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Cataract surgery is refractive surgery

2012; Lippincott Williams & Wilkins; Volume: 38; Issue: 2 Linguagem: Inglês

10.1016/j.jcrs.2011.12.015

1873-4502

Emanuel Rosen,

Corneal surgery and disorders

The evolution of modern cataract surgery from a time when the cataract could be removed through a small incision (astigmatically neutral) to the time when intraocular lens (IOL) manufacture caught up with the small-incision parameters was the true beginning of cataract refractive surgery, which is the aim of every cataract surgical procedure. Variation in IOL dioptric power is used to alter the refraction of the eye having surgery. Relaxing incisions and toric IOLs are used to fine tune the refractive outcome. Therefore, the obvious question arises: What additional refractive elements are used by adding femtosecond incisions, capsulorhexis, and nucleus fragmentation? The current hype for laser-assisted cataract surgery has included the frequently used term laser-assisted refractive cataract surgery. All cataract surgery is refractive surgery so it is fair to ask, what is the purpose of including the word “refractive,” as some authors do? What are the credentials that would allow this descriptive term to differentiate it from what all cataract surgeons aspire to? In femtosecond laser–assisted cataract surgery, the clear corneal incision (CCI) can be made with great precision but in refractive terms, that element of the process is carried out by the majority using diamond or steel knives, their aim being to achieve an astigmatically neutral incision or, when the CCI is placed on the steep meridian and varied in width, to reduce preexisting corneal astigmatism. It is too early to confirm whether femtosecond laser–created corneal relaxing incisions prove to be a real advantage in neutralizing preexisting corneal astigmatism. Comparative data with manual relaxing incisions are awaited. The capsulorhexis is, in itself, not a refractive element (although unconfirmed claims are made that femtosecond laser capsulorhexes improve IOL centration with refractive effect) in cataract surgery, nor is nucleus fragmentation, although it can be argued that any aspect of the surgery that reduces phaco power could be contributory. The article by Sorensen et al. in this issue (pages 227-233) provides some evidence on this aspect. Incisional wound contracture—“a consequence of ultrasound-induced frictional heat generation resulting in acute collagen contracture once the incisional temperature reaches 60°C”—will potentially alter corneal shape and therefore its refraction. Sorensen et al. identify many reasons that incision contracture occurs, the 2 major ones being lack of surgeon expertise and or experience and an untoward effect of some ophthalmic viscosurgical devices on the cooling flow of irrigating fluid. If femtosecond laser nucleus fragmentation reduces phaco power, the implication of the Sorenesen et al. study indirectly suggests that phaco burns will be correspondingly less likely. Current cataract surgery has achieved a level of excellence in the hands of well-trained surgeons. The design of IOLs now matches the technical achievements of small-incision surgery. The refinements and precision that femtosecond laser–assisted elements of cataract surgery can bring to the process await the evidential conclusions that its cost and time requirements will justify its general acceptance as a true advance in the continuing evolution of cataract surgery. INTRAOCULAR LENS OUTCOME Since its inception, the IOL design has been a mixture of entrepreneurial efforts and scientific evolution, aided in the most dramatic fashion by the remarkable achievements of the late Professor David Apple.1 It is therefore good to see that the work he initiated to unravel the pathophysiology of IOL designs and materials continues, as shown in this issue by the work of Ollerton et al. (pages 368-372). The authors’ dissection of a modified Choyce-type VIII anterior chamber IOL (circa 1963; inserted in 1978 as a secondary IOL) reminds us that the trials and tribulations of evolving IOL design were based on inadequate theory and initial lack of clinical and pathological evidence, while practical experience was being achieved through the process of trial and error. In describing the rigid anterior chamber IOL design, Choyce noted no fewer than 18 attributes: use as primary or secondary IOL following any type of cataract surgery, round pupil not essential, minimal contact with iris and cornea, cannot move forward against cornea in case of wound leaks, posterior dislocation very rare, secondary capsulotomy easy, removal easy, no sutures required for fixation, vitreous in anterior chamber not a contraindication to use, pupil can be fully dilated, 100% visible by slitlamp and gonioscope, only IOL whose haptics can be tinted (especially useful in aniridia), ideal for combination with penetrating keratoplasty, no pseudophacodonesis, used continuously for 25 years, modest endothelial loss, very low incidence of corneal decompensation, excellent replacement (tertiary implantation).2 Despite 25 years’ experience with Choyce anterior chamber IOLs at that time, the attributes, albeit with mainly intracapsular cataract extraction, were clinically proven to be false; with the benefit of hindsight and pathological analysis, grossly so. The Ollerton et al. case report is from a 1978 secondary implantation in an aphakic eye following much earlier congenital cataract surgery and confirms that validated, careful clinical trials of all IOLs was an essential aspect of the introduction of new IOL designs and materials, which of course obtains today.