Twelve subjects aged 33 to 78 years (average, 60.7 ± 15.4; three men, nine women) gave informed consent to take part in the study. All had had phacoemulsification cataract surgery and insertion of a one-component-unit (1CU) accommodative IOL (HumanOptics AG, Erlangen, Germany) implanted in one (four subjects) or both (eight subjects) eyes (20 eyes in total). Inclusion–exclusion criteria were a lenticular opacity affecting the visual demand of the subject, in an otherwise healthy eye (no other ophthalmic abnormality such as diabetic retinopathy, glaucoma, corneal problems or macular problems). The patients received bilateral 1CUs if both eyes met the inclusion–exclusion criteria. Each subject underwent a full subjective binocular refraction at 6 m. Informed consent was obtained from the subjects after explanation of the nature and possible consequences of the study. The research complied with the tenets of the Declaration of Helsinki and was approved by institutional review board.
The 1CU lens is a single-piece, hydrophilic, acrylic, ultraviolet-inhibited IOL with a refractive index of 1.46. It has been shown to result in stable refraction and subjective accommodation over a 1-year period.
31 The central optic portion, 5.5 mm in diameter, is designed to rest postcapsularly after the crystalline lens matrix has been removed by phacoemulsification cataract surgery. The optic has a hinged connection to four haptic legs, which are thinner near the optic, to aid flexibility and allow movement of the optic anteriorly, secondary to ciliary muscle contraction.
The first assessment was conducted a mean of 127.7 ± 70.9 days after lens implantation. After retinoscopy and subjective refraction, best corrected threshold letter acuity was measured at far with high (90%) and low (10%) contrast (at 3 m) and near threshold word acuity at near (40 cm) with logMAR (logarithm of the minimum angle of resolution) progression charts.
32 Each letter was scored as 0.02 logMAR, and guessing was encouraged. Subjects with residual refractive error after surgery were made functionally emmetropic with ultrathin soft contact lenses (Acuvue Dailies, HEMA [hydroxyethyl methacrylate], 58% water content material; Vistakon, Johnson & Johnson, Jacksonville, FL) to ensure that the accommodative demand of the viewing task for each subject was virtually identical.
Amplitude of accommodation was measured with an RAF (Royal Air Force accommodation vergence measurement) binocular gauge (ClementClarke/Haag-Streit, Harlow, UK). Subjects viewed the N6 (0.75 M units) size letters from a distance of 50 cm. The letters were moved (approximately 5 cm/s) toward the subject, until the letters were no longer resolvable. The target was then moved to 10 cm from the subject and steadily moved away from them until the letters were first resolvable. The reciprocal of the average distance between these two measures was taken as the subjective amplitude of accommodation in diopters.
Accommodative responses were measured with the PowerRefractor (PlusOptiX, Nürnberg, Germany)
33 and the SRW-5000 (Shin-Nippon Commerce Inc., Tokyo, Japan)
34 autorefractors through undilated pupils in a randomized order. The subject’s head was positioned on a head and chin rest. The PowerRefractor was positioned 1 m from the subject, aligned with the right eye, but positioned to image both of the subject’s eyes. The SRW-5000 was aligned with the visual axis of the eye under examination and measured the accommodative response of this eye only, although the subject had a binocular open-field view of the targets. Subjects viewed a static 90%-contrast Maltese cross located at 0.17, 0.50, 1.00, 1.50, 2.00, 2.50, 3.00, and 4.00 D of accommodative demand (6.00, 2.00, 1.00, 0.75, 0.50, 0.40, 0.33, and 0.25 m, respectively), in real space (matched for angular subtense and luminance), in random order. Five static readings were taken with both the PowerRefractor (full-refraction mode) and SRW-5000 at each distance. All patients were asked to focus on the target and to try to keep it clear, as if they were reading, while the measurements were obtained.
35 The luminance of the targets was kept constant at 40 lux. This particular luminance was chosen to maintain a pupil size adequate to achieve measurements at all distances with the PowerRefractor.
36 The luminance was kept the same for the SRW-5000 measures, so as not to affect the stimulus response curve.
37
Continuous recording of dynamic accommodation was measured with the SRW-5000 with the subject viewing a target moving from 0.0 to 2.5 D at 0.3 Hz through a +5.0 D Badal lens system. The SRW-5000 is able to monitor the accommodative response dynamically, with high resolution and a frequency of up to 60 Hz.
38 The data were smoothed by averaging the 10 time points on either side (approximately 0.2 seconds), and blinks were removed.
39 The dynamic amplitude of accommodation and time lag was calculated from the average of five cycles.
Aberrations across the undilated pupil were quantified with a wavefront-sensing device (Zywave; Bausch & Lomb, Rochester, New York) that is based on the Hartman-Shack principle.
40 The measured deviation of the 780-nm wavefront (at 70–75 locations within the pupil area) as it passed through the optics of the cornea and IOL was assessed in terms of lower order aberrations (i.e., sphere and cylinder, combined to give a predicted photopter refraction [PRP] term).
Subjects’ refraction, best corrected distance and near visual acuity, objective accommodative stimulus response curve (measured with the SRW-5000) and subjective amplitude of accommodation were remeasured a mean of 695.4 ± 124.6 days after phacoemulsification cataract surgery. Lenticular capsule clarity was also assessed by an ophthalmologist with a slit lamp biomicroscope.
Static prescriptions were converted into mean spherical equivalents (MSEs), and the slope and Pearson’s product moment coefficients were calculated.