Ординатура / Офтальмология / Английские материалы / Mastering theTechniques of Lens Based Refractive Surgery (Phakic IOLs)_Garg, Alio, Dementiev_2005

post-operative period. These could be of specific use in the pediatric age group where amblyopia is a major concern. Being able to correct vision for both distance and near would be of immense benefit in these cases.

Pseudoaccommodation has been a feature of many lenses, both silicone and acrylic, that have been used for microincision cataract surgery. This has been hypothesized to be due to the ultra thin thickness of these lenses which aids the normal physiological accommodative response of the capsular bag upon contraction of the ciliary muscle. Longer trials are required to authenticate these hypotheses.

The symbiosis and subsequent syntheses of the newer generation IOLs incorporating larger lenses with accommodative and multifocal optics and the ultra-thin lenses with the quality of pseudo-accommodation for use in microincision cataract surgery remains a dream today. But just as the dreams of yesterday have become realities today in our continuous quest for perfection,

there is no reason to think that true accommodative and multifocal IOLs that can be incorporated through a microincision of 1 to 1.5 mm will not become a viable reality tomorrow.

BIBLIOGRAPHY

1.Findl O, Kiss B, Petternel V, Menapace R, Georgopoulos M, et al. Intraocular lens movement caused by ciliary body contraction. J Cataract Refract Surg 2003;29:669-76.

2.Humming JS, Slade SG, Chayet A, AT-45 Study Group. Clinical evaluation of the model AT-45 silicone accommodating intraocular lens: Results of feasibility and the initial phase of the FDA Clinical Trial. Ophthalmology 2001;108:2005-10.

3.Kuchle M, Seitz B, Langenbucher A, Gusek-Schneider GC, Martus P, et al. The Erlangen Accommodative Intraocular Lens Study Group. Comparison of 6 month results of implantation of the 1 CU accommodative intraocular lenses with conventional intraocular lenses. Ophthalmology 2004;111:825-34.

4.Montes-Mico R, Alio JL. Distance and near contrast

sensitivity function after multifocal intraocular lens implantation. J Cataract Refract Surg 2003;29:703-

11.

Amulya Sahu (India)

INTRODUCTION

Refractive surgery is a growing and expanding branch of ophthalmology today.

The days have gone when lens removal was done only for cataracts. It is nowadays increasingly being used as a tool for correcting various refractive errors.

Eye is an intriguing organ where refraction of rays of light primarily takes place at the cornea and lenticular surface. So any refractive error can be corrected by either altering the corneal surface or removing the lens and replacing it with a artificial lens of the desired power.

Lens exchange can be used for correcting myopia, hyperopia, presbyopia and even astigmatism.

HIGH MYOPIA

Mypoia > 10 D is defined as high/ pathological myopia. The idea of doing lens extraction for high myopia was first mooted by Verzella in mid 80’s.

There are various methods for tackling myopia like spectacles, contact lens and Lasik.

But patients often feel uncomfortable wearing thick glasses and many of them find it difficult to adjust to contact lens.

Though lasik is an established and effective method for correcting high myopia, it has its own set of intra and post-operative complications like corneal perforation, inadequate size of the flap, flap detachment, infections and so on.

So, this brings us to the concept of clear lens extraction for high myopia.

The technique is as in routine cataract surgery except for the fact that you have to do a small rhexis so that the taut lens-iris diaphragm supports the vitreous and decreases the chances of retinal detachment.

In his series, Verzella has 0.7-1 percent rate of retinal detachment which compares favorably with 0.7 percent of retinal detachment in myopes > 10 D who have not undergone surgery.

Colin and Centurion also have studies which shows similar rate of retinal detachment but slightly disappointing visual results. As only 75 percent of patients achieved 2 D or less of residual myopia.

In Our center we have operated 12 cases of high myopia ranging from –10 to –19 D without any complications like retinal detachment, Endophthalmitis, etc. The visual result was disappointing as 4 patient (33 percent cases) had residual myopia > 1.5 D. Followup was for a period of 6 months, further follow-up is required to evaluate the result more scientifically.

HIGH HYPEROPIA

Hyperopia can be defines as low hyperopia 0 to 2 D, moderate hyperopia 2 to 6 D and high hyperopia above 6 D.

Hyperopia is generally uncommon till age 50, at which time there is marked increase in hyperopia.

Between age groups 43 and 54 years incidence is 22 percent whereas between 65 and 74 years it is 67 percent.

Hyperopia can be managed using spectacles and contact lens and if one wants to do away with them, there are other options like epikeratophakia, hexagonal keratotomy, hyperopic ALK, thermokeratoplasty, hyperopic PRK and LASIK.

In our center, we operated 6 cases of hyperopia ranging from 5 – 8 D with xl of 28.8. Post-operative refraction varied from-0.4 to + 1. Patients were highly satisfied but the experience limited to 6 months. It needs long-term follow-up.

Of all the above mentioned methods, only two methods can compare with clear lens extraction, one is hyperopic PRK and other is LASIK.

But given the fact that, hyperopia is more common as age increases, lensectomy is a better and more permanent solution as it takes care of the changing refractive status of the eye due to lens changes.

Table 26.1: Various studies conducted so far

in 2 eyes

Radial keratotomy in 1 eye Astigmatic keratomy

in 1 eye

Similar studies have been reported by Siganos and Associates from Greece, Salz and coworkers with similar results.

These studies brought forth the two main problems faced in hyperopic lensectomy.

Firstly, the post-operative correction being required was quite high reflecting the inadequacies of the IOL calculating formulae.

Though, modern day 3 generation formulae like Holladay II, Hoffner, SRK – T have improved calculation quite a bit.

Further improvement is needed to increase the accuracy.

Secondly, the availability of IOLs of high powers at the present moment is poor.

To overcome this problem, Gayton introduced the concept of piggybacking of IOLs in 1993. He used two plano convex lens and fit the two plano sides together to make one biconvex lens, placing the posterior most

IOL in the capsular bag and the haptics of the second IOL in the sulcus.

He later modified his technique by placing two PMMA or acrylic biconvex lens in the bag.

CONCLUSION

At the present time, clear lens extraction is a valid alternative to contact lens and spectacle intolerance in high hyperopic patients.

No, discussion on clear lens extraction as a refractive surgery is complete without exploring the possibility of using this technique in conditions like:

Presbyopia and astigmatism.

PRESBYOPIA

Presbyopia as is commonly known is an age related phenomenon which occurs due to failure of accommodation.

Accommodation can fail:

1.Due to hardening of lens (Helmholtz)

2.Due to loss of ciliary body effectiveness in increasing the diameter of the lens (Schachar).

Going by the first theory if we replace the natural

lens with Crysta Lens (accommodative lens) presbyopia can be managed.

Cumming reported that silicone IOLs with plate haptics demonstrated a more posterior position within the capsular bag space compared with silicone multipiece looped lenses. Kammann and colleagues reported a more posterior position within the capsular bag space with silicone plate lenses with a 5 mm optic.

In 1991, Cumming began the development of an IOL designed to exploit and maximize the axial movement of an IOL during accommodative effort. Together with Kammann, Cumming developed an IOL with plate haptics for a more posterior position in the capsular bag and hinged haptics to facilitate a maximal forward movement of the optic.

The AT-45 CrystaLens is a modified silicone, platehaptic lens. The CrystaLens has a hinge at the junction

of the haptic and optic to facilitate forward movement of the optic, and T-shaped polyamide haptics at the end of the plates. The lens is 11.5 mm from loop tip to loop tip and the length as measured from the ends of the plate haptics is 10.5 mm. The lens. The feasibility study reported on 28 eyes in 14 patients and the initial phase study reported on 48 eyes in 48 patients more than 3 months after implantation. has a bic. In the 48 clinical trial patients, 88 percent of patients achieved uncorrected distance visual acuity of 20/40 or better. All patients achieved best-corrected distance visual acuity of 20/40 or better; 96 percent of patients achieved uncorrected near visual acuity of 20/30 (J3) or better; 96 percent of patients achieved distance-corrected near visual acuity of 20/30 (J3) or better; and 100 percent of patients achieved best-corrected near visual acuity of 20/30 (J3) or better. The percentage of patients achieving 20/20 visual acuity, at distance or at near, was not reported.onvex optic that is 4.5 mm in diameter.

ICU IOL

1 Place, 3 dimens foldable acrylic IOL, optic 5.5 mm, haptic IOL 9.8

This IOL is being tried out in European market. Further reports are still awaited. The widespread use of the toric IOL has been aided by the acceptance of clear corneal small-incision cataract surgery, as well as the availability of foldable toric IOLs that pass through small incisions. Unlike the other methods currently available for correcting preexisting astigmatism in the cataract population, the toric IOL is particularly appealing to the cataract surgeon. It does not require the alteration of current surgical technique or the acquisition of new instrumentation or skills for successful outcomes. Additionally, should the outcome of surgery prove unacceptable, the toric IOL implantation procedure is reversible. The toric IOL is available with a preset level of astigmatic correction or it can be customized to meet the specific needs of a patient. The surgery requires matching the axis of the toric IOL with the steeper anterior corneal cylinder meridian as determined by preoperative

keratometry. This cylinder meridian is marked preoperatively with the patient in an upright position. By avoiding the natural torsional eye movements occurring when patients are placed in the supine position, incorrect assessment of the axis of astigmatism is avoided.

Toric IOL available c preset level of astigmatic correction or can be customized. Surgery includes matching the axis of toric IOL c steeper corneal axis.

1.Shinzu and colleagues worked on 47 pts 1994. 5.7 mm scleral incision, PE

IOLs were either 2D or 3D

Those c renamed withi 10 percent of preset axis achieved average reduction of 2D and 1.5D Toric IOLs long-term rotational stability determines its success.

Rotation >30 negates correction and adds to preexisting cylinder.

2.Grabow

Foldable toric IOL 81 cases

77 cases were within 30 of preset axis

feels this is superior to limbal relaxing incisions or laser corneal refractive sx.

Okihiro Nishi

Kayo Nishi (Japan)

INTRODUCTION

Refilling the lens capsule while preserving the integrity of the lens capsule, zonules and ciliary muscles, offers the potential of restoring ocular accommodation after cataract surgery. The idea of restoring ocular accommodation by retrieving crystalline lens following cataract surgery appears to the authors to be simple, so they were not surprised that Tadiny or Casamata conceived the idea in the 18th century when they suggested an intraocular lens (IOL) as the replacement of a cataractous crystalline lens, for they must have known the anatomy of crystalline lens sufficiently at least to understand that the lens performs ocular accommodation.

The first attempts, however, to refill the lens capsule to restore accommodation were made in the 1960s (Kessler, 1964 and Agarwal, 1967), who succeeded in refilling the lens in young rabbits in vivo with silicone elastomer. Surgical procedures for lens refilling fundamentally consists of two techniques: (i) endocapsular removal of lens substance through a small capsular opening while preserving the lens capsule, zonules and ciliary muscles, and (ii) refilling the empty capsular bag with an injectable material avoiding any leakage. The pertinent microsurgical technique for endocapsular removal of lens substance was still unsophisticated at that time. Leakage of the injected silicone from the capsular bag was a persistent problem and these studies were discontinued. In the late 1960s, Kelman developed the phacoemulsification technique, in which the nucleus is emulsified by ultrasound and then aspirated. The advent of this technique and

curvilinear circular capsulorhexis at least facilitated endocapsular removal of a nucleus that was not hard.

The materials that have been used to date are silicone compounds, collagen, and acrylate copolymer. Among them, silicone compounds currently provide the most appropriate material in terms of refractive index, elasticity, non-toxicity, transparency and biocompatibility. The technical problem in the use of liquid silicone was its leakage from the capsular bag. Parel and Heafliger (1986) refilled the lens capsule of the nonhuman primate eye with precured silicone elastomers and demonstrated that the anterior capsule curvature was steepened by intracameral pilocarpine. However, the silicone compound used is very slow to cross-link (12 h) and therefore, tends to leak from the capsular bag. To avoid leakage of filling material, Nishi (1989) developed a soft, elastic, inflatable, endocapsular balloon that is introduced into the capsular bag. A mixture of two silicone compounds that polymerizes in 2 h in vitro is then injected through the delivery tube of the balloon, and the inflated balloon fills the capsular bag. Hettlich (1992) developed a method to quickly polymerize acrylic copolymer by exposure to blue light. Recently, as an alternative method, the authors developed a new refilling technique using a plug that seals the capsular opening to avoid leakage. Both methods developed by the authors and in vivo results are reported and the problems involved are discussed.

LENS REFILLING PROCEDURE USING

AN INFLATABLE ENDOCAPSULAR BALLOON

Surgical Procedure

Preparation of Endocapsular Balloons

Two types of balloons were developed (Fig. 27.1). The nonaccommodation balloon approximating the shape of the lens in the nonaccommodative state was constructed according to the values obtained during nonaccommodation of the lens, the accommodation balloon approximating the shape of the lens in the accommodative state, according to the values obtained

Figure 27.1: Inflatable endocapsular balloon refilled with the silicone polymer: (Left) a balloon approximating the nonaccommodated state of the crystalline lens (equatorial diameter 8.5 mm), and (right), a balloon approximating the accommodated state (equatorial diameter, 7.5 mm)

during accommodation. A thin delivery tube (Outer diameter, 0.365 mm, inner diameter, 0.305 mm) was positioned at the preequatorial zone. The inner lumen of the delivery tube was filled with a soft, cured silicone polymeric gel, preventing any reflux of the injected liquid silicone.

Lens Refilling Procedure

Anterior capsulotomy continuous curvilinear Minicapsulorhexis After maximal mydriasis was obtained with the topical application of tropicamide and phenylephrine hydrochloride, hyaluronate sodium was injected into the anterior chamber and an upper, small circular capsulorhexis (1.2 to 1.5 mm in diameter) was made by grasping the capsular edge and tearing with the capsulorhexis forceps after the anterior capsule was pricked with a disposable 27 gauge needle (Fig. 27.2).

Endocapsular phacoemulsification and cortex removal: The lens nucleus was then emulsified within the capsular bag using an 0.8 mm endocapsular tip [(sleeve diameter, 1.2 mm) (Fig. 27.3)]. The residual cortex was aspirated using an I/A tip 0.8 mm in diameter (Fig. 27.4). Heparin sodium, 1000 U, and epinephrine, 0.5 mg, were added to 500 ml of an irrigating balanced salt solution (Alcon Surgical Inc, Fort Worth, Tex) for these procedures.

Figure 27.3: Endocapsular phacoemulsification through the minirhexis

Removal of residual lens epithelial cells: Ethylenediaminetetraacetic acid (EDTA), 10 mmol/L, dissolved in hyaluronate sodium (Healon, Kabi Pharmacia Ophthalmics AB, Uppsala, Sweden) was injected into the capsular bag after pure hyaluronate was injected into the anterior chamber to protect the corneal endothelium. The EDTA chelates calcium and loosens the junctional complexes of the lens epithelial cells (LECs). After 2

Figure 27.4: Cortex aspiration

minutes, EDTA-hyaluronate and the loosened LECs in the capsular bag were removed with low-level aspiration. Lens epithelial cells at the 12 o’clock position were removed with a Simcoe (American Surgical Instrument Corp, Westmont, Ill) cannula designed for removal of the cortex at that position.

Insertion of endocapsular balloon:The balloon in either the nonaccommodated or the accommodated state was selected. After the capsular bag and anterior chamber were filled with hyaluronate, the equator opposite the delivery tube was grasped with Miyake-Simcoe (Inami and Company, Ltd, Tokyo, Japan) lens forceps, and the inflatable balloon was introduced through the 3 mm corneal incision and the small upper capsular opening into the capsular bag (Figs 27.5 to 27.7).

Injection of silicone mixture: The two liquid silicone polymers of polymethyldisiloxane (the main component) and hydrogenpolysiloxane (a cross-linking agent) were mixed at a 2:1 (vol/vol) ratio. The liquid silicone mixture (Menicon Company, Nagoya, Japan), which polymerizes in 2 hours in vitro, was injected through the delivery tube with an odontologic syringe injector (Citoject, Bayer Dental Nippon, Osaka, Japan) equipped with a 27gauge

Figure 27.5: Insertion of a balloon into the capsular bag. The balloon is rolled like a scroll while it is fed through the minirhexis. The balloon unfolded as soon as it entered the capsular bag

needle (Fig. 27.8). The balloons were filled with 0.15 to 0.25 ml of the silicone mixture (Figs 27.9 and 27.10). After the balloon was filled, the residual air in the balloon was aspirated through the delivery tube using a 32 gauge needle (Fig. 27.11). The delivery tube was then cut at its root. The tube stub containing the cured silicone was left in place within the wall of the balloon to prevent leakage of the liquid silicone mixture. One percent atropine sulfate ointment was applied in the conjunctival sack at the end of the operation to maintain zonular relaxation when the nonaccommodation balloon was used.

Results

Success Rate of the Procedure

Twenty-one lenses in 21 young macaco monkeys were refilled with inflatable endocapsular balloons. The lenses were refilled with the nonaccommodation balloon (Fig. 27.12) and 11 with the accommodation balloon. Fifteen of 21 lenses could be refilled. The failure in six lenses was mainly due to capsule rupture during the operation.

Figures 27.6 and 27.7: Insertion of a balloon into the capsular bag. The balloon is rolled like a scroll while it is fed through the minirhexis. The balloon unfolded as soon as it entered the capsular bag

Amplitude of Accommodation Measured by Automated Refractometry

In nine of the 15 refilled lenses, automated refractometry was possible. The preoperative and postoperative amplitudes of accommodation of the five lenses refilled with the nonaccommodation balloon and of the four lenses refilled with the accommodation balloon are shown in Table 27.1. There was a significant difference in the accommodation amplitude 2 weeks after surgery between the eyes with a nonaccommodative type of

Figure 27.9: Injection of a liquid silicone mixture through the delivery tube using an odontology syringe

balloon and those with an accommodative type of balloon.

CONCLUSION

We concluded from the study that when refilling the lens, the lens capsule should be restored to its nonaccommodated state in order to obtain the optimal accommodation amplitude.

This is understandable if we briefly consider the modern theory of accommodation. According to the classic theory of Helmholtz, the natural lens shape is in the accommodated form. This conforms to the nonaccommodative, or relaxed form by the zonular

Figure 27.11: The air was removed with a 32 gauge needle through the delivery tube

tension that is generated by ciliary muscle relaxation. This theory has obviously been overtaken by the modern theory. The modern theory is based mainly on Fisher’s findings, as described in the Figure 27.13. Fisher cut all the zonules. The crystalline lens spontaneously conformed to its accommodated state, after the lens was freed from zonular stretch. Then, he carefully decapsulated the lens. He eventually found that the lens capsule remained in the accommodated shape, while