted with different formulas (table B on bmj.com). The various regression formulas of Sanders, Retzlaff, and Kraff have become very popular because they are simple to derive and use.7-10 However, some of the other formulas are more accurate in patients with unusually long or short eyes—for example, Holladay-II.
Operative considerations
Patients often notice a useful improvement in their vision the day after phacoemulsification, compared with several weeks in those having large incision surgery. However, before the final outcome can be ascertained the eye must be allowed to settle down for three to four weeks. An optometrist in the community usually obtains the final correction with glasses, but this information is vital to monitor outcomes. The postoperative assessment is also vital for the diagnosis and management of potential complications resulting from the surgery (table C on bmj.com).
Box 4: Fine tuning results
Intraocular lens exchange
Piggyback intraocular lens:
"in the bag"
in the sulcus
anterior chamber
Laser refractive surgery
Astigmatic keratotomies
Fine tuning
Postoperative data must be constantly audited to ensure that appropriate standards are maintained and also to identify areas for potential improvement. Computerised databases can be of great use in this sort of audit, especially when integrated into the day to day running of a unit. For example, we can identify whether the preoperative measurements are continuing to be taken accurately enough and whether our incisions are causing excessive flattening of the corneas.
What is next?
The treatment of cataracts has progressed enormously since the days when the "couchers" used to roam from town to town dislocating cataractous lenses with needles, and it continues to evolve in the 21st century with an increasing trend towards customisation to the individual patient's needs (fig 4). What is clear, however, is that the provision of cataract surgery customised to the individual patient relies on far more than just the skill of the surgeon removing the cataract. Customised cataract surgery needs a multidisciplinary approach at several levels. Industry has a vital role in the development of new technologies, as do health services in the provision of appropriate eye care to populations. At the level of the individual patient such surgery involves the close cooperation of several professional groups, including physicians, anaesthetists, surgeons, opticians, and nurses, sharing information to carefully plan, carry out, and assess the results of every procedure. The future for people with cataracts is bright.
Fig 4 Customised cataract surgery
Three extra tables and extra references appear on bmj.com
Contributors: MW did most of the background research, wrote the text and tables, referenced the paper, and created or sourced the figures. SS had the idea of writing the paper, helped to plan the content, and did much of the editing. RJS provided most of the information on the new developments in cataract surgery, helped to plan the preoperative assessment section, and edited the final paper. MW and SS accept full responsibility for the content of the paper and controlled the decision to publish.
Funding: None.
Competing interests: None declared.
References
Reidy A, Minassian DC, Vafidis G, Joseph J, Farrow S, Wu J, et al. Prevalence of serious eye disease and visual impairment in a north London population: population based, cross sectional study. BMJ 1998;316: 1643-6.
Owsley C, McGwin G Jr, Sloane M, Wells J, Stalvey BT, Gauthreaux S. Impact of cataract surgery on motor vehicle crash involvement by older adults. JAMA. 2002;288: 841-9.
Royal College of Ophthalmologists. Cataract surgery: guidelines, February 2001. London: Royal College of Ophthalmologists, 2001:7. Available at www.rcophth.ac.uk/publications/guidelines/cataract_surgery.html
Speaker MJ, Guerriero PN, Met JA, Coad CT, Berger A, Marmor M. A case-control study of risk factors for intraoperative suprachoroidal haemorrhage. Ophthalmology 1991;98: 202-10.
Olsen T. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 1992;18: 125-9.
Findl O, Drexler W, Menapace R, Heinzl H, Hitzenberger CK, Fercher AF. Improved prediction of intraocular lens power using partial coherence interferometry. J Cataract Refract Surg 2001;27: 861-7.
Sanders DR, Kraff MC. Improvement of intraocular lens power calculation using empirical data .Am Intra-Ocular Implant Soc J 1980;6: 263-7.
Retzlaff J. A new intraocular lens calculation formula. Am Intra-Ocular Implant Soc J 1980;6: 148-52.
Sanders DR, Retzlaff J, Kraff MC. Comparison of the accuracy of the Binkhorst, Colenbrander, and SRKTM implant power prediction formulas. Am Intra-Ocular Implant Soc J 1981;7: 337-40.
Sanders DR, Retzlaff J, Kraff MC. Comparison of empirically derived and theoretical aphakic refraction formulas. Arch Ophthalmol 1983;101: 965-7.
Ernest P, Tipperman R, Eagle R, Kardasis C, Lavery K, Sensoli A, et al. Is there a difference in incision healing based on location? J Cataract Refract Surg 1998;24: 482-6.
Nielsen PJ. Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incisions. J Cataract Refract Surg 1995;21: 43-8.(Malcolm Woodcock, ophthal)