From the Ophthalmology Department, Faculty of Medicine Ain Shams University, Cairo, Egypt; and Magrabi Eye & Ear Center, Jeddah, Saudi Arabia.
The author has no proprietary interest in the materials presented herein.
Rich Bains, a consultant to NIDEK Co Ltd, assisted with critical revision of the manuscript.
Presented at the 10th Middle East African Council of Ophthalmology International Congress; March 26–30, 2009; Manama, Kingdom of Bahrain.
Correspondence: Islam Mahmoud Hamdi, FRCS(Glasg), MD, PhD, Magrabi Eye & Ear Center, Madina Rd, PO Box 20377, Jeddah, 21455, Saudi Arabia. Tel: 966 556888135; Fax: 966 2 6650200; E-mail: Islammhamdi@hotmail.com
The NIDEK OPD-Scan II (Optical Path Difference Scanning System II; NIDEK Co Ltd, Gamagori, Japan) is a multipurpose instrument that combines Placido-based corneal topography with wavefront aberrometry of the entire eye.1 Aberrometry is performed based on the principle of automated retinoscopy acquiring 1440 points over a 6-mm pupil.2 A unique feature of this instrument is the ability to determine the internal aberrations of the eye. Internal aberrations comprise all wavefront aberrations behind the front corneal surface including lenticular aberrations. In eyes with normal corneas, the aberrations of the physiologic lens or intraocular lens (IOL) tend to dominate the aberration map. In cases of severely distorted corneas either due to surgery or disease, corneal aberrations generally dominate the internal aberration maps (posterior corneal surface).3,4 The internal aberration map is plotted as a refractive wavefront map in diopters and as a traditional wavefront map in micrometers of optical distortion. Clinical applications of this map include the determination of surgically induced aberrations, optical effect of internal aberrations, centration of IOL implants, and alignment of toric implants.1
The Toric Implantable Collamer Lens (TICL; STAAR Surgical Co, Monrovia, Calif) is a posterior chamber, sulcus-supported, phakic IOL used to reduce or eliminate myopic astigmatism.5,6 To achieve the desired visual and optical quality from the lens, proper axis orientation is fundamental. This article reports the use of the internal OPD maps and other wavefront maps for the pre- and postoperative assessment of a patient in whom the TICL was implanted at the wrong axis and the subsequent surgical interventions to eliminate residual refractive error.
A 22-year-old man with bilateral compound myopic astigmatism presented for a refractive surgery evaluation. Manifest refraction was −3.50 −3.00 × 15° in the right eye and −4.00 −4.00 × 160° in the left eye. Both eyes had 20/20 best spectacle-corrected visual acuity (BSCVA). Slit-lamp microscopy, intraocular pressure, and dilated funduscopy were normal in both eyes. Bilaterally, there were symmetrical bowtie patterns on the corneal topography maps and corneal thickness was 492 μm in right eye and 490 μm in left eye. The Randleman score for predicting ectasia after LASIK7 was 6 in the right eye and 7 in the left eye calculated as follows: 2 points (for each eye) for age (22); another 2 points (for each eye) for preoperative corneal thickness (481 to 510 μm); and an additional 2 points (for the right eye) for the predicted residual stromal bed thickness after ablation calculation using Final Fit V 1.13 ablation planning software (NIDEK Co Ltd) (275 μm) and 3 points for the left eye (255 μm). The Randleman score classified both eyes as high risk for development of ectasia postoperatively. The patient was counseled against LASIK and offered bilateral phakic IOL implantation. The patient agreed to undergo TICL implantation. Anterior chamber depth was 3.24 mm (as measured by A-scan ultrasonography) and white-to-white diameter was 12 mm (as measured by a hand-held caliper) for the right eye. Anterior chamber depth was 3.24 mm and white-to-white diameter was 12 mm in the left eye.
The TICL calculation software selected a lens power of −12.00 +5.50 × 70° for the left eye. The actual power of the lens implanted in the left eye was −12.00 +5.00 × 71°. The difference in cylinder power was clinically acceptable as was the 1° axis difference that did not require rotation. After implantation, the patient had 20/20 uncorrected visual acuity (UCVA) with plano refraction. OPD-Scan II/Station reports demonstrated excellent optical quality (maps not included) and the patient was subjectively satisfied with the vision in this eye. The lens had a vault of half the corneal thickness as estimated by slit-lamp microscopy.
For the right eye, the calculation software selected a lens power of −10.00 +4.50 × 105°. The lens implanted was −9.50 −4.50 × 109°. The difference in sphere power was acceptable and the difference in axis required a rotation of 4° clockwise. The amount and direction of intraoperative rotation was determined by the calculation software. An axis difference <5° was difficult to estimate intraoperatively.
One week after implantation, the patient had UCVA of 20/50 and BSCVA of 20/22 with a phoropter refraction of −0.50 −2.50 × 160°. The patient complained of a reduction in visual quality postoperatively. Review of the operative details and the original plan of implantation as monitored by OPD-Scan II/Station analysis and refraction showed that the lens was implanted in the opposite direction than intended, creating an 8° to 10° difference from the planned axis (Fig 1). The original plan of implantation as extracted from the calculating software was to implant at 4° clockwise. The lens was implanted 4° counterclockwise. The cause was likely misinterpretation of the direction of the small angle of rotation required, which resulted in the lens being placed at the wrong axis. Postoperatively, corneal astigmatism was unchanged; however, the postoperative internal OPD map showed significant internal astigmatism due to the TICL (see Fig 1). The higher order aberrations increased by 0.661 μm postoperatively with trefoil and quadrafoil dominating the aberration profile (see Fig 1). The point spread function (PSF) was significantly distorted and a minimal increase was noted in the A/B ratio in the modulation transfer function (MTF), which compares the area under the MTF of the eye being measured (A) to a sample of the best emmetropic eyes (B) (see Fig 1).
Figure 1. A) Preoperative and B) 1-Week Postoperative OPD Station Analysis of an Eye that Underwent Toric Implantable Collamer Lens Implantation. Measurements Were Performed for a Physiologically Dilated Pupil of 4.40 mm Preoperatively and Cropped on the Postoperative Map to the Same Diameter to Maintain Consistency. All Wavefront Measurements are Plotted to the 6th Radial Order.
The lens was rotated based on the original plan and monitored with the OPD-Scan II and the postoperative manifest refraction. OPD Station analysis 9 days after rotation indicated good axis alignment on the internal OPD map and a reduction in quadrafoil from 0.625 μm before rotation to 0.083 μm after rotation (Fig 2A). Corneal astigmatism remained stable, indicating no surgically induced corneal astigmatism (see Fig 2A). Best spectacle-corrected visual acuity was 20/20 with −1.00 −1.00 × 140°. The patient was offered photorefractive keratectomy (PRK) for elimination of the residual refraction. Six weeks after rotation, PRK with profile 1 of the optimized aspheric treatment zone algorithm (NI-DEK Co Ltd) and the NIDEK Advanced Vision Excimer Laser System (NAVEX, NIDEK Co Ltd) was performed. Wavefront aberrations were not corrected during PRK as a conservative treatment was preferred to reduce tissue removal due to the classification of high risk of ectasia. Excimer laser ablation removed 26.0 μm of tissue. After PRK, UCVA was 20/20 with plano refraction and the patient reported resolution of symptoms and was satisfied with the outcome. The OPD Station analysis shows an increase in the A/B ratio of the MTF from 17.7% (Fig 1B) after the original TICL implantation to 42.2% after surface ablation (Fig 2B). The PSF became progressively tighter with each step of the treatment (see Figs 1B, 2A, and 2B).
Figure 2. OPD Station Analysis of an Eye that Underwent A) Toric Implantable Collamer Lens Rotation (9 Days After Rotation) Followed by B) Excimer Laser Treatment (photorefractive Keratectomy) for Residual Refractive Error (6 Weeks After Excimer Laser Treatment). The Original Preoperative Measurements were Performed for a Physiologically Dilated Pupil of 4.40 mm and All Remaining Maps were Cropped to This Diameter to Maintain Consistency. All Wavefront Measurements are Plotted to the 6th Radial Order.
Toric Implantable Collamer Lenses are an alternative to LASIK for the treatment of high astigmatism and in cases at risk of ectasia after LASIK. Although bitoric and cross-cylinder ablations provide excellent outcomes, they remove significant amounts of corneal tissue.8–10 Clinically, the greater ablation depth would have created an unacceptable risk for ectasia after LASIK. In cases of high astigmatism such as the one presented herein, correct alignment of the cylinder is imperative. From this perspective, the internal OPD map was clinically important in the determination of the alignment of the TICL postoperatively as it removes the effects of corneal astigmatism (from the front corneal surface). For example, the alignment of the axis of toric IOLs can be determined by evaluating the orientation of the bowtie of astigmatism in the Internal OPD map and the values of cylinder in the printout (see Figs 1B and 2A). However, due to minor cyclotorsional differences between separate examinations, the axis of the cylinder on the axial map can be used as a reference. Three repeat measurements are routinely performed for assessing the internal axis and ensuring that the measurements are within 2° of each other. However, one must be cognizant of the fact that after TICL implantation the eye is effectively a three lens system: the cornea, the TICL, and the crystalline lens. The “anatomical” deviation in such cases would not correspond exactly to the “optical” deviation. Hence, the rotation of the TICL was based on anatomical facts (wrong axis in comparison to the original plan) rather than optical results. The outcome after rotation supports this observation.
OPD-Scan II/Station assessment provides an objective optical assessment of the lens orientation, rather than anatomical assessment with other instruments such as slit lamp photography and ultrasound biomicroscopy used in previous studies.6,11 Additionally, it provides a tool to monitor stability of the lens over time. The scale of the internal OPD maps is plotted in diopters, facilitating easy clinical interpretation of the magnitude and effects of misalignment and correlation to the refraction.
The increase in ocular aberrations in the right eye after the initial implant was due to the IOL axis misalignment (see Fig 1). After TICL rotation and subsequent PRK, the reduction in higher order aberrations caused a reduction of symptoms as documented by the PSF and better visual performance postoperatively documented by the MTF curves (see Figs 1B and 2). For example, A/B ratio increased by 24.5% from the initial TICL implantation. This increase indicates an objective enhancement of visual performance. Quadrafoil, a form of astigmatism with four axes, was reduced significantly from the initial TICL implantation to after PRK (see Figs 1B and 2B). This decrease is likely due to the misaligned axis of the TICL, as the greatest decrease in quadrafoil was seen once the TICL was rotated to the correct axis (see Fig 2A). There is no data on the clinical implications of quadrafoil and a thorough explanation of this observation is beyond the scope of this study. One possibility is that interference of the physiologic astigmatism and cylinder of the misaligned TICL gave rise to the quadrafoil pattern. This is the second study to document changes in quadrafoil due to phakic IOL misalignment and re-rotation. A previous report by Gatinel and Hoang-Xuan12 reported 69% reduction in quadrafoil after repositioning of a dislocated iris-fixated anterior chamber lens; however, they did not explain the origin of the quadrafoil.
In the current study, TICL implantation and surface ablation were used as complementary procedures to reduce refractive error. This was a successful strategy that was objectively documented by the progressive increase in optical quality seen in the PSF and MTF curves. It was further confirmed by the resolution of the patient’s symptoms.
Emmetropia was achieved in an eye with an initially misaligned TICL by combining intraocular and surface ablation procedures. The outcome of each step was evaluated with internal and surface aberrometry maps that allowed the surface astigmatism to be dichotomized from internal astigmatism with subsequent TICL rotation and PRK.
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