In 1989, J. Stuart Cumming, MD, first intuited the feasibility of an IOL that moves back and forth within the eye. When examining cataract surgery patients implanted with plate lenses, he realized that some could read J1 at near through their distance correction. He found that their IOLs tended to be located more posteriorly as compared with loop-haptic lenses, and their IOLs always situated themselves posteriorly in the bag against the vitreous face. A-scanning revealed that the lens optic moved forward approximately 0.7 mm during pharmacologically induced accommodation, an action only possible through the functioning of the ciliary muscle.
High-resolution MRI studies1,2 have demonstrated that, in patients of all ages, the ciliary muscle maintains its contractility. The real cause of presbyopia lies in the ectodermal structure of the lens, which produces new cells throughout life. The zonules become floppy as the lens grows larger and the distance between it and the ciliary muscle decreases. This change induces a loss of accommodation. The ciliary muscle constantly tries to alter the shape of the lens, but it is unsuccessful because the zonules are loose.
Patients aged 45 years or older consider the onset of presbyopia to be a handicap in their professional and private lives. Implanting an IOL that successfully treats presbyopia is probably the most physiologic solution for them. Another benefit of this treatment is that the patient will never develop cataracts.
REFRACTIVE LENS EXCHANGE
Refractive lens exchange allows the surgeon to address all elements of a patient's refractive error, including presbyopia. Every anterior segment surgeon is familiar with cataract and IOL technologies, which are significantly less expensive than laser equipment.
Mechanism of the CrystaLens
I offer the option of refractive lens exchange using the CrystaLens (C&C Vision, Aliso Viejo, CA) to all of my presbyopic patients who are 45 years or older. The IOL's total length is 10.5 mm, and its optic diameter is 4.5 mm. The lens is made of third-generation silicone. Upon implantation, the CrystaLens' polyimide loops are trapped between the anterior and posterior capsules; the knobs on the ends of the loops prevent their slippage, and natural fibrotic processes hold them firmly in the capsular bag.
After implantation of the lens, the contraction of the ciliary muscle increases pressure on the vitreous and thereby pushes the optic forward. Lucio Buratto, MD, examined the movement of the CrystaLens during accommodation and found a 1.3-mm mean variation of the anterior chamber depth. He applied a fogging technique in order to measure these patients' average range of postoperative accommodation, which was 2.10 D on average.3
Preoperative Concerns
I have found that precise biometry is mandatory for obtaining reliable preoperative measurements of the eye's axial length. Applanation biometry flattens the cornea and leads to inaccurate results, which are particularly detrimental to surgical outcomes with accommodative lenses.
It is very important to inform patients that they may be unable to read well for up to 2 months. These individuals also must train their near vision and should not use reading glasses or other visual aids during that time.
Implanting the Lens
The surgical technique for implanting the CrystaLens and a standard phacoemulsification cataract extraction do not differ significantly. The former involves enlarging a phaco incision to 3.5 mm. There are only two technical variations between the procedures. First, the CrystaLens patient receives atropine drops for 1 week postoperatively in order to paralyze his ciliary muscle while fibrotic processes affix the loops to the capsule. This step allows perfect centration of the IOL.
Second, the sizes of the capsulorhexes differ. When I began implanting the CrystaLens, I created a smaller capsulorhexis, which I thought would prevent the lens from shifting forward and dislocating. I later realized that, upon capsular shrinkage, a small capsulorhexis sometimes has the effect of a buttonhole: it can trap the capsule behind the lens optic. After operating on a few eyes, I switched to a larger capsulorhexis of 5 mm and thereby eliminated the problem.
STUDY RESULTS
The subjects of a prospective study4 I conducted included 24 women and 21 men aged 47 to 83 years. All were able to achieve a BCVA of 20/30 or better preoperatively and had not undergone any previous ocular surgery. Most of the patients had less than 1.00 D of corneal astigmatism preoperatively, but a few had higher amounts of cylinder. The investigators corrected pre-existing astigmatism via limbal relaxing incisions.
Only three of 39 patients who received the implants bilaterally required reading glasses after a follow-up period of at least 3 months. A minority of patients complained of nighttime glare and halos, both of which disappeared a few weeks following surgery. The unwanted visual phenomena were mainly due to the atropine effect. Although the optic of the lens is very small, glare and halos are not a problem because the lens is positioned quite posteriorly toward the retina and sits closer to the focal point of the eye (Figure 1).
The binocular UCVA was 20/25 or better in 91% of patients, 20/32 or better in 95% of patients, and 20/40 or better in all eyes. Twenty-three percent of the subjects achieved a near UCVA of J1 or better, 64% saw J2 or better, and 90% saw J3 or better. The monocular UCVA was 20/25 or better in 74% of patients, 20/32 or better in 89% of patients, and 20/40 or better in all subjects. Seventeen percent of patients achieved a monocular near UCVA of J1 or better, 50% saw J2 or better, and 87% saw J3 or better. The monocular, distance-corrected near vision was J1 or better in 17% of subjects, J2 or better in 49%, and J3 or better in 81%. Twenty-three percent attained binocular, distance-corrected near vision of J1 or better, J2 or better in 62%, and J3 or better in 92%. Eighty-one percent of the eyes achieved J3 or better monocular vision with distance correction, and the patients therefore depended on reading glasses much less.
I have found that the CrystaLens also provides excellent intermediate vision, so card and pool players who receive the IOL are extremely pleased. Patients typically pay the entire cost of refractive lens exchange. Approximately 10% of my cataract surgery patients also wish to receive the CrystaLens. In this situation, their insurance company will cover the cost of the cataract procedure, but it will not reimburse the cost of the lens, as it will a monofocal IOL. Instead, the patient must pay the full price of the CrystaLens. I offer the CrystaLens option to eligible candidates and let them choose which IOL to receive. I therefore describe the implantation of this IOL as refractive lens surgery.
CONCLUSION
Future developments in phacoemulsification technologies, smaller incisions, and accurate axial length measurements will increase the safety, predictability, and accuracy of refractive lens exchange. The rapid visual recovery experienced by individuals undergoing this procedure will attract more patients from the presbyopic age group.
1. Strenk SA, Semmlow JL, Strenk LM, et al. Age-related changes in human ciliary muscle and lens: A magnetic resonance imaging study. Invest Ophthalmol Vis Sci. 1999;40:1162-1169.
2. Strenk SA, Strenk LM, Semmlow JL. High resolution MRI study of circumlental space in the aging eye. J Refract Surg. 2000;16(supp):S659-6560.
3. Cimberle M. More than 2,000 CrystaLens IOLs implanted worldwide. Ocular Surgery News. 2002;20:16:12-14.
4. Mertens EL. Restoration of accommodation after cataract refractive surgery with the CrystaLens AT-45 IOL. Paper presented at: VII ESCRS Winter Meeting; February 8, 2003; Rome, Italy.
