Optical factors influencing the amplitude of accommodation

BCLA CLEAR presbyopia: Mechanism and optics

With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.

Comparison of Patients With Emmetropia and Presbyopia and Different Accommodation Who Undergo Unilateral or Bilateral Implantation of a Trifocal IOL

PURPOSE

To compare visual outcomes and satisfaction in patients with emmetropia, presbyopia, and greater or lesser residual accommodation who undergo unilateral or bilateral implantation of a trifocal diffractive intraocular lens (IOL).

METHODS

A multicenter, multisurgeon study was performed to evaluate outcomes in patients with emmetropia and presbyopia who underwent refractive lens exchange followed by implantation of a FineVision trifocal IOL (PhysIOL). The inclusion criteria were as follows: emmetropia, sphere -0.25 to +0.50 diopters (D), cylinder less than 0.75 D, and manifest refractive spherical equivalent (MRSE) of -0.25 to +0.25 D. All patients also had to have an uncorrected distance visual acuity (UDVA) of Snellen 0.9 or better in each eye. The sample was divided into different clusters based on two variables: eyes operated on (monocular or binocular) and age either younger than 55 years or 55 years or older. Thus, four possible groups were created. Visual and refractive performance, patient satisfaction, and spectacle independence were assessed.

RESULTS

A total of 690 eyes from 431 patients were evaluated. There was no difference in postoperative uncorrected (UDVA) and corrected (CDVA) distance visual acuity between the groups. Binocular uncorrected near vision (UNVA) was better in patients who underwent surgery on both eyes regardless of age (median [interquartile range]: 0.00 [0.00; 0.10] vs 0.10 [0.00; 0.10] logMAR; P < .001). Binocular uncorrected intermediate vision (UIVA) was better in patients who underwent surgery on both eyes aged younger than 55 years than in those who underwent surgery in one eye aged 55 years or older (median [interquartile range]: 0.18 [0.10; 0.18] vs 0.30 [0.18; 0.30] logMAR; P < .001). The efficacy and safety indexes were 0.98 ± 0.09 and 1.01 ± 0.06, respectively. A total of 93.3% of eyes were within the 0.50 D range in postoperative MRSE. Visual dysphotopsia was worse in patients with both eyes operated on, although the differences were not statistically significant.

CONCLUSIONS

The study shows that after refractive lens exchange, patients with emmetropia and presbyopia who received a trifocal IOL in one or both eyes achieved good UNVA, UIVA, and UDVA. Regarding near binocular visual acuity, results were better for patients who underwent surgery on both eyes than for those who underwent surgery on one eye. Regarding binocular intermediate visual acuity, patients aged younger than 55 years with both lenses replaced had better results than those 55 years or older with only one lens replaced. However, no significant differences were observed in UDVA or patient satisfaction. [J Refract Surg. 2023;39(12):817-824.].

Predicting subjective refraction with dynamic retinal image quality analysis

The aim of this work is to evaluate the performance of a novel algorithm that combines dynamic wavefront aberrometry data and descriptors of the retinal image quality from objective autorefractor measurements to predict subjective refraction. We conducted a retrospective study of the prediction accuracy and precision of the novel algorithm compared to standard search-based retinal image quality optimization algorithms. Dynamic measurements from 34 adult patients were taken with a handheld wavefront autorefractor and static data was obtained with a high-end desktop wavefront aberrometer. The search-based algorithms did not significantly improve the results of the desktop system, while the dynamic approach was able to simultaneously reduce the standard deviation (up to a 15% for reduction of spherical equivalent power) and the mean bias error of the predictions (up to 80% reduction of spherical equivalent power) for the handheld aberrometer. These results suggest that dynamic retinal image analysis can substantially improve the accuracy and precision of the portable wavefront autorefractor relative to subjective refraction.

Gullstrand Intracapsular Accommodation Mechanism Revised

More than a century has passed since Allvar Gullstrand proposed his so called “mechanism of intracapsular accommodation” based on the concept that the change in lens power during accommodation can be larger if the lens is modeled by two different refractive indexes (cortex and nucleus) than if it is homogenous. Intracapsular accommodation of the original eye model proposed by Gullstrand is compared with that of a six-surfaces model eye built based on actual experimental data obtained with precise imaging techniques of the lens change during accommodation. The results show that nearly half (42%) of the accommodation of the Gullstrand model eye is produced by said mechanism, while a model eye based on actual data produces a small intracapsular dis-accommodation. The main reason for the discrepancy is the larger change in the radii of curvature of the lens nucleus during accommodation proposed by Gullstrand, which is necessary because his model likely did not take into account the reduction in the change in lens power produced by depth-of-focus.

A Novel Intraocular Lens Simulator that Allows Patients to Experience the World Through Multifocal Intraocular Lenses Before Surgeries

Purpose

The purpose of this study was to investigate whether the intraocular lens (IOL) simulator can simulate how the world appears to patients with multifocal IOLs by allowing the patients to see far and near objects through the IOL simulator.

Methods

Twenty eyes from 20 patients (age = 50-70 years old) were included in the study. The IOL simulator we developed consists of a trial lens frame adapter, a lens tube, a concave lens, a spacer, a wet cell, and an IOL. We used two IOLs: Tecnis monofocal and Tecnis bifocal IOL (add +3.25 diopter [D]). Patients wore a trial lens frame with an IOL simulator on distant corrected trial lenses and underwent the following tests: defocus curve, satisfaction with distance and near vision, halo around the light, and near point accommodation (NPA). To check how the world appears to the patients through this simulator, a machine vision lens and a scientific camera were attached to the simulator, and far and near objects were photographed.

Results

In the defocus curve of multifocal IOL, the visual acuity showed the second peak at -4 D. Compared to monofocal IOL, satisfaction with distant vision was slightly worse, more halos were felt, satisfaction with near vision was higher, and the NPA was shorter in multifocal IOL. In the scientific camera test, through the multifocal IOL, the waiting room was blurry, the halo around the ceiling light was prominent, and the characteristics on the near visual acuity chart were clear.

Conclusion

Subjects could experience the functions of multifocal IOLs with our newly developed IOL simulator.

Translational Relevance

This IOL simulator using geometric optics allows patients to experience the function of multifocal IOLs before cataract surgery.

The Effect of Retinal Illuminance on the Subjective Amplitude of Accommodation

SIGNIFICANCE

We show that the amplitude of accommodation decreases with retinal illumination even under photopic reading conditions and a constant pupil size. This result provides a basis for clinical approaches that are not based on an optical explanation.

PURPOSE

We investigated the effect of retinal illuminance on the amplitude of accommodation while the pupil of the eye remained constant.

METHODS

The amplitudes of accommodation of 10 young subjects (from 20 to 38 years of age) and that of 10 presbyopic subjects (from 45 to 54 years of age) were measured subjectively through an artificial pupil of 5 mm using a Badal optometer and for four values of retinal illuminance: 222, 821, 2138, and 5074 trolands. Phenylephrine was instilled to all the subjects to ensure that their natural pupil was greater than the artificial one in all experimental runs. Linear mixed-effects model for repeated measures with age and log luminance as covariates were used to check whether changes in amplitude of accommodation with retinal illumination were statistically significant.

RESULTS

In the range of illuminances tested, the amplitude of accommodation decreased on average from 6.34 to 4.35 D in the young subjects and from 1.69 to 1.04 D in the presbyopic subjects. Illuminance was associated with the amplitude of accommodation in both young and presbyopic groups, with P < .01.

CONCLUSIONS

The reduction in the amplitude of accommodation with target illumination (a phenomenon named night presbyopia) under photopic light conditions is not only due to a reduction in the depth of focus as a consequence of pupil dilation; it is strongly affected by the decrease of retinal illumination.

Difference in Pupillary Diameter as an Important Factor for Evaluating Amplitude of Accommodation: A Prospective Observational Study

Presbyopia is increasing globally due to aging and the widespread use of visual display terminals. Presbyopia is a decrease in the eye's amplitude of accommodation (AA) due to loss of crystalline lens elasticity. AA differs widely among individuals. We aimed to determine the factors that cause presbyopia, other than advanced age, for early medical intervention. We examined 95 eyes of 95 healthy volunteers (33 men, 62 women) aged 22-62 years (mean: 37.22 ± 9.77 years) with a corrected visual acuity of ≥1.0 and without other eye afflictions except ametropia. Subjective refraction, AA, maximum and minimum pupillary diameters during accommodation, axial length of the eye, and crystalline lens thickness were measured. AA was measured using an auto refractometer/keratometer/tonometer/pachymeter. The difference between maximum and minimum pupillary diameters was calculated. On multiple regression analysis, age and difference in pupillary diameter were both significantly and independently associated with AA in participants aged <44 years, but not in those aged ≥45 years. Our results suggest that the difference in pupillary diameter could be an important age-independent factor for evaluating AA in healthy individuals without cataract. Thus, improving the difference in pupillary diameter values could be an early treatment target for presbyopia.

Factors Influencing Pseudo-Accommodation-The Difference between Subjectively Reported Range of Clear Focus and Objectively Measured Accommodation Range

The key determinants of the range of clear focus in pre-presbyopes and their relative contributions to the difference between subjective range of focus and objective accommodation assessments have not been previously quantified. Fifty participants (aged 33.0 ± 6.4 years) underwent simultaneous monocular subjective (visual acuity measured with an electronic test-chart) and objective (dynamic accommodation measured with an Aston open-field aberrometer) defocus curve testing for lenses between +2.00 to −10.00 DS in +0.50 DS steps in a randomized order. Pupil diameter and ocular aberrations (converted to visual metrics normalized for pupil size) at each level of blur were measured. The difference between objective range over which the power of the crystalline lens changes and the subjective range of clear focus was quantified and the results modelled using pupil size, refractive error, tolerance to blur, and ocular aberrations. The subjective range of clear focus was principally accounted for by age (46.4%) and pupil size (19.3%). The objectively assessed accommodative range was also principally accounted for by age (27.6%) and pupil size (15.4%). Over one-quarter (26.0%) of the difference between objective accommodation and subjective range of clear focus was accounted for by age (14.0%) and spherical aberration at maximum accommodation (12.0%). There was no significant change in the objective accommodative response (F = 1.426, p = 0.229) or pupil size (F = 0.799, p = 0.554) of participants for levels of defocus above their amplitude of accommodation. Pre-presbyopes benefit from an increased subjective range of clear vision beyond their objective accommodation due in part to neural factors, resulting in a measured depth-of-focus of, on average, 1.0 D.

Effect of phenylephrine on static and dynamic accommodation

PURPOSE

We tested the hypothesis that changes in accommodation after instillation of Phenylephrine Hydrochloride (PHCl) observed in some studies could be caused by changes in optics.

METHODS

We performed two experiments to test the effects of PHCl on static and on dynamic accommodation in 8 and 6 subjects, respectively. Objective wavefront measurements were recorded of the static accommodation response to a stimulus at different distances or dynamic accommodation response to a sinusoidally moving stimulus (between 1 and 3 D of accommodative demand at 0.2Hz). The responses were characterized using two methods: one that takes into account the mydriatic optical effects on the accommodation produced by higher-order aberrations of the eye and another that takes into account only power changes paraxially due to the action of the ciliary muscle and regardless of the pupil size.

RESULTS

When mydriatic optical effects were taken into account, differences in responses before and after PHCl instillation were 0.51±0.53 D, and 0.12±0.15, for static and dynamic accommodation, respectively, and were statistically significant (p<0.039). When mydriatic optical effects were not taken into account, the differences in responses before and after PHCl instillation were -0.20±0.51 D, and -0.05±0.14, for static and dynamic accommodation, respectively, and were not statistically significant (p>0.313).

CONCLUSIONS

The mydriatic effect of the PHCl causes optical changes in the eye that can reduce the objective and subjective measurement of accommodation.

Distribution and progression of add power among people in need of near correction

IMPORTANCE

This study helps to better understand the need and trend in presbyopic add power in the aging society.

BACKGROUND

Distribution and progression of presbyopic add power in East Asian population is largely unknown.

DESIGN

Prospective cohort study.

PARTICIPANTS

About 303 participants from a population-based study of residents aged 35 years and older in Guangzhou, China.

METHODS

Visual acuity (VA) test and non-cycloplegic automated refraction were performed at baseline in 2008 and the 6-year follow-up per standardized protocol. Participants with presenting near VA ≤ 20/40 underwent distance subjective refraction and add power measurement by increasing plus lens at a standard distance of 40 cm at each visit.

MAIN OUTCOME MEASURES

Add power at baseline and follow-ups.

RESULTS

Mean (standard deviation) age of the study participants was 57.6 (11.1) years and 50.2% were female. The mean add power at baseline was 1.43, 1.73, 2.03 and 2.20 diopters (D) for individuals in the age groups of 35-44, 45-54, 55-64 and 65+ years, respectively. Participants with older age and lower educational level had significantly higher add power requirements (P < 0.001). The overall 6-year increase in add power was 0.15D (95% CI: 0.06 to 0.25), and was smaller in myopic subjects (P = 0.03). Baseline age and add power, but not changes in biometric factors, were associated with longitudinal change in add power (P < 0.001).

CONCLUSIONS AND RELEVANCE

Distribution and progression of add power in Chinese was different from that previously suggested by Caucasian studies. More studies are needed to establish up-to-date age-related add power prescription norms for population of different ethnicities.