Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001
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THE ART OF PHACOEMULSIFICATION
Figs 20.3A to D: (a) Phacoprobe is inserted in the hemisection, (b) Chopper is inserted in the hemisection from the site port, (c and d) lateral force is applied to split the hemisection into two quadrants
Figs 20.3E and F: (e) Four sinuses are created for intranuclear nucleotomy, and
(f) four sinuses are broken to create four quadrants
Sinus fracture was performed in 50 cases with grade IV nuclear density by a single surgeon (VKD). No intraoperative or postoperative complications were encountered. Successful phacoemulsification was achieved in all eyes. Visual acuity of > 20/40 was obtained in all cases at the end of 1 week. The mean phaco time was 1.09 + 0.6 minutes and mean endothelial cell loss at the end of 3 months was 4.6% + 0.7%.
This technique is especially advantageous as the phaco tip is buried deep into the inferior hemisection and thus it reduces the amount of ultrasound energy
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directed towards the corneal endothelium and the posterior capsule. The turbulence within the eye is decreased which cuts down the production of free radicals generated by the ultrasonic energy hitting the endothelium. The procedure is especially effective on grade IV hard nuclei which might be considered difficult to perform using other phaco techniques. Since no sharp objects approach the posterior capsule, this technique is safer than conventional chopping procedures. The chopper is not inserted underneath the capsule or the iris and therefore the chopping is accomplished far away from the edge of the capsulorrhexis and the endothelium, within the pupil. The large nuclear fragments do not shift into the anterior chamber, thereby decreasing the possibility of endothelium damage. This technique offers higher safety against damaging the capsule and should be adopted as a routine in phacoemulsification of hard and brunescent nuclei.
SLIT NUCLEOTOMY
Phacoemulsification in soft cataracts is as challenging as phacoemulsification in hard cataracts as the capsular bag is relatively loose and phaco probe may cut through the nuclear material without being emulsified. In soft cataracts, a vertical narrow and a deep slit facilitates fracture more easily as there is no cheese wiring (Figs 20.4A and B). Further enough support occurs to ensure adequate purchase on the walls which ensures a cleaner fractures. We do not recommend a wide crater in soft cataracts as enough nuclear material is not present to ensure an adequate fracture.
Figs 20.4A and B: (A) Slit is created with the phacoprobe, and
(B) slit is split to create two hemisections
R E F E R E N C E S
1. Leaming DV: Practice styles and preferences of ASCRS members—1996 survey. J Cataract Refract Surg 23: 527-35, 1997.
2. Seibel BS: Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification. Slack Inc: Thorofare, 1993.
3. Gimbel HV: Nuclear phacoemulsification. In Steinert (Ed): Cataract Surgery : Technique, Complications and Management. WB Saunders: Philadelphia; 148-161, 1995.
4. Bron A, Smith R et al : Changes in light scatter and width measurement from the human lens cortex with age. Eye 6:55-59, 1992.
5. Duke Elder S: Anatomy of the visual system. In System of Ophthalmology. Vol.II, CV Mosby: St. Louis, 320-23, 1961.
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Rasik B Vajpayee |
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Tanuj Dada |
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Vishal Gupta |
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Phacoemulsification |
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in White Cataracts |
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I N T R O D U C T I O N
The white cataract, for most surgeons, is perceived as a major challenge to their skill. In ophthalmic practice in the developed world the incidence of these cataracts is low, whereas in the developing countries they represent a significant number of patients seen and operated upon. These eyes are often looked upon with foreboding because of the potential pitfalls envisaged in their surgery. In this chapter, alogical framework is provided to allow many of the problems to be overcome.
REASONS FOR CATARACTS TURNING WHITE
Cataracts are caused in many cases by separation of lamellae within the lens and imbibition of water into these spaces. As this process continues the lens starts to swell and once this occurs it is described as intumescent, these cataracts may be immature or mature. However, the common feature is that the cortex has swollen so that it no longer transmits light and has a shiny hyaline appearance. The nucleus is frequently chalky and small but may also, particularly in older patients, contain a large brunescent nucleus. A later stage of development is the hypermature lens where fluid has begun to leak from the lens and the capsule is wrinkled.
MORPHOLOGICAL CLASSIFICATION
Let us first consider the main types of lenses that are found with white cataracts.
Type A (Fig. 21.1)
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Fig. 21.1: Type A white cataract |
Fig. 21.2: Type B white cataract |
Posterior subcapsular cataracts that have been allowed to proceed to maturity
These are generally found in younger patients and in the author’s practice in patients of Asian origin. These cataracts have small nuclei and considerable amounts of liquefied lens material.
Type B (Fig. 21.2)
Hypermature cataracts in older patients often uniocular in non-dominant eyes They tend to have large highly sclerotic nuclei and a thin overlying layer—white cortical matter. The nucleus may have become mobile within the capsular bag as in morgagnian cataracts.
Type C (Fig. 21.3)
Shrunken fibrotic lenses as seen in complicated uveitic cataracts and eyes that have had a penetrating injury In the latter, there is often little by way of nucleus or cortex between the leaves of the capsule, it may have liquefied and leaked out through a small capsular perforation. The uveitic lenses are often calcified and may need to be removed manually (Fig. 21.4) in a piecemeal manner or
Fig. 21.3: Type C white cataract |
Fig.21.4: Manual removal of lens |
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with a vitreous cutter. Often the implant if |
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used will require scleral fixation as no |
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adequate capsular remnants will exist (Fig. |
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21.5). |
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Type D |
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Infantile cataracts such as those caused by |
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maternal rubella very often present as white |
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cataracts. These are normally dealt with by |
Fig. 21.5: Close-up view of uveitic cataract |
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MANAGEMENT |
OF WHITE |
CATARACTS |
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Preoperative |
Considerations |
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Ophthalmic History
Take a careful history to ascertain the following
•If there have been any obvious predisposing factors such as trauma or infla– mmatory disease.
•The length of the time that vision has been poor and is the problem uniocular. This is important because a long-standing uniocular cataract may well hide significant posterior segment disease of which the patient is unaware.
•Precataract vision should be ascertained if possible, there is no point removing a white cataract from an amblyopic eye except for cosmetic reasons.
Examination
•When checking visual acuity in patients with dense cataracts of this type it is important to carry out a test of light projection. This should be done in an otherwise darkened room using a strong point source of light in each quadrant of vision. Failure to point accurately to the light in any quadrant may indicate significant posterior segment disease.
•The anterior segment examination may show evidence of previous penetrating injury. There may be synechiae or pigment on the anterior lens surface indicating inflammatory disease or anterior chamber activity.
•Always check the intraocular pressure (IOP), if it is raised there may be unsuspected uniocular glaucoma or because the cataract is swollen and surgery is going to be necessary urgently. If it is low the eye may be becoming phthisical posterior segment problems such as unrepaired retinal detachment may cause this.
•Check the cataract itself. Is it swollen and has it shallowed the anterior chamber. Is the nucleus visible at all through the cortex and is it brunescent or morgagnian. Has the capsule become wrinkled indicating leakage of fluid from the lens.
•Check the fellow eye. It is most unusual that the other eye, even if it does contain a cataract, will be so bad that no fundal view is precluded. A knowledge that there is age-related maculopathy present is useful in advising the patient about the possible prognosis for vision.
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Further Tests
It is essential to carry out an ultrasonic B-scan in patients where the posterior pole is obscured by cataract. This is done to exclude such things as ocular tumors like malignant melanoma of the choroid or retinal detachments. Problems of this type are usually seen where the history has been long-standing and the cataract is uniocular.
Surgical Considerations
The reasons why these cataracts represent so much of a challenge to the surgeon are three-fold: (i) the lack of any red reflex, (ii) the effect on the ocular tissues of the advanced nature of the disease process, and (iii) the nuclei in these eyes are often small and mobile, whilst some are brittle others can be very hard. Although the capsulorrhexis is certainly the most likely part of the operation to cause difficulty, even if that is successfully achieved, the rest of the ocular tissues in the anterior chamber are more friable than usual and the nucleus may be more difficult to control.
Capsulotomy
Owing to the difficulties of visualizing the capsule, capsulorrhexis, if the chosen method, presents the most taxing part of the operation in most of these eyes. However as capsulorrhexis confers distinct advantages for the rest of the operation it should ideally be the method used.
General Tips to Help Improve Visibility during Capsulorrhexis
•Operate from the temporal aspect, the visibility and overall surgical access is surprisingly improved.
•Tilt the microscope eyepieces towards you to create oblique illumination, like the sun in winter this creates shadows and throws the capsule into relief. The torn edge of the capsule also has an edge reflection to enhance its location against the white cortex. Some microscopes have an oblique non-coaxial light which is even better for this. A fiberoptic light pipe introduced into the anterior chamber can enhance the view of the tearing capsule very considerably (Fig. 21.6). The room and microscope lights need to be extinguished to get the best effect from this maneuver.
•Use very high magnification during the capsulotomy and focus accurately at the plane of the anterior cap.
•Overfill the anterior chamber with viscoelastic, a cohesive material like Viscoat (Alcon) or high concentration sodium hyaluronate such as Healon GV (Pharmacia Upjohn) are best for this as they are less likely to escape from the eye at awkward moments. This will flatten the anterior capsule and thus lessen the tendency for the capsule to tear to the periphery. Also the full anterior chamber (AC) will contain the liquid lens matter escaping and minimizes loss of visibility.
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Fig. 21.6: Using the light pipe for the |
Fig. 21.7: |
Starting the rhexis |
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capsulotomy |
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•Attempts have been made in the past to stain the anterior capsule but until recently unsuccessfully. Indocyanin green has now been used to achieve this and aid capsular visibility for capsulorrhexis.
•Take your time. Reassess frequently where the tear is and be prepared to top up viscoelastic or refocus or move the light as required to get the best view.
Specific Tips
•Begin the capsulorrhexis in the center of the capsule with a small tear to allow lens milk to escape (Fig. 21.7).
If there is extensive milky fluid obscuring the view of the capsule, remove the cystitome and use the I/A handpieces to aspirate this (Fig. 21.8), also go under the capsule for anterior soft lens material.
This lessens the highly reflective nature of the anterior cortex and improves the visibility of the capsule. Using high magnification will allow the surgeon to observe the subtle difference between cortex covered by capsule and that, which is not (Fig. 21.9).
•Grasp the torn edge of the capsule firmly, attempt only a small 4.5 mm rhexis. These capsules are often friable and easily extend. A small capsulotomy can always be enlarged later if required.
•If the edge of the capsule is lost STOP. Reinflate the AC with viscoelastic, very often this will demonstrate where the capsulotomy has reached and control can be regained. If the edge is still not seen try changing the angle of the microscope to allow the light to play differently on the capsule, increase the magnification further and refocus on where you think it is.
•If the rhexis edge is still illusive, consider beginning it again in the opposite direction. This can usually be achieved using the cystitome; begin on the capsule and cut towards the center (Fig. 21.10). This produces a flap which when lifted by viscoelastic can be grasped in the forceps and the two halves of the rhexis may thus be joined.
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Fig. 21.8: Using the bimanual I/A to clear lens fluid
Fig. 21.9: Slight color difference apparent with oblique illumination
By using these few simple maneuvers in an unhurried manner, a satisfactory rhexis can generally be achieved. If the rhexis is known to be compromised and cannot be retrieved either revert to a canopener capsulotomy and then perform iris plane phaco as described by Maloney and others or use cautious nucleofractis. In both instances remember that these capsules, both anterior and posterior, are easily damaged.
Fig. 21.10: Restarting the rhexis
Radiofrequency Endodiathermy for Capsulotomy
An alternative method for achieving a capsular opening which does not require such accurate visualization of the capsule is to use an endodiathermy. The tip of the device is moved slowly around the
anterior capsule to create a circular opening. This is achieved due to thermal effect and anneals the capsular edge. Although as a number of studies have shown this edge is not as strong as a capsulorrhexis, it is at least better than a torn or incomplete rhexis when IOL stability within the capsular bag is considered. Also if the device is available it removes much of the anxiety associated with this type of eye. The major disadvantage is the cost if white
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the capsulotomy |
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Hydrodissection
Both in the softer more liquid white cataracts and those with hard nuclei, hydrodissection is usually easily achieved as the cortex is rarely very adherent. Do not use great pressure on the syringe or soft lens matter under the nucleus will be washed out of the eye and thus will not be able to provide any protection for the posterior capsule during nucleus removal. The loose cortex in these eyes means these nuclei tend to be mobilized with minimal manipulation.
Tips for Nuclear Removal
Type A Cataracts
In type A cataracts the nuclei are small and chalky though not usually very hard. Their mobility may make removal difficult because of the tendency to move away from the phaco tip.
•Use the manipulator to stabilize the nucleus (Fig. 21.12).
•Use higher phaco power, i.e. 70 to 80 percent to accelerate the tip into the nucleus in conjunction with higher vacuum to hold the tip and thus control it.
•Whether cracking or chopping (Fig. 21.13) be aware that the fragments of these nuclei can damage either capsule or endothelium because of their mobility. A layer of Viscoat above and below the nucleus prior to nuclear removal can be helpful in this regard.
If successful rhexis has been achieved these nuclei do not normally tax the surgeon’s skill.
Type B Cataracts
Type B cataracts have nuclei that are often brunescent. Remember the posterior capsule is not protected by a good layer of epinucleus and what is present is often washed out by the irrigating fluid. As above remember that the capsule and endothelium are particularly at risk. Also the zonules are often less strong than normal. Consider:
• The use of viscoelastic as above. The capsule protector suggested by Dr Michael
Fig. 21.12: The manipulator is used to |
Fig. 21.13: |
Cracking the nucleus |
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Colvard if available would be useful to slip under the nucleus to protect the posterior capsule.
•Whatever technique is used to break up the nucleus that must be employed with great
caution. Chopping may be particularly difficult and hazardous if the rhexis edge is not clearly
seen. The chopper can be passed over the top of the rhexis and when chopping is
attempted the zonule disinserted. If after nucleofractis the quadrants are too big for
easy removal, they can be chopped individually in the center of the rhexis.
•Use a modern phaco machine with high vacuum capability and advanced fluidics to control the nuclear fragments (Fig. 21.14). With these very hard nuclei, it is particularly important to avoid anterior chamber collapse as both endothelium and posterior capsule are at risk. However using high vacuum to minimize ultrasound energy used with a machine that does not have some sort of surge control mechanism of the fluidics is much more likely to lead to anterior chamber instability.
Type C Cataracts
This last group of cataracts is rather more varied in etiology, i.e. from uveitis to trauma but they generally present a similar picture. The capsule is shrunken, often very leathery and frequently with calcified plaques on either surface. The lens matter may have leaked out to a large extent so that anterior and posterior capsules are fused. If this last is not recognized attempting to do any capsulotomy may result in rupturing the anterior hyaloid. Lensectomy, using a guillotine suction cutter is a good method, phacoemulsification is generally impossible. Sometimes the lenses are so tough that they cannot be cut up and need to be removed intracapsularly as a whole (Fig. 21.5).
Tips for Cortical Aspiration
• As already stated the cortex in these eyes tends to be very liquid, most of it will therefore wash out.
•Occasionally, however, a tough shell of epinucleus may be left behind after the nucleus has been removed. These can prove rather tiresome because the edge is not easy to aspirate. Viscoelastic injected under this plate to lift it and using the phaco tip rather than the I/A tip with its wider bore often helps.
•Even with a complete rhexis prior to nuclear removal it is not unusual to find that whatever method has been used to get rid of the nucleus a rhexis break has resulted. It is important to recognize this and to make sure any edges to the capsular tear are not aspirated by mistake during I/A. Using bimanual I/A allows for a deeper chamber and better control of the capsular edge.