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

Refractive and ocular biometric characteristics of non-myopic and pseudomyopic eyes in mild hyperopic Chinese children aged 3-12 years

Purpose

To investigate the refractive and ocular biometric characteristics of children with mild hyperopia and distinguish between non-myopic and pseudomyopic eyes before cycloplegia.

Methods

The eligible children underwent refractive error measurements using a NIDEK autorefractor before and after the administration of 0.5 % tropicamide. Ocular biometric parameters, including axial length (AL), anterior chamber depth (ACD), and lens thickness (LT), were measured using the IOLMaster 700 before cycloplegia. We performed comparative analyses between the non-myopic and pseudomyopic groups, categorized based on whether the spherical equivalent (SE) before cycloplegia exceeded -0.50 diopters (D). Univariable and multivariable regression analyses were performed to control for confounding factors.

Results

The final analysis included 968 eyes. The participants with pseudomyopia were more likely to be boys (P = 0.029), younger (P = 0.004), less hyperopic (P < 0.001) after cycloplegia, and exhibit a higher delta SE (P < 0.001) compared to the non-myopic participants. Pseudomyopic eyes were associated with a shallower ACD (P = 0.004) and thicker LT (P < 0.001) than non-myopic eyes. After adjusting for sex, age, and SE, pseudomyopic eyes showed increased AL (P = 0.001) and LT (P < 0.001) and decreased ACD (P = 0.005) compared with non-myopic eyes before cycloplegia.

Conclusions

Among the children with mild hyperopia, pseudomyopia was more common in younger boys with a lower cycloplegic SE and higher delta SE. A thicker LT, shallower ACD, and increased AL may indicate the presence of pseudomyopia, which may provide insights into the rapid progression of myopia in children with pseudomyopia.

Dynamic Stimulation Aberrometry: Objectively Measured Accommodation and Pupil Dynamics after Phakic Iris-Fixated Intraocular Lens Implantation

Purpose

Anterior iris-claw phakic intraocular lens (pIOL) implantation is a treatment option for refractive, ametropic patients. However, the postoperative accommodative ability has not been systematically researched. Dynamic stimulation aberrometry allows the objective and dynamical measurement of accommodation by observing ocular aberrations during the accommodation process. We investigated the dynamic accommodative ability after pIOL implantation compared with a healthy age- and gender-matched control group.

Design

Clinical, comparative case-control study.

Subjects

We included patients aged 18-50 years that either underwent pIOL implantation > 1 month ago or served as a healthy, phakic control group.

Methods

The accommodative ability and pupil dynamics of both groups were investigated using dynamic stimulation aberrometry. The method allows the analysis of dynamic parameters during accommodation, such as the accommodation speed. A 1:1 propensity score matching was conducted based on the patients' age and gender.

Main Outcome Measures

Parameters of objective accommodation, such as accommodative amplitude and pupil dynamic during accommodation.

Results

Fifty-eight healthy, phakic eyes < 50 years of age and 21 eyes after pIOL implantation to correct myopia (pIOL, Verisyse, AMO, Inc) were enrolled. Patients that underwent anterior pIOL implantation were examined on average 24 ± 18 months after surgery. After matching, the mean age of both groups was not significantly different (35 ± 8 vs. 34 ± 8 years). No significant difference in dynamic parameters of accommodation or the accommodative amplitude (2.8 ± 1.4 and 2.9 ± 1.4 diopters [D] for pIOL and control group, P = 0.82) were seen. Maximum and minimum pupil sizes were not significantly different. The change in pupil size during deaccommodation was significantly faster in patients after pIOL implantation (P < 0.001).

Conclusions

Dynamic stimulation aberrometry allowed the objective, dynamic, measurement of wavefronts in subjects with accommodative amplitudes up to 7 D. Phakic intraocular lens implantation does not impair the accommodative ability. It alters pupil dynamics during deaccommodation.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Accommodation and Binocular Vision in Children with Myopic Anisometropia

Purpose

To assess the differences in accommodation and binocular vision in children with myopic anisometropia and determine the correlation with anisometropia.

Method

A total of 110 patients with myopia aged 8-15 years were recruited from June 2021 to February 2022 from the Affiliated Hospital of Xuzhou Medical University. Based on the interocular differences of spherical equivalent refraction, patients were divided into the isometropia (35 children), low anisometropia (LA group, 42 children), and high anisometropia (HA group, 33 children). The variables assessed were refraction, heterophoria, amplitude of accommodation (AMP), accommodative response (AR), gradient AC/A, positive and negative relative accommodation (PRA/NRA), and near stereopsis in the three groups. Pearson's correlation coefficient tests were used to investigate the possible association between each parameter and interocular differences (IODs).

Results

Among 110 subjects, there were 49 males and 61 females with a mean age of 11.39 ± 2.28 years. Compared with those in the isometropia group, AMP was lower and near stereopsis was higher in the LA group, and the distance and near heterophoria, PRA, AR, and near stereopsis were higher, and PRA, AMP, and gradient AC/A were lower in the HA group (all P < 0.05). Compared with those in the LA group, the near stereopsis, AR, and the near stereopsis were higher in the HA group, and the gradient AC/A was lower (all P < 0.05). However, no significant differences existed in the negative relative accommodation (P > 0.05). The distance and near heterophoria, AR, AMP, and near stereopsis were observed to be correlated with IODs, respectively (r = -0.259, p = 0.006; r = -0.201, p = 0.036; r = 0.306, p = 0.001; r = -0.315, p = 0.001; r = 0.535, p < 0.001).

Conclusion

Our results suggested that with the increase of anisometropia, distance and near heterophoria, AR, AMP, and near stereopsis had a tendency to get worse in children with myopic anisometropia.

The Combined Effect of Tropicamide and Phenylephrine on Corneal Astigmatism Axis

PURPOSE

To analyze astigmatism axis changes after tropicamide and phenylephrine combined instillation.

METHOD

One hundred and thirty-one eyes from 66 patients enrolled this cross-sectional study. An extensive ocular examination was carried out prior to tropicamide and phenylephrine instillation. Power and axis value from flat, steep, and mean keratometry were calculated using an Auto Kerato-Refractometer (AKR). Later, topography and tomography maps were evaluated with Pentacam HR® (Oculus, Wetzlar, Germany). Subsequently, a single drop of tropicamide 1% and phenylephrine hydrochloride 10% were instilled twice, with a five-minute gap between each instillation. After 30 minutes, the AKR and Pentacam HR® tests were repeated.

RESULTS

Incyclotorsion was found in 59 eyes (45.1%) and mean absolute incyclotorsion change was 3.91 ± 3.62 degrees (0.10 to 14.20). Excyclotorsion was found in 72 eyes (54.9%) and mean excyclotorsion change was 4.99 ± 5.94 degrees (0.20 to 36.20). We observed that 74.6% and 68.1% of eyes experienced incyclotorsion and excyclotorsion within 0 to 5 degrees, respectively. Fewer patients experienced incyclotorsion and excyclotorsion changes within 5 to 10 degrees, precisely 11.8% and 19.4%, respectively. Eyes that experienced over 10 degrees of incyclotorsion and excyclotorsion were 13.6% and 12.5%, respectively.

CONCLUSION

Astigmatism axis could change after combined tropicamide and phenylephrine instillation. Reference axis marking in astigmatism correction surgery should be performed under the same circumstances as the astigmatism axis has been measured.

IMI Accommodation and Binocular Vision in Myopia Development and Progression

The role of accommodation in myopia development and progression has been debated for decades. More recently, the understanding of the mechanisms involved in accommodation and the consequent alterations in ocular parameters has expanded. This International Myopia Institute white paper reviews the variations in ocular parameters that occur with accommodation and the mechanisms involved in accommodation and myopia development and progression. Convergence is synergistically linked with accommodation and the impact of this on myopia has also been critiqued. Specific topics reviewed included accommodation and myopia, role of spatial frequency, and contrast of the task of objects in the near environment, color cues to accommodation, lag of accommodation, accommodative-convergence ratio, and near phoria status. Aspects of retinal blur from the lag of accommodation, the impact of spatial frequency at near and a short working distance may all be implicated in myopia development and progression. The response of the ciliary body and its links with changes in the choroid remain to be explored. Further research is critical to understanding the factors underlying accommodative and binocular mechanisms for myopia development and its progression and to guide recommendations for targeted interventions to slow myopia progression.

The acute effects of single cup of coffee on ocular biometric parameters in healthy subjects

Purpose

To evaluate ocular biometric changes in healthy subjects after caffeine consumption from a cup of coffee.

Methods

A total of 36 subjects were included in this prospective observational study. Axial length (AL) and anterior segment parameters including aqueous depth (AD), anterior chamber depth (ACD), lens thickness (LT), and central corneal thickness (CCT) were measured with optic biometry, Lenstar LS 900 (Haag-Streit, Inc., Koeniz, Switzerland) before and 1 and 4 h after ingesting a cup of coffee (60 mg caffeine/100 mL).

Results

Mean age of the participants was 30.05 ± 7.43 years (range, 19–45). At baseline, 1st, and 4th hour, AL values were 23.9 ± 1.04 mm, 23.91 ± 1.04 mm, and 23.89 ± 1.04 mm, respectively, and no significant difference was observed (P>0.05). At baseline, 1st, and 4th hour, AD values were 3.06 ± 0.3 mm, 3.11 ± 0.3 mm, and 3.09 ± 0.3 mm, and ACD values were 3.6 ± 0.32, 3.66 ± 0.31, and 3.64 ± 0.31, respectively. AD and ACD values were significantly greater than baseline at 1st and 4th hours following coffee ingestion. Coffee intake caused a significant reduction in LT, compared with baseline and at the 1st and 4th hours which were 3.76 ± 0.28 mm, 3.69 ± 0.32 mm, and 3.72 ± 0.27 mm, respectively. No statistically significant difference was determined in between the 3 measurements in terms of CCT (P>0.05).

Conclusion

Caffeine causes a significant increase in AD and ACD and a significant decrease in LT following oral intake, for at least 4 h.

Assessment of eye fatigue caused by head-mounted displays using eye-tracking

BACKGROUND

Head-mounted displays (HMDs) and virtual reality (VR) have been frequently used in recent years, and a user's experience and computation efficiency could be assessed by mounting eye-trackers. However, in addition to visually induced motion sickness (VIMS), eye fatigue has increasingly emerged during and after the viewing experience, highlighting the necessity of quantitatively assessment of the detrimental effects. As no measurement method for the eye fatigue caused by HMDs has been widely accepted, we detected parameters related to optometry test. We proposed a novel computational approach for estimation of eye fatigue by providing various verifiable models.

RESULTS

We implemented three classifications and two regressions to investigate different feature sets, which led to present two valid assessment models for eye fatigue by employing blinking features and eye movement features with the ground truth of indicators for optometry test. Three graded results and one continuous result were provided by each model, respectively, which caused the whole result to be repeatable and comparable.

CONCLUSION

We showed differences between VIMS and eye fatigue, and we also presented a new scheme to assess eye fatigue of HMDs users by analysis of parameters of the eye tracker.

Optical Coherence Tomography Reveals Sigmoidal Crystalline Lens Changes during Accommodation

This study aimed to quantify biometric modifications of the anterior segment (AS) during accommodation and to compare them against changes in both accommodative demand and response. Thirty adults, aged 18–25 years were rendered functionally emmetropic with contact lenses. AS optical coherence tomography (AS-OCT) images were captured along the 180° meridian (Visante, Zeiss Meditec, Jena, Germany) under stimulated accommodative demands (0–4 D). Images were analysed and lens thickness (LT) was measured, applying a refractive index correction of 1.00. Accommodative responses were also measured sequentially through a Badal optical system fitted to an autorefractor (Shin Nippon NVision-K 5001, Rexxam, Japan). Data were compared with Dubbelman schematic eye calculations. Significant changes occurred in LT, anterior chamber depth (ACD), lens centroid (i.e., ACD + LT/2), and AS length (ASL = ACD + LT) with accommodation (all p < 0.01). There was no significant change in CT with accommodation (p = 0.81). Measured CT, ACD, and lens centroid values were similar to Dubbelman modelled parameters, however AS-OCT overestimated LT and ASL. As expected, the accommodative response was less than the demand. Interestingly, up until approximately 1.5 D of response (2.0 D demand), the anterior crystalline lens surface appears to be the primary correlate. Beyond this point, the posterior lens surface moves posteriorly resulting in an over-all sigmoidal trajectory. he posterior crystalline lens surface demonstrates a sigmoidal response with increasing accommodative effort.

A scalable and deformable stylized model of the adult human eye for radiation dose assessment

With recent changes in the recommended annual limit on eye lens exposures to ionizing radiation, there is considerable interest in predictive computational dosimetry models of the human eye and its various ocular structures including the crystalline lens, ciliary body, cornea, retina, optic nerve, and central retinal artery. Computational eye models to date have been constructed as stylized models, high-resolution voxel models, and polygon mesh models. Their common feature, however, is that they are typically constructed of nominal size and of a roughly spherical shape associated with the emmetropic eye. In this study, we present a geometric eye model that is both scalable (allowing for changes in eye size) and deformable (allowing for changes in eye shape), and that is suitable for use in radiation transport studies of ocular exposures and radiation treatments of eye disease. The model allows continuous and variable changes in eye size (axial lengths from 20 to 26 mm) and eye shape (diopters from  -12 to  +6). As an explanatory example of its use, five models (emmetropic eyes of small, average, and large size, as well as average size eyes of  -12D and  +6D) were constructed and subjected to normally incident beams of monoenergetic electrons and photons, with resultant energy-dependent dose coefficients presented for both anterior and posterior eye structures. Electron dose coefficients were found to vary with changes to both eye size and shape for the posterior eye structures, while their values for the crystalline lens were found to be sensitive to changes in only eye size. No dependence upon eye size or eye shape was found for photon dose coefficients at energies below 2 MeV. Future applications of the model can include more extensive tabulations of dose coefficients to all ocular structures (not only the lens) as a function of eye size and shape, as well as the assessment of x-ray therapies for ocular disease for patients with non-emmetropic eyes.

Anterior Segment Changes during Accommodation in Accommodative Esotropia

Purpose

To evaluate the anterior segment biometric parameters of non-accommodative and accommodative refractive accommodative esotropia (RAE).

Methods

Eighty-one eyes of 81 patients were included in this prospective, case-control study. The patients were divided into three groups as follows: the RAE group (n = 31), the hypermetropia group (n = 25), and the emmetropia group (n = 25). Measurements were obtained in the non-accommodative (0.0 diopters) and accommodative status (-5.0 diopters) using a Pentacam HR. The anterior chamber depth (ACD), anterior chamber volume (ACV), pupil diameter (PD), and anterior chamber angle (ACA) were evaluated at all four quadrants.

Results

The ACD, ACV and PD values in the RAE group were lower than those of the other groups in both states (p < 0.05). The ACD values were lower in the hypermetropia group than in the emmetropia group for the non-accommodative status (p = 0.024) but were similar for the accommodative status (p = 0.225). PD and ACV values were lower in the hypermetropia group than in the emmetropia group in both states (non-accommodative status, p = 0.011 and p = 0.022; accommodative status, p = 0.026 and p = 0.034, respectively). Changes in ACD, ACV and PD during accommodation (Δ) were not significant in the RAE group but were significant for the other groups (hypermetropia: ΔACD, p = 0.001; ΔACV, p = 0.001; ΔPD, p = 0.002; emmetropia: ΔACD, p < 0.001; ΔACV, p = 0.001; ΔPD, p < 0.001). These changes were significantly lower in the hypermetropia group than in the emmetropia group (ΔACD, p = 0.012; ΔACV, p = 0.031; ΔPD, p = 0.034).

Conclusions

The anterior chamber in RAE patients was shallower and the increase in convexity of the anterior surface or forward movement of the crystalline lens was more limited during accommodation in RAE.

Effect of Cycloplegia on Corneal Biometrics and Refractive State

Purpose

To determine changes in refractive state and corneal parameters after cycloplegia with cyclopentolate hydrochloride 1% using a dual Scheimpflug imaging system.

Methods

In this prospective cross-sectional study patients aged 10 to 40 years who were referred for optometric evaluation enrolled and underwent autorefraction and corneal imaging with the Galilei dual Scheimpflug system before and 30 minutes after twice instillation of medication. Changes in refraction and astigmatism were investigated. Corneal biometrics including anterior and posterior corneal curvatures, total corneal power and corneal pachymetry were compared before and after cycloplegia.

Results

Two hundred and twelve eyes of 106 subjects with mean age of 28 ± 5 years including 201 myopic and 11 hyperopic eyes were evaluated. Mean spherical equivalent refractive error before cycloplegia was -3.4 ± 2.6 D. A mean hyperopic shift of 0.4 ± 0.5 D occurred after cycloplegia (P < 0.001). The astigmatism power did not significantly change (P = 0.8), however, 26.8% of eyes with significant astigmatism experienced a change of more than 5 degrees in the axis of astigmatism. Changes in posterior corneal curvature were scant but statistically significant (P = 0.001). Moreover, corneal thickness was slightly increased in the central and paracentral regions (P < 0.001 and P < 0.001, respectively).

Conclusion

Cycloplegia causes a hyperopic shift and astigmatism axis changes, along with an increase in central and paracentral corneal thickness and change in posterior corneal curvature. The effects of cycloplegia on refraction and corneal biometrics should be considered before cataract and refractive surgeries.

Ocular biometric changes with different accommodative stimuli using swept-source optical coherence tomography

PURPOSE

To evaluate ocular biometric changes with different accommodative stimuli using a new swept-source optical biometer.

METHODS

Only the right eye was analyzed. Each subject was measured six times with the IOLMaster 700 swept-source optical biometer (Carl Zeiss Meditec, Jena, Germany) with the subject looking at the stimulus shown by the instrument and with the subject looking at a target placed outside the instrument at 0D of vergence. Axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), lens thickness (LT), white-to-white (WTW), and keratometry readings (K1 and K2) were evaluated in both cases. To assess if the changes found may affect the intraocular (IOL) power calculation for surgical applications, we have applied some formulae, using the software provided by the optical biometer manufacturer, to the ocular parameters found in both situations for three different types of IOLs.

RESULTS

No statistically significant differences were found for AL, CCT, WTW, K1 and K2 between the subject looking at the stimulus of the biometer and looking at the outside target at 0D of vergence (p > 0.05). However, the measurement of ACD revealed a statistically significant reduction of 20 microns (p = 0.03) and, on the contrary, LT increased significantly 30 microns (p = 0.02). ACD and LT changes were highly correlated (R² = 0.91). As for the IOL power calculation, in all cases, the mean change was lower than 0.25 D both for IOL power selection and residual refraction.

CONCLUSIONS

Although ACD and LT change significantly with different accommodative stimuli measured by swept-source optical biometry, these changes are not clinically relevant.

The effect of topical administration of cyclopentolate on ocular biometry: An analysis for mouse and human models

Mydriasis with muscarinic antagonists have been used routinely prior to retinal examination and sometimes prior to refractive measurements of the mouse eye. However, biometric changes during topical administration of muscarinic antagonists have not been fully investigated in mice and humans. We found that the mouse eyes treated with cyclopentolate developed a hyperopia with a reduction in both the vitreous chamber depth and axial length. In humans, prior to the cyclopentolate treatment, a 6D accommodative stimulus produced a myopic shift with a reduced anterior chamber depth, choroidal thickness and anterior lens radius of curvature and an increase in lens thickness. After the cyclopentolate treatment, human eyes developed a hyperopic shift with an increased anterior chamber depth and anterior lens radius of curvature and a reduced lens thickness. Therefore, the biometric changes associated with this hyperopic shift were mainly located in the posterior segment of the eye in mice. However, it is the anterior segment of the eye that plays a main role in the hyperopic shift in human subjects. These results further indicate that mouse eyes do not have accommodation which needs to be taken into account when they are used for the study of human refractive errors.

Predicting Accommodative Response Using Paraxial Schematic Eye Models

PURPOSE

Previous ultrasound biomicroscopy (UBM) studies showed that accommodative optical response (AOR) can be predicted from accommodative biometric changes in a young and a pre-presbyopic population from linear relationships between accommodative optical and biometric changes, with a standard deviation of less than 0.55D. Here, paraxial schematic eyes (SE) were constructed from measured accommodative ocular biometry parameters to see if predictions are improved.

METHODS

Measured ocular biometry (OCT, A-scan, and UBM) parameters from 24 young and 24 pre-presbyopic subjects were used to construct paraxial SEs for each individual subject (individual SEs) for three different lens equivalent refractive index methods. Refraction and AOR calculated from the individual SEs were compared with Grand Seiko (GS) autorefractor measured refraction and AOR. Refraction and AOR were also calculated from individual SEs constructed using the average population accommodative change in UBM measured parameters (average SEs).

RESULTS

Schematic eye calculated and GS measured AOR were linearly related (young subjects: slope = 0.77, r = 0.86; pre-presbyopic subjects: slope = 0.64, r = 0.55). The mean difference in AOR (GS - individual SEs) for the young subjects was -0.27D and for the pre-presbyopic subjects was 0.33D. For individual SEs, the mean ± SD of the absolute differences in AOR between the GS and SEs was 0.50 ± 0.39D for the young subjects and 0.50 ± 0.37D for the pre-presbyopic subjects. For average SEs, the mean ± SD of the absolute differences in AOR between the GS and the SEs was 0.77 ± 0.88D for the young subjects and 0.51 ± 0.49D for the pre-presbyopic subjects.

CONCLUSIONS

Individual paraxial SEs predict AOR, on average, with a standard deviation of 0.50D in young and pre-presbyopic subject populations. Although this prediction is only marginally better than from individual linear regressions, it does consider all the ocular biometric parameters.

Comparison of ocular biometric measurements between a new swept-source optical coherence tomography and a common optical low coherence reflectometry

The purpose of the current study was to compare the measurements between a new optical biometer based on swept-source optical coherence tomography (SS-OCT), the OA-2000 (Tomey, Japan), and an optical biometer based on optical low coherence reflectometry (OLCR), the Lenstar (Haag-Streit, Switzerland). Ninety-nine eyes of 99 healthy subjects were included. The axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AD), lens thickness (LT), keratometry (K) readings, including flat K (Kf), steep K (Ks), mean K (Km), astigmatism vectors J₀, J₄₅ at diameters of 2.5 and 3.0 mm, and white-to-white diameter (WTW) were measured three times each using both biometer in normal eyes by random sequence. Bland-Altman analysis showed good agreement between the SS-OCT and OLCR devices for AL, AD, ACD, LT, with narrow 95% LoA (−0.05 to 0.07 mm, −0.09 to 0.10 mm, −0.10 to 0.09 mm, and −0.06 to 0.22 mm, respectively), and the P values of ACD were both >0.05. The CCT, Kf, Ks, Km, J₀, J₄₅ and WTW values provided by the OA-2000 were in good agreement with the Lenstar, and statistically significant differences were detected for some of them but not clinical differences. The agreement was excellent especially for AL.

Scheimpflug image-based changes in anterior segment parameters during accommodation induced by short-term reading

PURPOSE

To analyze the effect of the accommodation on the anterior segment data (corneal and anterior chamber parameters) induced by short-time reading in a healthy, nonpresbyopic adult patient group.

METHODS

Images of both eyes of nonpresbyopic volunteers were captured with a Scheimpflug device (Pentacam HR) in a nonaccommodative state. Fifteen minutes of reading followed and through fixation of the built-in target of Pentacam HR further accommodation was achieved and new images were captured by the device. Anterior segment parameters were observed and the differences were analyzed.

RESULTS

Fifty-two healthy eyes of 26 subjects (range 20.04-28.58 years) were analyzed. No significant differences were observed in the keratometric values before and after the accommodative task (p = 0.35). A statistically significant difference was measured in the 5.0-mm-diameter and the 7.0-mm-diameter corneal volume (p = 0.01 and p = 0.03) between accommodation states. Corneal aberrometric data did not change significantly during short-term accommodation. Significant differences were observed between nonaccommodative and accommodative states of the eyes for all measured anterior chamber parameters.

CONCLUSIONS

Among the parameters of the cornea, only corneal volume changed during the short-term accommodation process, showing some fine changes with accommodation of the cornea in young, emmetropic patients. The position of the pupil and the anterior chamber parameters were observed to change with accommodation as captured by a Scheimpflug device.

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.

Prediction of accommodative optical response in prepresbyopic subjects using ultrasound biomicroscopy

PURPOSE

To determine whether relatively low-resolution ultrasound biomicroscopy (UBM) can be used to predict the accommodative optical response in prepresbyopic eyes as well as in a previous study of young phakic subjects, despite lower accommodative amplitudes.

SETTING

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

DESIGN

Observational cross-sectional study.

METHODS

Static accommodative optical response was measured with infrared photorefraction and an autorefractor (WR-5100K) in subjects aged 36 to 46 years. A 35 MHz UBM device (Vumax, Sonomed Escalon) was used to image the left eye, while the right eye viewed accommodative stimuli. Custom-developed Matlab image-analysis software was used to perform automated analysis of UBM images to measure the ocular biometry parameters. The accommodative optical response was predicted from biometry parameters using linear regression, 95% confidence intervals (CIs), and 95% prediction intervals.

RESULTS

The study evaluated 25 subjects. Per-diopter (D) accommodative changes in anterior chamber depth (ACD), lens thickness, anterior and posterior lens radii of curvature, and anterior segment length were similar to previous values from young subjects. The standard deviations (SDs) of accommodative optical response predicted from linear regressions for UBM-measured biometry parameters were ACD, 0.15 D; lens thickness, 0.25 D; anterior lens radii of curvature, 0.09 D; posterior lens radii of curvature, 0.37 D; and anterior segment length, 0.42 D.

CONCLUSIONS

Ultrasound biomicroscopy parameters can, on average, predict accommodative optical responses with SDs of less than 0.55 D using linear regressions and 95% CIs. Ultrasound biomicroscopy can be used to visualize and quantify accommodative biometric changes and predict accommodative optical response in prepresbyopic eyes.

Objective measurement of accommodative biometric changes using ultrasound biomicroscopy

PURPOSE

To demonstrate that ultrasound biomicroscopy (UBM) can be used for objective quantitative measurements of anterior segment accommodative changes.

SETTING

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

DESIGN

Prospective cross-sectional study.

METHODS

Anterior segment biometric changes in response to 0 to 6.0 diopters (D) of accommodative stimuli in 1.0 D steps were measured in eyes of human subjects aged 21 to 36 years. Imaging was performed in the left eye using a 35 MHz UBM (Vumax) and an A-scan ultrasound (A-5500) while the right eye viewed the accommodative stimuli. An automated Matlab image-analysis program was developed to measure the biometry parameters from the UBM images.

RESULTS

The UBM-measured accommodative changes in anterior chamber depth (ACD), lens thickness, anterior lens radius of curvature, posterior lens radius of curvature, and anterior segment length were statistically significantly linearly correlated with accommodative stimulus demands. Standard deviations of the UBM-measured parameters were independent of the accommodative stimulus demands (ACD: 0.0176 mm; lens thickness: 0.0294 mm; anterior lens radius of curvature: 0.3350 mm; posterior lens radius of curvature: 0.1580 mm; and anterior segment length: 0.0340 mm). The mean difference between the A-scan and UBM measurements was -0.070 mm for ACD and 0.166 mm for lens thickness.

CONCLUSIONS

Accommodating phakic eyes imaged using UBM allowed visualization of the accommodative response, and automated image analysis of the UBM images allowed reliable, objective, quantitative measurements of the accommodative intraocular biometric changes.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.

Functional spasm of accommodation: Changes on scheimpflug imaging

Spasm of accommodation is a rare condition characterized by a sudden increase in myopia. It can occur in emmetropes, hypermetropes and myopes. All the physiological changes that occur in normal accommodation are exaggerated. Mostly the cause is functional disorder and the condition gradually improves. We hereby present the changes occurring in spasm of accommodation as seen on Scheimpflug imaging.

Pharmacologically and Edinger-Westphal stimulated accommodation in rhesus monkeys does not rely on changes in anterior chamber pressure

This study was undertaken to understand the role of anterior chamber pressure (ACP) during pharmacological and Edinger-Westphal (EW) stimulated accommodation in anesthetized monkeys. Experiments were performed on one iridectomized eye each of 7 anesthetized adolescent rhesus monkeys. Accommodation was induced by EW stimulation (n = 2) and intravenous administration of 0.25-4.0 mg/kg pilocarpine (n = 6). Accommodative refractive and biometric changes were measured with continuous 60 Hz infrared photorefraction (n = 6) and 100 Hz A-scan ultrasound biometry (n = 1). An ocular perfusion system was used to measure and manipulate ACP. Pressure was recorded via a 27-gauge needle in the anterior chamber connected to a pressure transducer (n = 7). The needle was also connected to a fluid reservoir to allow ACP to be manipulated and clamped (n = 4) by raising or lowering the fluid reservoir. In all six pharmacologically stimulated monkeys ACP increased during accommodation, from 0.70 to 2.38 mmHg, four of which showed pressure decreases preceding the pressure increases. Two eyes also showed increases in ACP during EW-stimulated accommodation of 2.8 and 7.2 mmHg. ACP increased with increasing EW stimulus amplitudes (n = 2). Clamping or externally manipulating ACP had no effect on resting refraction or on EW and pharmacologically stimulated accommodation in four eyes. The results show that EW stimulated and pharmacologically stimulated accommodation do not rely on ACP in rhesus monkeys.

Axial elongation associated with biomechanical factors during near work

PURPOSE

To investigate the changes occurring in the axial length, choroidal thickness, and anterior biometrics of the eye during a 10-minute near task performed in downward gaze.

METHODS

Twenty young adult subjects (10 emmetropes and 10 myopes) participated in this study. To measure ocular biometrics in downward gaze, an optical biometer was inclined on a custom-built height- and tilt-adjustable table. Baseline measures were collected after each subject performed a distance primary gaze control task for 10 minutes to provide washout period for previous visual tasks before each of three different accommodation/gaze conditions. These other three conditions included a near task (2.5 diopters [D]) in primary gaze and a near (2.5 D) and a far (0 D) accommodative task in downward gaze (25 degrees), all for 10 minutes' duration. Immediately after and then 5 and 10 minutes from the commencement of each trial, measurements of ocular biometrics (e.g., anterior biometrics, axial length, choroidal thickness, and retinal thickness) were obtained.

RESULTS

Axial length increased with accommodation and was significantly greater for downward gaze with accommodation (mean ± SD change, 23 ± 13 μm at 10 minutes) compared with primary gaze with accommodation (8 ± 15 μm at 10 minutes) (p < 0.05). A small amount of choroidal thinning was also found during accommodation that was statistically significant in downward gaze (13 ± 14 μm at 10 minutes; p < 0.05). Accommodation in downward gaze also caused greater changes in anterior chamber depth and lens thickness compared with accommodation in primary gaze.

CONCLUSIONS

Axial length, choroidal thickness, and anterior eye biometrics change significantly during accommodation in downward gaze as a function of time. These changes seem to be caused by the combined influence of biomechanical factors (i.e., extraocular muscle forces, ciliary muscle contraction) associated with near tasks in downward gaze.

Repeatability of OCT lens thickness measures with age and accommodation

PURPOSE

To investigate crystalline lens thickness (LT) across a range of ages and accommodative demands and to evaluate the repeatability of LT measurements using the Visante Anterior Segment Optical Coherence Tomographer (AS-OCT) (Zeiss Meditec, Germany) under non-cycloplegic conditions.

METHODS

Participants were 98 visually normal adults aged 18-75 years, stratified into age groups of 18-29, 30-39, 40-49, 50-59, and 60-75 years of age. Images of the crystalline lens were taken using the Visante AS-OCT during stimulation of accommodation at demands of 0, 1, 2, 3, 4, 5, and 8 D with accommodative response measured in a subgroup of participants. Images were analyzed and LT measured assuming a refractive index of 1.42. Repeat measures were taken from 86 participants for each accommodative demand at a second visit.

RESULTS

The mean unaccommodated LT for all participants was 4.07 ± 0.40 mm. An average increase in LT of 20 μm per year was calculated (linear regression, R² = 0.61, F(1,89) = 143.92, p < 0.00001). Increase in LT with accommodation was shown to be significant in the 18- to 29-year-olds (repeated measures ANOVA, F(6,105) = 96.31, p < 0.00001), 30- to 39-year-olds (F(6,93) = 71.25, p < 0.00001), and 40- to 49-year-olds (F(6,90) = 12.60, p < 0.01) with little or no measureable change in the older age groups. Eighty-six participants returned for a second visit. The mean difference in LT in the unaccommodated state for all participants between visit 1 and visit 2 was 0.0006 mm (95% limits of agreement of -0.07 to 0.07 mm). The 95% limits of agreement were widest for youngest age groups and narrowest for the oldest participants.

CONCLUSIONS

This study is the first to report the repeatability of LT measures using the Visante AS-OCT in the non-cyclopleged eye. It has also demonstrated the ability of the Visante AS-OCT to detect small changes in lens thickness with accommodation.

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.

Changes in ciliary muscle thickness during accommodation in children

PURPOSE

To investigate the morphology of the ciliary muscle during the act of accommodation in a population of children.

METHODS

Thirty children aged 6 to 12 years were enrolled. Accommodative response was measured through habitual correction. Height was measured as a control variable. Central axial length was measured with the IOLMaster. Four images of the temporal ciliary muscle were taken with the Visante Optical Coherence Tomographer at three different stimulus levels (0, 4, and 6 D) while accommodative response was monitored concurrently with the PowerRefractor. Accommodative response monitoring was time-matched to ciliary muscle image capture, and the mean was calculated for 5 s surrounding this time point. Four cycloplegic images of the temporal ciliary muscle were also taken. Ciliary muscle thickness measurements were made at the point of maximum thickness (CMTMAX) and at 1 mm (CMT1), 2 mm (CMT2) and 3 mm (CMT3) posterior to the sclera spur.

RESULTS

Increasing accommodative response was correlated with increases in the thickness of CMTMAX (p = <0.001) and CMT1 (p = <0.001) and decreases in the thickness of CMT3 (p = <0.001). Thicker values of CMTMAX under cycloplegic conditions were significantly correlated with values of CMTMAX (p = <0.001) and CMT1 (p = 0.001) while accommodating and approached significance in modeling CMT3 (p = 0.06). Mean axial length was correlated with the amount of thinning at CMT3 with accommodation (p = 0.002). Axial length was not significantly correlated with thickness values at CMTMAX (p = 0.7) or CMT1 (p = 0.6).

CONCLUSIONS

In a manner similar to previous adult studies, ciliary muscle thickness at CMTMAX and CMT1 increased with accommodation and CMT3 thinned with accommodation. Further investigation is necessary to determine whether CMT2 is a "fulcrum" point along the length of the ciliary muscle where the net change with accommodation is always zero or whether that point varies across subjects or with varying levels of accommodative effort.

Manipulation of intraocular pressure for studying the effects on accommodation

A reliable experimental system in which IOP can be manipulated or a rapid IOP change can be induced while simultaneously and continuously measuring IOP and the ocular accommodative changes would be useful for understanding the physiological effect of intraocular pressure (IOP) on the accommodative mechanism. In this study, an IOP perfusion and recording system was developed and tested using 13 enucleated pig eyes. The vitreous chamber of the pig eyes was cannulated with a needle connected to two fluid reservoirs at different heights. One reservoir was set to achieve one of three baseline pressures of 5.5 mmHg, 13.0 mmHg and 20.5 mmHg. The other reservoir was moved to achieve pressures of 1.5 mmHg, 3.0 mmHg, 4.5 mmHg and 6.0 mmHg higher than the baseline pressure. The height differential between the reservoirs determined the amplitude of IOP changes. Rapid IOP changes were induced by switching the reservoirs with a solenoid pinch-valve. Two needles, one each attached to a pressure transducer were inserted into the anterior chamber and vitreous chamber respectively. Custom developed software was used to measure the anterior chamber pressure and vitreous chamber pressure at 80 Hz. A high-resolution continuous A-scan ultrasound biometer (CUB) was used to dynamically measure changes in ocular biometry including anterior chamber depth (ACD), lens thickness (LT) and vitreous chamber depth (VCD) while the vitreous chamber pressure was manipulated. The changes in ACD, LT and VCD were analyzed as a function of the pressure change. Perfusion-induced axial biometric changes were quantified by the slopes of linear regression relationships. Both anterior chamber pressure and vitreous chamber pressure changed relatively systematically with the induced vitreous chamber pressure changes (anterior chamber: y = 0.863x + 0.030, r(2) = 0.983; vitreous chamber: y = 0.883x + 0.009, r(2) = 0.981). At perfusion pressures of 5.5, 13.0 and 20.5 mmHg, the slopes for ACD were -5.72, -2.75 and -2.36 μm/mmHg, for LT were -3.31, -1.59 and -1.03 μm/mmHg and for VCD were 19.05, 8.63 and 5.18 μm/mmHg. The system was able to manipulate and monitor IOP while axial biometry changes were recorded. This system will allow the relationship between IOP and accommodation to be studied in non-human primate eyes.

A method for profiling biometric changes during disaccommodation

PURPOSE

To demonstrate the application of low-coherence reflectometry to the study of biometric changes during disaccommodation responses in human eyes after cessation of a near task and to evaluate the effect of contact lenses on low-coherence reflectometry biometric measurements.

METHODS

Ocular biometric parameters of crystalline lens thickness (LT) and anterior chamber depth (ACD) were measured with the LenStar device during and immediately after a 5 D accommodative task in 10 participants. In a separate trial, accommodation responses were recorded with a Shin-Nippon WAM-5500 optometer in a subset of two participants. Biometric data were interleaved to form a profile of post-task anterior segment changes. In a further experiment, the effect of soft contact lenses on LenStar measurements was evaluated in 15 participants.

RESULTS

In 10 adult participants, increased LT and reduced ACD was seen during the 5 D task. Post-task, during fixation of a 0 D target, a profile of the change in LT and ACD against time was observed. In the two participants with accommodation data (one a sufferer of nearwork-induced transient myopia and other a non-sufferer), the post-task changes in refraction compared favorably with the interleaved LenStar biometry data. The insertion of soft contact lenses did not have a significant effect on LenStar measures of ACD or LT (mean change: -0.007 mm, p = 0.265 and + 0.001 mm, p = 0.875, respectively).

CONCLUSIONS

With the addition of a relatively simple stimulus modification, the LenStar instrument can be used to produce a profile of post-task changes in LT and ACD. The spatial and temporal resolution of the system is sufficient for the investigation of nearwork-induced transient myopia from a biometric viewpoint. LenStar measurements of ACD and LT remain valid after the fitting of soft contact lenses.

Analysis of changes in crystalline lens thickness and its refractive power after laser in situ keratomileusis

AIM

To evaluate changes in the anterior chamber depth (ACD), crystalline lens thickness (LT) and its refractive power after laser in situ keratomileusis (LASIK).

METHODS

In all cases, the preoperative and postoperative central ACD which were measured with Pentacam, Orbscan, IOL-Master and A-scan ultrasonography, central corneal true net power which was measured with the Pentacam, Orbscan and IOL-Master, axial length (AL) which was measured with IOL-Master and LT which was measured with the A-scan ultrasonography were compared using the paired sample t test. Ocular refractive errors and lens refractive power at corneal plane were calculated and their correlations were also evaluated before and after LASIK.

RESULTS

At 1 week after LASIK, LT and crystalline lens refractive power at corneal plane (Dlens) which were associated with the IOL-Master and Pentacam increased significantly (P≤0.005), ACD decreased significantly (P≤0.001), but no significant increase was observed in the Dlens which was associated with the Orbscan (P=0.261). Significant correlations between the changes in the ocular refractive errors and Dlens which were associated with the Pentacam were observed at 1 week and 6 months after LASIK (P=0.028; P=0.001).

CONCLUSION

LT increased significantly after LASIK, and this might partially lead to ACD decrease, Dlens increase and a small quantity of myopic regression.

Axial length changes during accommodation in myopes and emmetropes

PURPOSE

To investigate the influence of accommodation on axial length (AXL) and a comprehensive range of ocular biometric parameters) in populations of young adult myopic and emmetropic subjects.

METHODS

Forty young adult subjects had ocular biometry measured using a noncontact optical biometer (Lenstar LS 900) based on the principle of optical low coherence reflectometry under 3 different accommodation demands (0 D, 3 D, and 6 D). Subjects were classified as emmetropes (n = 19) or myopes (n = 21) based on their spherical equivalent refraction (mean emmetropic refraction -0.05 +/- 0.27 D and mean myopic refraction -1.82 +/- 0.84 D).

RESULTS

AXL changed significantly with accommodation, with a mean increase of 11.9 +/- 12.3 mum and 24.1 +/- 22.7 mum for the 3 D and 6 D accommodation stimuli, respectively. A significant axial elongation associated with accommodation was still evident even after correction of the AXL data for potential error because of lens thickness change. The mean "corrected" increase in AXL was 5.2 +/- 11.2 mum and 7.4 +/- 18.9 mum for the 3 D and 6 D stimuli, respectively. There was no significant difference between the myopic and emmetropic populations in terms of the magnitude of change in AXL with accommodation, regardless of whether the data were corrected or not. A number of other ocular biometric parameters, such as anterior chamber depth, lens thickness, and vitreous chamber depth also exhibited significant change with accommodation. The myopic and emmetropic populations also exhibited no significant difference in the magnitude of change in these parameters with accommodation.

CONCLUSIONS

The eye undergoes a significant axial elongation associated with a brief period of accommodation, and the magnitude of this change in eye length increases for larger accommodation demands, however, there is no significant difference in the magnitude of eye elongation in myopic and emmetropic subjects.

Anterior chamber depth and iridocorneal angle in healthy White subjects: effects of age, gender and refraction

PURPOSE

Prior to phakic intraocular lens implantation, it is important to obtain precise knowledge of the anterior chamber depth (ACD). Accurate topographic evaluation of the iridocorneal angle is helpful in estimating risk for angle-closure glaucoma. This study investigated the use of the Orbscan II system to measure ACD and the iridocorneal angle in healthy subjects and assessed the influences of age, gender and spherical equivalent on these parameters.

METHODS

The Orbscan II system was used to determine the ACD and iridocorneal angle in eight different positions in 390 healthy White subjects with a mean age of 41± 16years (range 10-80 years). The sample included 242 male and 148 female subjects. The influences of age, gender and spherical equivalent were assessed using multiple regression analysis.

RESULTS

Mean ACD was 2.87 ± 0.04 mm in male subjects and 2.81±0.37mm in female subjects. The explanatory variables relevant to the ACD were age (partial regression coefficient B = -0.0115, p < 0.0001), spherical equivalent (B = - 0.0562, p< 0.0001) and gender (B = 0.0996, p=0.0036). The mean iridocorneal angle (MIA) was 30.7 ± 2.0 ° in male and 31.6 ± 2.1° in female subjects. The variables relevant to the MIA were gender (B =- 0.865, p < 0.0001), age (B =- 0.017, p = 0.0007) and spherical equivalent (B = - 0.121, p = 0.001). The superior iridocorneal angle displayed the strongest negative correlation with age, whereas the temporal angle exhibited the least correlation with age.

CONCLUSIONS

The decline in ACD appears to be linear with age, amounting to a mean of 0.58 mm over 50 years. This may become clinically relevant in the use of phakic intraocular lenses. In addition, the angle is more severely constricted in the superior quadrant than in the temporal quadrant.

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.

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.

Lens diameter and thickness as a function of age and pharmacologically stimulated accommodation in rhesus monkeys

Uncertainty exists regarding accommodative and age changes in lens diameter and thickness in humans and monkeys. In this study, unaccommodated and accommodated refraction, lens diameter, and lens thickness were measured in rhesus monkeys across a range of ages. Iridectomized eyes were studied in 33 anesthetized monkeys aged 4-23 years. Refraction was measured using a Hartinger coincidence refractometer and lens thickness was measured with A-scan ultrasound. Lens diameters were measured with image analysis from slit-lamp images captured via a video camera while a saline filled, plano perfusion lens was placed on the cornea. Accommodation was pharmacologically stimulated with 2% pilocarpine via the perfusion lens in 21 of the monkeys and lens diameters were measured until a stable minimum was achieved. Refraction and lens thickness were measured again after the eye was accommodated. Unaccommodated lens thickness increased linearly with age by 0.029 mm/year while unaccommodated lens diameter showed no systematic change with age. Accommodative amplitude decreased by 0.462 D/year in response to pilocarpine. The accommodative increase in lens thickness decreased with age by 0.022 mm/year. The accommodative decrease in lens diameter declined linearly with age by 0.021 mm/year. Rhesus monkeys undergo the expected presbyopic changes including increasing lens thickness and a decreasing ability of the lens to undergo changes in thickness and diameter with accommodation, however without an age-related change in unaccommodated lens diameter. As in humans, the age-related decrease in accommodative amplitude in rhesus monkeys cannot be attributed to an age-related increase in lens diameter.

Changes in crystalline lens radii of curvature and lens tilt and decentration during dynamic accommodation in rhesus monkeys

Dynamic changes in crystalline lens radii of curvature and lens tilt and decentration were measured during centrally stimulated accommodation in four iridectomized eyes of two adolescent rhesus monkeys. Phakometry measurements were performed dynamically using a custom-built, video-based, Purkinje-image instrument. Lens anterior and posterior radii were calculated from reflections of paired light sources from the ocular surfaces (Purkinje images PI, PIII, and PIV). Lens tilt and decentration were calculated assuming linearity between Purkinje image positions, eye rotation, lens tilt, and decentration. Because the monkey eyes were iridectomized, Purkinje images were referred to the mid-point of the double first Purkinje image (PI). Mean unaccommodated values of anterior and posterior lens radii of curvature were 11.11 +/- 1.58 mm and -6.64 +/- 0.62 mm, respectively, and these decreased relatively linearly with accommodation in all eyes, at a rate of 0.48 +/- 0.14 mm/D and 0.17 +/- 0.03 mm/D for anterior and posterior lens surfaces, respectively. Tilt and decentration did not change significantly with accommodation except for tilt around the horizontal axis, which changed at a rate of 0.147 +/- 0.25 deg/D. These results are important to fully characterize accommodation in rhesus monkeys.

Anterior segment changes with age and during accommodation measured with partial coherence interferometry

PURPOSE

To evaluate anterior segment alterations with age and during accommodation in different age groups.

SETTING

Department of Ophthalmology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary.

METHODS

Fifty-three subjects (101 normal eyes) were enrolled in this study and divided into 3 age groups: younger than 30 years (Group 1), between 31 years and 44 years (Group 2), and older than 45 years (Group 3). The total amplitude of accommodation was determined with a defocusing technique, and anterior segment measurements were performed by partial coherence interferometry.

RESULTS

Group 1 comprised 32 eyes; Group 2, 37 eyes; and Group 3, 32 eyes. The total amplitude of accommodation decreased with age (P<.0001). With the target position at infinity, the lens thickness (LT) and anterior segment length (ASL) increased and the anterior chamber depth (ACD) decreased significantly with age (P<.0001). During accommodation in the youngest group, the mean change in LT was 36.3 mum/diopter (D) and in ACD, -26.7 mum/D. The mean accommodation-induced ACD change was -0.08 mm +/- 0.06 (SD) in Group 1, -0.064 +/- 0.087 mm in Group 2, and -0.03 +/- 0.06 mm in Group 3 (P = .0004). The mean LT change during near fixation was 0.109 +/- 0.063 mm in Group 1, 0.103 +/- 0.136 mm in Group 2, and 0.006 +/- 0.05 mm in Group 3 (P<.0001). The mean ASL change during accommodation was 0.029 +/- 0.037 mm, 0.039 +/- 0.114 mm, and -0.023 +/- 0.051, respectively (P<.0001).

CONCLUSIONS

In addition to forward movement of the anterior lens surface with age, the posterior surface moved backward. Alterations in LT and ACD sufficient for a unit of refractive power change during accommodation might be smaller than previously thought. Anterior shifting of the lens may also participate in the accommodative response.

The effect of human in vivo accommodation on crystalline lens stability

AIM

To determine the effect of human in vivo accommodation on the stability of the crystalline lens.

METHODS

Using a dual Purkinje image (DPI) eyetracker, the phase-time difference and amplitudes of Purkinje images I (P(I)) and IV (P(1V)) were measured in 37 normal emmetropic subjects (34 women and 3 men; mean age 19.8, range 18-22 years) when they changed focus from 70 to 15 cm and simultaneously rotated their heads horizontally from side to side or made horizontal saccades between two targets 6.8 degrees apart.

RESULTS

When the subjects changed focus from 70 to 15 cm and rotated their heads or made eye saccades, the phase-time difference between P(I) and P(IV) decreased. During saccades, the amplitude of both P(I) and P(IV) overshoots significantly increased with focus at 15 cm; however, their ratio (P(IV) overshoot amplitude/P(I) overshoot amplitude) significantly declined.

CONCLUSIONS

The lens is stable during accommodation. The implications of these findings on the mechanism of accommodation are discussed.