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

equatorial capsular tear, vitreous hemorrhage, and phacoantigenic glaucoma. This patient underwent multiple vitreoretinal surgeries for macular edema retinal detachment and epiretinal membrane. The patient also underwent a corneal transplant, which unfortunately failed. Following multiple surgeries, the multiple-fin prosthetic iris implants and IOL appear to have dislocated slightly anterior. This patient is currently scheduled for a repeat penetrating keratoplasty and exchange of the endocapsular prosthetic iris rings/IOL for a single-piece prosthetic iris/IOL that will be sutured to the ciliary sulcus.

Visual Acuity

Visual acuity improved in 36 of 58 eyes (62%) averaging 3.7 lines for the entire group (Table 1-1). Subgroup analysis demonstrated that the eyes with congenital iris deficiencies gained an average of 2.7 lines, while the eyes with traumatic or surgical iris loss gained an average of 4.4 lines of Snellen visual acuity. The 5 eyes with iris atrophy, averaged an improvement of 6.0 lines of Snellen visual acuity. Three eyes with traumatic aniridia, aphakia, and sensory exotropia demonstrated a significant improvement of visual acuity and gradual reversal of the exotropia after implantation of a sin- gle-piece iris diaphragm IOL. Only 2 eyes in the study lost 2 lines of visual acuity, and only 1 eye lost 3 lines of visual acuity. One patient with congenital aniridia, aphakia, and corneal surface disease accounts for 2 of these eyes. Preoperatively the patient was wearing rigid gas permeable (RGP) contact lenses, which helped overcome some of his corneal surface irregularity. However, he was becoming intolerant to the contact lenses and was happy with his reduction in glare after implantation of single-piece prosthetic iris devices despite his small loss of visual acuity.

Glare

Glare disability was assessed by directly questioning patients and recording their subjective appraisal of their preoperative and postoperative impairment in bright lights and high contrast settings. The average preoperative glare disability reported for the entire group was 2.8 using the following scale: none = 0, mild = 1, moderate = 2, and severe = 3. Glare disability was improved in 46 of the 48 eyes (96%) for which we attained a response to our survey, resulting in an overall average postoperative glare score of 1.0 (Table 1- 2).

Subgroup analysis demonstrated that subjective glare disability was reduced from an average of 2.6 preoperatively to 1.3 postoperatively in eyes with congenital iris deficiencies. The average glare disability reduction was equally impressive in eyes with traumatic iris loss (2.7 to 0.7), and in the group of eyes with iris atrophy (3.0 to 1.0).

Visual Acuity Outcomes

The preoperative visual acuity is plotted horizontally while the final postoperative visual acuity is plotted vertically. The diagonal line represents the level at which the preoperative and postoperative visual acuities are equal. The postoperative visual acuity improved for all points plotted above the diagonal.

T A B L E

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Glaucoma

Coexisting glaucoma was a frequent problem. Over 43% (25 of 58) of all eyes had a preexisting diagnosis of glaucoma requiring medication or surgery. Glaucoma control worsened in 4 eyes during the follow up period. Three of these eyes received a single-piece iris diaphragm IOL in the ciliary sulcus, while the fourth eye underwent implantation of the 50C multiple fin iris rings with a foldable acrylic IOL. It is unclear if any causal relationship exists between implantation of the prosthetic iris devices and worsening of glaucoma control, even though 1 of these 4 cases did have prolonged (3 months) low-grade inflammation that may have contributed to the worsening glaucoma. Many of these eyes are prone to develop glaucoma as a result of their underlying disease or injury. Our rates of both prolonged inflammation and the development of glaucoma are much lower than reported previously.8,10 We attribute these results to the fact that the majority of devices in this study were implanted within the capsular bag, avoiding irritation to the ciliary body. In addition, the single-piece iris diaphragm IOL was usually sutured to the scleral wall minimizing any intermittent contact that it might have with the trabecular meshwork.

Graphic representation of the subjective glare disability for each eye. Glare is preoperatively depicted by the height of the light bars, while postoperative glare is depicted by dark bars.

T A B L E

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CONCLUSION

Operating on a traumatized or congenitally aniridic eye presents special challenges, and implantation of an artificial iris device appears to be a safe and effective method for reducing the subjective perception of glare resulting from iris deficiency. Prosthetic iris devices provide a novel way to rehabilitate these symptomatic eyes for which there was previously no alternative.

1.Shaw M, Falls H, Neel J. Congenital aniridia. Am J Hum Genet. 1960;12:389.

2.Hittner H. Aniridia. In: Ritch R, Shields M, Krupin T, eds. The glaucomas. St. Louis: CV Mosby; 1989;873-879.

3.Nelson LB, Spaeth GL, Nowinski T, et al. Aniridia: a review.

Surv Ophthalmol. 1984;28:621.

4.Reihnhard T, Sundmacher R, Althaus C. Irisblenden-IOL bei traumatischer aniridie. Klin Monatsbl Augenheilkd. 1994;205: 196-200.

5.Sundmacher R, Reihnhard T, Althaus C. Black diaphragm intraocular lens for correction of aniridia. Ophthalmic Surg Lasers. 1994;25:180-185.

6.Tanzer DJ, Smith RE. Black iris-diaphragm intraocular lens for aniridia and aphakia. J Cataract Refract Surg. 1999;25: 1548-1551.

7.Thompson CG, Fawzy K, Bryce IG, Noble BA. Implantation of a black diaphragm intraocular lens for traumatic aniridia. J Cataract Refract Surg. 1999;25:808-813.

8.Reinhard T, Engelhardt S, Sundmacher R. Black diaphragm aniridia intraocular lens for congenital aniridia: long term fol- low-up. J Cataract Refract Surg. 2000;26:375-381.

9.Osher RH, Burk SE. Cataract surgery combined with implantation of an artificial iris. J Cataract Refract Surg. 1999;25:1540-1547.

10.Burk SE, Da Mata AP, Snyder ME, Cionni RJ, Cohen JS, Osher RH. Prosthetic iris implantation for congenital, traumatic, or functional iris deficiencies. J Cataract Refract Surg. 2001;27(11):1732-40.

11.Schneider S, Osher RH, Burk SE, Lutz TB, Montione, R. Thinning of the anterior capsule: a new finding associated with congenital aniridia. J Cataract Refract Surg. 2003;29:64551.

12.Osher RH. Slow motion phacoemulsification approach (Letter). J Cataract Refract Surg. 1993;19:667.

13.Zanoni D, Rosenbaum AL. A new method for evaluating visual acuity. J Pediatr Ophthalmol Strabismus. 1991;28:255260.

Bioptics is the combined use of any 2 refractive systems to correct myopia or hyperopia. Myopia is defined as an overpowered eye in which parallel light rays from distant objects are brought to focus in front of the retina. Hyperopia is defined as a condition in which the eye is underpowered. Thus light rays coming from a distant object strike the retina before coming to sharp focus; true focus is said to be “behind the retina.” Astigmatism is the condition where parallel rays of light from an external source converge or diverge unequally in different meridians. The obvious objective is to get the light rays to focus at a point on the retina (Figures 2-1, 2-2, and 2-3).

Myopia and hyperopia can be corrected with an IOL power designed to create emmetropia or reduce myopia or hyperopia to the desired level. Other lenticular options include phakic IOLs, astigmatism IOLs, and piggyback IOLs. These lenses are designed for implantation in the posterior capsular bag (Table 2-1).

Corneal options for bioptics include corneal relaxing incisions (CRI), anterior limbal relaxing incisions (ALRI), laserassisted epithelial keratomileusis (LASEK), photorefractive keratectomy (PRK), radial keratotomy (RK), laser thermal keratoplasty (LTK), conductive keratoplasty (CK), thermal keratoplasty (TK), and intracorneal rings (ICRs).1-13

This chapter will include corneal incision nomograms and techniques for the correction of astigmatism post cataract surgery, the results of a randomized prospective

Figure 2-1. Distant light rays focus anterior to the retina.

study comparing ALRIs to the original STAAR toric IOLs, and a brief discussion corneal procedures in pseudophakic patients.

In the early 1970s, Richard Troutman, MD, introduced CRIs and wedge resections to correct astigmatism. Initially, incisions were made at the limbus. These results were limited, especially in young people, so incisions were placed farther into the cornea, at times creating optical zones as small

Figure 2-2. Distant light rays focus behind the retina.

as 5 mm. This caused glare and optical aberrations, resulting in the consensus that the smallest optical zone with a favorable risk-benefit ratio was 8 mm.14

ANTERIOR CORNEAL

RELAXING INCISIONS

Our most commonly used technique for correcting astigmatism in refractive cataract or refractive lensectomy patient is anterior corneal relaxing incisions, based on the Nasal Corneal Relaxing Nomogram (Table 2-2). The amount of astigmatism to be corrected is based on the central 2 mm of EyeSys corneal topographical astigmatism. If the patient is phakic or pseudophakic, the amount of correction is determined by the refractive cylinder. If the prepseudophakic patient is young or has extremely high levels of astigmatism, either a toric IOL is combined with CRIs or an excimer laser corneal refractive procedure is performed when the postoperative refraction is stable (Figures 2-4 and 2-5).

The anterior limbal nomogram was based on patients aged 70 to 79 years because the majority of my patients were cataract patients. I chose the nasal anterior limbus because most of the visually distorting astigmatism in this age group is against the rule. Though the incisions are created in a circumferential pattern, the amount is measured in cord lengths. An advantage of this technique compared with corneal degrees is that surgeons can use calipers instead of purchasing new measuring instruments.

For each age decade below 70, 1 mm is added to the cord length for the desired correction. The length of the incision is also varied depending on the location of the astigmatism.

Figure 2-3. Distant light rays diverge or converge unequally in different meridians.

Intraocular Lens Powers

From Various Manufacturers

* Lowest range of IOLS

T A B L E

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I do not adjust the nomogram for nasal incisions. For temporal incisions, 2 mm are added; for vertical incisions, 1 mm is added; for oblique temporal incisions, 1.5 mm are added; for nasal oblique incisions, 0.5 mm is added (Figure 2-6). Generally, I do not correct against-the-rule astigmatism <+0.50 D or with-the-rule astigmatism <+1.00 D.

If 1 incision does not correct the astigmatism, I add a second ALRI. If the first one was placed nasally, the sutureless temporal corneal incision must not be cut. Bisecting the temporal corneal incision often creates wound leaks. In these cases, I use a 2-step temporal, ALRI on axis with the plus axis of astigmatism. I use the cord length to fit the nomogram. The second incision usually yields about half of the correction of the first incision. If more correction is needed, either a toric IOL is implanted or a corneal relaxing incision is made at the 8-mm optical zone. This nomogram is presented in Table 2-3.

I attempt to correct all of the against-the-rule astigmatism; occasionally, if patients want depth of focus, I induce approximately 1.00 D of with-the-rule astigmatism. On the other hand, I try not to overcorrect with-the-rule astigmatism. Some patients prefer to have about 1.00 D with-the- rule astigmatism, and many tend to get multifocal corneas, as discussed by Dr. James Gills and others. Therefore, I tend to overcorrect against-the-rule astigmatism and undercorrect with-the-rule astigmatism.

MEASUREMENT

I rely primarily on the central 2 mm of topographical corneal astigmatism as measured by the EyeSys corneal topographical system in prepseudophakic patients. It is important to compare the patient’s old refraction(s) and present K- readings to help confirm the topography. Second, before any keratometric or topographical analysis is made, other tests

Figure 2-6. Millimeters in cord length added to nasal ALRI nomogram for other astigmatic meridians.

including A-scans and tensions by applanation should be avoided. Patients should blink until the tear film covers the cornea. If the surface is distorted, consider using artificial tears, having the patients blink, and repeating the test. If topography is not reproducible, surgical astigmatism correction should not be performed until the postoperative refraction is stable. At that time the refractive cylinder can be used to correct the astigmatism, per the nomogram listed in Table 2-2. In the postoperative pseudophake or in phakic eyes, corneal topography and keratometric readings play secondary or confirmatory roles in determining astigmatism. I almost never rely solely on keratometric readings in phakic or pseudophakic patients to determine the amount of astigmatism to be corrected.

Martin's 8-mm ALRI Nomogram for Astigmatism

(Correction in diopters per mm.)

Optical zone at 8 mm.

Cuts at 100% intraoperative pachymetric reading at the site(s) of incision(s).

Cuts three 2 mm; cuts are arcuate. Do not exceed 60 degrees at any OZ.

Second series of cuts at OZ 9 or 10 (cord length 4.5 to 5 mm or 60 degrees) gives 1/3 of the amount of correction obtained at OZ 8.

DO NOT exceed 4-mm cut at OZ 8.

Avoid cuts OZ 5.

A series of cuts anterior limbal with a cord length of 5mm should add about 1/3 more correction. If the steep area exceeds 45 degrees, add Canrobert "C" procedure (2 or more arcuates on the bisector meridians). 15 degrees toward steep meridian.

T A B L E

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PREOPERATIVE MARKING

There are 3 options for marking with the patient at the slit lamp: at the 180-degree and 90-degree meridians, at the

Figure 2-7. A surgical marking pen used at slit lamp to mark the corneal limbus.

plus axis of astigmatism, or a combination of the two. We have enough experience so that we usually mark the plus axis of astigmatism. If only the vertical and horizontal meridians are marked at the slit lamp, then a degree marker such as a Mendez ring can be used in surgery to determine the appropriate surgical astigmatic axis. Before all markings, we apply proparacaine hydrochloride (lidocaine 4% and sensorcaine 0.75%, 1:1). To assure proper head position, it is very important to take into account that the anatomical center of the visual axis is not in the center of the pupil. Frequently, a 90-degree mark is shifted nasally because the visual axis is in the nasal pupil. Determining the appropriate visual axis rather than the anatomical center of the pupil is very important to improve the accurate placing of astigmatic keratotomies (Figure 2-7).

Figure 2-8. Caliper straddling plus axis of astigmatism.

Figure 2-9. Multiple pachymetric readings are taken along the anterior limbus.

SURGICAL TECHNIQUE

After being marked, the patient is prepped and draped. We perform almost all cases under topical anesthesia. If the plus axis of astigmatism has not been marked, then we use the Mendez ring to determine the appropriate plus axis astigmatism. After the plus axis of astigmatism has been identified, I use a caliper with the cord length determined by the nomogram. I place the caliper straddling the plus axis of astigmatism at the anterior limbus (Figure 2-8) and take intraoperative pachymetric readings across the cord length (Figure 2-9). If the cord length is long and there are significant differences in depth, then we may use a second micrometer diamond knife setting to treat the deeper section of the cornea (Figure 2-10). Across a 4-mm cord length, it is not uncommon to find pachymetric depth variances of 40 to

50µm.

All diamonds are set at 500 µm at the micronscope by an

experienced technician to ensure the accuracy (Figure 2-11).

Figure 2-10. Arcuate cuts made in anterior limbus.

The knives are transported to the operating room suite in a sterile diamond knife carrying case. The technician then adjusts the micrometer diamond knife setting so that it equals 40 µm more shallow than the most shallow pachymetric measurement. I create an incision immediately anterior to the anterior limbus. For cases with more astigmatism than my nomogram manages, I move the incision 0.5 mm more central.

EQUIPMENT PREPARATION

Micronscopes, calipers, and pachymetric equipment are critical and are serviced and maintained so that they measure accurately. We use the micronscopes on each case prior to prepping and draping to assure that the diamond is not chipped and that the footplates are smooth, without burrs or protein build-up. After examination, the technician sets the micron diamond blade at 500 µm in a sterile setting and the micrometer diamond is placed in a sterile protective case to be transported to the operative suite (Figure 2-12).

Figure 2-11. Technician adjusts micron diamond knife setting.

Figure 2-12. Technician examines micron diamond for quality and sets it at 500 microns.

I adamantly oppose using “permanently” set diamonds or metal blades. It is well known that settings vary from manufacturer to manufacturer, from case to case, and over time from regular use. In my experience, 1, 2, or 3 blade settings do not fit all eyes. I believe that the blades should be checked along with all other instruments the surgeon uses on each case to ensure that the depth is appropriate for that particular case. Any nomogram is a starting point that should provide immediate good results that will improve over time as the surgeon adjusts his or her nomogram based on clinical experience.

PREOPERATIVE CONDITIONS

Preoperative evaluation and treatment are often necessary to achieve the best outcomes. For example, patients with poor personal hygiene have a greater risk of infection. In many of these cases it may be wise to avoid additional incisions due to their increased risk for infection. Patients with blepharitis must be treated before surgery. It is important to

remember that patients with dry eyes often have abnormal keratometric and topographical imaging. The following preoperative and postoperative topography of dry eye patients show the dramatic changes that occur after the dry eye is treated. Resolution of their dry eye condition allowed a much more accurate refractive surgical technique. The following case is a 55-year-old female with cataracts and dry eyes. Her Schirmer test was 16 mm and 6 mm respectively in the right and left eyes. Tear break-up time was instantaneous OU. The patient was treated with punctal plugs, HydroEye (Science Based Health, Carson City, Nev) 2 by mouth BID and lubrication. The central 2 mm of topographical astigmatism was reduced from 5.00 D to 1.50 D in the right eye and from 5.00 D to 2.50 D in the left eye. As you can see, CRI surgery based on the initial “dry eye” topography would have given an overcorrection. The patient

Figure 2-13. 5.00 D of astigmatism in the central 2 mm of the topography.

Figure 2-14. 1.50 D of astigmatism in the central 2 mm of the topography.

ended up with 20/25+ UCVA postoperation OU (Figures 2- 13, 2-14, 2-15, and 2-16).

Patients who present with the above dry eye pattern topography or a very irregular topographical pattern should not be treated because this pattern is almost always abnormal. We treat these patients with increased hydration, increased humidity, artificial tears, HydroEye, and punctual plugs until corneal topography is stable.

Corneal lesions such as pterygia, Salzmann’s nodular degeneration, and epithelial basement disease almost always distort the corneal image. For example, horizontal pterygia give plus axis vertical astigmatism. I almost always remove the pterygium before correcting corneal astigmatism if the pterygium is inducing astigmatism.

Correcting astigmatism coexisting with pterygia is, in my opinion, unwise. The pterygium should be removed and the

Figure 2-15. 5.00 D of astigmatism in the central 2 mm of the topography.

Figure 2-16. 2.50 D of astigmatism in the central 2 mm of the topography.

cornea stabilized before any corneal refractive surgery. This holds true when implanting a toric IOL or using other refractive techniques.

Patients with other conditions such as epithelial basement membrane disease, corneal degenerations, or dystrophies are at risk for image distortions and misinterpretations and abrasions or perforations at surgery. Some anterior corneal disorders such as epithelial basement membrane disease or Salzmann’s nodular degeneration may be treated with epitheliectomy or superficial keratectomy before performing cataract or refractive corneal surgery. After the cornea stabilizes, keratometry and topographical analysis must be repeated. These measurements will almost always be significantly different.

Previous corneal surgery, including penetrating keratoplasty or refractive corneal surgery such as LTK or CK can

cause overcorrections. In these cases, I reduce the nomogram by a half. I also use an intraoperative corneoscope ring or keratometer to avoid overcorrections even when using half the nomogram. Furthermore, when possible I perform an immediate postoperative refraction to determine if more surgery is needed.

I do not recommend performing ALRI in grafts to correct induced astigmatism; I prefer CRIs placed just inside the donor-host recipient wound. Small amounts of astigmatic keratoplasty can give corrections 2 to 3 times the amount predicted by nomograms. Again, much less correction, perhaps one-half as much, is needed to avoid undesirable overcorrections. An intraoperative corneoscope or keratometer is helpful in these cases. It is best to remove the lid speculum to avoid corneal distortion and misinterpretation.