The eye in focus: accommodation and presbyopia

Clinical application of accommodating intraocular lens

The present review describes recent advances in application of accommodating intraocular lenses (AIOLs). Standard monofocal intraocular lenses (MIOLs) only correct distance vision, while AIOLs are designed to allow both good distance vision and near vision, which is achieved through the contraction and relaxation of ciliary muscles by providing transformation of the axial movement or curvature of the lens. Thus, AIOLs may be a better choice for those patients who demand a higher level of visual performance. Since techniques to analyze the performance of AIOLs have not been standardized, and there is a variety of both subjective and objective methods, it is hard to measure the performance of these intraocular lenses. By evaluating advantages and disadvantages of various AIOLs, and introducing techniques for measurement the performance postoperative, this paper can provide some relative information on choosing the type of AIOLs in the clinic.

Is it possible to relate accommodative visual dysfunctions to neck pain?

The aim of this study was to establish whether there is a relationship between conditions of accommodative visual dysfunctions and cervical complaints. Fifty-two participants were included. Variables were accommodative amplitude, positive and negative relative accommodation (NRA), accommodative response, and accommodative facility. Subjects were classified as accommodative insufficiency, accommodative excess, or normal. Neck complaints were measured with the Neck Disability Index, the Visual Analogue Scale, and by cervical range of motion, deep flexor muscle activation score, and performance index. We found the following significant relationships: between NRA and both performance index and left-side bending; accommodative amplitude right-eye with right-side bending and with left-side bending; accommodative amplitude left-eye with right-side bending; and accommodative facility left-eye with both performance index and left-side bending. In accommodative amplitude right-eye, aIl participants showed significant values and greater than those with accommodative excess. In both groups, performance index values were decreased. Greater pain and lower right-rotation were found in participants with accommodative excess than in those with accommodative insufficiency. We conclude that accommodative dysfunctions are related to low performance index, decreased range of motion, as well as greater neck pain.

Correction of presbyopia: An integrated update for the practical surgeon

Presbyopia results from loss or insufficiency of the eye's accommodative ability, and clinically manifests as the inability to focus near objects on the retina. It is one of the most common causes of visual impairment worldwide especially in adults of productive or working age. Various means of compensating for the loss of accommodative ability have been devised from optical tools such as spectacles and contact lenses, to topical medications and to surgical procedures. A comprehensive search on journal articles about topical and surgical correction of presbyopia was undertaken. The various techniques for presbyopia correction, as enumerated in these articles, are discussed in this paper with the addition of our personal experience and perspective on the future of these techniques.

Near vision spectacle coverage and barriers to near vision correction among adults in the Cape Coast Metropolis of Ghana

PURPOSE

To determine the near vision spectacle coverage and barriers to obtaining near vision correction among adults aged 35 years and older in the Cape Coast Metropolis of Ghana.

METHODS

A population-based cross-sectional study design was adopted and 500 out of 576 participants aged 35 years and older were examined from 12 randomly selected clusters in Cape Coast, Ghana. All participants underwent a comprehensive eye examination which included: distance and near visual acuities measurements and external and internal ocular health assessments. Distance and near refractions were performed using subjective refraction technique. Information on participants' demographics, near vision correction status, near visual needs and barriers to acquiring near vision correction were obtained through a questionnaire administered as part of the study.

RESULTS

The mean age of participants was 52.3±10.3 years of whom 280 (56%) were females and 220 (44%) were males. The near vision spectacle coverage was 25%, 33% "met need" for near vision correction in the presbyopic population, and 64% unmet need in the entire study population. After controlling for other variables, age (5^th and 6^th decades) and educational level were associated with "met need" for near vision correction (OR=2.7 (1.55-4.68), p =0.00, and OR=2.36 (1.18-4.72), p=0.02 respectively). Among those who needed but did not have near vision correction, 64 (26%) did not feel the need for correction, 55 (22%) stated that they were unaware of available interventions, and 53 (21%) found the cost of near vision correction prohibitive.

CONCLUSION

There was a low near vision spectacle coverage in this population which suggests the need for strategies on health education and promotion to address the lack of awareness of spectacle need and cost of services.

Adaptation to Progressive Additive Lenses: Potential Factors to Consider

People develop presbyopia as part of the normal aging process. Most presbyopes adapt to progressive additive lens (PALs), while others do not. This investigation sought to determine whether the ability to modify disparity vergence or phoria was correlated to PALs adaptation. In experiment 1, a double-step paradigm quantified the ability to modify convergence responses in sixteen presbyopes. In experiment 2, thirty-one incipient presbyopes participated in a 5-minute sustained fixation task to evoke phoria adaptation where the magnitude and rate of phoria adaptation were measured. Then, the experiment was repeated after wearing PALs for one month. Linear regression analyses were conducted between the following parameters: near point of convergence, positive fusional vergence at near, vergence facility, net change in the magnitude of phoria adaptation, and the rate of phoria adaptation. The ability to change convergence average peak velocity was significantly greater (p < 0.03) in presbyopic PALs adapters compared to presbyopic PALs non-adapters. The rate of phoria adaptation and vergence facility were significantly greater (p < 0.03) in incipient presbyopic PALs adapters compared to incipient presbyopic PALs non-adapters. Vergence facility and the rate of phoria adaptation may have potential clinical utility in differentiating which patients may adapt to PALs and which ones will have more difficulty.

Ultrasound biomicroscopy value in evaluation of restoration of ciliary muscles contractility after cataract extraction

Purpose

To assess the changes in the contractility of the ciliary muscle in eyes with presbyopia before and after phacoemulsification and intracapsular lens implantation using ultrasound biomicroscopy (UBM).

Patients and methods

This prospective study included 50 eyes of 30 consecutive subjects operated at the Department of Ophthalmology. Patients with any ocular disorder affecting visual acuity, corneal surface irregularities, had posterior capsular perforation or intensive postoperative corneal edema, or were <35 years of age, were excluded. A clear corneal phacoemulsification and posterior chamber intraocular lens were implanted. UBM was performed with and without instilling 2% pilocarpine. Ciliary body axial length (CBAXL), anterior chamber depth, and angle were measured before and 1 month after surgery.

Results

The CBAXL showed a greater contractile shortening (P<0.5), with centripetal, contractile shift of ciliary muscle mass.

Conclusion

After phacoemulsification and intracapsular lens implantation, ultrasonic biomicroscopy showed significant centripetal movement of the ciliary body compared with that before surgery. This shows that a lenticular sclerotic component may influence both lens movement and the contractility of the ciliary muscle and is believed to be related to the presbyopia.

Does transient increase in axial length during accommodation attenuate with age?

Background

The aim was to profile transient accommodative axial length changes from early adulthood to advanced presbyopia and to determine whether any differences exist between the responses of myopic and emmetropic individuals.

Methods

Ocular biometry was measured by the LenStar biometer (Haag‐Streit, Switzerland) in response to zero, 3.00 and 4.50 D accommodative stimuli in 35 emmetropes and 37 myopes, aged 18 to 60 years. All results were corrected to reduce errors arising from the increase in crystalline lens thickness with accommodation. Accommodative responses were measured sequentially by the WAM 5500 Auto Ref/Keratometer (Grand Seiko, Hiroshima, Japan).

Results

Axial length increased significantly with accommodation (p < 0.001), with a mean corrected increase in axial length of 2 ± 18 µm and 8 ± 16 µm observed at 3.00 and 4.50 D, respectively. The magnitude of accommodative change in axial length was not dependent on refractive error classification (p = 0.959); however, a significant reduction in the magnitude and variance of axial length change was evident after 43 to 44 years of age (p < 0.002).

Conclusion

The negative association between transient increase in axial length and age, in combination with reduced variance of data after age 43 to 44 years, is consistent with a significant increase in posterior ocular rigidity, which may be influential in the development of presbyopia.

Evaluating relaxed ciliary muscle tone in presbyopic eyes

PURPOSE

Studies of age-related changes in ciliary muscle (CM) morphology and contractility have variously reported that CM weakens or strengthens with age. In response, the aim of this study was to evaluate relaxed CM tone in vivo in pre-presbyopic and presbyopic patients using a predictor value (P_CM).

METHODS

Two groups of eyes-40 eyes of 40 healthy volunteers with a mean age of 28.1 ± 5.8 years and 40 eyes of 40 healthy volunteers with a mean age of 56.6 ± 7.3 years-formed the sample for this prospective, observational cross-sectional study. Used to evaluate relaxed CM tone, P_CM was calculated as the difference between the change in mean anterior chamber depth (ACD) and lens thickness (LT) before and after cycloplegia, as measured with swept-source optical biometry.

RESULTS

The P_CM for relaxed CM tone was 0.04 ± 0.04 mm in pre-presbyopic participants, 0.06 ± 0.03 mm in presbyopic ones, and significantly greater in presbyopic patients (p = .018).

CONCLUSION

The statistical significance of P_CM between pre-presbyopic and presbyopic eyes might not signify clinical significance, since the difference was close to the repeatability limits for swept-source optical biometry. When relaxed, CM tone does not diminish with presbyopia according to changes in anterior chamber parameters due to cycloplegia.

Accommodation in human eye models: a comparison between the optical designs of Navarro, Arizona and Liou-Brennan

AIM

To simulate and compare accommodation in accommodative and non-accommodative human eye models.

METHODS

Ray tracing and optical design program was used. Three eye models were designed and studied: the Navarro, the Arizona and the Liou-Brennan. In order to make the Navarro and Liou-Brennan models to accommodate, specific geometric parameters of the models were altered with values that were chosen from the literature. For the Arizona model, its' mathematical functions for accommodation were used for the same accommodative demands. The simulation included four distances of accommodation for each model: at infinity, 3, 1 and 0.5 m.The results were diffraction images of a "letter F" for graphical comparison, spot diagrams on the retinal field and Modulation Transfer Function (MTF) graphs.

RESULTS

Zernike coefficients for the aberrations, Airy disk diameter, root mean square (RMS) error diameter and total axial length of the model were provided from the program. These were compared between them in all distances. The Navarro model had the smallest axial length change as a simple model. The Arizona did not change its axial length because it is designed to be accommodative. The Liou-Brennan model had different results concerning the aberrations because of the decentration of the pupil. The MTF graphs showed small differences between the models because of the differences in their designs.

CONCLUSION

All the three models are able to simulate accommodation with the expected results. There is no model that can be assumed as the best choice. Accommodation can be simulated in non-accommodativemodels and in customized ones.

Effect of Cycloplegia on Keratometric and Biometric Parameters in Keratoconus

Purpose. To obtain information about effect of cycloplegia on keratometry and biometry in keratoconus. Methods. 48 keratoconus (Group 1) and 52 healthy subjects (Group 2) were included in the study. We measured the flat meridian of the anterior corneal surface (K1), steep meridian of the anterior corneal surface (K2), lens thickness (LT), anterior chamber depth (ACD), and axial length (AL) using the Lenstar LS 900 before and after cycloplegia. Results. The median K1 in Group 1 was 45.64 D before and 45.42 D after cycloplegia, and the difference was statistically significant (P < 0.05). The median K2 in Group 1 was 50.96 D before and 50.17 D after cycloplegia, and the difference was significant (P < 0.05). The median K1 and K2 in Group 2 were 42.84 and 44.49 D, respectively, before cycloplegia, and 42.84 and 44.56 D after cycloplegia, and the differences were not statistically significant (all P > 0.05). There were significant differences in SE, LT, ACD, and RLP between before and after cycloplegia in either Group 1 (all P < 0.05) or Group 2 (all P < 0.05). There were not statistically significant differences in AL between before cycloplegia and after cycloplegia in either Group 1 (P = 0.533) or group 2 (P = 0.529). Conclusions. Flattened corneal curvature and increase in ACD following cycloplegia in keratoconus patients were detected.

Changes in Ocular Parameters and Intraocular Lens Powers in Aging Cycloplegic Eyes

PURPOSE

Age-related changes in lens elasticity and ciliary muscle contractility can affect how ocular parameters respond to cycloplegia, and therefore intraocular lens (IOL) power measurements calculated by formulas using anterior chamber depth (ACD), lens thickness (LT), or white-to-white (WtW) for effective lens position prediction can vary. In response, using swept-source optical biometry in prepresbyopic and presbyopic eyes, we investigated changes in ocular parameters and IOL power calculations attributable to cycloplegia.

DESIGN

Cross-sectional study.

METHODS

In 38 prepresbyopic and 42 presbyopic eyes, we measured pupil diameter, radius of corneal curvature values, central corneal thickness, WtW, ACD, LT, and axial length both before and after cycloplegia. We determined IOL power calculations with the Sanders-Retzlaff-Kraff/theoretical, Holladay 2, and Haigis formulas. To pinpoint the effect of cycloplegia, we recorded refractive predictions in pre- and postdilation conditions according to the same IOL power calculations, even if postdilation IOL power calculations had changed.

RESULTS

With cycloplegia, pupil diameter changed significantly more in presbyopic eyes (P < .001). Central corneal thickness decreased in prepresbyopic eyes (P = .048), whereas WtW increased in presbyopic eyes (P = .02). In both groups, ACD and LT changed significantly (P < .001). IOL power calculations according to the Holladay 2 formula differed in prepresbyopic eyes (P = .042), and refractive predictions with the Holladay 2 and Haigis formulas differed significantly in prepresbyopic eyes (P = .043 and P = .022, respectively).

CONCLUSION

Surgeons should consider the effect of cycloplegia on refractive prediction errors and IOL power calculations determined with Haigis and Holladay 2 formulas, especially in prepresbyopic ages.

The impact of intraocular pressure on elastic wave velocity estimates in the crystalline lens

Intraocular pressure (IOP) is believed to influence the mechanical properties of ocular tissues including cornea and sclera. The elastic properties of the crystalline lens have been mainly investigated with regard to presbyopia, the age-related loss of accommodation power of the eye. However, the relationship between the elastic properties of the lens and IOP remains to be established. The objective of this study is to measure the elastic wave velocity, which represents the mechanical properties of tissue, in the crystalline lens ex vivo in response to changes in IOP. The elastic wave velocities in the cornea and lens from seven enucleated bovine globe samples were estimated using ultrasound shear wave elasticity imaging. To generate and then image the elastic wave propagation, an ultrasound imaging system was used to transmit a 600 µs pushing pulse at 4.5 MHz center frequency and to acquire ultrasound tracking frames at 6 kHz frame rate. The pushing beams were separately applied to the cornea and lens. IOP in the eyeballs was varied from 5 to 50 mmHg. The results indicate that while the elastic wave velocity in the cornea increased from 0.96  ±  0.30 m s^-1 to 6.27  ±  0.75 m s^-1 as IOP was elevated from 5 to 50 mmHg, there were insignificant changes in the elastic wave velocity in the crystalline lens with the minimum and the maximum speeds of 1.44  ±  0.27 m s^-1 and 2.03  ±  0.46 m s^-1, respectively. This study shows that ultrasound shear wave elasticity imaging can be used to assess the biomechanical properties of the crystalline lens noninvasively. Also, it was observed that the dependency of the crystalline lens stiffness on the IOP was significantly lower in comparison with that of cornea.

Clinical outcomes of combined versus separate carbachol and brimonidine drops in correcting presbyopia

Background

To test and compare in a masked fashion the efficacy of using a parasympathomimetic drug (3% carbachol) and an alpha-2 agonist (0.2% brimonidine) in both combined and separate forms to create optically beneficial miosis to pharmacologically improve vision in presbyopia.

Methods

A prospective, double-masked, randomized, controlled clinical trial was conducted. Ten naturally emmetropic and presbyopic subjects between 42 and 58 years old with uncorrected distance visual acuity of at least 20/20 in both eyes without additional ocular pathology were eligible for inclusion. All subjects received 3% carbachol and 0.2% brimonidine in both combined and separate forms, 3% carbachol alone and 0.2% brimonidine (control) alone in their non-dominant eye in a crossover manner with one week washout between tests. The subjects’ pupil sizes and both near and distance visual acuities will be evaluated pre- and post-treatment at 1, 2, 4, and 8 h, by a masked examiner at the same room illumination.

Results

Statistically significant improvement in mean near visual acuity (NVA) was achieved in all subjects who received combined 3% carbachol and 0.2% brimonidine in the same formula compared with those who received separate forms or carbachol alone or brimonidine alone (P < 0.0001).

Conclusion

Based on the data, the combined solution demonstrated greater efficacy than the other solutions that were tested. Improving the depth of focus by making the pupil small caused statistically significant improvement in near visual acuity, with no change in binocular distance vision.

Trial registration

ACTRN12616001565437. Registered 11 November 2016.

Comparison of Anterior Segment Parameters Obtained by Dual-Scheimpflug Analyzer Before and After Cycloplegia in Children

PURPOSE

To assess the changes of anterior segment parameters with cycloplegia.

METHODS

A cross-sectional study of healthy pediatric patients was performed. Anterior segment parameters were obtained by the Galilei Dual-Scheimpflug analyzer (Ziemer Group, Port, Switzerland) before and 40 minutes after the instillation of cyclopentolate. The effect of gender was evaluated.

RESULTS

There were 43 boys and 50 girls with a mean age of 7.76 ± 2.7 years. There was a significant increase in anterior chamber depth, anterior chamber volume, and pupil diameter after the cycloplegia (P < .05). The anterior chamber angle increased after cycloplegia in the nasal, temporal, and inferior quadrants (P < .05), but not in the superior quadrant (P > .05). The mean values of anterior segment parameters were similar in both genders.

CONCLUSIONS

The values of anterior chamber depth, anterior chamber volume, anterior chamber angle, and pupil diameter measured with the Galilei Dual-Scheimpflug analyzer increased significantly after cycloplegia. Gender did not have an effect on anterior segment parameters. [J Pediatr Ophthalmol Strabismus. 2016;53(4):234-237.].

An overlooked effect of systemic anticholinergics: alteration on accommodation amplitude

AIM

To investigate the effect of oral solifenacin succinate, tolterodine-L-tartarate and oxybutinin hydrochloride (HCl) on accommodation amplitude.

METHODS

Female overactive bladder syndrome (OAB) patients who were planned to use oral anticholinergics, patients that uses solifenacin succinate 5 mg (Group I, n=25), tolterodine-L-tartarate 4 mg (Group II, n=25), and oxybutinin HCl 5 mg b.i.d (Group III, n=25) and age matched healthy female subjects (Group IV, n=25) were recruited and complete ophthalmological examination and accommodation amplitude assessment were done at baseline and 4wk after initiation of treatment.

RESULTS

The mean age of 100 consecutive female subjects was 51.6±5.7 (40-60)y and there were no statistically significant difference with regard to the mean age (P=0.107) and baseline accommodation amplitude (P=0.148) between study groups. All treatment groups showed a significant decrease in accommodation amplitude following a 4-week course of anticholinergic treatment (P=0.008 in Group I, P=0.002 in Group II, P=0.001 in Group III), but there was no statistically significant difference in Group IV (P=0.065).

CONCLUSION

A 4-week course of oral anticholinergic treatment have statistically significant effect on accommodation amplitude. Clinicians should avoid both overestimating this result, as this would unnecessarily restrict therapeutic possibilities, and also underestimating it which may lead to drug intolerance.

Wavefront Derived Refraction and Full Eye Biometry in Pseudophakic Eyes

Purpose

To assess wavefront derived refraction and full eye biometry including ciliary muscle dimension and full eye axial geometry in pseudophakic eyes using spectral domain OCT equipped with a Shack-Hartmann wavefront sensor.

Methods

Twenty-eight adult subjects (32 pseudophakic eyes) having recently undergone cataract surgery were enrolled in this study. A custom system combining two optical coherence tomography systems with a Shack-Hartmann wavefront sensor was constructed to image and monitor changes in whole eye biometry, the ciliary muscle and ocular aberration in the pseudophakic eye. A Badal optical channel and a visual target aligning with the wavefront sensor were incorporated into the system for measuring the wavefront-derived refraction. The imaging acquisition was performed twice. The coefficients of repeatability (CoR) and intraclass correlation coefficient (ICC) were calculated.

Results

Images were acquired and processed successfully in all patients. No significant difference was detected between repeated measurements of ciliary muscle dimension, full-eye biometry or defocus aberration. The CoR of full-eye biometry ranged from 0.36% to 3.04% and the ICC ranged from 0.981 to 0.999. The CoR for ciliary muscle dimensions ranged from 12.2% to 41.6% and the ICC ranged from 0.767 to 0.919. The defocus aberrations of the two measurements were 0.443 ± 0.534 D and 0.447 ± 0.586 D and the ICC was 0.951.

Conclusions

The combined system is capable of measuring full eye biometry and refraction with good repeatability. The system is suitable for future investigation of pseudoaccommodation in the pseudophakic eye.

A survey of the criteria for prescribing in cases of borderline refractive errors

PURPOSE

This research investigated the reported optometric prescribing criteria of Israeli optometrists.

METHODS

An online questionnaire based on previous studies was distributed via email and social networking sites to optometrists in Israel. The questionnaire surveyed the level of refractive error at which respondents would prescribe for different types of refractive error at various ages with and without symptoms.

RESULTS

124 responses were obtained, yielding a response rate of approximately 12-22%, 92% of whom had trained in Israel. For all refractive errors, the presence of symptoms strongly influenced prescribing criteria. For example, for 10-20 year old patients the degree of hyperopia for which 50% of practitioners would prescribe is +0.75 D in the presence of symptoms but twice this value (+1.50 D) in the absence of symptoms. As might be expected, optometrists prescribed at lower degrees of hyperopia for older compared with younger patients. There was a trend for more experienced practitioners to be less likely to prescribe for lower degrees of myopia and presbyopia. Practitioner gender, country of training, the type of practice environment, and financial incentives were not strongly related to prescribing criteria.

CONCLUSIONS

The prescribing criteria found in this study are broadly comparable with those in previous studies and with published prescribing guidelines. Subtle indications suggest that optometrists may become more conservative in their prescribing criteria with experience.

Changes of Accommodative Power in Vitrectomized Eyes with Crystalline Lenses

PURPOSE

To evaluate changes of accommodative power in phakic eyes after uneventful pars plana vitrectomy (PPV) in patients aged younger than 45 years without presbyopia.

METHODS

We investigated patients aged younger than 45 years who underwent PPV without crystalline lens extraction because of vitreoretinal disorders. Twelve weeks after vitrectomy, the near point of accommodation, high-frequency component of accommodative microfluctuation, axial length, and anterior chamber depth of vitrectomized and contralateral nonvitrectomized eyes were examined.

RESULTS

Ten eyes of 10 patients were included. The average patient age was 39.8 (±4.3) years. None experienced cataract progression in the vitrectomized eye up to 12 weeks after surgery. Near point of accommodation was significantly lower in the vitrectomized eye than in the opposite eye at 12 weeks after vitrectomy (5.23 [±1.39] diopters vs. 5.91 [±1.83] diopters, p < 0.001). The high-frequency components in the vitrectomized eyes were significantly greater than those in the contralateral eyes (p = 0.01). However, anterior chamber depth and axial length were similar in value to the preoperative observations.

CONCLUSIONS

Uneventful PPV in relatively young patients without presbyopia reduced accommodative power during the early postoperative period with no cataract progression.

Measurement of Crystalline Lens Volume During Accommodation in a Lens Stretcher

PURPOSE

To determine if the lens volume changes during accommodation.

METHODS

The study used data acquired on 36 cynomolgus monkey lenses that were stretched in a stepwise fashion to simulate disaccommodation. At each step, stretching force and dioptric power were measured and a cross-sectional image of the lens was acquired using an optical coherence tomography system. Images were corrected for refractive distortions and lens volume was calculated assuming rotational symmetry. The average change in lens volume was calculated and the relation between volume change and power change, and between volume change and stretching force, were quantified. Linear regressions of volume-power and volume-force plots were calculated.

RESULTS

The mean (± SD) volume in the unstretched (accommodated) state was 97 ± 8 mm3. On average, there was a small but statistically significant (P = 0.002) increase in measured lens volume with stretching. The mean change in lens volume was +0.8 ± 1.3 mm3. The mean volume-power and volume-load slopes were -0.018 ± 0.058 mm3/D and +0.16 ± 0.40 mm3/g.

CONCLUSIONS

Lens volume remains effectively constant during accommodation, with changes that are less than 1% on average. This result supports a hypothesis that the change in lens shape with accommodation is accompanied by a redistribution of tissue within the capsular bag without significant compression of the lens contents or fluid exchange through the capsule.

Dynamic imaging of accommodation by swept-source anterior segment optical coherence tomography

PURPOSE

To study the accommodation process in normal eyes using a commercially available clinical system based on swept-source anterior segment optical coherence tomography (AS-OCT).

SETTING

Ophthalmology Department, University of Parma, Italy.

DESIGN

Evaluation of diagnostic technology.

METHODS

Right eyes were analyzed using swept-source AS-OCT (Casia SS-1000). The optical vergence of the internal coaxial fixation target was adjusted during imaging to obtain monocular accommodation stimuli with different amplitudes (0, 3.0, 6.0, and 9.0 diopters [D]). Overlapping of real and conjugate OCT images enabled imaging of all the anterior segment optical surfaces in a single frame. Central corneal thickness (CCT), anterior chamber depth (ACD), and lens thickness were extracted from the OCT scans acquired at different static accommodation stimulus amplitudes. The crystalline lens was analyzed dynamically during accommodation and disaccommodation by acquiring sequential OCT images of the anterior segment at a rate of 8 frames per second. The lens thickness was extracted from the temporal sequence of OCT images and plotted as a function of time.

RESULTS

The study analyzed 14 eyes of 14 subjects aged 18 to 46 years. During accommodation, the decrease in the ACD was statistically significant (P < .05), as were the increase in the lens thickness (P < .001) and the slight movement forward of the lens central point (P < .01). The CCT and anterior chamber width measurements did not change statistically significantly during accommodation. The lens thickness at 0 D was positively correlated with age (P < .01).

CONCLUSION

High-resolution real-time imaging and biometry of the accommodating anterior segment can be effectively performed using a commercially available swept-source AS-OCT clinical device.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Assessing age-related changes in the biomechanical properties of rabbit lens using a coaligned ultrasound and optical coherence elastography system

PURPOSE

To evaluate the capability of a novel, coaligned focused ultrasound and phase-sensitive optical coherence elastography (US-OCE) system to assess age-related changes in biomechanical properties of the crystalline lens in situ.

METHODS

Low-amplitude elastic deformations in young and mature rabbit lenses were measured by an US-OCE system consisting of a spectral-domain optical coherence tomography (OCT) system coaligned with a focused ultrasound system used to produce a transient force on the lens surface. Uniaxial compressional tests were used to validate the OCE data.

RESULTS

The OCE measurements showed that the maximum displacements of the young rabbit lenses were significantly larger than those of the mature lenses, indicating a gradual increase of the lens stiffness with age. Temporal analyses of the displacements also demonstrate a similar trend of elastic properties in these lenses. The stress-strain measurements using uniaxial mechanical tests confirmed the results obtained by the US-OCE system.

CONCLUSIONS

The results demonstrate that the US-OCE system can be used for noninvasive analysis and quantification of lens biomechanical properties in situ and possibly in vivo.

Biometry of anterior segment of human eye on both horizontal and vertical meridians during accommodation imaged with extended scan depth optical coherence tomography

Purpose

To determine the biometry of anterior segment dimensions of the human eye on both horizontal and vertical meridians with extended scan depth optical coherence tomography (OCT) during accommodation.

Methods

Twenty pre-presbyopic volunteers, aged between 24 and 30, were recruited. The ocular anterior segment of each subject was imaged using an extended scan depth OCT under non- and 3.0 diopters (D) of accommodative demands on both horizontal and vertical meridians. All the images were analyzed to yield the following parameters: pupil diameter (PD), anterior chamber depth (ACD), anterior and posterior surface curvatures of the crystalline lens (ASC and PSC) and the lens thickness (LT). Two consecutive measurements were performed to assess the repeatability and reproducibility of this OCT. They were evaluated by calculating the within-subject standard deviation (SD), a paired t-test, intra-class correlation coefficients (ICC) and the coefficient of repeatability/reproducibility (CoR).

Results

There were no significant differences between two consecutive measurements on either horizontal or vertical meridians under both two different accommodative statuses (P>0.05). The ICC for all parameters ranged from 0.775 to 0.998, except for the PSC (0.550) on the horizontal meridian under the non-accommodative status. In addition, the CoR for most of the parameters were excellent (0.004% to 4.89%). In all the parameters, only PD and PSC were found different between the horizontal and vertical meridians under both accommodative statuses (P<0.05). PD, ACD, ASC and PSC under accommodative status were significantly smaller than those under the non-accommodative status, except that the PSC at the vertical meridian did not change. In addition, LT was significantly increased when accommodation.

Conclusion

The extended scan depth OCT successfully measured the dimensions of the anterior eye during accommodation with good repeatability and reproducibility on both horizontal and vertical meridians. The asymmetry of lens posterior surface and oval-shaped pupil were found during accommodation.

Apparent progression of presbyopia after laser in situ keratomileusis in patients with early presbyopia

PURPOSE

To assess the effect of laser in situ keratomileusis (LASIK) on near visual function in presbyopic patients.

DESIGN

Retrospective cohort study.

METHODS

Fifty-three eyes of 40 patients 45 years of age and older who had undergone LASIK for high myopia (-6 diopters [D] and over) were included. The minimal add powers for obtaining the best-corrected near visual acuity (add powers) were measured preoperatively and 3 months postoperatively, and the correlations with the powers corrected by LASIK, corneal higher-order aberrations (HOAs), ocular HOAs, and patient ages were evaluated using univariate analysis. Factors correlated with the changes in add powers were evaluated further by multivariate analysis.

RESULTS

The mean ± standard deviation patient age was 50.0 ± 4.1 years; the power corrected by LASIK was -7.56 ± 1.06 D. The mean add power was 1.80 ± 0.60 D preoperatively, which increased significantly (P < .001) to 2.18 ± 0.69 D postoperatively. Significant correlations with the increased add powers were detected with age (P = .01) and the power corrected by LASIK (P = .04) but not with corneal and ocular HOAs (P > .05). Multivariate analysis showed that only age was correlated significantly (P = .01). The percentage of eyes with increased add powers of 0.5 D or more was 60.4%, which was significantly (P = .02) higher in younger patients.

CONCLUSIONS

This study verified the apparent progression of presbyopia after LASIK and the importance of obtaining informed consent from patients, especially those with early presbyopia.

Measurement of wavefront aberrations and lens deformation in the accommodated eye with optical coherence tomography-equipped wavefront system

To quantitatively approach the relationship between optical changes in an accommodated eye and the geometrical deformation of its crystalline lens, a long scan-depth anterior segment OCT equipped wavefront sensor was developed and integrated with a Badal system. With this system, accommodation was stimulated up to 6.0D in the left eye and also measured in the same eye for three subjects. High correlations between the accommodative responses of refractive power and the radius of the anterior lens surface were found for the three subjects (r>0.98). The change in spherical aberration was also highly correlated with the change in lens thickness (r>0.98). The measurement was very well repeated at a 2nd measurement session on the same day for the three subjects and after two weeks for one subject. The novelty of incorporating the Badal system into the OCT equipped wavefront sensor eliminated axial misalignment of the measurement system with the test eye due to accommodative vergence, as in the contralateral paradigm. The design also allowed the wavefront sensor to capture conjugated sharp Hartmann-Shack images in accommodated eyes to accurately analyze wavefront aberrations. In addition, this design extended the accommodation range up to 10.0D. By using this system, for the first time, we demonstrated linear relationships of the changes between the refractive power and the lens curvature and also between the spherical aberration and the lens thickness during accommodation in vivo. This new system provides an accurate and useful technique to quantitatively study accommodation.

Developments in the correction of presbyopia II: surgical approaches

PURPOSE

To discuss the various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances.

CONTENT

Static methods broadly adopt the same optical techniques as those used in presbyopic contact lens correction and aim to satisfy the needs of the presbyope by increasing binocular depth-of-focus, often using monovision as well as simultaneous-imagery. Dynamic methods generally attempt to make use of at least some of the still-active elements of the accommodation system. They include procedures which are supposed to modify the relative geometry of the ciliary muscle and lens, or which reduce the stiffness of the presbyopic lens either by replacing it with other natural or man-made material or by subjecting it to femtosecond laser treatment. Alternatively the natural lens may be replaced by some form of intraocular lens which changes power as a result of forces derived from the still-active ciliary muscle, zonule and capsule, or other sources.

CONCLUSIONS

At present, multifocal intraocular lenses appear to offer the most consistent and reliable surgical approach to surgical presbyopic correction. They have obvious advantages in convenience and stability over optically-similar, simultaneous-image presbyopic contact lenses but this must be balanced against their relative inflexibility in cases of patient dissatisfaction. Dynamic methods remain largely experimental. Although some approaches show promise, as yet no method has demonstrated a reliable, long-term ability to correct distance refractive error and to appropriately change ocular power in response to changes in viewing distance over the normal range of interest.

Presbyopia: a pilot investigation of the barriers and benefits of near visual acuity correction among a rural Filipino population

Background

Presbyopia is the age-related decline in accommodation that diminishes the ability of the eye to focus on near objects. Presbyopia is common and easy to correct; however, many communities lack access to basic eye care. The purpose of this project was to assess the burden of uncorrected presbyopia in a rural Filipino population and to pilot an intervention aimed at increasing access to reading glasses in the community.

Methods

Individuals above the age of 40 who presented to a health outreach in the Philippines were invited to undergo a near vision exam to detect the presence of functional presbyopia and be fitted with ready-made, single-vision glasses. The change in stereoacuity was used as a surrogate measure of functional improvement after near vision correction. A questionnaire was administered to assess this population’s perceived barriers and benefits to correcting near vision.

Results

The average age of the participants was 57 ± 11 years, with 87.6% of participants having an uncorrected near visual acuity of <20/50. Reading glasses improved near vision to 20/40 or better in 77.7% of participants having near-vision impairment (uncorrected near visual acuity of <20/40). Over 75% of participants also showed improvement in stereoacuity. Cost, rather than availability, was perceived to be the greater barrier to the procurement of glasses, and 84% of participants reported that the glasses dispensed would greatly improve their ability to earn a living.

Conclusions

Dispensing ready-made, single-vision glasses is a simple and cost-effective intervention to improve near vision and enhance depth perception. A greater understanding of the barriers and benefits to correcting near vision will inform the design and execution of a sustainable program to correct presbyopia in developing countries.

Lens extrusion from Laminin alpha 1 mutant zebrafish

We report analysis of the ocular lens phenotype of the recessive, larval lethal zebrafish mutant, lama1^a69/a69. Previous work revealed that this mutant has a shortened body axis and eye defects including a defective hyaloid vasculature, focal corneal dysplasia, and loss of the crystalline lens. While these studies highlight the importance of laminin α1 in lens development, a detailed analysis of the lens defects seen in these mutants was not reported. In the present study, we analyze the lenticular anomalies seen in the lama1^a69/a69 mutants and show that the lens defects result from the anterior extrusion of lens material from the eye secondary to structural defects in the lens capsule and developing corneal epithelium associated with basement membrane loss. Our analysis provides further insights into the role of the lens capsule and corneal basement membrane in the structural integrity of the developing eye.

Retinal image quality during accommodation

PURPOSE

We asked if retinal image quality is maximum during accommodation, or sub-optimal due to accommodative error, when subjects perform an acuity task.

METHODS

Subjects viewed a monochromatic (552 nm), high-contrast letter target placed at various viewing distances. Wavefront aberrations of the accommodating eye were measured near the endpoint of an acuity staircase paradigm. Refractive state, defined as the optimum target vergence for maximising retinal image quality, was computed by through-focus wavefront analysis to find the power of the virtual correcting lens that maximizes visual Strehl ratio.

RESULTS

Despite changes in ocular aberrations and pupil size during binocular viewing, retinal image quality and visual acuity typically remain high for all target vergences. When accommodative errors lead to sub-optimal retinal image quality, acuity and measured image quality both decline. However, the effect of accommodation errors of on visual acuity are mitigated by pupillary constriction associated with accommodation and binocular convergence and also to binocular summation of dissimilar retinal image blur. Under monocular viewing conditions some subjects displayed significant accommodative lag that reduced visual performance, an effect that was exacerbated by pharmacological dilation of the pupil.

CONCLUSIONS

Spurious measurement of accommodative error can be avoided when the image quality metric used to determine refractive state is compatible with the focusing criteria used by the visual system to control accommodation. Real focusing errors of the accommodating eye do not necessarily produce a reliably measurable loss of image quality or clinically significant loss of visual performance, probably because of increased depth-of-focus due to pupil constriction. When retinal image quality is close to maximum achievable (given the eye's higher-order aberrations), acuity is also near maximum. A combination of accommodative lag, reduced image quality, and reduced visual function may be a useful sign for diagnosing functionally-significant accommodative errors indicating the need for therapeutic intervention.

Developments in the correction of presbyopia I: spectacle and contact lenses

PURPOSE

To outline the refractive problems associated with presbyopia and to review the basis and relative merits of currently-available methods for their correction, with detailed consideration of spectacle and contact lens approaches.

CONTENTS

In the developed world, most of the present population will spend roughly half their lives as presbyopes. The well-known presbyopic changes with age in amplitude of accommodation and required near addition are briefly reviewed, together with the less widely acknowledged slow drifts that occur in distance refraction. The desirability of restoring to presbyopes clear vision for objects at any distance, ideally corresponding to vergences within the range of at least 0 to -5 D, in any viewing direction, is stressed. A general outline is given of possible corrective methods. Methods which satisfy the needs of a 50 year-old may not be suitable for the 80 year-old. Corrections may involve both fixed- and variable-focus lens systems, and surgical methods which modify the optics of the cornea, replace the crystalline lens with different fixed optics, or attempt to at least partially restore active accommodation. Some more recent methods of spectacle and contact lens correction are described in more detail. Particular attention is given to recent commercially-developed spectacles in which the corrective power can be varied actively by either mechanical (liquid-filled deformable lenses or Alvarez lenses) or electrical (liquid crystal lenses) means to allow objects at different distances to be seen clearly. Contact lens corrections show less progress and are still preferred only by a minority of older patients, most of whom are early presbyopes.

SUMMARY

The rising proportion of presbyopes in the population, covering an age span of around 40 years, represents both a problem for those concerned with giving their patients the best vision possible at both far and near viewing distances and a commercial opportunity. Traditional single-vision distance and near, bifocal, and progressive spectacle lens solutions, together with contact lens modalities for presbyopic correction, are being challenged by a variety of new approaches. It remains to be seen whether the latter will receive wide acceptance in practice.

The mechanical properties of ex vivo bovine and porcine crystalline lenses: age-related changes and location-dependent variations

The mechanical properties of ex vivo animal lenses from three groups were evaluated: old bovine (25-30 mo old, n = 4), young bovine (6 mo old, n = 4) and young porcine (6 mo old, n = 4) eye globes. We measured the dynamics of laser-induced microbubbles created at different locations within the crystalline lenses. An impulsive acoustic radiation force was applied to the microbubble, and the microbubble displacements were measured using a custom-built high pulse repetition frequency ultrasound system. Based on the measured dynamics of the microbubbles, Young's moduli of bovine and porcine lens tissue in the vicinity of the microbubbles were reconstructed. Age-related changes and location-dependent variations in the Young's modulus of the lenses were observed. Near the center, the old bovine lenses had a Young's modulus approximately fivefold higher than that of young bovine and porcine lenses. The gradient of Young's modulus with respect to radial distance was observed in the lenses from three groups.

The horizontal dark oculomotor rest position

BACKGROUND

This study sought to investigate whether eye dominance and age are related to the stimulus-free oculomotor resting state described via the dark disconjugate position (near or far), the dark conjugate position (left to right), and the near dissociated phoria.

METHODS

Nineteen non-presbyopes and 25 presbyopes with normal binocular vision participated in two identical sessions. The left-eye and the right-eye positions were recorded using a video-based infrared eye tracker while the subjects were in total darkness. Dark disconjugate responses and dark conjugate responses were calculated by computing the difference and the average of the left-eye and the right-eye response, respectively. The right-eye decaying to the phoria level was recorded for 15 s.

RESULTS

A one-way ANOVA assessed statistical differences in dark conjugate and dark disconjugate positions, comparing 1) the right-eye and the left-eye sensory and/or motor dominant groups and 2) the non-presbyope and presbyope groups. The test-retests of the dark disconjugate position, the dark conjugate position and the near dissociated heterophoria were high between sessions (r > 0.85; p < 0.00001). For non-presbyopes the right-eye (left-eye) motor and sensory dominant subjects showed a rightward (leftward) dark conjugate position (p < 0.01). The dark disconjugate position was receded in presbyopes compared to non-presbyopes (p < 0.0001).

CONCLUSION

The data support that the left-eye, or the right-eye, motor and sensory dominance predicts the direction of the dark conjugate position. Future studies could investigate the underlying neural substrates that may, in part, contribute to the resting state of the oculomotor system in a stimulus-free environment. Knowledge of the brain-behavior governing visual-field preference has implications for understanding the natural aging process of the visual system.

Quantification of age-related and per diopter accommodative changes of the lens and ciliary muscle in the emmetropic human eye

PURPOSE

To calculate age-related and per diopter (D) accommodative changes in crystalline lens and ciliary muscle dimensions in vivo in a single cohort of emmetropic human adults ages 30 to 50 years.

METHODS

The right eyes of 26 emmetropic adults were examined using ultrasonography, phakometry, anterior segment optical coherence tomography, and high resolution magnetic resonance imaging. Accommodation was measured both subjectively and objectively.

RESULTS

In agreement with previous research, older age was linearly correlated with a thicker lens, steeper anterior lens curvature, shallower anterior chamber, and lower lens equivalent refractive index (all P < 0.01). Age was not related to ciliary muscle ring diameter (CMRD) or lens equatorial diameter (LED). With accommodation, lens thickness increased (+0.064 mm/D, P < 0.001), LED decreased (-0.075 mm/D, P < 0.001), CMRD decreased (-0.105 mm/D, P < 0.001), and the ciliary muscle thickened anteriorly (+0.013 to +0.026 mm/D, P < 0.001) and thinned posteriorly (-0.011 to -0.015, P < 0.01). The changes per diopter of accommodation in LED, CMRD, and ciliary muscle thickness were not related to subject age.

CONCLUSIONS

The per diopter ciliary muscle contraction is age independent, even as total accommodative amplitude declines. Quantifying normal biometric dimensions of the accommodative structures and changes with age and accommodative effort will further the development of new IOLs designed to harness ciliary muscle forces.

Accommodative changes in human eye observed by Kitasato anterior segment optical coherence tomography

PURPOSE

To study accommodative changes in the human lens using swept-source optical coherence tomography (Kitasato anterior segment OCT/KAs-OCT), which can image the whole anterior segment of the eye.

METHODS

Thirty-five healthy subjects (mean age 41 years, range 13-79 years) were recruited. Using KAs-OCT, we measured the curvature of the anterior (ASC) and posterior surfaces (PSC), the thickness (LT) of the lens and the anterior chamber depth (ACD) in response to far (0.4 D) and near (10 D) accommodative stimuli.

RESULTS

In response to accommodative stimuli (0.4/10 D), the mean values ± standard deviations were: radius of ASC, 9.72 ± 2.53/7.84 ± 1.85 mm (Wilcoxon ranked-sign test, p < 0.0001); radius of PSC, 5.06 ± 0.71/4.70 ± 0.76 mm (p = 0.0012); LT, 3.86 ± 0.77/4.00 ± 0.76 mm (p < 0.0001); ACD, 2.72 ± 0.61/2.61 ± 0.54 mm (p = 0.0002). The rate of accommodation-associated changes in ASC, LT, and ACD showed significant correlation with aging (Pearson correlation coefficient: r = -0.725, p < 0.0001; r = -0.626, p = 0.0001; r = -0.720, p < 0.0001, respectively), but there was no such correlation in PSC (r = -0.064, p = 0.401).

CONCLUSION

The radius of ASC and PSC decreased with accommodation, and the rates of changes in ASC were larger than those in PSC.

Anterior segment biometry during accommodation imaged with ultralong scan depth optical coherence tomography

PURPOSE

To measure by ultralong scan depth optical coherence tomography (UL-OCT) dimensional changes in the anterior segment of human eyes during accommodation.

DESIGN

Evaluation of diagnostic test or technology.

PARTICIPANTS

Forty-one right eyes of healthy subjects with a mean age of 34 years (range, 22-41 years) and a mean refraction of -2.5 ± 2.6 diopters were imaged in 2 repeated measurements at minimal and maximal accommodations.

METHODS

A specially adapted and designed UL-OCT instrument was used to image from the front surface of the cornea to the back surface of the crystalline lens. Custom software corrected the optical distortion of the images and yielded the biometric measurements. The coefficient of repeatability and the intraclass correlation coefficient were calculated to evaluate the repeatability and reliability.

MAIN OUTCOME MEASURES

Anterior segment parameters and associated repeatability and reliability upon accommodation. The dimensional results included central corneal thickness (CCT), anterior chamber depth and width (ACD, ACW), pupil diameter (PD), lens thickness (LT), anterior segment length (ASL = ACD + LT), lens central position (LCP = ACD + 1/2LT), and horizontal radii of the lens anterior and posterior surface curvatures (LAC, LPC).

RESULTS

Repeated measurements of each variable within each accommodative state did not differ significantly (P>0.05). The coefficients of repeatability (CORs) and intraclass correlation coefficients for CCT, ACW, ACD, LT, LCP, and ASL were excellent (1.2%- 3.59% and 0.998-0.877, respectively). They were higher for PD (18.90%-21.63% and 0.880-0.874, respectively) and moderate for LAC and LPC (34.86%-42.72% and 0.669-0.251, respectively) in the 2 accommodative states. Compared with minimal accommodation, PD, ACD, LAC, LPC, and LCP decreased and LT and ASL increased significantly at maximal accommodation (P<0.05), whereas CCT and ACW did not change (P>0.05).

CONCLUSIONS

The UL-OCT measured changes in anterior segment dimensions during accommodation with good repeatability and reliability. During accommodation, the back surface of the lens became steeper as the lens moved forward.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

A high pulse repetition frequency ultrasound system for the ex vivo measurement of mechanical properties of crystalline lenses with laser-induced microbubbles interrogated by acoustic radiation force

A high pulse repetition frequency ultrasound system for an ex vivo measurement of mechanical properties of an animal crystalline lens was developed and validated. We measured the bulk displacement of laser-induced microbubbles created at different positions within the lens using nanosecond laser pulses. An impulsive acoustic radiation force was applied to the microbubble, and spatio-temporal measurements of the microbubble displacement were assessed using a custom-made high pulse repetition frequency ultrasound system consisting of two 25 MHz focused ultrasound transducers. One of these transducers was used to emit a train of ultrasound pulses and another transducer was used to receive the ultrasound echoes reflected from the microbubble. The developed system was operating at 1 MHz pulse repetition frequency. Based on the measured motion of the microbubble, Young's moduli of surrounding tissue were reconstructed and the values were compared with those measured using the indentation test. Measured values of Young's moduli of four bovine lenses ranged from 2.6 ± 0.1 to 26 ± 1.4 kPa, and there was good agreement between the two methods. Therefore, our studies, utilizing the high pulse repetition frequency ultrasound system, suggest that the developed approach can be used to assess the mechanical properties of ex vivo crystalline lenses. Furthermore, the potential of the presented approach for in vivo measurements is discussed.

High refractive index polysiloxane as injectable, in situ curable accommodating intraocular lens

Functionalised siloxane macromonomers, with properties designed for application as an injectable, in situ curable accommodating intraocular lens (A-IOL), were prepared via re-equilibration of a phenyl group-containing polysiloxane of very high molecular weight with octamethylcyclotetrasiloxane (D₄) and 2,4,6,8-tetra(n-propyl-3-methacrylate)-2,4,6,8-tetramethyl-cyclotetrasiloxane (D₄(AM)) in toluene using trifluoromethanesulfonic acid as a catalyst. Hexaethyldisiloxane was used as an end group to control the molecular weight of the polymer. The generated polymers had a consistency suitable for injection into the empty lens capsule. The polymers contained a low ratio of polymerisable groups so that, in the presence of a photo-initiator, they could be cured on demand in situ within 5 min under irradiation of blue light to form an intraocular lens within the lens capsule. All resulting polysiloxane soft gels had a low elastic modulus and thus should be able to restore accommodation. The pre-cure viscosity and post-cure modulus of the generated polysiloxanes were controlled by the end group and D₄(AM) concentrations respectively in the re-equilibration reactions. The refractive index could be precisely controlled by adjusting the aromatic ratio in the polymer to suit such application as an artificial lens. Lens stretching experiments with both human and non-human primate cadaver lenses of different ages refilled with polysiloxane polymers provided a significant increase in amplitude of accommodation (up to 4 D more than that of the respective natural lens). Both in vitro cytotoxicity study using L929 cell lines and in vivo biocompatibility study in rabbit models demonstrated the non-cytotoxicity and ocular biocompatibility of the polymer.

Double peacock eye optical element for extended focal depth imaging with ophthalmic applications

The aged human eye is commonly affected by presbyopia, and therefore, it gradually loses its capability to form images of objects placed at different distances. Extended depth of focus (EDOF) imaging elements can overcome this inability, despite the introduction of a certain amount of aberration. This paper evaluates the EDOF imaging performance of the so-called peacock eye phase diffractive element, which focuses an incident plane wave into a segment of the optical axis and explores the element's potential use for ophthalmic presbyopia compensation optics. Two designs of the element are analyzed: the single peacock eye, which produces one focal segment along the axis, and the double peacock eye, which is a spatially multiplexed element that produces two focal segments with partial overlapping along the axis. The performances of the peacock eye elements are compared with those of multifocal lenses through numerical simulations as well as optical experiments in the image space. The results demonstrate that the peacock eye elements form sharper images along the focal segment than the multifocal lenses and, therefore, are more suitable for presbyopia compensation. The extreme points of the depth of field in the object space, which represent the remote and the near object points, have been experimentally obtained for both the single and the double peacock eye optical elements. The double peacock eye element has better imaging quality for relatively short and intermediate distances than the single peacock eye, whereas the latter seems better for far distance vision.

Correlations between refractive error and biometric parameters in human eyes using the LenStar 900

PURPOSE

To investigate the relationship between refractive error and ocular biometry in healthy subjects using a new optical low coherence reflectometry device.

METHODS

Biometric measurements were obtained with a LenStar LS 900 (Haag Streit, Switzerland) on one eye of 70 phakic subjects (mean ± SD age; 29 ± 9 years). Forty myopes and 30 non-myopes (best sphere range -9.63 D to +0.63 D) were included. Outcome measures were compared for the two groups using one way between groups ANOVA. These included; keratometry, central corneal thickness, iris width, anterior chamber depth, pupil diameter, lens thickness, axial length and retinal thickness. No mydriatic or cycloplegic agents were used.

RESULTS

There were significant differences between groups for keratometry readings (p = 0.021 and p = 0.038 for steep and flat k readings respectively), anterior chamber depth (p = 0.001), lens thickness (p = 0.026) and axial length (p<0.001). As expected significant correlations were found between spherical equivalent power and axial length (Pearson product-moment correlation r = -0.75, p<0.001) and between spherical equivalent power and anterior chamber depth (r = -0.29, p = 0.018). Anterior chamber depth and pupil diameter decreased with age (r = -0.429, p<0.001 and r = -0.386, p = 0.001 respectively) whereas lens thickness increased with age (r = 0.618, p < 0.001).

CONCLUSIONS

Our data showed significant differences between myopes and non-myopes for the key biometric parameters assessed and provides information about the relationships between these biometric parameters and age. The results, coupled with a unique ability to image and analyse the ocular structures non-invasively make the LenStar a promising new instrument for ocular evaluation in research and clinical practice.

Vergence analysis reveals the influence of axial distances on accommodation with age and axial ametropia

Despite numerous investigations, the aetiology and mechanism of accommodation and presbyopia remains equivocal. Using Gaussian first-order ray tracing calculations, we examine the contribution that ocular axial distances make to the accommodation response. Further, the influence of age and ametropia are also considered. The data show that all changes in axial distances during accommodation reduce the accommodation response, with the reduction in anterior chamber depth contributing most to this overall attenuation. Although the total power loss due to the changes in axial distances remained constant with increasing age, hyperopes exhibited less accommodation than myopes. The study, therefore, enhances our understanding of biometric accommodative changes and demonstrates the utility of vergence analysis in the assessment of accommodation.

Age-dependent variation of the Gradient Index profile in human crystalline lenses

PURPOSE: To reconstruct the gradient index (GRIN) profile of human crystalline lenses ex-vivo using Optical Coherence Tomography (OCT) imaging with an optimization technique and to study the dependence of the GRIN profile with age. METHODS: Cross-sectional images of nine isolated human crystalline lenses with ages ranging from 6 to 72 (post mortem time 1 to 4 days) were obtained using a custom-made OCT system. Lenses were extracted from whole cadaver globes and placed in a measurement chamber filled with preservation medium (DMEM). Lenses were imaged with the anterior surface up and then flipped over and imaged again, to obtain posterior lens surface profiles both undistorted and distorted by the refraction through the anterior crystalline lens and GRIN. The GRIN distribution of the lens was described with three variables by means of power function, with variables being the nucleus and surface index, and a power coefficient that describes the decay of the refractive index from the nucleus to the surface. An optimization method was used to search for the parameters that produced the best match of the distorted posterior surface. RESULTS: The distorted surface was simulated with accuracy around the resolution of the OCT system (under 15 µm). The reconstructed refractive index values ranged from 1.356 to 1.388 for the surface, and from 1.396 to 1.434 for the nucleus. The power coefficient ranged between 3 and 18. The power coefficient increased significantly with age, at a rate of 0.24 per year. CONCLUSION: Optical Coherence Tomography allowed optical, non-invasive measurement of the 2-D gradient index profile of the isolated human crystalline lens ex vivo. The age-dependent variation of the changes is consistent with previous data using magnetic resonance imaging, and the progressive formation of a refractive index plateau.