Ординатура / Офтальмология / Английские материалы / Master Techniques in Cataract and Refractive Surgery_Hampton Roy, Arzabe_2004

The dominant limitation seen after using this treatment was that, although all patients were less hyperopic after LASIK, they were not emmetropic. Moreover, some accommodative stimulus persisted after the procedure.

The presence of nystagmus must not be taken as a limitation when it comes to performing refractive surgery. With the aid of technological advances, such as eye trackers and the use of forceps (Bores or Kramer) to hold the eye allows us to overcome this problem and perform the surgery.

LASEK must be considered like a treatment option for those patients that present any sort of impediment to do a flap.

Refractive surgery must be taken into consideration as one more tool available even for pediatric as well as adult cases.

REFERENCES

1.Nemet P, Levinger S. Refractive surgery for refractive errors which cause strabismus:. a report of eight cases. Binocular Vision and Strabismus Quarterly. 2002;17(3):187-190.

2.Kushner JB, Ronano PE, Molteno AC. BJ Correspondence.

Binocular Vision and Strabismus Quarterly. 2000;5(4):315318.

3.Stidham DB, Borrissova O, Borrison V. Effect of hyperopic laser in situ keratomileusis on ocular alignment and stereopsis in patients with accommodative esotropia. Am J Ophthalmol. 2002;109(6):1148-1153.

4.Nano HD Jr, Muzzin S. Excimer laser photorefractive keratectomy in pediatric patients. J Cataract Refract Surg. 1997; 23:736-739.

EVALUATION

A phakic lens implantation is intraocularly invasive. If an aphakic lens could be sequestrated as we do with an in the bag IOL, it could be classed a safe procedure on a long-term basis. However, that is not the case.1-5

Every phakic lens touches, presses, or erodes a uveal tissue. It occupies an ever-shrinking space. Phakic lens surgery may or may not introduce an astigmatic error, but it usually leaves the preexisting one untouched.6 With a phakic IOL, it is difficult indeed to fine tune refraction to emmetropia. Every phakic lens patient needs a lifelong regular, thorough follow-up including endothelial count. The need for a regular follow-up increases with the passage of time. If and when a cataract develops, a phakic lens shall need explantation before cataract surgery.12 Whether an implanted phakic lens will lead to an earlier onset of cataract or accelerated depletion of endothelial cells in a certain percentage of cases is not known, though entirely possible.

The great advantage of a phakic IOL is that a good cataract surgeon can safely do the procedure without buying costly additional equipment. A phakic lens procedure is reversible (explantation) if a situation so demands.7,8 A phakic lens implant procedure therefore has the potential of getting adopted far and wide. In some countries, the lens implantation is reimbursable, while a laser refractive procedure is not.

A moderate blunt trauma to the eyeball may produce cataract years after the incident. A disturbance in the anterior chamber during the performance of phakic lens implantation, may induce a biophysical or biochemical trauma that may manifest years later as cataract.12 Phakic lenses are yet in their infancy. Even the materials and designs of the lenses are changing. Only recently foldable Artisan and angle-support- ed lenses have been introduced. It is too early for a competent answer to the most important issues of long-term tissue tolerance and their possible role in the initiation of inflammation, glaucoma, and cataract in implanted eyes. Their possible unmonitored widespread use in less than most competent hands is fraught with a grave danger (Figure 9-1). The world might experience an unprecedented epidemic of phakic lens related ocular morbidity in the coming years and decades.

Phakic IOLs appeared in mid-80s as attractive alternatives to RK for myopia and RK with deep cautery for hyperopia. The early phakic lens studies soon got nearly drowned in the flood/dawn of excimer laser corneal surgery. Excimer laser PRK was abandoned very early in favor of the more corneoinvasive LASIK. In spite of serious operative and postoperative complications connected with the use of a keratome, LASIK has thrived.

Besides other simmering safety issues, there has recently been an increasing concern about the upper refractive limits for LASIK. Thus restrained, many refractive surgeons are

Figure 9-1. A dreaded future. An angle-support- ed phakic lens implanted to correct hyperopia resulting from RK, in a child 12 years old. The endothelial cell count is 1200 cells. The quality of the surgery appears to be poor.

turning to a phakic IOL solution all alone or as a combination of phakic lens with LASIK to achieve higher refractive corrections. A new approach for hyperopia is to overcorrect hyperopia with a phakic plus lens followed by laser refractive surgery for the resultant myopia and astigmatism. For high myopia, the approach is to somewhat undercorrect with a phakic minus lens and follow it with laser refractive surgery for the remaining myopia and astigmatism if any. Myopia laser surgery approach is preferred for final correction, since it is more accurate than hyperopia correction.

Three types of phakic IOLs exist:

1.Precrystalline lens (implantable contact lens)

2.Angle supported lens

3.Iris-fixated lens (Artisan lens)

Implantation of any kind of a phakic lens needs to be learned from a master. Early postoperative problems are related to the lens design and the meticulous details of the surgery and postoperative management. The late complications result from a prolonged interaction of the IOL with the adjacent tissues. Lifelong regular follow-up is therefore necessary.

To implant a phakic lens to correct hyperopia or myopia, a momentous decision has to be made after detailed examination and consultation with the patient. The pros and cons of the options of contact lens, extracapsular cataract extraction (ECCE) with monofocal or multifocal IOL, phakic IOL, and excimer laser procedure for the individual patient are considered. The surgeon has to convince himself and the patient why a phakic lens is the right procedure for the latter. The surgeon’s own experience and the type of facilities available with him or her create a bias in favor of a particu-

Figure 9-2. Well-tolerated phakic Artisan lens for myopia, 14 years postoperative, in a 34-year-old patient. The endothelial cell count is 2300. The pupil can be fully dilated for fundus examination.

lar technique. If a phakic IOL is decided upon, then a choice with a bias is made between a phakic posterior chamber, an angle-supported and an iris-supported lens. The phakic lenses are available from powers of ±1.00 D upward. What is the most sensible lowest limit of a phakic lens implant is debatable. Phakic lenses are also available to treat pure plus or minus cylindrical errors.

I have been using phakic iris claw (Artisan, Ophtec, the Netherlands) lens implantation for high myopia and high hyperopia since 1987 (Figure 9-2), PRK for myopia (1991) and hyperopia (1994) with a scanning slit beam excimer laser, and PRK with flying spot laser cum wavefront analyzed assisted corneal ablation (WASCA) since August, 2001. The results of PRK for all grades of myopia were satisfactory from the beginning and they improved steadily. Results with WASCA are certainly better than with unassisted PRK. Eight years back, over a dozen patients received a phakic lens in 1 eye and PRK procedure in the other. In spite of initial slow recovery with PRK, most of the patients thought both the procedures as equally good. In my practice phakic lens for any degree of myopia, was gradually discontinued in 1996. For very high myopes, an planned residual myopia after PRK is helpful in coping with the near vision problems created by the present or the future central retinochoroidal changes. Hyperopia phakic lens in my practice, however, continues to be a good choice in suitable high error cases.11

Laser refractive surgery scores over a phakic lens in that beyond a few months to a year, regular lifetime attention is not required. It also reduces or removes existing astigmatism, which a phakic lens normally does not. Our choice of a phakic iris-claw lens/Artisan lens is based on its long track record (Figure 9-3). The only place this lens touches the tissues is where it holds the iris. Our own 23 years of experience with aphakic and 15 years of phakic implants shows that the lens

Figure 9-3. The iris tissue in the claw of an Artisan lens shows limited loss of pigment, which was shed by manipulations at the time of implantation. The surrounding iris looks healthy. One year postoperative hyperopia patient.

Figure 9-5. A 7.25 mm wide, with 4.25-mm optic, Artisan plus lens with claws 180 degrees apart. There is slight downward decentration 1 year after surgery.

is well tolerated. It does not produce angle-related, posterior pigment epithelium and crystalline lens-related problems. However, forceful rubbing of the eye can cause endothelial touch in case of Artisan as also angle-supported lenses.

ANATOMY

The availability of space for lens implantation, its lifetime tolerance by the related tissues, and age-related dimensional changes in the tissues and spaces are important.

Figure 9-4. An oblique view of the lens edge showing the floating vaulted Artisan lens, which is fixed at the claws.

The posterior chamber has a volume of 65 µm, base-out apex in, with zero depth at pupillary margin. The narrowest part of this space gets occupied by the thickest part (optic) of a posterior chamber lens. A phakic posterior chamber lens shall also touch, press, or rub the ciliary epithelium (that overlies highly permeable large caliber capillaries), the anterior surface of the crystalline lens and the posterior pigment epithelium of the iris, somewhere or the other. The increasing volume of the crystalline lens with age, from 150 µm to 240 µm in a matter of 60 years, encroaches on this already cramped space. Some increase in resistance to the free flow of aqueous is therefore possible.

The average anterior chamber depth is 3.15 mm. The volume of the anterior chamber is 250 µm, which decreases by 7.5% per decade, an important issue of concern for angle supported and iris supported lenses. The iris is about 0.5 mm thick at the root and 0.6 mm at the collarette. It is thicker in brown and black eyes. An Artisan lens gets fixed through its claws that hold the midperiphery of the iris. The concave back curvature of phakic Artisan lens keeps it not only away from the crystalline lens, but also away from the iris surface. A correctly fixed lens optic and its 0.17 mm thick haptic are far away from the angle and the corneal endothelium. The maximum width of Artisan lens is 8.5 mm with an optic of 5 mm or 6 mm. However, I prefer to use lenses that are 7.25 mm wide and have an optic of 4.25 mm. The reason is that in the scotopic conditions, the pupil in my black-eye population is smaller than in blue-eye patients (Figures 9-4 through 9-7).

The blood vessels in the anterior border layer of the iris have thick adventitia that helps the claw of the Artisan lens grip better. The capillary endothelium in the human iris is nonfenestrated, therefore less prone to blood-aqueous barri-

Figure 9-6. A 7.25 mm wide, with 4.25-mm optic iris claw lens. With eccentric claws in a dark eyed patient, 1 month after surgery.

er breakdown, as compared to ciliary capillary endothelium that is fenestrated as if designed to leak.

There is minimum touch/friction between the edge of the vaulted optic and the anterior surface of the iris. It is as if the Artisan lens floats in the aqueous, while it is anchored to 2 points on the iris. The main cause of an early dislocation is a poor fixation. The iris tissue that is actually caught inside the claws gets compressed from day 1 onwards. A breakdown of blood-aqueous barrier in the early postoperative period is possible. If the compressed iris tissue in the claw gets atrophied as it often does, usually it does not affect the fixation. This state can be likened to the passage of an earring through the lobule. However if the tissue bite had been small, the lens get dislocated. The inclusion of excessive iris tissue in the claws during surgery can push the implanted lens against the iris and the natural lens. This can interfere with the free circulation of the aqueous through the pupil, sometimes resulting in the formation of posterior synechia.

A well-designed angle-supported lens is said to rest against the scleral spur. Actually it presses against the corneoscleral trabeculae, Schlemm canal, the ciliary body in the angle recess and sometimes the blood vessels and nerves in the vicinity. Sizing of an angle-supported lens is difficult. There is nothing like a correct size. A lens has to be somewhat over-sized (press the tissues too) to stay in place. Even a slight undersize will make the lens move around, if not fixed by tissue reaction. Over a period of time, a haptic may press on the segmental blood supply of the iris, causing ischemia and iris atrophy that manifests as progressive ovalization of the pupil. A haptic can also erode the angle tissues and lodge in the ciliary body. Uveitis-glaucoma-hyphema

Figure 9-7. A 4.25 mm optic, 7.25-mm wide, well-centered hyperopia Artisan lens, 1 year postoperative.

(UGH) syndrome and its reflection in the retina as CME are fearful possibilities.

In every kind of phakic lens implantation, the role of lifelong microtrauma and macrotrauma in causing implant tissue friction, pressure, or erosion should be kept in mind. All of the iris claw lens and most of the angle-supported lens can be observed under the slit lamp microscope. Gonioscopy can reveal the uveal-haptic relationship. The most crucial periphery of a posterior chamber phakic lens and its relationship/interaction with the uveal tissues cannot be examined. If the pupil fails to dilate due to any reason, only ultrasoundbiomicroscopy can provide an indirect partial information about the tissue-implant status.

PHAKIC LENS POWER

CALCULATION

The lens power calculation is based on corneal curvature (K), the anterior chamber depth (ACD) and the spectacle correction (at 12-mm vertex). The following tables provided by Ophtec are useful in selecting a myopia or a hyperopia lens (Tables 9-1 and 9-2).

INDICATIONS AND

CONTRAINDICATIONS

Indications are obvious. A patient who is averse to use a pair of glasses or contact lens, who does not wish to be treated with PRK, LASEK, or LASIK for his refractive error, but

likes the idea of a phakic refractive IOL, after understanding the pros and cons of various modalities, is a candidate for this surgery. The other group of patients has high refractive errors, for which usually the surgeon suggests a phakic lens or a dual operation of phakic lens implant, followed after some interval, by a laser refractive technique so that a most accurate refractive correction is achieved.

A myopic patient should not be younger than 18 years. Some suggest minimum age to be 30 years. There is no hard

line for hyperopia, because in them the eye does not continue to grow. Phakic IOL is contraindicated in myopia other than axial, in the presence of lens sclerosis or early cataract, history of uveitis, presence of posterior synechia, history of glaucoma or IOP more than 20 mm, personal or family history of retinal detachment, diabetes mellitus, arthritis, and when the depth of the anterior chamber is less than 3 mm. Some of the above contraindications are relative to the discretion of the surgeon and on the needs of the patients.

There are relative contraindications like the age and the intelligence of the patient, when the patient cannot be prevented from habitual rubbing the eye. Some lens designs are not available for phakic eye implantation, if the corneal diameter is smaller than normal. The presence of amblyopia is not a contraindication.

ANESTHESIA

While it is possible to implant a phakic lens after surfacecum intracameral, subconjunctival, peribulbar or retrobulbar anesthesia, my preference is general anesthesia. With general anesthesia, the surgeon’s only concern is a good operation under ideal surgical conditions. The operation takes about 5 to 7 minutes in all.

PREPARATION FOR OPERATION

1.Calculation of phakic IOL power from the results of refraction, the depth of the anterior chamber and the keratometric readings, with the help of the tables for different types of intraocular lens. The myopia and hyperopia tables for Artisan lens are given above

2.Conjunctival swab for culture and sensitivity

3.Instillation of ofloxacin or ciprofloxacin eye drops 6 to 8 times on the preceding day and 4 to 6 times on the morning of the operation

4.Pilocarpine 2% drops to contract the pupil, for Artisan or angle-supported lenses. The pupil is dilated for posterior chamber phakic lens implant

In the operation theater:

1.Painting the skin around the eye with povidine-iodine 10%

2.Washing the conjunctival sac with povidine-iodine 5%

3.Passing a superior rectus suture and a suture through the lower lid

4.Plastic adhesive drape and an eye speculum. I use none of these, because they seem to put pressure on the eye ball. The cilia are cut if they are likely to touch the operating instruments or the IOL. The lid margin and the conjunctival sac are thoroughly washed with povi- dine-iodine 5%

Figure 9-8. Making a side pocket incision with a trifacet diamond knife.

Figure 9-10. A 4.25 mm wide pocket incision with a diamond knife. The pocket should be 1.5 mm deep. This sharp-tipped knife should never point towards the iris or lens.

STEPS OF PHAKIC

LENS IMPLANTATION

Artisan Lens

For incisions, a trifacet adjustable depth diamond knife is used to make 0.3 mm deep grooves on the limbus, 1 mm wide on the sides and 4.25 mm to 6 mm (according to lens size) at the upper limbus. The side ports are opened in to the

Figure 9-9. Making the eye firm by injecting HPMC from the side port. A firm eye helps in making a good pocket incision at the upper limbus.

anterior chamber as 1 mm deep pockets in the clear cornea (Figure 9-8).

A sharp, pointed diamond knife is not used, for fear of an accidental injury to the iris or the lens. The anterior chamber is filled firmly with viscoelastic material. I use 2% hydroxypropyl methylcellulose (HPMC). It is available in a syringe pack of 2 mL. HPMC should be injected, after taking the cannula clearly in to the anterior chamber (Figure 9- 9). Injecting merely inside the pocket can sometimes cause a disastrous separation of the Descemet membrane. The top incision is made with a 4.25-mm diamond knife and a 1.5-mm pocket is fashioned. A diamond knife makes the cleanest cut. While making pocket incisions, it is important to watch the tip of the diamond knife, lest it strikes the iris or the lens. The knife should be moved in the plane of the iris and never toward it (Figure 9-10).

PERIPHERAL IRIDECTOMY/IRIDOTOMY

If so desired, a peripheral iridectomy or iridotomy is performed close to the internal opening of the upper pocket incision. A peripheral iridectomy somewhat reduces the tendency of the iris to prolapse during phakic lens implantation. In the postoperative period, it is a safety valve, if for any reason the pupil gets blocked. To do an iridotomy or iridectomy, a utility forceps lifts the iris just inside the incision. The iris is snipped by a scissors inside the anterior chamber. The iris is never pulled out of the incision line, as this can tear the iris root and cause bleeding. The other option is to proceed, the iridectomy being done later (Figures 9-11A and B).

LENS IMPLANTATION

Make sure the pupil is contracted. If not, an intracameral preparation of carbachol, acetylcholine, or pilocarpine is used to effect the same.The Artisan lens is vaulted and has a

B

Figure 9-11A and B. Peripheral iridectomy/iridotomy is performed by taking the forceps and the scissors inside the anterior chamber.

convexo-concave optic (Figure 9-12). The lens is introduced inside the anterior chamber, taking care of the position of the claws (Figure 9-13). I commonly use a lens with eccentric claws, which need to face superiorly for proper fixation.When a lens with claws 180 degrees apart is used, no such precaution is necessary (see Figures 9-5 and 9-14). The IOL is slipped in so that it crosses the pupil without touching the iris or the crystalline lens. Keeping the anterior chamber well supplied with HPMC, the IOL is rotated to make it horizontal (Figure 9-15). The rotation can be effected by an irrigating cannula, either physically or by the push of viscoelastic material. Any fine lens hook can do the same. I like to see the lens floating in the anterior chamber, so that when the lens holding forceps enters the anterior chamber, the upper edge of the IOL floats in to the open jaws of the lens-holding forceps.

The lens-holding forceps is designed to hold an IOL with a concave posterior surface (Figure 9-16). It is shaped like the tail of a dolphin. The grip on the lens is excellent.

Figure 9-12. Convexo-concave vaulted construction of the phakic Artisan lens. The eccentric claws are clearly visible.

Figure 9-13. The phakic Artisan lens is introduced parallel to the iris surface. Note the pocket of the incision.

The basic philosophy of Artisan lens implantation is to hold the centrally positioned lens steady, with the lens holder, while a second instrument introduced through the side port passes a fold of the iris through the claw of the lens (Figure 9-17).

Passing a fold of iris through the claw needs to be understood clearly. Each haptic of the Artisan lens has a springy flexible claw. The claw can be opened by anything stiff—a thin forceps, a hook, or a cannula. The iris can be introduced into the claw either by:

1.Carrying it along with the stiff instrument that opens the claw.

2.By gently pressing the claw on the iris, while an instrument opens the claw in a fluid motion; the moment