Ординатура / Офтальмология / Английские материалы / Hyperopia and Presbyopia_Tsubota, Boxer Wachler, Azar_2003

Figure 1 New intraocular lenses from C&C are designed to move forward into the anterior chamber to accommodate much like the natural lens. (Courtesy of C&C Vision).

two flexible arms located 180 degrees apart (Fig. 1). These flexible arms allow the lens to move forward and backward in the posterior chamber on constriction and relaxation of the ciliary muscle. At the end of each arm is a T-shaped polyamide haptic that follows the curve of the capsular bag after implantation and maintains centration and stability by resting in the capsular bag. The HumanOptics designs had a modified steering wheel appearance which has been modified to allow greater accomodation.

C. MULTICOMPONENT IOLs

Since the advent of refractive surgery, we have been able to correct ametropia to what is achievable with spectacle and contact lens corrections. This has been especially applicable to the calculation of intraocular lens power if cataracts occur after refractive surgery. Several formulas have been used to improve the predictability of IOL calculations after

Figure 2 Intraocular lens from HumanOptics designed to move forward into the anterior chamber to accommodate, much like the natural lens. (Courtesy of HumanOptics).

refractive surgery, but surprises are occasionally encountered. Patients who have had refractive surgery and subsequent cataract surgery demonstrate surprising hyperopic errors in IOL power determination. The ability to correct hyperopic surprises after cataract surgery in patients who have undergone previous refractive surgery would be desirable in the group of patients who are accustomed to spectacle-free vision (4). The use of adjustable or multicomponent intraocular lenses is a new concept that allows fine tuning of an already fairly accurate refractive procedure (Fig. 2).

1. Description of Multicomponent IOLs

The multicomponent intraocular lens is a three-component lens consisting of a base lens and two additional refractive attachments. The base lens has a planoconvex optical, and the overall mechanical design of the lens is similar to that of currently used posterior chamber lenses. The lens is made of polymethylmethacrylate (PMMA) and consists of one piece, with a diameter of 6.0 mm and an optical aperture of 5.5 mm. The basic lens looks much like a conventional posterior chamber IOL (PCIOL). The base lens has two machined slots whose thickness is approximately 1.2 mm. These slots accept the cap lens and hold the assembly together. The base lens is placed into the posterior capsular bag permanently heals there (Fig. 3). After its implantation, it acts as a platform for the other two detachable refractive elements (3).

Attached to the base lens are two additional refractive elements. The middle lens, or sandwich lens, carries the astigmatic (4.00-D sphere and 0.00 to 4.00-D diopter cylinder

Figure 3 Multicomponent IOL. (From Werblin TP. Multicomponent intraocular lens. J Refract Surg. 1996S:187–189, with permission).

macromer and photoinitiator. This action effectively locks in the refractive power of the lens (4).

The surgeon may induce a myopic change by irradiating the edges of the LAL to effectively drive macromer and photoinitiator out of the lens central region, thereby increasing the radius of curvature and decreasing the power.

One concern with the LAL is that after irradiation, the lens may not necessarily maintain a resolution efficiency acceptable to the patient. However, preliminary data show that this light-adjustable silicone IOL materials may provide a means to precisely and noninvasively adjust IOL power postop, after the refractive status of the eye has stabilized.

E.RESULTS OF ACCOMMODATING AND MULTIFOCAL IOL IMPLANTATION

Calhoun’s adjustable silicone formulations may become a platform technology useful in both pseudophakic and phakic IOLs. As additional IOLs are developed, such as the accommodating IOLs of C&C Vision and Human Optics (Erlangen, Germany), the ability to overcome imprecision in IOL power calculation by postoperative light adjustment has the potential to add value to these and other novel IOL designs (1–4).

The accommodating IOL is implanted after conventional phacoemulsification surgery through a 3- or 5-mm incision. The AT45 lens is maximally positioned against the vitreous face and sealed in place with 3 weeks of atropine treatment posoperatively. At the base of the arms of lens are hinges that allow the lens to move forward, based on ciliary contraction and pressure from vitreous. Any forward movement of the lens allows for near vision, simulating natural accommodation (1,2).

The early results of a phase 1 clinical trial show the lens to be safe, complicationfree, and well tolerated. The lens appeared to provide some accommodation. The lens is still in the evaluation stage and further clinical trials are in progress (2).

The multicomponent lens is still in the process of development, and results of clinical trials are awaited. The multicomponent lens has been used in a cat model; at 6-month follow-up, it was well tolerated.

Werblin has developed a hypothetical human surgical procedure that is analogous to routine phacoemulsification surgery with implantation of a PCIOL through a 7.00mm incision (Fig. 3) (3). Once the base lens is implanted, the cap-and-lens assembly is intraoperatively affixed by the surgeon to the base lens. The sandwich lens is oriented at the appropriate astigmatic axis, based on the preoperative assessment of anticipated postoperative astigmatism.

Once refractive stability is achieved, the patient’s refractive status is evaluated and the refractive attachments can be removed or changed, depending on the amplitude and type of residual refractive error or, in case of a multifocal attachment, if the patient is not satisfied with the quality of vision. Such change or removal involves a second operative procedure consisting of opening the original wound, detaching the cap-and-sandwich lens component, and replacing it with new attachments (1,3).

In contrast to accommodating and adjustable IOLs, several clinical studies have evaluated the feasibility and efficacy of multifocal IOLs (1,5–15).

In a prospective study, Vaquero et al. compared the results of implanting the AMO array multifocal lenses with implanting a monofocal lens (5). Although distance acuity and contrast sensitivity were similar in both groups, patients with the multifocal lens had significantly better near acuity. In a prospective, double-masked, comparative clinical trial,

Steinert et al. reported that significantly less correction was required in the multifocal group than the monofocal group. However, patients in the multifocal group sustained a small loss of contrast sensitivity (6).

Holladay et al. have evaluated the optical performances of several multifocal lenses using laboratory and photographic studies (7). They found a twoto threefold increase in depth of field for all multifocals but also showed a 50% reduction in contrast in retinal image and a one-line drop in best corrected acuity. Percival and Setty conducted several clinical trials of multifocal lenses and found them to provide better simultaneous distance and near acuities in a significantly higher number of patients (8). Bleckman and coauthors found multifocal progressive IOLs to provide adequate visual performance at various distances but only in optimal light conditions (9).

In a small-sample retrospective study, Negishi et al. demonstrated that eyes implanted with the five-zone refractive multifocal lenses showed better near visual acuity than control eyes and that the results compared favorably in other aspects of visual function (10). In a clinical trial, Wille reported a better performance of monofocal lenses for distance vision when compared to multifocal lenses (11). The mean postoperative acuity was 0.5 line higher in the monofocal than in the multifocal group.

After testing contrast sensitivity and glare in patients implanted with diffractive multifocal IOLs, Winther-Nielsen and coworkers concluded that the most significant loss of contrast sensitivity is found with central glare under twilight conditions (12).

In a comparative study of monofocal versus multifocal lenses, Vaqero-Ruano, et al. reported a wider depth of focus and significantly better near vision without addition in patients with multifocal lenses (13). The contrast sensitivity results at 96 and 50% were similar. Walkow et al. prospectively evaluated a diffractive versus a refractive multifocal IOL and found similar and satisfactory functional results with both except that near uncorrected vision was significantly better with the diffractive lens (14).

In a case control study, Javitt et al. measured functional status and quality of life after bilateral implantation of multifocal versus a monofocal IOLs (15). The subjects with bilateral multifocal IOLs reported better overall vision, less limitation in visual function, and less spectacle usage than the control subjects with monofocal lenses. The difference was most significant in ratings of near vision without spectacles.

H. CONCLUSIONS

Based on the relatively high success rate of multifocal IOLs, it is likely that several design adjustments may need to be incorporated into accommodating and adjustable IOLs before their use becomes commonplace. It is also likely that several of these technological advances may have to be combined in order to provide increased predictability for distance acuity without correction after cataract surgery as well as excellent near visual acuity. The multifocal IOLs’ ability to provide good distance and near visual acuity is not without visually disturbing loss of contrast sensitivity. Similarly, the success of monovision refractive surgery does not exceed the 80% mark in most studies (16–19). Accordingly there will be ample room for innovation in technology and surgical technique to provide excellent uncorrected distance and near acuities without optical aberrations. The successful preliminary results of accommodating and adjustable IOLs will provide the incentive for continued efforts and developments in this exciting field of research.

REFERENCES

1.Vajpayee RB, Jain S, Azar DT. Astigmatic intraocular lenses, multifocal intraocular lenses, and other specialized intraocular lenses. In: Azar DT, ed. Intraocular Lenses in Cataract and Refractive Surgery. Philadelphia: Saunders, 2001: 299–306.

2.New IOL restored some accommodation in trial. Ocul Surg News. 1999.

3.Werblin TP. Multicomponent intraocualar lens. J Refract Surg 1996; 12:187–189.

4.Schwiegerling JT, Schwartz DM, Sandstedt CA, Jethmalani J. Light-adjustable intraocular lenses: finessing the outcome. Rev Refract Surg 2002: 23–25.

5.Vaquero M, Encinas JL, Jimenez F. Visual function with monofocal versus multifocal IOLs. J Cataract Refract Surg 1996; 22:1222–1225.

6.Steinert RF, Post CT Jr, Brint SF, Fritch CD, Hall DL, Wilder LW, Fine IH, Lichtenstein SB, Masket S, Casebeer C. A prospective, randomized, double-masked comparison of a zonal—progressive multifocal intraocular lens and a monofocal intraocular lens. Ophthalmology 1992; 99:853–861.

7.Holladay JT, van Dijk H, Lang A, Portney V, Willis TR, Sun R, Oksman HC. Optical performance of multifocal intraocular lenses. J Cataract Refract Surg 1990; 16:413–422.

8.Percival SPB, Setty SS. Prospectively randomized trial comparing the pseudoaccommodation of the AMO ARRAY multifocal lens and a monofocal lens. J Cataract Refract Surg 1993; 19: 26–31.

9.Bleckmann H, Schmidt O, Sunde T, Kaluzny J. Visual results of progressive multifocal posterior chamber intraocular lens implantation. J Cataract Refract Surg 1996; 22:1102–1107.

10.Negishi K, Nagamoto T, Hara E, Kurosaka D, Bissen-Miyajima H. Clinical evaluation of a five-zone refractive multifocal intraocular lens. J Cataract Refract Surg 1996; 22:110–115.

11.Wille H. Distance visual acuity with diffractive multifocal and monofocal intraocular lenses. J Cataract Refract Surg 1993; 19:251–253.

12.Winther-Nielsen A, Corydon L, Olsen T. Contrast sensitivity and glare in patients with a diffractive multifocal intraocular lens. J Cataract Refract Surg 1993; 19:254–257.

13.Vaquero-Ruano M, Encinas JL, Millan I, Hijos M, Cajigal C. AMO Array multifocal versus monofocal intraocular lenses: long-term follow-up. J Cataract Refract Surg 1998; 24:118–123.

14.Walkow T, Liekfeld A, Anders N, Pham DT, Hartmann C, Wollensak J. A Prospective evaluation of a diffractive versus a refractive designed multifocal intraocular lens. Ophthalmology 1997; 104:1380–1386.

15.Javitt JC, Wang F, Trentacost DJ, Rowe M, Tarantino N. Outcomes of cataract extraction with multifocal intraocular lens implantation. Functional status and quality of life. Ophthalmology 1997; 104:589–599.

16.Jain S, Azar DT. Eye infections after refractive keratotomy. J Refract Surg 1996; 12(1): 148–155.

17.Jain S, Arora I, Azar DT. Success of monovision presbyopes: review of the literature and potential applications to refractive surgery. Surv Ophthalmol 1996; 40(6):491–499.

18.Sippel KC, Jain S, Azar DT. Monovision achieved with excimer laser refractive surgery. Int Ophthalmol Clin 2001; 41(2):91–101.

19.Chang MA, Kloek CE, Zafar S, Jain S, Azar DT. Analysis of strict monovision and minimonovision LASIK surgery in presbyopes. Arch Ophthalmol. Submitted.

Figure 1 Dynamic retinoscopy without lenses. The patient (A), wearing refractive correction if any, looks alternately between a distant target and a near accommodative target that the examiner holds just beneath the retinoscope peephole (B). Accommodation is observed objectively by neutralization of the “with” retinoscopic reflex when the patient accommodates to the plane of the near target.

accommodation, a method well described in the literature (2–4) (see Fig. 1) but not familiar to most ophthalmologists. The typical appearance is strong “with” movement with the patient looking past the edge of the retinoscope at the distance fixation target. As attention is shifted to the accommodative target just beneath the peephole of the retinoscope and as the eyes accommodate to this distance, the retinoscopic reflex broadens to neutralization over about 1/2 s. In other words, the pupil fills with light, and neither “with” nor “against” movement is visible. This striking change in the retinoscopic reflex can be observed repeatedly as the patient is instructed to look back and forth between distance and near. The speed, completeness, and stability of accommodation can thus be observed objectively. Residual astigmatism is easily detected, and when the procedure is performed under binocular conditions, anisometropia is evident by unequal neutralization of the two reflexes.

To my surprise, my “rejuvenated” presbyope showed absolutely no perceptible change in the retinoscopic reflexes when looking from distance to near, and yet she could easily read the smallest letters on the near acuity chart. The clue to this total lack of objective accommodation, even though subjective accommodation appeared restored, was the shape of the retinoscopic reflexes.

C. RETINOSCOPIC REFLEXES

The streak retinoscope gives a linear reflex in eyes with regular spherical or astigmatic refractive error. In other words, the streak is the same width everywhere along its length.

Figure 2 The retinoscopic reflex seen with (A) the eye focused well beyond the retinoscope; (B) the eye focused just beyond the retinoscope; (C) a multifocal crystalline lens focused for distance in the center of the pupil and for near in the periphery of the pupil.

Typical reflexes are illustrated in Figure 2A, which shows the eye focused well beyond the retinoscope. Figure 2B shows the eye focused just beyond the retinoscope. If the eye were focused exactly in the plane of the retinoscope peephole, the red retinoscopic reflex would totally fill the pupil.

D. MULTIFOCAL CRYSTALLINE LENS

My patient’s reflexes correlated with neither Figure 2A nor Figure 2B but rather with Figure 2C. The streak was narrow in the center and broad at the top and bottom, in an hourglass shape. This shape persisted as the streak was rotated from one meridian to the next. Clearly the eye was focused for distance in the center of the pupil and for near in its periphery. A multifocal crystalline lens appeared to have been created by the procedure. (This appearance changed little as the retinoscope was moved off axis, indicating that the multifocal effect was in the crystalline lens, not in the cornea.)

E. INCREASED DEPTH OF FOCUS

It now became clear how this presbyopic patient was able to see clearly at both distances. She had been given multifocal crystalline lenses by the surgery. Because the retinoscopic reflex had not changed from distance fixation to near fixation, no true accommodation was occurring. The new multifocal effect simply created a huge depth of focus that enabled both distance and near vision without any active accommodation.

By adding plus lenses to neutralize the center of the retinoscopic reflex, I observed the peripheral portion of the reflex to move strongly “against,” confirming that the periphery of the pupil was myopic with respect to the center. This type of refractive aberration is called “positive” spherical aberration, most commonly occurring naturally in young children. When it occurs naturally, however, the zones in the center and periphery are more clearly defined, with linear streak reflexes in each zone. In my “rejuvenated” presbyope, the transition from the emmetropic central zone to the myopic peripheral zone appeared more continuous, resulting in the hourglass-shaped reflex.

F.TRADITIONAL TECHNIQUES FOR MEASURING ACCOMMODATION

I have not yet had the opportunity to confirm this retinoscopic appearance in other patients after surgery for presbyopia. If indeed this finding is routinely present, then traditional methods for measuring accommodation are not applicable to these patients.