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Laboratory science

Feasibility and safety of laser treatments in eyes with an intraocular implantable miniature telescope

Rosner, Mordechai MD*,a; Ben-Simon, Gai MDa; Sachs, Dan MDa

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Journal of Cataract & Refractive Surgery: May 2003 - Volume 29 - Issue 5 - p 1005-1010
doi: 10.1016/S0886-3350(02)01647-4
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Abstract

The implantable miniature telescope (IMT) (VisionCare Ophthalmic Technologies Ltd.) was developed by Dr. I. Lipshitz to improve the central vision of patients with bilateral impairment of central vision as a result of age-related macular degeneration (ARMD) or other macular pathology. This monocular device is designed for implantation in the capsular bag or ciliary sulcus of patients during cataract surgery.1 Together with the cornea, the IMT functions as a telephoto lens. The implanted eye provides central vision, while the fellow eye provides peripheral vision for navigation.

The IMT is a telescope 3.0 mm in diameter and 4.4 mm long that incorporates an anterior plus and a posterior minus lens, which produce a lens of –120 diopters (D) (in air) and ×3 magnification. The lenses are mounted inside a quartz tube, which is sealed at both ends and contains 3 air spaces. The telescope is mounted on a clear poly(methyl methacrylate) (PMMA) carrier plate with haptics. An opaque blue PMMA cap holds the telescope and plate together (Figure 1). The device has a total diameter of 13.5 mm and weighs 46 mg in aqueous.

Figure 1.
Figure 1.:
(Rosner) The IMT designed for implantation in the lens capsular bag in patients with ARMD.

Patients with an IMT may develop secondary cataract, similar to that seen in patients after cataract surgery with an implanted intraocular lens (IOL). In rare cases, acute angle-closure glaucoma may develop. Patients may also develop retinal diseases such as diabetic retinopathy and central or branch vein occlusion or retinal tears that require treatment by laser photocoagulation of the macula or the retinal periphery.

This study evaluated the feasibility and safety of laser treatments in eyes fitted with an IMT using an animal model of pigmented rabbits.

Materials and Methods

Animals

Nineteen adult pigmented rabbits were used. They were kept at the animal facility of the Goldschleger Eye Institute. Before surgery and prior to laser treatment, the rabbits were anesthetized by intramuscular injection of ketamine hydochloride (Ketaset®) 100 mg/mL and xylazine hydrochloride (Chanazine®) 20 mg/mL. Before the eyes were enucleated, the rabbits were killed by an intravenous injection of pentobarbital sodium (Nembutal®). All animals were handled in accordance with the Statement for Use of Animals in Ophthalmic and Vision Research issued by the Association for Research in Vision and Ophthalmology.

Implantation of the IMT

An IMT was implanted in the right eye of each rabbit. After the pupil was dilated with tropicamide 0.5% eyedrops (Mydramide®), 1 of the authors (D.S.) performed extracapsular lens extraction using a surgical microscope (Wild M690). The surgical procedure for IMT implantation was similar to that for implantation of rigid PMMA IOLs. A mixture of balanced salt solution (BSS®) 500 mL and 5000 IU heparin (25 000 units/5 mL) was infused intraocularly to prevent fibrin formation in the anterior chamber. Two paracenteses were formed with a stiletto blade. An anterior chamber maintainer (ACM) connected to the BSS–heparin infusion was introduced into the eye through 1 paracentesis; a capsulorhexis was started with a bent needle through the second paracentesis. The corneal opening was enlarged, and the capsulorhexis was completed with a forceps. After the lens was hydrodissected, the nucleus was removed and the cortical material withdrawn manually using a McIntyre needle.

Sodium hyaluronate 2.3% (Healon®5), 23 mg/mL was used to deepen the anterior chamber and cover the IMT before it was introduced into the eye (Figure 2, A). The IMT was implanted in the capsular bag (Figure 2, B and C), and the surgical wound was closed with 7 or 8 polyester fiber (Mersilene®) 10-0 sutures. The viscoelastic agent and the ACM were then removed. In the event of leakage, the ACM paracentesis was sutured. At the end of surgery, betamethasone disodium phosphate and betamethasone acetate (Celestone Chronodose®) and gentamicin-IKA 80 mg (Garamycin®) were injected subconjunctivally and chloramphenicol 5% ointment (Synthomycetin®) was applied to the eye. Dexamethasone sodium phosphate 1 mg and neomycin sulfate (Dexamycin®) 5 mg were instilled in the operated eye twice daily for 1 week.

Figure 2.
Figure 2.:
(Rosner) Implantation of the IMT: The IMT is covered with Healon5 (A) and implanted in the lens capsular bag (B and C).

Laser Treatment

One rabbit did not receive laser treatment and was excluded from the study because the IMT subluxated into the anterior chamber. After the other 18 rabbits had recovered from implantation surgery, they were anesthetized and had various laser treatments.

Before laser posterior capsulotomy and retinal laser treatments, the pupils were dilated by instillation of tropicamide 0.5% eyedrops. The pupils were not dilated in rabbits scheduled for laser iridectomy. Laser treatment was performed with the anesthetized rabbit lying on a platform fixed to a stable photographic tripod in front of the laser apparatus (Figure 3). Laser peripheral iridectomy was performed in 4 rabbits using a YC-1400 Ophthalmic YAG Laser System (Nidek) and a Mandelkorn iris/cap laser lens (Ocular Instruments). The same neodymium:YAG (Nd:YAG) laser system and lens were used to perform laser posterior capsulotomy in 8 rabbits.

Figure 3.
Figure 3.:
(Rosner) Neodymium:YAG laser treatment (A) and argon laser treatment (B).

To examine the retina and perform the retinal photocoagulation, 5 handheld lenses were used: the 3-mirror universal laser lens (OG3MSA, 18 mm OD), the Mainster ultra-field PRP (OMRA PRP), the Mainster wide-field laser lens, and the OMRA Mainster retina laser lens (all Mainster lenses from Ocular Instruments), and a +90 D lens (Volk II BIO 90 D, Precision Optical Machine). The retina was best viewed with the 3-mirror lens, which was also used for laser photocoagulation.

Retinal photocoagulation was performed in 6 rabbits using an argon laser (Coherent Novus-2000). The retinal treatments simulated macular treatment, panretinal photocoagulation, and laser treatment at the retinal periphery. Data on the ability to perform the various laser treatments were recorded.

Histopathological Examinations

One day after laser treatment, the rabbits were killed and their eyes enucleated for histopathological evaluation. After fixation in formaldehyde, the eyes were sectioned into 2 compartments through the pars plana. The anterior segment included the cornea, ciliary body, iris, and lens capsular bag with the IMT. The posterior segment contained the sclera, choroid, and retina. The 2 parts of the eyes were embedded in paraffin, sectioned, and stained with hematoxylin and eosin. In eyes that had had retinal laser treatment, sections with laser lesions were also prepared for histological evaluation. The stained sections were evaluated by light microscopy.

Examination of the IMT

The implanted IMTs were removed when the eyes were sectioned and sent to VisionCare Ophthalmic Technologies Ltd. for evaluation. The examinations determined the effect of the laser treatment on the integrity of the IMT and the component parts. To test whether the telescopic cylinder had remained watertight, the IMTs were immersed in a 75 mm high glass cylinder filled with water. After 48 hours the IMTs were removed, dried, and tested for the presence of water in the optical cylinder of the telescope. The IMT was then disassembled into its component parts, each of which was evaluated. All examinations were carried out by an observer blinded to the treatment received by the rabbits using a video microscope with ×90 magnification.

Results

Neodymium:Yag Laser Iridectomy

The IMT did not reach the area that was subjected to peripheral iridectomy and thus did not interfere with this procedure (Figure 4). The laser settings were 1 to 3 pulses per burst and 4.3 to 5.7 mJ of energy. Opening the iridectomy required 10 to 16 bursts. The laser caused significant bleeding from the iris in the rabbits. It was possible to establish where the haptic loops of the IMT were located and to plan the procedure to avoid them during the iridectomy.

Figure 4.
Figure 4.:
(Rosner) Clinical picture of the iridectomy at the periphery of the iris (arrow) performed with the Nd:YAG laser.

No damage to the cornea or retina as a result of the Nd:YAG laser iridectomy was detectable on the histopathological examination.

In 1 IMT removed from the eyes, the haptic loop at the base of the carrier plate was broken. However, this occurred during removal of the IMT from the eye and not during implantation or laser treatment. All other IMTs were intact.

Neodymium:Yag Laser Posterior Capsulotomy

In the 8 eyes that had an Nd:YAG laser posterior capsulotomy after IMP implantation, the procedure was performed without difficulty (Figure 5). The laser settings included a retro-focus of 250 μm, 1 pulse per burst, and 2.0 to 2.7 mJ of energy. Completion of the posterior capsulotomy required 100 to 138 bursts. When the Nd:YAG laser beam hit the surfaces of the carrier plate, the haptics, or the cap, it could produce small cracks in the PMMA material. Capsulotomy could not be done through the opaque cap, but the haptic was not a barrier to the laser beam.

Figure 5.
Figure 5.:
(Rosner) Left: Clinical picture of an opacified posterior capsule (white asterisk). Right: Opening made with the Nd:YAG laser (black arrow).

In 1 rabbit, adhesions between the iris margin and the optical cylinder of the IMT were observed. The adhesions were dissected using the Nd:YAG laser, and then the posterior capsulotomy could be performed. However, this rabbit developed a strong fibrin reaction that prevented completion of the posterior capsulotomy. In 1 rabbit, a fibrin plug developed in front of the telescopic lens and was successfully dispersed with the laser.

On histopathological examination, no section showed evidence of damage to the cornea, ciliary body, iris, or retina as a result of the Nd:YAG laser posterior capsulotomy.

One IMT removed from the eyes had multiple cracks in the carrier plates, caused during the attempt to perform a capsulotomy through the plates. A broken haptic was seen in 2 other lenses, caused in both cases by removal of the device from the eyes and not by implantation or laser treatment. All other IMTs were undamaged.

Argon Laser Treatment of the Retina

Six eyes were treated with the argon laser. The retina could be viewed through the area between the IMT and the pupil border using a 3-mirror lens. None of the other 4 lenses (Mainster ultra-field PRP, Mainster wide-field laser lens, OMRA Mainster retina laser lens, or +90 D lens) allowed adequate visualization of the retina for examination or treatment. Adhesions between the iris border and the IMT made it difficult to examine the retina. The laser beam was aimed around the IMT optic to focus it on the area related to the macula, the equator, and the retinal periphery. In 2 cases, the laser beam was successfully focused on the retina through the optic cylinder of the IMT and produced laser lesions on the retina. However, only a small area of the retina was visible when the retina was viewed through the telescope, and no retinal landmarks could be seen. It was thus not possible to know precisely where on the retina the laser treatment would be located.

The argon laser settings were as follows: exposure, 0.1 to 0.2 second; energy, 300 to 600 mW. When the exposure time was 0.1 second and the energy 600 mW, strong, chalk-white photocoagulation lesions were seen on the retina. Energy of 300 to 400 mW was usually sufficient to obtain adequate photocoagulation. The transparent PMMA parts of the haptic did not interfere with aiming the laser on the retina and applying argon laser treatment.

When the fixed eyes were dissected, gross examination revealed laser lesions at the posterior pole and the periphery of the retina (Figure 6).

Figure 6.
Figure 6.:
(Rosner) Laser lesions at the posterior pole of the rabbit eye (arrows).

No damage to the cornea, ciliary body, or iris that might have been caused by argon laser treatment to the retina was detected in any examined section on histopathological examination. The laser-induced lesions could be seen on the retina and included a laser lesion in the outer layers of the retina with formation of adhesions between the retina and the choroid at the local area of the laser lesion. These laser-induced lesions prevented artifacts of retinal detachment seen in other areas of the posterior pole (Figure 7).

Figure 7.
Figure 7.:
(Rosner) Histopathology of retinal laser photocoagulation (arrow). The laser lesion caused adhesions between the retina and the choroid, preventing the artifact detachment surrounding the lesion.

In 2 IMTs removed after argon laser treatment to the retina, there was damage to the telescope. One IMT had a broken haptic and the other, irregularities on the sides of the carrier plate. The damage occurred during removal of the IMTs from the eyes and not during implantation or laser treatment. All other IMTs were intact.

Discussion

Age-related macular degeneration may cause severe deterioration of the central vision and is a leading cause of visual loss in adults older than 60 years.2 Optical devices that magnify images may help patients with ARMD. However, the disadvantages of handheld and spectacle-mounted telescopes limit their use in many patients. Koziol et al.3 report the use of a teledioptric lens implant with a high-minus central zone (2.5 mm); in combination with special eyeglasses, this forms a telescopic system. Although it provides good magnification, 2.6 times greater than that achieved using an external telescope, the disadvantages of this partially external telescopic system have prevented its adoption by ARMD patients. The IMT substantially reduces the discomfort and inconvenience of external or partially external telescopic devices. The IMT has been clinically evaluated in a limited number of patients with geographic atrophy and disciform-scar ARMD. Only short-term data on the clinical performance of the IMT have been published.4 More extensive clinical evaluations are planned.

The present study was designed to evaluate the feasibility and safety of laser treatments in eyes with an IMT. The treatments examined were laser iridectomy, laser capsulotomy, and laser photocoagulation of the posterior pole and the equatorial and peripheral retina. These treatments were designed to simulate macular treatment as well as panretinal photocoagulation and laser treatment for peripheral retinal tears. Their effects were evaluated in vivo in an animal model of pigmented rabbits. The eyes of these rabbits are similar in size to human eyes, and the findings can therefore be extrapolated to human patients.

Laser iridectomy and laser posterior capsulotomy were performed without difficulty in rabbit eyes with the IMT. The protocols of these procedures were similar to standard practices used in eyes with conventional IOLs after cataract surgery. However, retinal photocoagulation in eyes with IMTs is applied around the optical cylinder of the IMT and not through the optic of the implanted IOL. We found that it was occasionally possible to focus the laser beam on the retina through the optic cylinder of the IMT and thus produce laser lesions on the retina. It is not feasible to treat the retina in this way, however, as the area of the retina that can be viewed is very small, no retinal landmarks are visible, and it is not possible to know precisely where the laser beam is focused on the retina. Thus, photocoagulation of the retina should be performed with the laser aimed between the IMT and the pupil margin.

The transparent PMMA parts of the haptic did not constitute an obstacle to aiming the beam or to laser treatment of the retina. It was not difficult to focus the laser on the macular, equatorial, or peripheral parts of the retina and to produce laser photocoagulation there. The 3-mirror lens was the most convenient of the various lenses tried for retinal examination and laser treatment. Retinal photocoagulation at the posterior pole, the equator, and the periphery could be seen at the time of treatment and were also clearly visible at the gross examination when the fixed eyes were dissected.

Neither posterior capsulotomy nor retinal photocoagulation could be performed when adhesions between the pupil margin and the IMT were present. In these cases, we suggest the surgeon first attempt to open the adhesions and then try to continue the procedure.

The IMT did not cause unintended damage to ocular tissues from the laser treatments. The laser treatments did not damage the IMTs.

The treatments evaluated in our model did not include photodynamic therapy (PDT), the new retinal treatment for choroidal neovascularization. Since we had no difficulty focusing the argon laser or producing photocoagulation in the area around the macula, it should be feasible to treat by PDT the macular area in eyes with an IMT.

The bulky IMT, which is 4.4 mm long and weighs 46 mg in aqueous, should be implanted in the capsular bag with good centration because of its size and optical characteristics. The device should be positioned with the haptic loops in the 12 o'clock to 6 o'clock position. On the basis of their ultrasound biomicroscopic examination, García-Feijoó et al.4 point out that if the IMT is not implanted in the bag and centered, the distance between the device and the endothelium may not be sufficient to prevent endothelial damage over the long term. The authors recommend intracapsular implantation to optimize the distance between the optical cylinder and the endothelium. The results of the present study show that when there are adhesions between the pupil margin and the IMT, it is not possible to perform laser posterior capsulotomy or laser retinal treatments. Thus, another important reason for implanting the IMT in the capsular bag is to keep it away from the iris margin, reducing the risk of adhesions between the iris and the IMT.

In conclusion, this study, performed using pigmented rabbits as a model, demonstrated that various ocular laser treatments can be safely performed after implantation of an IMT.

References

1. Lipshitz I, Loewenstein A, Reingewirth M, Lazar M. An intraocular telescopic lens for macular degeneration. Ophthalmic Surg Lasers 1997; 28:513-517
2. Vingerling JR, Dielemans I, Hofman A, et al. The prevalence of age-related maculopathy in the Rotterdam study. Ophthalmology 1995; 102:205-210
3. Koziol J, Peyman GA, Cionni R, et al. Evaluation and implantation of a teledioptric lens system for cataract and age-related macular degeneration. Ophthalmic Surg 1994; 25:675-684
4. García-Feijoó J, Durń-Poveda S, Cuiña-Sardiña R, et al. Ultrasound biomicroscopy of an implantable miniaturized telescope. Arch Ophthalmol 2001; 119:1544-1546
© 2003 by Lippincott Williams & Wilkins, Inc.