Journal of Refractive Surgery

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Ultrasound Biomicroscopy for Determining Visian Implantable Contact Lens Length in Phakic IOL Implantation

Ki Hwan Choi, MD; Song Ee Chung, MD; Tae Young Chung, MD; Eui Sang Chung, MD

Abstract

ABSTRACT

PURPOSE: To assess the efficacy of the ultrasound biomicroscopic (UBM) method in estimating the sulcus-to-sulcus horizontal diameter for Visian Implantable Contact Lens (ICL, model V4) length determination to obtain optimal ICL vault.

METHODS: The results of postoperative ICL vaults in 30 eyes of 18 patients were retrospectively analyzed. In 17 eyes, ICL length was determined using the conventional method, and in 13 eyes, ICL length was determined using the UBM method. The UBM method was carried out by measuring the sulcus to limbus distance on each side by 50 MHz UBM and adding the white-to-white diameter by caliper or Orbscan. The ICL vaults were measured using the UBM method at 1 and 6 months postoperatively and the results were compared between the two groups. Ideal ICL vault was defined as vault between 250 and 750 µm. The relation between the ICL vault, footplate location, and ICL power was also investigated.

RESULTS: In the UBM method group, ICL vault was within the ideal range in all 13 (100%) eyes at 1 and 6 months postoperatively, whereas in the conventional method group, 10 (58.8%) eyes showed ideal vault at 1 month postoperatively (P=.01) and 9 (52.9%) eyes showed ideal vault at 6 months postoperatively (P<.01). The ideal ICL footplate location was achieved in the ciliary sulcus in 11 (84.6%) eyes of the UBM method group and 10 (64.7%) eyes of the conventional method group. However, the differences between the two groups were not statistically significant. The ICL vault was not significantly affected by the ICL power.

CONCLUSIONS: Implantable Contact Lens length determined by the UBM method achieved significantly more ideal ICL vault than that of the conventional white-to-white method. The UBM method is superior to the conventional method in terms of predicting the sulcus-to-sulcus horizontal diameter for ICL length determination. [J Refract Surg. 2007;23:362-367.]

Abstract

ABSTRACT

PURPOSE: To assess the efficacy of the ultrasound biomicroscopic (UBM) method in estimating the sulcus-to-sulcus horizontal diameter for Visian Implantable Contact Lens (ICL, model V4) length determination to obtain optimal ICL vault.

METHODS: The results of postoperative ICL vaults in 30 eyes of 18 patients were retrospectively analyzed. In 17 eyes, ICL length was determined using the conventional method, and in 13 eyes, ICL length was determined using the UBM method. The UBM method was carried out by measuring the sulcus to limbus distance on each side by 50 MHz UBM and adding the white-to-white diameter by caliper or Orbscan. The ICL vaults were measured using the UBM method at 1 and 6 months postoperatively and the results were compared between the two groups. Ideal ICL vault was defined as vault between 250 and 750 µm. The relation between the ICL vault, footplate location, and ICL power was also investigated.

RESULTS: In the UBM method group, ICL vault was within the ideal range in all 13 (100%) eyes at 1 and 6 months postoperatively, whereas in the conventional method group, 10 (58.8%) eyes showed ideal vault at 1 month postoperatively (P=.01) and 9 (52.9%) eyes showed ideal vault at 6 months postoperatively (P<.01). The ideal ICL footplate location was achieved in the ciliary sulcus in 11 (84.6%) eyes of the UBM method group and 10 (64.7%) eyes of the conventional method group. However, the differences between the two groups were not statistically significant. The ICL vault was not significantly affected by the ICL power.

CONCLUSIONS: Implantable Contact Lens length determined by the UBM method achieved significantly more ideal ICL vault than that of the conventional white-to-white method. The UBM method is superior to the conventional method in terms of predicting the sulcus-to-sulcus horizontal diameter for ICL length determination. [J Refract Surg. 2007;23:362-367.]

Posterior chamber phakic intraocular lens (IOL) implantation represents a new alternative for surgical correction of high myopia, which has been proven to be effective and predictable.1-8 The posterior chamber phakic Implantable Contact Lens (Visian ICL; Staar Surgical, Monrovia, Calif) is a flat plate-haptic, single-piece lens made of collamer (hydrophilic porcine collagen/hydroxyethyl methacrylate copolymer). It is designed to be implanted in the posterior chamber behind the iris and in front of the anterior capsule of the crystalline lens, with the haptic resting on the ciliary sulcus. It incorporates distinct footplates and an anterior vault designed to minimize contact with the crystalline lens.

Ideal ICL crystalline lens distance (ICL vault), which is the distance from the anterior capsule of the crystalline lens to the posterior surface of the ICL, is approximately 500 µm. The ICL length is believed to be the major determinant of vault. For example, ICL length that is too long results in high vault (>1000 µm) and ICL length that is too short results in low vault (<125 µm). Ideal ICL vault is critical in phakic ICL surgery, as high vault may induce peripheral anterior synechiae and pigment dispersion and low vault may induce cataract formation. The conventional method of determining ICL length is by measuring the white-to-white horizontal corneal diameter with calipers or Orbscan (Bausch & Lomb, Rochester, NY) and adding 0.5 or 1.0 mm based on the patient's anterior chamber depth. However, ICL length determination using this conventional method is not reliable or reproducible because the white-to-white horizontal corneal diameter alone does not represent the true sulcus-to-sulcus distance.9

Figure 1. UBM method in determining the sulcus-to-sulcus horizontal diameter (STH). An epithelial dimple marking (L) is made prior to UBM examination at 9 o'clock and 3 o'clock. At 9 o'clock, an imaginary vertical line (V) is drawn from the epithelial dimple marking (L) to the posterior surface of the iris (dotted lines), which is shown as the orange arrow line (V). The horizontal distance between the ciliary sulcus (S) and the orange line, which is shown as a pink line, is termed D. The same is done at the 3 o'clock UBM cross-sectional image and the distance from the intersection of the imaginary perpendicular line and posterior iris plane to the ciliary sulcus is measured and termed D′. The sulcus-to-sulcus horizontal distance is calculated as the sum of the white-to-white horizontal corneal diameter (WTH), D, and D′: STH = D + WTH + D′.

Figure 1. UBM method in determining the sulcus-to-sulcus horizontal diameter (STH). An epithelial dimple marking (L) is made prior to UBM examination at 9 o'clock and 3 o'clock. At 9 o'clock, an imaginary vertical line (V) is drawn from the epithelial dimple marking (L) to the posterior surface of the iris (dotted lines), which is shown as the orange arrow line (V). The horizontal distance between the ciliary sulcus (S) and the orange line, which is shown as a pink line, is termed D. The same is done at the 3 o'clock UBM cross-sectional image and the distance from the intersection of the imaginary perpendicular line and posterior iris plane to the ciliary sulcus is measured and termed D′. The sulcus-to-sulcus horizontal distance is calculated as the sum of the white-to-white horizontal corneal diameter (WTH), D, and D′: STH = D + WTH + D′.

An ultrasound biomicroscope (UBM) with a 50 MHz probe is a high-resolution device that allows the examination of the anterior segment and the peripheral retina.10-12 It produces clear images of the posterior chamber structures, especially the ciliary sulcus.

The purpose of this study was to evaluate the vault results of ICL length determined using the UBM method and compare the results to those of the conventional method. Other contributing factors of the vault such as footplate location or ICL power were also evaluated.

PATIENTS AND METHODS

The medical records of 30 eyes of 18 patients (3 men and 15 women) who underwent Visian ICL (model V4) implantation were reviewed retrospectively. Mean patient age was 28.7 years (range: 22 to 45 years). All eyes were operated by the same surgeon (E.S.C.) at Samsung Medical Center, Seoul, Korea, between November 2002 and September 2003. In accordance with the Helsinki Declaration, oral and written informed consent were obtained from all patients.

Inclusion criteria were age ranging from 21 to 45 years, spherical equivalent refraction between -9.00 and -20.00 diopters (D), best spectacle-corrected visual acuity (BSCVA) of at least 20/100, stable refraction for at least 1 year, intraocular pressure ≤21 mmHg, grade 0 of the anterior chamber angle with the Scheie classification, trabecular meshwork pigmentation grade ≤2, anterior chamber depth from the endothelium ≥2.8 mm, endothelial cell count >2250 cells/mmp 2, and absence of ocular pathology.

All patients underwent complete preoperative ocular examination including uncorrected visual acuity (UCVA) and BSCVA, manifest and cycloplegic refractions, slit-lamp and fundus examination, keratometry, and corneal topography. All ICL power calculations were performed with formulas developed by Staar using a modified vertex formula. The ICL length was determined using either conventional method or UBM method.

CONVENTIONAL METHOD

The ICL length was determined using the white-towhite horizontal corneal diameter measurement and anterior chamber depth. For eyes with anterior chamber depth between 2.8 and 3.5 mm, the ICL length was calculated by adding 0.5 mm to the white-to-white horizontal corneal diameter. Eyes exhibiting anterior chamber depth >3.5 mm required the addition of 1.0 mm to the white-to-white horizontal corneal diameter. White-to-white measurements were obtained using calipers or Orbscan.

ULTRASOUND BIOMICROSCOPY METHOD

The ICL length was determined using the UBM (UBM 840; Zeiss-Humphrey, Jena, Germany) performed by the same examiner under topical anesthesia (0.5% Alcaine; Alcon Laboratories, Ft Worth, Tex). First, dimples that recognize the position of the Hmbus as a physical marker were made using a caliper at the 9 o'clock horizontal limbus (Fig 1). Second, the patient was reclined, and a 20-, 22-, or 24-mm open shell was inserted between the upper and lower eyelids and filled with sterile balanced salt solution. The reclined patient was asked to fixate on a target with the fellow eye maintaining fixation. Cross-sectional images were obtained through the cornea, iris, ciliary body, and lens at 3, 6, 9, and 12 o'clock position covering 360° of the anterior chamber. At the 9 o'clock cross-sectional image, an imaginary line was drawn from the limbal dimple perpendicular to the posterior surface of the iris. The distance from the intersection of the imaginary perpendicular line and posterior iris plane to the ciliary sulcus was measured from the UBM scan. Similarly, the distance was also measured 180° apart at the 3 o'clock horizontal limbus. These distances (D, D′) were added to the white-to- white horizontal corneal diameter (WTH) to determine the sulcus-to-sulcus horizontal diameter (STH): STH = D + WTH + D′. Because the UBM gave a partial view of sulcus, the sulcus-to-sulcus horizontal diameter distance was estimated by adding sulcus to limbus distance measured on each side by UBM and white-to-white horizontal corneal diameter measured by Orbscan or caliper.

Table

TABLE 1Comparison of Eyes With Ideal ICL Vault Between the Conventional Method and UBM Method Groups at 1 and 6 Months After ICL Implantation

TABLE 1

Comparison of Eyes With Ideal ICL Vault Between the Conventional Method and UBM Method Groups at 1 and 6 Months After ICL Implantation

The ICL vault evaluation was done using UBM at 1 and 6 months after ICL implantation. The ICL vault was determined as the distance between the posterior reflection of the ICL and the crystalline lens surface (first reflection) at the center. Ideal vault was defined as 250 to 750 µm, excessive vault as >750 µm, and insufficient vault as <250 µm, Multiple measurements were taken and averaged by a single technician.

SURGICAL PROCEDURE

One week prior to ICL implantation, all patients received two peripheral and superior iridotomies positioned 90° apart with Nd:YAG to prevent postoperative pupillary block. All surgeries were performed under topical anesthesia. Two paracenteses and a 3.2-mm temporal clear corneal incision were made with a diamond knife. Viscoelastic was injected into the anterior chamber. The ICL was injected into the anterior chamber through the incision with an injector (Staar MicroSTAAR injector) and allowed to slowly unfold. The distal and proximal footplates were tucked under the iris with a modified intraocular spatula. Correct positioning of the ICL was verified before intraocular miotics were used. Any remaining viscoelastic material was meticulously aspirated using irrigation and aspiration. Two hours after the surgery, intraocular pressure was measured and topical anti-glaucoma eye drops were used if necessary. Levofloxacin (Cravit; Taejoon Pharm Co, Seoul, Korea) and fluorometholone (Flumetholon; Santen, Osaka, Japan) eye drops were used four times a day for 2 weeks.

STATISTICAL ANALYSIS

SPSS version 10.0 for Windows (SPSS Ine, Chicago, 111) was used for statistical analysis. Postoperative data were compared using the Mann-Whitney test, Fisher's exact test, and Pearson's correlation analysis. Visual acuities were converted to a log unit for statistical analyses. Fisher's exact test and Mann-Whitney ranked sum test were used due to the small sample size. Results were considered statistically significant when P<.05.

RESULTS

Mean postoperative follow-up was 10.3 months (range: 6 to 16 months). In 17 eyes, ICL length was determined using the conventional method and in 13 eyes, ICL length was determined using the UBM method.

Postoperative UCVA, BSCVA, and spherical equivalent refraction were not statistically different between the conventional method group and UBM method group at 6 months postoperatively [P=. 432, P=.385, and P=.621, respectively; Mann-Whitney test). Visual acuities were converted to log units prior to performing statistics.

The ICL vault was within the ideal range (250-750 µm) in all 13 (100%) eyes in the UBM method group at 1 and 6 months postoperatively. In the conventional method group, 10 (58.8%) eyes showed ideal vault at 1 month postoperatively and 9 (52.9%) eyes showed ideal vault at 6 months postoperatively. The differences between the two groups were statistically significant (P=.01 for 1 month postoperative and P<.01 for 6 months postoperative, Fisher's exact test) (Table 1). All 3 eyes with excessive vault (>750 µm) at 1 month postoperative in the conventional method group showed a tendency for the vault to decrease at 6 months postoperatively, although it was still not within the ideal vault range. One eye in the conventional method group with the vault in the ideal range at 1 month postoperatively showed a decrease in the vault, resulting in insufficient vault at 6 months postoperatively. Of the 4 eyes with insufficient vault at 1 month postoperatively in the conventional method group, 1 eye had ICL vault <125 µm and showed the ICL nearly touching the crystalline lens at 6 months postoperatively, resulting in ICL exchange (Table 2).

The ICL footplate locations were also evaluated in the conventional method and UBM method groups. In 17 eyes of the conventional method group, ICL footplates were placed ideally in the ciliary sulcus in 10 (64.7%) eyes, whereas in the 13 eyes of the UBM method group, ICL footplates were placed ideally in the ciliary sulcus in 11 (84.6%) eyes. However, the differences between the groups were not statistically significant (Table 3).

Table

TABLE 2ICL Vault Change at 1 and 6 Months After ICL Implantation in Eyes With Inappropriate Vault Using the Conventional Method for ICL Length DeterminationTABLE 3Comparison of ICL Footplate Location Between the Conventional Method and UBM Method Groups at ß Months After ICL Implantation

TABLE 2

ICL Vault Change at 1 and 6 Months After ICL Implantation in Eyes With Inappropriate Vault Using the Conventional Method for ICL Length Determination

TABLE 3

Comparison of ICL Footplate Location Between the Conventional Method and UBM Method Groups at ß Months After ICL Implantation

The correlation between the ICL power and ICL vault was analyzed in eyes with footplates placed in the ciliary sulcus. No significant correlation was found between the ICL power and ICL vault (Pearson r=0.103) (Fig 2).

DISCUSSION

Ideal ICL vault is approximately 500 µm, which is roughly one corneal thickness. There are concerns about high vault (>1000 µm) leading to angle crowding and resulting in angle closure or synechiae formation. High vault may also increase iris chaffing and pigment dispersion, resulting in pigmentary glaucoma. Furthermore, low vault (<125 µm) may cause ICL contact with the crystalline lens and increase the risk of cataract formation over time.8,9

The major determinant of ICL vault is the ICL length or size. Overestimated ICL length results in high (excessive) vault and underestimated ICL length results in low (insufficient) vault. Moreover, complications after ICL implantation result largely from improper ICL sizing.13 However, the chance of ICL replacement from improper ICL sizing seems to be relatively low. According to the Implantable Contact Lens in Treatment of Myopia study group,14 0.8% of ICL implanted patients underwent ICL replacement from long and short ICL size.

Figure 2. Correlation between the ICL power and the postoperative ICL vault (Pearson r=0.103).

Figure 2. Correlation between the ICL power and the postoperative ICL vault (Pearson r=0.103).

To determine the proper ICL length, accurate estimation of sulcus-to-sulcus horizontal diameter is crucial. Conventionally, the sulcus-to-sulcus horizontal diameter is estimated by measuring the white-to-white horizontal corneal diameter using caliper or Orbscan and adding 0.5 or 1.0 mm according to the anterior chamber depth. Pop et al,9 however, reported that the conventional sulcus-to-sulcus horizontal diameter estimation is inadequate because white-to-white horizontal corneal diameter alone cannot predict sulcus-to-sulcus horizontal diameter accurately. In our study, we assumed that the sulcus-to-sulcus horizontal diameter is long if the anterior chamber is deep, as has been described previously.15 Because the purpose of our study was to compare the sulcus-to-sulcus horizontal diameter estimation between conventional and UBM methods, we did not compare the vault based on adding 0.5 or 1.0 mm depending on anterior chamber depth in the conventional group. Initially, we used both caliper and Orbscan for white-to-white measurements. However, after confirming that the difference between the caliper and Orbscan was not significant, we only used Orbscan for white-to-white measurements. As previously stated, for eyes with anterior chamber depth between 2.8 and 3.5 mm, the ICL length was calculated by adding 0.5 mm to the white-to-white horizontal corneal diameter. Eyes exhibiting anterior chamber depth >3.5 mm required the addition of 1.0 mm to the white-to- white horizontal corneal diameter.

We have demonstrated an alternative method for sulcus-to-sulcus horizontal diameter estimation using UBM. Ultrasound biomicroscopy was used to measure the distance between the ciliary sulcus and the point where the perpendicular line from the limbus meets the posterior iris plane at the 3 and 9 o'clock position, respectively. The sulcus-to-sulcus horizontal diameter was estimated by adding these values to the Orbscan measured white-to-white horizontal corneal diameter.

Our UBM method achieved more desirable ICL vault than the conventional method at 1 and 6 months postoperatively [P=. 01 and P<.01, respectively). In the UBM method group, all 13 eyes showed ideal vault, whereas in the conventional method group, 10 (58.8%) eyes showed ideal vault, 3 (17.6%) eyes showed excessive vault, and 4 (23.6%) eyes showed insufficient vault at 1 month postoperatively. All excessive vault had a tendency to decrease over time. One eye with insufficient ICL vault was nearly touching the crystalline lens at 6 months postoperatively and was replaced with a longer length ICL.

The location of ICL footplates maybe another important factor determining the ICL vault. Ideally, the ICL footplates should be placed in the ciliary sulcus. The misplacement of ICL footplates is caused by improper ICL size, poor centration of the ICL, and structural abnormality of the sulcus such as ciliary body cyst and iris tumors. In a long ICL, footplates possibly slip backward and locate on the ciliary body. Also, improper or asymmetric location of footplates may result in ICL decentration with unexpected vault. In our study, 11 (64.7%) eyes in the conventional group and 11 (84.6%) eyes in the UBM group had ICL footplates in the ciliary sulcus. However, the differences between the groups were not statistically significant.

Another factor that may influence the ICL vault is ICL power. Central ICL has a constant thickness of 0.11 mm. However, in the ICL V4 model, the peripheral overall height of a -10.00-D ICL is 1.45 mm, -15.00-D ICL is 1.54 mm, -20.00-D ICL is 1.66 mm, and -23.00-D ICL is 1.74 mm. Accordingly, the peripheral overall height increases as the ICL power increases, resulting in ICL vault increase. However, our study showed that ICL power had no statistically significant correlation with the ICL vault if the footplates were located in the ciliary sulcus.

Our UBM method for estimating the sulcus-to-sulcus horizontal diameter has some limitations. Ultrasound biomicroscopy can produce only 5×5-mm fields per scan, limiting the visualization of the whole cornea and making measurement of the direct sulcus-to-sulcus horizontal diameter not possible. In patients with abnormal iris configuration, the sulcus-to-sulcus horizontal diameter estimation was difficult because the posterior surface of the iris was assumed to be parallel to the sulcus-to-sulcus horizontal plane. Moreover, ICL vault measurement using the UBM in the supine position may differ from that in the upright position.16

In estimating the sulcus-to-sulcus horizontal diameter, our UBM method showed more ideal ICL vault results when compared to that of the conventional method. The ICL power seemed to have no significant influence on the ICL vault. Because of the small sample size, short follow-up period, and retrospective study design, outcomes that were statistically significant in this study may not indicate clinically significant outcomes. We also believe that our percentage data may be more impressive than our inferential statistics. Further studies are warranted to determine the reproducibility of the UBM method by using the patient as his or her own control. The enhanced capabilities of the UBM method when compared with the conventional method promise to improve the determination of the ICL length. We are planning another study through the prospective double blind test in each eye of the same patient within a larger sample. Comparison of the results with other measuring tools, such as the STRATUS OCT (Optical Coherence Tomography; Carl Zeiss Meditec AG, Jena, Germany), Artemis (very high frequency ultrasound eye scanner; Ultralink LCC, St Petersburg, Fla), and HiScan (high frequency B-scan; Optikon, Rome, Italy), is also required for further investigations.

REFERENCES

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7. Pesando PM, Ghiringhello MP, Tagliavacche P. Posterior chamber collamer phakic intraocular lens for myopia and hyperopia. J Refract Surg. 1999;15:415-423.

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10. Pavlin CJ, Sherar MD, Foster FS. Subsurface ultrasound microscopic imaging of the intact eye. Ophthalmology. 1990;97:244-250.

11. Pavlin CJ, Harasiewicz K, Sherar MD, Foster FS. Clinical use of ultrasound biomicroscopy. Ophthalmology. 1991;98:287-295.

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13. Cimberle M. Methods of sizing ICLs should be improved, surgeon says. Ocular Surgery News. August 1, 1999:52.

14. The Implantable Contact Lens in Treatment of Myopia (ITM) Study Group. U.S. food and drug administration clinical trial of the implantable contact lens for moderate to high myopia. Ophthalmology. 2003;110:255-266.

15. The Implantable Contact Lens in Treatment of Myopia (ITM) Study Group. United States Food and Drug Administration clinical trial of the Implantable Collamer Lens (ICL) for moderate to high myopia: three-year follow-up. Ophthalmology. 2004;111:1683-1692.

16. Garcia-Feijoo J, Alfaro IJ, Cuina-Sardina R, Mendez-Hernandez C, Del Castillo JM, Garcia-Sanchez J. Ultrasound biomicroscopy examination of posterior chamber phakic intraocular lens position. Ophthalmology. 2003;110:163-172.

TABLE 1

Comparison of Eyes With Ideal ICL Vault Between the Conventional Method and UBM Method Groups at 1 and 6 Months After ICL Implantation

TABLE 2

ICL Vault Change at 1 and 6 Months After ICL Implantation in Eyes With Inappropriate Vault Using the Conventional Method for ICL Length Determination

TABLE 3

Comparison of ICL Footplate Location Between the Conventional Method and UBM Method Groups at ß Months After ICL Implantation

10.3928/1081-597X-20070401-08

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