Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009
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towards the vitreous. The settings at this stage is 50% phaco power, flow rate 24 ml/min and 110 mm Hg vacuum. When nearly half of the center of nucleus is embedded, the foot pedal is moved to position 2 as it helps to hold the nucleus due to vacuum rise. To avoid undue pressure on the posterior capsule the nucleus is lifted a bit and with the irrigating chopper in the left hand the nucleus chopped. This is done with a straight downward motion from the inner edge of the rhexis to the center of the nucleus and then to the left in the form of a laterally reversed L shape. Once the crack is created, the nucleus is split till the center. The nucleus is then rotated 180º and cracked again so that the nucleus is completely split into two halves.
The nucleus is then rotated 90º and embedding done in one-half of the nucleus with the probe directed horizontally. With the previously described technique, 3 pie-shaped quadrants are created in one half of the nucleus. Similarly 3 pie-shaped fragments are created in the other half of the nucleus. With a short burst of energy at pulse mode, each pie shaped fragment is lifted and brought at the level of iris where it is further emulsified and aspirated sequentially in pulse mode. Thus, the whole nucleus is removed. Cortical wash-up is the done with
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the bimanual irrigation aspiration technique. Microsurgical Technology (USA) have also designed a soft tip IA which is very safe for the posterior capsule.
One of the real bugbears in phakonit when we started it was about the problem of destabilization of the anterior chamber during surgery. This was solved to a certain extent by using an 18 gauge irrigating chopper. A development made by us (Sunita Agarwal) was to use an anti-chamber collapser which injects air into the infusion bottle. This is an air pump. This pushes in more fluid into the eye through the irrigating chopper and also prevents surge. Thus we were not only able to use a 20 gauge irrigating chopper but also solve the problem of destabilization of the anterior chamber during surgery. This increases the steady-state pressure of the eye making the anterior chamber deep and well maintained during the entire procedure. It even makes phacoemulsification a relatively safe procedure by reducing surge even at high vacuum levels. Thus, this can be used not only in Phakonit but also in phacoemulsification.
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Figure 4.7: Technique for implantation of the intrastromal corneal ring. The intrastromal ring consists of two semi-circular implants
(R). They are guided into the tracts (T) on each side of the optical zone (Z). Their final position is shown in the cross-section view below. Note how the rings alter the shape of the cornea as seen in the cross-section. (Courtesy: Benjamin F Boyd MD FACS Editor- in-Chief “Atlas of Refractive Surgery”—Highlights of Ophthalmology, English Edition, 2000).
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Intracorneal ring technology has shown rapid development, and clinical results are confirming outstanding results for the correction of low to moderate refractive myopias. The Intrastromal Corneal Ring Segments (ICRS® or Intacs®) results to date indicate the surgical procedure is safe and easily performed, visual results are excellent, and the device provides stable and predictable correction postoperatively. Enhancements can be easily performed by device exchange, and Intacs can be removed, reversing the refractive effect. The original 360° ICR was modified to consist of two 150° PMMA arc segments (ICRS) in order to facilitate the surgical procedure and avoid potential incision related complications. Each device segment is inserted into its respective semi-circular shaped intrastromal channel made through a single 1.8 mm radial incision located in the superior cornea near the limbus. An Intacs in situ is presented in Figure 4.7. They are very useful in keratoconus cases also.
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Figure 4.8: Crystalens (Figure & Text
Courtesy: Bruce Wallace)
A number of intraocular lenses (IOLs) are available for the surgical correction of presbyopia. Blended vision or
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monovision can be created with standard monofocal IOLs. Similar to contact lens monovision, not all patients will be happy with this choice, especially if they were unsuccessful with monovision contact lens trials. However, for the successful monovision contact lens wearer who has become contact lens intolerant, monovision with monofocal IOLs makes sense. We usually target plano to –0.50D for the dominant distance eye and –1.75D for the nondominant near eye. (However, there remains surprisingly limited evidence that ocular dominancy really matters for many monovision patients.) This combination can result in surprisingly good uncorrected near vision without sacrificing intermediate vision. Success with lower levels of myopia in the near eye compared to contact lens fitting may be due to a pseudoaccommodative effect of monofocal IOLs.
However, most cataract surgeons are choosing a PCIOL over monovision monofocal IOLs. Even though more costly, this method maintains binocularity and stereopsis. Multifocal and accommodative IOLs are the PC-IOLs available today. Similar to the early days of monofocal IOLs, multifocal IOLs have experienced a relatively slow acceptance. Clinical investigation for almost two decades has shown significantly better uncorrected near vision with
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multifocal IOLs compared to monofocal IOLs, yet unwanted visual sensations delayed their popularity.
One of the first successful multifocal IOLs was the Allergan Array IOL. The Array is a zonal progressive refractive IOL with five blended power zones of alternating distance and near that provide distance (50%), near (37%) and intermediate (13%). Many clinical studies demonstrated the refractive benefit of the Array IOL over monofocal IOL controls. Fortunately, most patients learned to ignore halos and glare after a period of visual cortical adaptation. Another concern about multifocal IOLs has been the potential for loss of contrast sensitivity. Even though some measurable loss of contrast has been detected in clinical studies, patients have not found contrast sensitivity loss with multifocal IOLs, like the Array, to be problematic.
Recently the Array IOL was replaced with the AMO ReZoom refractive IOL. The ReZoom is a second generation zonal refractive IOL manufactured on the acrylic 3-piece AR-40 Sensar monofocal platform. This lens is the result of extensive study of the optical changes necessary to reduce halos and glare occasionally experienced after Array IOL implantation. By altering zone diameters, there was found to be less of an incidence of
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unwanted visual sensations. Another advantage includes a round, square “Optiedge” to reduce posterior capsular opacification while at the same time avoiding dysphotopsia associated with peripheral retinal reflections from squared edges. Because of its three-piece design, the ReZoom can be implanted in the ciliary sulcus if a posterior capsular tear is encountered. Yet a power adjustment will be necessary due to relative anterior insertion compared to capsular bag placement. Because it has a refractive optic, all light is transmitted, which is an advantage over diffractive multifocal IOLs. Experience with the ReZoom has been encouraging with a large majority of patients never or almost never needing glasses after surgery. Compared to the Array, the ReZoom appears to offer better near vision and less halo and glare with early clinical use showing great promise.
Another multifocal IOL available today is the Alcon ReStor. Originally designed by 3M with a posterior diffractive surface, the ReStor’s diffractive component is on the central anterior surface of the IOL. The apodized diffractive-refractive Alcon ReStor IOL has rapidly become popular. The anterior optical surface of the monofocal Acrysof was modified by adding diffractive rings to the anterior central 3.6 mm of the 6.0 mm optic of the Acrysof
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IOL, which vary in step height and spacing in order to maximize multifocality and, at the same time, reduce halo and glare. As the pupil enlarges in scotopic conditions, there is more light for the distance vision and less light for near. This special modification of a diffractive optic has been termed apodization. Half of the 82 percent of light transmission is for distance and half for near with the remaining 18 percent lost to higher orders. This one-piece acrylic IOL with frosted square edges is also available in a three-piece version if sulcus implantation is indicated. FDA submitted data in the US showed that 80 % of bilaterally implanted ReStor patients never wore glasses after surgery. The newer aspheric ReSTOR may offer better quality of vision at all distances.
A more recent diffractive aspheric lens, the AMO Tecnis MIOL, has been gaining widespread popularity. The diffractive portion covers the entire posterior surface of the optic, making the Tecnis MIOL less pupil dependent. There appears to be surprisingly good intermediate vision with this PC-IOL.
Another category of PC-IOLs includes accommodating IOLs. These IOLs attempt to mimic natural accommodation of the crystalline lens. The current accommodative IOLs include the eyeonics crystalens and
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the HumanOptics 1CU. The most often implanted accommodative IOL is the eyeonics crystalens. This single piece silicone IOL has hinged haptics to allow for posterior vaulting and anterior-posterior movement of the 4.5 mm optic (Figure 4.8). FDA trials demonstrated impressive results with this lens design. A recent study has shown that some patients’ vision appears to improve during the first three years after implantation.
The Accomodative 1CU is a hydrophilic, acrylic, foldable IOL with four flexible haptics attached to a 5.5 mm optic. The lens can be implanted with folding forceps or by injector. Also under clinical investigation are a number of dual optic accommodative IOLs. The dual optic arrangement involves two attached lenses with one lens having a high minus power which remains fixed posteriorly and an anterior high plus lens that can travel anterior-posterior during accommodation. The Visiogen Synchrony and Bausch & Lomb Safarazzi IOLs are undergoing FDA trials. The Visiogen Synchrony has shown impressive accommodative amplitude.
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