Subjective and objective measurement of human accommodative amplitude

Objective accommodation measurement of the Crystalens HD compared to monofocal intraocular lenses

PURPOSE

Objective evaluation of accommodation with a bilateral accommodating intraocular lens (IOL) versus monofocal IOLs.

METHODS

Patients received accommodating IOL (Crystalens HD; Bausch & Lomb, Rochester, NY) bilaterally after cataract surgery. These were compared to a matched group receiving monofocal IOLs. Preoperative and postoperative distance corrected distance, intermediate, and near vision were evaluated. Objective accommodation was measured with the WAM-5500 Binocular Autorefractor/Keratometer (Grand Seiko, Pty Ltd., Hiroshima, Japan).

RESULTS

Nineteen patients were included. Ten received the Crystalens HD in both eyes and nine received one of three monofocal lenses in each eye. Mean postoperative distance corrected distance visual acuity was not statistically different between the two groups. Mean distance corrected intermediate vision was better in the Crystalens HD group (logMAR 0.24 ± 0.11 [control], logMAR 0.11 ± 0.10 [Crystalens HD], P = .033). The groups did not differ significantly for mean distance corrected near vision (logMAR 0.54 ± 0.12 [control], logMAR 0.42 ± 0.15 [Crystalens HD], P = .087). However, a significantly greater proportion of Crystalens HD eyes achieved 0.4 or 0.3 logMAR for near wearing their distance correction (P = .013). With distance correction, the mean spherical equivalent failed to show any myopia with accommodative effort in either group. Low contrast and low luminance contrast acuity were not significantly different.

CONCLUSION

The Crystalens HD showed some benefit for intermediate visual function compared to the monofocal IOLs with both groups wearing full correction for distance. There were no significant signs of accommodation in either group.

Age-related changes in accommodation measured with a double-pass system

PURPOSE

To measure the accommodative response in a wide age range population using the retinal image quality assessments provided by a double-pass system.

METHODS

The accommodative response was measured using a custom-built double-pass setup in 84 patients from 15 to 55 years of age. Patients were classified in four groups (A: 15-25 year old; B: 26-35; C: 36-45; D: 46-55). Accommodation was stimulated from 0 to 5 dioptres (D) with the push up method using an open field fixation test. The total accommodative response in the stimulated range, the accommodative stimulus-response curve, the slope and the progression of optical quality with accommodation were measured.

RESULTS

The total accommodation obtained in groups A and B was high, with a mean value of 4 D or higher, whereas values in older individuals were significantly lower. The accommodative stimulus-response curve and the slope were also high with a sudden decrease in patients over 35 years of age. The optical quality of the eye during accommodation did not change significantly.

CONCLUSIONS

Participants aged 15-35 years showed a good accommodative response. Thereafter, a significant decrease of the response in the total accommodation, stimulus response curve and slope was observed. The younger groups showed a larger accommodative response than previously published.

New Compact Accommodometer to Measure Accommodation Amplitude as a Biomarker

PURPOSE

This study aimed to evaluate a newly designed compact accommodometer (CA) and compare this with a conventional accommodometer for measuring accommodation as a biomarker for aging and lifestyle.

DESIGN

This is an observational case series.

METHODS

Accommodative amplitude was measured using 2 different accommodometers in 114 patients. We obtained the data of the near-point accommodation amplitude. Subsequently, we used smoking habit as an example of lifestyle-related factor to evaluate its effect on the accommodative power.

RESULTS

The first part of the study included 60 eyes of 60 men and 54 eyes of 54 women, with a mean (SD) age of 43.8 (12.9) years (range, 18-58 years). There was a consistency within each measuring method despite a significant difference between the 2 devices (P < 0.01). Measuring accommodation by CA was significantly faster than by conventional modality (190.9 ± 58.1 seconds for CA and 371.8 ± 123.6 seconds for D'ACOMO, P < 0.0001, paired t test). In the second part of the study, we found a significant correlation between age and accommodative amplitude both in smokers and in nonsmokers. The accommodative amplitude of the smoker group was significantly lower than that of the nonsmoker group (P < 0.001).

CONCLUSIONS

Compact accommodometer may work as an alternative and convenient method in place of the conventional accommodometer for measuring accommodative amplitude as an aging biomarker. Lifestyle factors can affect the magnitude of accommodation, which can be measured by this newly developed CA.

Measuring near-induced transient myopia in college students with visual discomfort

PURPOSE

Visual discomfort is a common problem, and our previous research indicated that 17% of college students experience moderate to high levels of discomfort when reading or studying. There have been several visual factors associated with visual discomfort, and in this study, we focused on measuring the near-induced transient myopia response in a group of college students with significant visual discomfort.

METHODS

Visual discomfort was evaluated with a survey developed by Conlon et al. (Conlon et al., Visual Cogn 1999;6:637-663). Twelve college students with high visual discomfort (scoring 1 SD higher than the mean value) and 12 college students with low visual discomfort (scoring within 0.5 SD of the mean value) participated in the study. All students had 20/25 or better visual acuity, no strabismus, and no significant uncorrected refractive error. All refractive error and accommodative measurements were made with the WAM-5500 autorefractor. A pretask distance refraction at 6 m was taken for 60 s, and then the students read a story for 10 min at 20 cm. After reading the passage, the posttask distance refraction was measured for 2 min at 6 m. Values for the pre- and posttask measures were averaged in 10-s blocks of time.

RESULTS

A mixed analysis of variance comparing discomfort group by pre- and postnear work distance refraction showed a significant interaction (p = 0.05). Comparing the means of the pre- and posttask distance refraction indicated that the high discomfort group showed no change in refractive error, but the low discomfort group showed a myopic shift of 0.13 diopter.

CONCLUSIONS

A near-induced transient myopia response is not associated with high visual discomfort experienced by college students when reading or doing near work.

Topical and intravenous pilocarpine stimulated accommodation in anesthetized rhesus monkeys

Many studies have used pilocarpine to stimulate accommodation in both humans and monkeys. However, the concentrations of pilocarpine used and the methods of administration vary. In this study, three different methods of pilocarpine administration are evaluated for their effectiveness in stimulating accommodation in rhesus monkeys. Experiments were performed in 17 iridectomized, anesthetized rhesus monkeys aged 4-16 years. Maximum accommodation was stimulated in all these monkeys with a 2% pilocarpine solution maintained on the cornea for at least 30 min in a specially designed perfusion lens. In subsequent topical pilocarpine experiments, baseline refraction was measured with a Hartinger coincidence refractometer and then while the monkeys were upright and facing forward, commercially available pilocarpine (2, 4, or 6%) was applied topically to the cornea as 2 or 4 drops in two applications or 6 drops in three applications over a five minute period with the eyelids closed between applications. Alternatively, while supine, 10-12 drops of pilocarpine were maintained on the cornea in a scleral cup for 5 min. Refraction measurements were begun 5 min after the second application of pilocarpine and continued for at least 30 min after initial administration until no further change in refraction occurred. In intravenous experiments, pilocarpine was given either as boluses ranging from 0.1mg/kg to 2mg/kg or boluses followed by a constant infusion at rates between 3.06 mg/kg/h and 11.6 mg/kg/h. Constant 2% pilocarpine solution on the eye in the perfusion lens produced 10.88+/-2.73 D (mean+/-SD) of accommodation. Topically applied pilocarpine produced 3.81 D+/-2.41, 5.49 D+/-4.08, and 5.55 D+/-3.27 using 2%, 4%, and 6% solutions respectively. When expressed as a percentage of the accommodative response amplitude obtained in the same monkey with constant 2% pilocarpine solution on the eye, the responses were 34.7% for 2% pilocarpine, 48.4% for 4% pilocarpine, and 44.6% for 6% pilocarpine. Topical 4% and 6% pilocarpine achieved similar, variable accommodative responses, but neither achieved maximum accommodation. IV boluses of pilocarpine achieved near maximal levels of accommodation at least ten times faster than topical methods. Doses effective for producing maximum accommodation ranged from 0.25mg/kg to 1.0mg/kg. IV pilocarpine boluses caused an anterior movement of the anterior lens surface, a posterior movement of the posterior lens surface, and a slight net anterior movement of the entire lens. Considerable variability in response amplitude occurred and maximum accommodative amplitude was rarely achieved with topical application of a variety of concentrations of commercially available pilocarpine. Intravenous infusion of pilocarpine was a rapid and reliable method of producing a nearly maximal accommodative response and maintaining accommodation when desired.

Visual discomfort and objective measures of static accommodation

PURPOSE

Accommodation insufficiency and fatigue have been associated with near work visual discomfort symptoms, but clinical measures of accommodation amplitude suggest insufficiency is uncommon and often not weak enough to cause symptoms. However, recent studies show that the clinical push-up test used to measure amplitude overestimates accommodative function. This study uses an open-field autorefractor to measure accommodative stimulus-response functions objectively in college students with and without near work induced discomfort symptoms.

METHODS

Using a Grand-Seiko WAM 5500 autorefractor, 2 min recordings were made each at five viewing distances (0 to 5 D) to measure an accommodative response function. Visual discomfort symptoms were assessed using the Conlon survey.

RESULTS

A strong and positive correlation between accommodative lag and visual discomfort symptoms was found under near work conditions. The prevalence of accommodative insufficiency was much higher than estimated by clinical measures.

CONCLUSIONS

Accommodative insufficiency and fatigue should be defined and described by objective methods using extended viewing times to assess function.

Objective accommodation measurements in pseudophakic subjects using an autorefractor and an aberrometer

PURPOSE

To compare objective measures of accommodation with the WR-5100K autorefractor and iTrace aberrometer to subjective push-down and defocus tests in normal phakic subjects and pseudophakic subjects with standard monofocal intraocular lenses (IOLs).

SETTING

University of Houston, College of Optometry, Houston, Texas, USA.

METHODS

The push-down test and defocus curves were used to stimulate and measure accommodation subjectively in pseudophakic subjects. For objective testing, a near target was pushed up and refraction measured objectively. For comparison, the same objective measurements were performed in phakic subjects. Calibration tests were performed with soft contact lenses in phakic subjects with varying refractive error and in pseudophakic subjects.

RESULTS

Fifteen phakic subjects (mean age 28.9 years+/-5.52 [SD]) and 10 pseudophakic subjects (mean age 66.2+/-11.23 years) participated. Subjectively measured accommodative amplitude in the pseudophakic group was 3.28+/-1.11 diopters (D) in the right eye and 3.64+/-1.38 D in the left eye. Defocus curves in the pseudophakic group had a range of 2.00 D for distance-corrected visual acuity of 20/40 or better. Objective measurements in the pseudophakic group were 0.11+/-0.50 D with the autorefractor and 0.10+/-0.47 D with the aberrometer. Contact lens calibrations showed good agreement with the 1:1 line.

CONCLUSIONS

The subjective tests overestimated accommodative amplitude relative to the objective measures. The autorefractor and aberrometer were accurate, reliable, and appropriate for objective accommodation measurements in pseudophakes. Objective accommodation measurements such as these can be used to evaluate the performance of accommodating IOLs.

Comparison of the ocular wavefront aberration between pharmacologically-induced and stimulus-driven accommodation

PURPOSE

To compare the ocular wavefront aberration between pharmacologically- and stimulus-driven accommodation in phakic eyes of young subjects.

METHODS

The aberration structure of the tested eye when accommodating was measured using the Complete Ophthalmic Analysis System (COAS; AMO WaveFront Sciences, Albuquerque, NM, USA). It was used in conjunction with a purposely-modified Badal optometer to allow blur-driven accommodation to be stimulated by a high contrast letter E with a vergence range between +0.84 D and -8.00 D. Pharmacological accommodation was induced with one drop of pilocarpine 4%. Data from six subjects (age range: 23-36 years) with dark irides were collected.

RESULTS

No correlation was found between the maximal levels of accommodative response achieved with an 8 D blur-driven stimulus and pharmacological stimulation. Pharmacological accommodation varied considerably among subjects: maximum accommodation, achieved within 38-85 min following application of pilocarpine, ranged from 2.7 D to 10.0 D. Furthermore, although the changes of spherical aberration and coma as a function of accommodation were indistinguishable between the two methods for low levels of response, a characteristic break in the pattern of aberration occurred at higher levels of pilocarpine-induced accommodation. This probably resulted from differences in the time course of biometric changes occurring with the two methods.

CONCLUSION

Measuring the pilocarpine-induced accommodative response at only one time point after its application may lead to misleading results. The considerable inter-individual differences in the time course of drug-induced accommodative response and its magnitude may lead to overestimation or underestimation of the corresponding amplitude of normal, blur-driven accommodation. Stimulating accommodation by topical application of pilocarpine is inappropriate for evaluating the efficacy of 'accommodating' IOLs.

Short-term adaptive modification of dynamic ocular accommodation

PURPOSE

Indirect observations suggest that the neural control of accommodation may undergo adaptive recalibration in response to age-related biomechanical changes in the accommodative system. However, there has been no direct demonstration of such an adaptive capability. This investigation was conducted to demonstrate short-term adaptation of accommodative step response dynamics to optically induced changes in neuromuscular demands.

METHODS

Repetitive changes in accommodative effort were induced in 15 subjects (18-34 years) with a double-step adaptation paradigm wherein an initial 2-D step change in blur was followed 350 ms later by either a 2-D step increase in blur (increasing-step paradigm) or a 1.75-D step decrease in blur (decreasing-step paradigm). Peak velocity, peak acceleration, and latency of 2-D single-step test responses were assessed before and after 1.5 hours of training with these paradigms.

RESULTS

Peak velocity and peak acceleration of 2-D step responses increased after adaptation to the increasing-step paradigm (9/12 subjects), and they decreased after adaptation to the decreasing-step paradigm (4/9 subjects). Adaptive changes in peak velocity and peak acceleration generalized to responses that were smaller (1 D) and larger (3 D) than the 2-D adaptation stimulus. The magnitude of adaptation correlated poorly with the subject's age, but it was significantly negatively correlated with the preadaptation dynamics. Response latency decreased after adaptation, irrespective of the direction of adaptation.

CONCLUSIONS

Short-term adaptive changes in accommodative step response dynamics could be induced, at least in some of our subjects between 18 and 34 years, with a directional bias toward increasing rather than decreasing the dynamics.

Objective Amplitude of Accommodation Computed from Optical Quality Metrics Applied to Wavefront Outcomes

Purpose

We studied the accuracy and precision of 32 objective wavefront methods for finding the amplitude of accommodation obtained in 180 eyes.

Methods

Ocular accommodation was stimulated with 0.5 D steps in target vergence spanning the full range of accommodation for each subject. Subjective monocular amplitude of accommodation was measured using two clinical methods, using negative lenses and with a custom Badal optometer.

Results

Both subjective methods gave similar results. Results obtained from the Badal optometer where used to test the accuracy of the objective methods. All objective methods showed lower amplitude of accommodation that the subjective ones by an amount that varied from 0.2 to 1.1 D depending on the method. The precision in this prediction also varied between subjects, with an average standard error of the mean of 0.1 D that decreased with age.

Conclusions

Depth of field increases subjective of amplitude of accommodation overestimating the objective amplitude obtained with all the metrics used. The change in the negative direction of spherical aberration during accommodation increases the amplitude of accommodation by an amount that varies with age.

Repeatability intraexaminer and agreement in amplitude of accommodation measurements

BACKGROUND

Clinical measurement of the amplitude of accommodation (AA) provides an indication of maximum accommodative ability. To determine whether there has been a significant change in the AA, it is important to have a good idea of the repeatability of the measurement method used. The aim of the present study was to compare AA measurements made using three different subjective clinical methods: the push-up, push-down, and minus lens techniques. These methods differ in terms of the apparent size of the target, the end point used, or the components of the accommodation response stimulated. Our working hypothesis was that these methods are likely to show different degrees of repeatability such that they should not be used interchangeably.

METHODS

The AA of the right eye was measured on two separate occasions in 61 visually normal subjects of mean age 19.7 years (range 18 to 32). The repeatability of the tests and agreement between them was estimated by the Bland and Altman method. We determined the mean difference (MD) and the 95% limits of agreement for the repeatability study (COR) and for the agreement study (COA).

RESULTS

The COR for the push-up, push-down, and minus lens techniques were +/-4.76, +/-4.00, and +/-2.52D, respectively. Higher values of AA were obtained using the push-up procedure compared to the push-down and minus lens methods. The push-down method also yielded a larger mean AA than the negative-lens method. MD between the three methods were high in clinical terms, always over 1.75D, and the COA differed substantially by at least +/-4.50D. The highest agreement interval was observed when we compared AA measurements made using minus lenses and the push-up method (+/-5.65D).

CONCLUSIONS

The minus lens method exhibited the best repeatability, least MD (-0.08D) and the smallest COR. Agreement between the three techniques was poor.

Lens thickness with age and accommodation by optical coherence tomography

PURPOSE

To utilize time-domain optical coherence tomography (OCT) to measure changes in the crystalline lens with age and accommodation.

METHODS

A cross-sectional study of pre-presbyopic and presbyopic subjects was conducted. Amplitude of accommodation was measured with the push-up test. Objective accommodation was measured with the Grand Seiko auto-refractor and a Badal lens system. Lens thickness was measured with the Zeiss Visante OCT and an internal optometer. The data were analysed using correlation coefficients, linear regression, and by calculating the average change in lens thickness per diopter change in objective accommodation.

RESULTS

Twenty-two subjects between the ages of 36 and 50 years completed the study. Subjective amplitude of accommodation ranged from 2.17 to 6.38 D. Objective accommodation ranged from 0.22 to 4.56 D. The mean lens thickness was 4.05+/-0.20 mm. The mean change in lens thickness for up to a 5-D accommodative stimulus ranged from 0.01 to 0.26 mm. The correlation coefficients were: age and subjective accommodation, r= -0.74; age and objective accommodation, r= -0.84; change in lens thickness and age, r= -0.65; change in lens thickness and subjective accommodation, r=0.74; change in lens thickness and objective accommodation, r=0.64; objective and subjective accommodation, r=0.82 (all p<0.01). An increase in lens thickness of 21 microm per year of age was determined by linear regression. For the subjects who showed at least 1 D of accommodative response on the Grand Seiko auto-refractor, there was an increase of 51+/-19 microm per dioptre of accommodation.

CONCLUSIONS

Optical coherence tomography is a non-invasive technique that can be used to quantify changes in the thickness of the crystalline lens. Subjective and objective measurements of accommodation, as well as age, were robustly correlated with the measured changes in lens thickness. Lens thickness changes with age and accommodation as measured with the Visante OCT compare well with previous findings using Scheimpflug photography and ultrasound.

Restoration of accommodation: surgical options for correction of presbyopia

Accommodation is a dioptric change in the power of the eye to see clearly at near. Ciliary muscle contraction causes a release in zonular tension at the lens equator, which permits the elastic capsule to mould the young lens into an accommodated form. Presbyopia, the gradual age-related loss of accommodation, occurs primarily through a gradual age-related stiffening of the lens. While there are many possible options for relieving the symptoms of presbyopia, only relatively recently has consideration been given to surgical restoration of accommodation to the presbyopic eye. To understand how this might be achieved, it is necessary to understand the accommodative anatomy, the mechanism of accommodation and the causes of presbyopia. A variety of different kinds of surgical procedures has been considered for restoring accommodation to the presbyopic eye, including surgical expansion of the sclera, using femtosecond lasers to treat the lens or with so-called accommodative intraocular lenses (IOLs). Evidence suggests that scleral expansion cannot and does not restore accommodation. Laser treatments of the lens are in their early infancy. Development and testing of accommodative IOLs are proliferating. They are designed to produce a myopic refractive change in the eye in response to ciliary muscle contraction either through a movement of an optic or through a change in surface curvature. Three general design principles are being considered. These are single optic IOLs that rely on a forward shift of the optic, dual optic IOLs that rely on an increased separation between the two optics, or IOLs that permit a change in surface curvature to produce an increase in optical power in response to ciliary muscle contraction. Several of these different IOLs are available and being used clinically, while many are still in research and development.

Objective accommodation measurements in prepresbyopic eyes using an autorefractor and an aberrometer

PURPOSE

To test the repeatability of the iTrace wavefront aberrometer (Tracey Technologies, Inc.) and the WR-5100K autorefractor (Grand Seiko Co., Ltd.) and to measure accomodation in young and phakic prepresbyopic subjects.

SETTING

University of Houston, College of Optometry, Houston, Texas, USA.

METHODS

This study comprised 30 young adults and 15 prepresbyopic subjects. Accommodation was stimulated with near charts presented at various distances. Measurements were repeated 3 times for each target distance with both instruments. For test-retest reliability, the entire protocol was repeated on 3 additional days in 3 prepresbyopic subjects as well as twice on the same day in the young adults.

RESULTS

The mean age was 25.5 years +/- 3.25 (SD) (range 21 to 31 years old) in the young adult group and 41.2 +/- 2.98 years (range 38 to 49 years) in the prepresbyopic group. Bland-Altman analysis of repeated measures of the young subjects had limits of agreements (LoA) of 1.58 diopters (D) or less for each instrument and when compared between instruments. Normalized mean stimulus response functions in the prepresbyopic group were similar for the 2 instruments. Bland-Altman analysis of the accommodation measurements between the 2 instruments showed a mean difference of 0.07 D and an LoA of 0.70 D. Repeated measures of 3 prepresbyopic subjects had a range of standard deviations from 0.07 to 0.51 D.

CONCLUSION

The accommodative responses measured with the 2 instruments were not significantly different, and testing showed both instruments to be suitable for objective measurement of accommodation in a phakic prepresbyopic population with low accommodative amplitudes.

Minus-lens-stimulated accommodative amplitude decreases sigmoidally with age: a study of objectively measured accommodative amplitudes from age 3

PURPOSE

Guidelines for predicting accommodative amplitude by age are often based on subjective push-up test data that overestimate the accommodative response. Studies in which objective measurements were used have defined expected amplitudes for adults, but expected amplitudes for children remain unknown. In this study, objective methods were used to measure accommodative amplitude in a wide age range of individuals, to define the relationship of amplitude and age from age 3.

METHODS

Accommodative responses were measured in 140 subjects aged 3 to 40 years. Measurements were taken with the Grand Seiko autorefractor (RyuSyo Industrial Co., Ltd., Kagawa, Japan) as the subjects viewed a high-contrast target at 33 cm through minus lenses of increasing power until the responses showed no further increase in accommodation.

RESULTS

The maximum accommodative amplitude of each subject was plotted by age, and a curvilinear function fit to the data: y = 7.33 - 0.0035(age - 3)(2) (P < 0.001). Tangent analysis of the fit indicated that the accommodative amplitude remained relatively stable until age 20. Data from this study were then pooled with objective amplitudes from previous studies of adults up to age 70. A sigmoidal function was fit to the data: y = 7.083/(1 + e([0.2031(age-36.2)-0.6109])) (P < 0.001). The sigmoidal function indicated relatively stable amplitudes below age 20 years, a rapid linear decline between 20 and 50 years, and a taper to 0 beyond 50 years.

CONCLUSIONS

These data indicate that accommodative amplitude decreases in a curvilinear manner from 3 to 40 years. When combined with data from previous studies, a sigmoidal function describes the overall trend throughout life with the biggest decrease occurring between 20 and 50 years.

[Measurement of accommodation using optical biometry]

BACKGROUND

Making accommodation possible for all age groups is a topic of great interest. We applied optical biometry in order to study the physiological mechanisms in detail. Longitudinal relations in the optical axis were measured during accommodation in volunteers of different ages and lens states.

METHODS

A total of 60 subjects (children, adolescents, adults, and pseudophakes) were examined using the IOL Master. We measured anterior chamber depth (ACD), axial length (AL), and changes in these two measurements during accommodation.

RESULTS

Near accommodation (NA) in adolescents caused the largest ACD decrease (0.14+/-0.03 mm). ACD decreased in adults during NA but not in pseudophakic patients of comparable age. AL increased during NA in all groups by 0.01+/-0.01 mm.

CONCLUSIONS

ACD decreased with age. Using a physiological stimulus, no change in ACD was measured during NA in pseudophakic patients. The documented increase in AL needs to be evaluated further.

Objective Accommodation Measurement with the Grand Seiko and Hartinger Coincidence Refractometer

PURPOSE

Subjective push-up tests and dynamic retinoscopy are standard clinical accommodation tests. These are inadequate for assessing if accommodation can be restored in presbyopes. Commercially available clinical autorefractors offer potentially reliable methods for objective accommodation measurement. This study evaluated accuracy and reliability of the Grand Seiko WR-5100K autorefractor for objective accommodation measurement in young adults.

METHODS

Twenty-two subjects, aged 21 to 30 years (mean 25.6 +/- 2.26) participated. Three methods were used to stimulate and measure accommodation: (1) subjective push-up test in free space, (2) a near target pushed-up on a near-point rod and the response measured with the WR-5100K and a Hartinger coincidence refractometer (HCR), and (3) a distant target viewed through increasing powered negative trial lenses and the response measured with the WR-5100K and the HCR. Trial lens calibration procedures were also used to test the accuracy of the instruments.

RESULTS

Average maximum accommodative amplitude with the subjective push-up test was 7.74 D +/- 0.36 D (mean +/- SE). For a 5 D stimulus, accommodation of 4.68 D +/- 0.10 D (mean +/- SE) and 4.13 D +/- 0.09 D was measured with the WR-5100K and the HCR, respectively. With a distant target viewed through a -5.00 D trial lens, the WR-5100K measured 4.07 D +/- 0.09 D and the HCR measured 4.05 D +/- 0.09 D of accommodation. Maximum mean response measured with trial lens-induced accommodation was 5.67 D +/- 0.15 D with the WR-5100K and 5.77 D +/- 0.18 D with the HCR.

CONCLUSIONS

The subjective push-up test overestimated accommodative amplitude relative to the objective measures. The WR-5100K showed good agreement in the responses measured for both pushed-up near targets and a distant target viewed through trial lenses with the HCR, a widely used laboratory instrument. The Grand Seiko WR-5100K, a commercially available instrument, has been demonstrated to be well suited for clinical, objective accommodation measurement using a population of normal young adults.

Is randomisation necessary for measuring defocus curves in pre-presbyopes?

PURPOSE

Defocus curves are used to evaluate the subjective range of clear vision of presbyopic corrections such as in eyes implanted with accommodating intraocular lenses (IOLs). This study determines whether letter sequences and/or lens presentation order ought to be randomised when measuring defocus curves.

METHODS

Defocus curves (range +2.00DS to -2.00DS) were measured on 18 pre-presbyopic subjects (mean age 24.1+/-4.2 years) for six combinations of sequential or randomised positive or negative lens progression and non-randomised or randomised letter sequences. The letters were presented on a computerised logMAR chart at 6m.

RESULTS

Overall there was a statistically significant difference between the six combinations (ANOVA, p<0.05) attributable to the combination of non-randomised letters with non-randomised lens progression from negative to positive defocus (p<0.01). There was no statistically significant difference in defocus curve measurements if both letters and lens order were randomised compared to if only one of these variables was randomised (p>0.05). Non-randomised letters, with a sequential lens progression from negative to positive, was significantly different to all other combinations when compared individually (Student's T-test, p<0.003 on all comparisons), and was confirmed as the sole source of the overall significant difference. There was no statistically significant difference if both lens presentation order and letter sequences were randomised compared to if only one or the other of these variables was randomised.

CONCLUSION

Non-randomised letters and non-randomised lens progression on their own did not affect the subjective amplitude of accommodation as measured by defocus curves, although their combination should be avoided.

On the relationship between lens stiffness and accommodative amplitude

The purpose of this study was to investigate the relationship between the stiffness of the material comprising the lens and the loss of accommodative amplitude with age. We used a validated mechanical model to determine the changes in the shape of the lens during accommodation and disaccommodation. The relative contribution of lens stiffness to loss of accommodative amplitude with age was determined by varying lens stiffness in the model. The changes in lens stiffness with age were based on the results of two recently published studies. In the first study we showed that lens stiffness increases exponentially with age, and in the second study we showed that there is a considerable stiffness gradient within the lens that changes with age. The results of both studies were incorporated in the mechanical model. The model showed that it is not the increasing stiffness of the lens with age, but rather the changing stiffness gradient that influences accommodative amplitude. The results show that the changing stiffness gradient in the lens may be responsible for almost the entire loss of accommodation with age.

Lens fluorescence and accommodative amplitude in pre-presbyopic and presbyopic subjects

Accommodative amplitude (AA; the difference, measured in diopters, between the near and far points of vision) declines steadily with age such that, by midlife, most individuals are unable to focus clearly on near objects and, thus, are said to be presbyopic. Conversely, intrinsic lens fluorescence (LF) increases steadily with age. Previous studies have suggested that AA and LF are negatively correlated, independent of age. Were this to be the case, it might suggest that the biochemical modifications underlying increased tissue fluorescence (for example, glycation of lens proteins) contribute to presbyopia. We used quantitative techniques to re-evaluate the relationship between AA and LF in 161 healthy volunteers aged between 25 and 70. Our data confirmed that AA decreases with age, becoming essentially zero by age 55, and LF increases with age. However, in marked contrast to previous reports, statistical analysis failed to detect any correlation between LF and AA independent of age. Thus, the biochemical processes responsible for increased LF observed in the aged lens are unlikely to contribute directly to presbyopia.

Linear relationship of refractive and biometric lenticular changes during accommodation in emmetropic and myopic eyes

AIM

Aim of this study was to investigate the relationship between refractive changes in the eye and biometric changes of the human crystalline lens during accommodation. Furthermore, differences in these relationships between young, healthy emmetropic and myopic subjects were analyzed.

METHODS

Mean relative change in anterior chamber depth (ACD), lens thickness (LT), anterior segment length (ASL = ACD + LT) and in objective refraction were simultaneously assessed during near-point-induced accommodation in 10 emmetropic and 10 myopic subjects. Via a beam splitter, measurements were performed simultaneously using partial coherence interferometry (PCI) and infrared (IR) photorefraction.

RESULTS

On average, for each diopter of accommodation LT increased by 0.063 mm in emmetropic and by 0.072 mm in myopic eyes, and ACD decreased by 0.047 mm and 0.057 mm, respectively. Mean ASL, indicating the position of the posterior lens pole, increased by 0.009 mm in emmetropic and by 0.013 mm in myopic eyes. The correlation between refractive and biometric changes was found to be essentially linear in both subgroups. Differences in ACD between emmetropic and myopic eyes were statistically significant at an accommodative stimulus of -1 D (p<0.04) and -2 D (p<0.02).

CONCLUSION

The biometric and refractive changes of the human lens are highly correlated and linear in function in both emmetropic and myopic eyes.

Analysis of patients with good uncorrected distance and near vision after monofocal intraocular lens implantation

PURPOSE

To analyze factors contributing to uncorrected visual acuity of at least 6/12 for distance and at least J4 for near (pseudoaccommodation) after monofocal intraocular lens (IOL) implantation.

SETTING

Iladevi Cataract and IOL Research Center, Ahmedabad, India.

METHODS

In a case-controlled study of 30 eyes (30 patients) that had phacoemulsification, those with pseudoaccommodation were assigned to cases and 30 eyes (30 patients) without pseudoaccommodation were designated as controls. Controls were matched by identical best corrected visual acuity, age, and postoperative duration. Subjective refraction was done with retinoscopy. Factors analyzed included corneal astigmatism, pupil size, axial IOL movement, amplitude of accommodation, axial length (AL), and age. Corneal astigmatism was noted on topography and interpreted as against the rule (ATR) (180 +/- 15 degrees), with the rule (WTR) (90 +/- 15 degrees), and oblique (OB) (45/135 +/- 30 degrees). Pupil size was noted on topographic display and AL and anterior chamber depth (ACD) on immersion A-scan. The axial IOL movement was calculated as the difference in ACD after instillation of cyclopentolate 1% (Cyclopent) and subsequently pilocarpine nitrate 2% (Carpinol) at separate visits, and amplitude of accommodation was measured with static and dynamic retinoscopy. Multivariate logistic regression and odds ratio with 95% confidence intervals were determined.

RESULTS

Mean spherical equivalent was -0.45 +/- 0.63 diopter (D) in cases and -0.35 +/- 0.83 D (P = .61) in controls. Multivariate logistic regression in cases versus controls: corneal astigmatism (ATR versus WTR and OB collectively): 10.19 [1.8,57.44], P = .009; pupil size: 0.45 [0.07,2.71], P = .38; axial IOL movement: 1.39 [0.51,0.77], P = .514; amplitude of accommodation: 2.95 [0.93,9.3], P = .065; AL: 0.55 [0.29,1.02], P = .058; and age: 0.98 [0.5,1.95], P = .963.

CONCLUSION

The study suggests a significant role of ATR corneal astigmatism in good uncorrected distance and near vision after monofocal IOL implantation.

Objective measurement of intraocular lens movement and dioptric change with a focus shift accommodating intraocular lens

PURPOSE

To objectively measure the shift and refractive change of the 1CU accommodating intraocular lens (IOL) (HumanOptics) and compare them to that of a monofocal AcrySof MA30 IOL (Alcon Laboratories) in the fellow eye.

SETTING

Ophthalmology Department, St. Thomas' Hospital, London, United Kingdom.

METHODS

Thirty patients who had bilateral cataract surgery 18 to 24 months previously with a 1CU IOL prospectively randomly allocated to 1 eye and an AcrySof MA30 monofocal IOL to the other eye were examined. Distance correction, near vision, reading fluency, near point, and defocus to minus spheres were measured. Intraocular lens shift to an accommodative stimulus following instillation of pilocarpine 4% was measured with the ACMaster. Refractive change between distance and near was measured with the Tracey wavefront analyzer.

RESULTS

Of the original 30 patients recruited, complete measurements could only be obtained for 20. There was no significant difference in near visual function with either IOL. A small anterior movement of the 1CU was seen with accommodation 0.010 mm +/- 0.028 (SD). After pilocarpine 4% instillation, a forward movement of 0.220 +/- 0.169 mm was seen with the 1CU compared to a backward movement of 0.028 +/- 0.095 with the MA30. There was no significant correlation between distance corrected near visual acuity and IOL movement. No change in spherical equivalent between distance and near was seen on wavefront analysis of either IOL.

CONCLUSIONS

Small forward movement of the 1CU IOL was seen with accommodation and increased following pilocarpine, compared to the posterior movement of the MA30 IOL. The amount of the IOL shift was not sufficient to provide useful near vision, but the difference suggests that the engineering concept behind the 1CU IOL is valid.

Pharmacological-induced Haptic Changes and the Accommodative Performance in Patients With the AT-45 Accommodative IOL

PURPOSE

To investigate the accommodative performance of the AT-45 (eyeonics Inc, Aliso Viejo, Calif) using three-dimensional ultrasound biomicroscopy.

METHODS

The AT-45 haptic region was visualized in vivo 1 month after surgery in four patients using an in-house developed three-dimensional ultrasound biomicroscope. Haptic changes, axial shift, and accommodation amplitude were determined under pharmacologically induced accommodation.

RESULTS

The angulation, depending on the accommodation state, could be distinguished and analyzed. In vivo a mean change in haptic angulation of 3.3 +/- 3.3 degrees (range: 0 degrees to 7 degrees) and a mean forward shift of 0.13 +/- 0.08 mm (range: 0.05 to 0.2 mm) were observed for the AT-45 using pharmacologically induced accommodation. A mean accommodative amplitude of 0.44 +/- 0.24 diopters (D) (range: 0.25 to 0.75 D) was found using a Hartinger coincidence refractometer.

CONCLUSIONS

Minimal angulation changes and axial movements of the AT-45 have been demonstrated using pharmacological stimulation and objective measurement methods. The mechanical performance of the AT-45 in these eyes does not appear to provide the range of accommodation necessary for close work.

Phacoemulsification and Implantation of an Accommodating IOL After PRK

PURPOSE

To present a case of phacoemulsification and implantation of an accommodating intraocular lens (IOL) in a patient with cataract formation after previous refractive surgery.

METHODS

A 50-year-old man, who initially had photorefractive keratectomy to correct moderate myopia, developed a cataract in one eye. He subsequently underwent phacoemulsification and implantation of a 1CU accommodating IOL, as he wished to remain spectacle independent.

RESULTS

The patient's distance vision was fully restored. However, accommodative function, which was assessed using subjective and novice objective techniques, was only partially restored.

CONCLUSIONS

Although the accommodating IOL fully restored the patient's distance vision, accommodative function was only partially restored.

Feasibility and development of a high-power real accommodating intraocular lens

PURPOSE

To develop an accommodating intraocular lens (IOL) that changes power with ciliary body action and generates a minimum of 8.0 diopters (D) by manipulation of a flexible material between a sulcus-fixated rigid plate and a ciliary muscle-operated capsular diaphragm.

SETTING

Vissum-Instituto Oftalmológico de Alicante and Miguel Hernández University, Alicante, Spain.

METHODS

The feasibility of the concept was tested by a laboratory lens model. An implantable measuring device was constructed to simulate the lens action. The device was implanted in monkey eyes to measure the various parameters involved with such IOLs. Based on these measurements, an accommodating IOL prototype was built and implanted in monkeys' eyes. Pharmacologic agents were used to achieve ciliary relaxation and spasm. Ultrasound biomicroscopy (UBM) imaging was used to document the active changes of the IOL flexible lens curvature as related to the ciliary muscles status.

RESULTS

The laboratory model produced more than 50.0 D of accommodation. The UBM demonstrated changes in lens curvature between cyclospasm to cycloplegia of calculated 9.0 to 53.0 D for flexible material with a refractive index of 1.41.

CONCLUSIONS

Flexible material is capable of being manipulated when placed between a scleral-fixated rigid plane and the ciliary muscles-operated capsular diaphragm. Such manipulation as used by the IOL concept presented here has generated an active change of more than 40.0 D in the monkey eye.

Fellow eye comparison between the 1CU accommodative intraocular lens and the Acrysof MA30 monofocal intraocular lens

PURPOSE

To examine the near visual clinical performance of an accommodative intraocular lens (IOL) when compared with a standard monofocal IOL in a fellow eye comparison.

DESIGN

Prospective, randomized fellow eye comparison.

METHODS

Thirty patients (60 eyes) with bilateral cataracts but otherwise normal eyes were recruited from a single university hospital cataract waiting list. Patients were randomized to receive either the 1CU accommodative IOL in their first eye or the Acrysof MA30 monofocal IOL. The alternative lens was then implanted in the second eye 4 to 6 weeks later. At all follow-up visits, a full assessment was made of distance, near and reading visual performance, and accommodative amplitude.

RESULTS

Data are available for all patients at 6 months and 20 patients at 1 year. At 6 months, no difference was found in distance-corrected visual acuity between the two IOLs. Of the 1CU eyes, nine patients (30%) could read J6 or better at a reading speed of 80 words/min or better. In these nine patients, the mean difference in the amplitude of accommodation between the two eyes was 0.71 diopters.

CONCLUSIONS

No measurable variable distinguished eyes that developed functional reading vision from those that did not. The accommodative IOL appears to produce improved near vision in some eyes, but it does not work in all eyes, and in eyes where there is apparent accommodation, there is a discrepancy between subjective reading performance and the modest measured increase of accommodative amplitude.

Comparison of pilocarpine-induced and stimulus-driven accommodation in phakic eyes

With the recent introduction of potentially accommodative intraocular lenses (IOL), there is a need for methods to evaluate their accommodative potential. In most studies assessing IOL movement, pilocarpine is used to stimulate contraction of the ciliary muscle. The aim of this study is to determine if pilocarpine-induced ciliary muscle contraction is comparable to physiological stimulus-driven accommodation in young and presbyopic subjects. Ten emmetropic young subjects (23-25 years) and 11 emmetropic presbyopic subjects (51-62 years) were included in this study. Anterior chamber depth (ACD) and lens thickness (LT) were assessed with partial coherence interferometry (PCI). A moveable stimulus was coupled to the PCI equipment for measurement of biometric lens changes. ACD was measured with the stimulus at infinity and then at the subjects individual nearpoint, and after application of two drops of 2% pilocarpine. In young subjects, there was no significant difference in lens change between nearpoint and pilocarpine stimulation. Presbyopic subjects showed no relevant lens change when accommodating at the nearpoint, however, under pharmacologically induced ciliary muscle contraction with pilocarpine, there was a significant forward shift of the anterior and posterior lens pole, leading to a translational forward lens shift of about 150 microm. This study demonstrates that pilocarpine acts "physiologically" in young phakic subjects, but is a "superstimulus" in presbyopic phakic subjects. Therefore, IOL movement may be overestimated when using pilocarpine to stimulate accommodation.

Comparisons between pharmacologically and Edinger-Westphal-stimulated accommodation in rhesus monkeys

PURPOSE

Accommodation results in increased lens thickness and lens surface curvatures. Previous studies suggest that lens biometric accommodative changes are different with pharmacological and voluntary accommodation. In this study, refractive and biometric changes during Edinger-Westphal (EW) and pharmacologically stimulated accommodation in rhesus monkeys were compared.

METHODS

Accommodation was stimulated by an indwelling permanent electrode in the EW nucleus of the midbrain in one eye each of four rhesus monkeys. Dynamic refractive changes were measured with infrared photorefraction, and lens biometric changes were measured with high-resolution, continuous A-scan ultrasonography for increasing stimulus current amplitudes, including supramaximal current amplitudes. Accommodation was then stimulated pharmacologically and biometry was measured continuously for 30 minutes.

RESULTS

During EW-stimulated accommodation, lens surfaces move linearly with refraction, with an increase in lens thickness of 0.06 mm/D, an anterior movement of the anterior lens surface of 0.04 mm/D, and a posterior movement of the posterior lens surface of 0.02 mm/D. Peak velocity of accommodation (diopters per second) and lens thickness (in millimeters per second) increased with supramaximal stimulus currents, but without further increase in amplitude or total lens thickness. After carbachol stimulation, there was initially an anterior movement of the anterior lens surface and a posterior movement of the posterior lens surface; but by 30 minutes, there was an overall anterior shift of the lens.

CONCLUSIONS

Ocular biometric changes differ with EW and pharmacological stimulation of accommodation. Pharmacological stimulation results in a greater increase in lens thickness, an overall forward movement of the lens and a greater change in dioptric power.

Accommodative intraocular lenses: current status

PURPOSE OF REVIEW

The possibility of using a monofocal IOL with accommodative ability allows refractive cataract surgery with a clearly decreased potential of photic phenomena. Three IOLs of different designs and materials have demonstrated accommodative ability, but the degree of accommodative amplitude has been reported to different extents and variabilities. The plate-haptic CrystaLens has a hinged design that might permit forward movement of the optic as a result of pressure changes in the vitreous cavity. The 1CU has modified haptics that bend in the bag as the lens capsule contracts, which are supposed to cause anterior displacement of the lens optic. With the dual-optic one-piece Synchrony, springlike haptics separate a high-plus anterior lens from a posterior minus lens. With accommodative effort, the capsular bag expands and the springs express kinetic energy, which might allow the optics to separate as the anterior lens moves forward.

RECENT FINDINGS

This article seeks to clarify and distinguish the concepts of true accommodation and pseudo accommodation. Current designs of accommodative IOLs are supposed to work by the focus-shift principle to allow true pseudophakic accommodation. Studies that biometrically assessed optic shift found no or only low amplitudes of forward movement. The amount of forward movement, if present, was highly variable between patients. To date, most studies present psychophysical data for the proof of concept, which alone seems insufficient. Capsule bag performance and posterior capsule opacification with accommodative IOLs seem worse than those with standard intraocular lenses.

SUMMARY

The potential clinical benefits of accommodative IOL technology for both cataract patients and refractive patients may place accommodative IOLs in a competitive position with multifocal IOL technology.

Potentially Accommodating Intraocular Lenses - An In Vitro and In Vivo Study Using Three-dimensional High-frequency Ultrasound

PURPOSE

To investigate the accommodative performance of new intraocular lenses (IOL) using the advantages of three-dimensional ultrasound biomicroscopy.

METHODS

An in vitro simulation device was designed to study IOL performance using an artificial capsular bag and a stretching device. The haptic region of the Akkommodative 1CU (HumanOptics AG) and CrystaLens AT-45 (Eyeonics Inc) was visualized in vitro in three dimensions, using an in-house developed three-dimensional ultrasound biomicroscope. The in vitro results were used to describe the in vivo situation in four patients with accommodative implants.

RESULTS

The haptic position and angulation in consideration of the accommodation state was distinguished and analyzed. In the simulation model, a maximal angulation change of 4.5 degrees and 4.3 degrees and a maximal forward shift of 0.33 mm and 0.28 mm was observed for the AT-45 and 1CU, respectively. In vivo, a change in haptic angulation <100 and a maximal forward shift of 0.50 mm was observed for the 1CU. These changes correspond to a theoretical approximate value of 0.50 diopters.

CONCLUSIONS

The in vitro simulation device examined with three-dimensional ultrasound biomicroscopy provided information on the accommodative performance of these potentially accommodative IOL designs. Using three-dimensional ultrasound biomicroscopy, corresponding changes in haptic angulation during pharmacological-induced accommodation were observed.

Accommodation measurements in a prepresbyopic and presbyopic population

PURPOSE

To study the efficacy of several subjective and objective methods of accommodation measurement in normal prepresbyopic and presbyopic populations to identify appropriate methods for measuring the outcome of accommodative restorative procedures.

SETTING

University of Houston, College of Optometry, Houston, Texas, USA.

METHODS

Thirty-one normal subjects with a mean age of 43.7 years (range 31 to 53 years) participated. Accommodation was measured monocularly using 3 subjective approaches--the push-up test, minus lenses to blur, and a focometer--and 2 approaches measured with a Hartinger coincidence refractometer, in which accommodation was stimulated with minus lenses to blur and topical pilocarpine 6%.

RESULTS

The push-up method overestimated accommodative amplitude relative to objective measures in 28 subjects. Two subjective methods, minus lenses to blur and the focometer, produced comparable results, but with lower amplitudes in younger subjects and higher amplitudes in older subjects compared with objective methods. Comparable results were obtained when accommodation was stimulated in 1 of 2 ways and measured with the Hartinger. Pilocarpine elicited stronger accommodative responses than distance blur for subjects with low accommodative amplitudes. Pilocarpine 6% produced stronger responses in subjects with light irides than in those with dark irides.

CONCLUSIONS

Hartinger-measured accommodation provides more realistic measurement of accommodative amplitude than the subjective methods tested, especially in the presbyopic population. In presbyopic subjects, the subjective tests resulted in accommodative amplitudes up to 4.0 diopters greater than those measured with objective tests. Measurements of accommodative amplitude are best achieved with objective methods to stimulate and measure accommodation.