Study Design
A prospective non-randomized case-series was designed to evaluate the safety and efficiency of diffractive IPCL surgeries, performed between February 2018 and August 2018, with a 12 months follow-up. This study followed the tenets of the “Declaration of Helsinki”, and was developed with the approval of the “Clínica de Ojos Dr. Nano´s” Institutional Review Board/Ethics Committee. A written consent was obtained after patients were informed about the characteristics and risks of the surgical procedure.
Inclusion/Exclusion Criteria.
Inclusion Criteria. Patients between 40 to 55 years of age, with myopia, with or without astigmatism, and with stable refraction for a minimum period of one year, were included.
Exclusion Criteria. Patients with cataracts and/or less than a corneal endothelial cell density (ECD) of 2000 cell/mm2, anterior chamber depth (ACD) less than 2.8 mm, and a history of glaucoma and/or glaucoma or retinal surgery. Also, cases with corneal disease (dystrophies, degeneration or injuries that could affect corneal transparency) were excluded. In the present series, hyperopia patients were also excluded.
Pre-operative Studies and Parameters to be Evaluated.
At baseline, all patients underwent a complete ophthalmic examination and the population information regarding age and gender was registered. The Pentacam imaging system (Oculus, Wetzlar, Germany) was used for pre-operative evaluation of the cornea (to detect regular vs. irregular astigmatism), and to measure the ACD. The IPCL lens size was determined based on the horizontal white-to-white distance (using the IOL-Master equipment).
The target in all cases was emmetropia. Manifested spherical equivalent (SE), and cylinder refraction were evaluated before and 12 months after surgery. The post-operative uncorrected distance visual acuity (UDVA) was compared with pre-operative corrected distance visual acuity (CDVA) in Snellen, and also, the logarithm of the minimal angle of resolution (logMAR) was also calculated to perform a defocus curve (additions from -4.0 to +2.0 D), 12 months after surgery.
Selection of the Addition.
The amount of near addition was calculated based on the age of the patients and their grade of myopia, with a personal nomogram (Table 1). A subjective evaluation was performed pre-operatively, with both eyes with the best correct visual acuity refraction, and two options could be possible.
Option A: In the dominant eye, put the highest addition that could be tolerated, and in the non-dominant eye always put more addition, between 0.50 to 1.0 D, as is shown in Table 1. This “addition blend” is designed with the purpose of avoiding spectacles for near vision, for the following years during the presbyopia period.
Option B: If the difference between the dominant and non-dominant eye was not pre-operatively tolerated, the addition chosen for both eyes is the same. Always choosing the highest amount of addition which could be subjectively tolerated, according age and amount of myopia.
The corneal ECD and CCT were registered pre-operative and 12 months post-operation using an electronic specular microscope (TOMEY EM4000). Intra-ocular pressure (IOP) was evaluated at baseline, day1, day 7, month 1 and month 12 after surgery, using a Goldmann tonometer. Previous iridotomy was not performed. The IPCL vault was evaluated at 6 and 12 months post-surgery with the ultra-bio microscopy AvisoTM; Quantel Medical.
If the astigmatism was ≥ 1.0 D, a toric diffractive IPCL V2.0 model was selected. The presence of intraoperative and/or post-operative complications was also evaluated, specifically to detect signs of cataract development (by slit lamp graded always by the same observer) according to the LOCS III classification.
Diffractive IPCL V2.0 Characteristics (obtained from the official brochure at http://caregroupiol.com/products/phakic-lenses/ipcl/)
The IPCL is a foldable, hydrophilic acrylic, single-piece, injectable, posterior chamber pIOL. It is designed to be placed in the posterior chamber of the eye behind the iris, with the haptic zone resting on the ciliary sulcus, and can be directly delivered through a 2.8 mm corneal incision. Its design includes 6 haptics to increase stability, 2 holes in the peripheral portion from the upper zone to decrease glare and halos, and 4 holes outside the optical zone. The V 2.0 has a central conic hole (380 µm) to facilitate its alignment and aqueous humor circulation. The thickness of the IPCL is 80 µm. It is designed to correct myopia in a dioptric power range of −1.00 to −33.00 diopters (D) and hyperopia from +1.0 to +15.0 D. It has an aspheric optic zone, with zero aberration. The diameter of the optic is from 5.75 to 6.20 mm, and the overall diameter ranges from 11.0 mm to 14.00 mm (with 0.25 mm steps). Moreover, the optical diameter could be customized to 6.50, 6.80, 7.20 or 7.50 mm, according to the patient´s pupil size. This lens has a diffractive-refractive technology (trifocal optical design) with concentric rings to support near addition (ADD) from +1.5 to +4.0 (with 0.5 D steps), and intermediate Add of +2.10. The diffractive zone has an angle step to decrease light-scattering to 8% or less. The angle steps progression goes from 6° at the center to 65° at the lens´ periphery. And the angles from this step decrease from the center to the periphery, beginning from 1.8 µm at the center, to 90Nm at the periphery.
Surgical Technique Description: Steps and Tips.
All surgeries were performed by the same surgeon, and the use of viscoelastic substances were completely avoided, as was previously published [24]. Briefly, under corneal topical anesthesia, a corneal incision (located at 45 degrees) was made with the 20g V-lance, and the anterior chamber was maintained with an infusion/irrigation cannula (a 23g bi-manual I/A cannula). A second corneal 2.8-mm incision was performed (located at 130 degrees) following the first one. Finally, the phakic lens was inserted while the anterior chamber was irrigated with the balanced salt solution (BSS) fluid circulation. The lens was then unfolded carefully with the aid of an I/A cannula, and the haptics were correctly placed behind the iris, into the sulcus, from 3 o’clock to 9 o’clock. The post-operative topical treatment was the same for all cases, starting three days before the surgery with gatifloxacin 0.5% and bromfenac 0.09%, four times daily. Patients continued the treatment after surgery, adding one more drop of difluprednate 0.05%, four times daily. All drops were maintained for two weeks.
Statistical Evaluation
Descriptive statistical results were presented as mean, standard deviation (SD) and range. Normality of data was checked using the Kolmogorov-Smirnov test. To compare the differences between the mean endothelial CD, CCT (baseline vs. 12 months post-operative) and vault (6 vs. 12 months after surgery), a Wilcoxon signed-rank test was performed. To compare the mean IOP, ANOVA (single factor) was used. A statistically significant result was considered with a p-value less than 0.05. The coefficient of determination (R2) was calculated as part of the linear regression analysis to evaluate the correlation between the attempted and achieved spherical equivalent (SE) change. Statistical analysis was performed with the XLMiner Analysis ToolPak software (Frontline Systems Inc.). Data is available at “Clínica de Ojos Dr. Nano”.