Klaus Ehrmann - Academia.edu (original) (raw)

Papers by Klaus Ehrmann

Proceedings of SPIE - The International Society for Optical Engineering

ABSTRACT

Journal of optometry, Jan 16, 2015

To determine if a fogging lens ameliorates accommodative effects driven by the closed-view design... more To determine if a fogging lens ameliorates accommodative effects driven by the closed-view design of the BHVI-EyeMapper (EM) instrument. We compared cycloplegic refraction and higher-order aberration measurements of the EM with those obtained with a fogging lens. Twenty-six, young, participants (15F, 25±5 years, range: 18-35 years, SE: +0.25D and -3.50D) with good ocular health were recruited. Five independent measurements of on- and off-axis refraction and higher-order aberrations were recorded across the horizontal visual field, under two conditions: non-cycloplegic measurements with +1.00D fogging lens and cycloplegia, always in the same sequence. The contralateral eye was occluded during the measurements. Two drops of 1% Tropicamide delivered within 5min facilitated cycloplegic measurements. All participants were refracted 30min after installation of the second drop. Mean spherical equivalent measures of the non-cycloplegic condition were significantly more myopic than their cyc...

Contact Lens and Anterior Eye, 2015

To assess visual performance of single vision and multifocal soft contact lenses. At baseline, fo... more To assess visual performance of single vision and multifocal soft contact lenses. At baseline, forty-four myopic participants (aged 18-35 years) were fitted bilaterally with a control lens (AirOptix Aqua). At the four follow-up visits, a total of 16 study lenses (5 single vision, 11 multifocal lenses) were fitted contralaterally. After 1h of lens wear, participants rated (scale 1-10) vision clarity (distance, intermediate and near), magnitude of ghosting at distance, comfort during head movement, and overall comfort. Distance high contrast visual acuity (HCVA), central refraction and higher order aberrations, and contact lens centration were measured. For single vision lenses, vision ratings were not significantly different to the control (p>0.005). The control outperformed Acuvue Oasys, Clariti Monthly and Night and Day in HCVA (mean VA: -0.10±0.07 logMAR, p<0.005). Most refraction and higher order aberration measures were not different between lenses. The Night and Day lens showed greatest differences compared to the control, i.e., C[4, 0] was more positive (p<0.005) at distance (Δ=0.019μm) and near (Δ=0.028μm). For multifocal lenses, the majority of vision ratings (84%) were better with the control (p<0.005). HCVA was better with the control (p<0.005). Proclear Multifocal lenses showed greatest differences for M, C[3, -1] and C[4, 0] at distance and near, and were inferiorly de-centered (p<0.005). Design differences between single vision lenses had a small impact on visual performance. Lenses featuring multifocality decreased visual performance, in particular when power variations across the optic zone were large and/or the lens was significantly de-centered.

Ophthalmic Technologies XV, 2005

ABSTRACT The ex vivo accommodation simulator stretches crystalline lenses radially under controll... more ABSTRACT The ex vivo accommodation simulator stretches crystalline lenses radially under controlled conditions, while monitoring the changes in zonular tension and lens diameter. A dual coaxial laser beam system was added for measuring changes in optical power as the lens is stretched. The EVAS instrument was fully characterized and calibrated. The results from 3 porcine eyes will be presented. Several crystalline lenses, similar in shape and size to porcine lenses, were cast molded in silicone gels of different stiffness. These lenses were evaluated using the EVAS instrument and custom made lens holding fixtures. With their well defined shape and material properties, results from these measurements will be useful for cross-validation of finite element models.

Journal of Medical Devices, 2010

Finite Element Modeling of Inverted (Inside Out) Soft Contact Lenses. [Journal of Medical Devices... more Finite Element Modeling of Inverted (Inside Out) Soft Contact Lenses. [Journal of Medical Devices 4, 024501 (2010)]. Fabian Conrad, Klaus Ehrmann, Jennifer D. Choo, Brien A. Holden. Abstract. Soft contact lenses (SCLs) can ...

Ophthalmic Technologies XXII, 2012

ABSTRACT Interest in measuring peripheral refraction rapidly and accurately has been stimulated b... more ABSTRACT Interest in measuring peripheral refraction rapidly and accurately has been stimulated by increasing evidence that the eye's peripheral refractive state can influence axial growth. In response to this, a new clinical instrument, the EyeMapper, was developed which performs quasi real-time global (central and peripheral) refraction measurements of the human eye. The EyeMapper is an aberrometer comprising a unique deflection system to permit an extremely rapid visual field scan. Refraction measurements are taken from -50° to +50° in 10° steps within 0.45 seconds. Multiple pupil imaging paths through the deflection system provide improved lateral and axial pupil alignment, and by rotating the instrument around its main optical axis, global power maps of the eye can be generated. Using a model eye with a pivoting and translating reflective surface to simulate the peripheral and central retina, the EyeMapper was cross-validated against a conventional aberrometer (COAS-HD, Wavefront Sciences, USA) and an autorefractor (Shin-Nippon NVision K5001, Japan). In addition, the right eyes of ten participants were measured across the horizontal visual field and in one eye, refraction measurements were performed globally. Overall, the EyeMapper showed good agreement and improved repeatability when compared to the other two instruments.

Ophthalmic Technologies XIX, 2009

ABSTRACT A new instrument has been developed and built to measure the spatially resolved optical ... more ABSTRACT A new instrument has been developed and built to measure the spatially resolved optical power of intra-ocular and contact lenses. Currently available instruments are based on either Hartmann Shack or Moiré Fringe techniques, which both have inherent limitations in terms of measurement range, sensitivity and achievable lateral resolution. Our new method uses a narrow laser beam which is scanned paraxially across the surface of the lens. The angle of the deflected beam is determined by capturing the lateral laser spot position at two different axial locations by means of a beam-splitter and two position sensitive, optical detectors. From the matrix of deflection angles, the spherical and cylindrical power components as well as higher order aberrations can be extracted and displayed as spatially resolved power maps. While measurement speed is compromised due to the scanning operation, the achievable lateral resolution can be as high as 20µm and the power accuracy in the order of milli-diopters. Soft contact lenses and foldable IOLs can be placed in wet cells to maintain hydration and form stability. Sample measurements of contact and intra ocular lenses are presented.

Ophthalmic Technologies XVIII, 2008

ABSTRACT Cataract surgery usually involves the replacement of the natural crystalline lens with a... more ABSTRACT Cataract surgery usually involves the replacement of the natural crystalline lens with a rigid or foldable intraocular lens to restore clear vision for the patient. While great efforts have been placed on optimising the shape and optical characteristics of IOLs, little is know about the mechanical properties of these devices and how they interact with the capsular bag once implanted. Mechanical properties measurements were performed on 8 of the most commonly implanted IOLs using a custom build micro tensometer. Measurement data will be presented for the stiffness of the haptic elements, the buckling resistance of foldable IOLs, the dynamic behaviour of the different lens materials and the axial compressibility. The biggest difference between the lens types was found between one-piece and 3-piece lenses with respect to the flexibility of the haptic elements

Ophthalmic Technologies XIV, 2004

ABSTRACT A new instrument was developed to simulate the accommodation of excised human and animal... more ABSTRACT A new instrument was developed to simulate the accommodation of excised human and animal crystalline lenses. The sclera is attached to 8 radially arranged translation stages and dissected into 8 segments. Change in accommodation is simulated by pulling and releasing the scleral segments, varying the load on the zonules and the capsular bag. Each translation stage is equipped with a sensitive force transducer for simultaneous recording of load and displacement. Additionally, changes in optical power, lens diameter, lens thickness and lens shape can be observed and quantified while the lens is stretched and released. The sensitivity and accuracy of the instrument was verified using steel springs and elastic bands. Preliminary results from sensitivity testing and instrument calibration are presented.

Ophthalmic Technologies XIX, 2009

We propose a novel theoretical design of gradient index (GRIN) multifocal contact lens (MFCL) to ... more We propose a novel theoretical design of gradient index (GRIN) multifocal contact lens (MFCL) to compensate presbyopia and make predictions regarding its performance on a schematic model eye and to compare its performance with conventional aspheric progressive MFCL.

Optometry and Vision Science, 2014

Optometry and vision science : official publication of the American Academy of Optometry, 2009

The recently discovered link between myopia development and peripheral refraction has triggered a... more The recently discovered link between myopia development and peripheral refraction has triggered a stream of clinical and animal investigations to confirm the theory and to understand the underlying mechanisms. For this, precise peripheral refractometry has now gained importance in myopia research. For more than 70 years, many researchers have measured off-axis refraction of the eye in horizontal and sometimes vertical meridians over a range of angles, using several modified refraction techniques. These techniques varied not only with respect to the instrumentation used, but also the modifications performed to enable off-axis refraction. Modifications included either head or eye turn of the participant with respect to the peripheral angle tested or rotation of the instrument itself around the center of the eye. The main focus of this study is to review and compare all refraction techniques for off-axis measurements including necessary modifications made to equipment or procedures. Be...

Ophthalmic Technologies X, 2000

ABSTRACT With the increasing complexity of contact lens designs and the demand on visual performa... more ABSTRACT With the increasing complexity of contact lens designs and the demand on visual performance required by wearers, the ability to assess the design and optical quality of a contact lens is an important capability. While more complex systems such as Hartmann-Shack devices exist, practitioners often call for a simple, quick and inexpensive system that can provide the above functions. A simple optical system based on modifying the knife-edge test has been developed for assessing design and optical quality. Incorporation of a Badal-type lens layout added lens power measurement capability. This system provides the practitioner with the ability to undertake rapid visual assessment of a contact lens's quality.

Journal of Optometry, 2015

To compare the contributions of single vision (SVCL) and multifocal contact lenses (MFCL) to the ... more To compare the contributions of single vision (SVCL) and multifocal contact lenses (MFCL) to the relative peripheral refraction (RPR) profiles obtained via an autorefractor and an aberrometer in a pilot study. Two instruments, Shin-Nippon NVision K5001 (SN) and COAS-HD, were modified to permit open field PR measurements. Two myopic adults (CF, RB) were refracted (cycloplegia) under eight conditions: baseline (no CL); three SVCLs: Focus Dailies(®) (Alcon, USA), PureVision(®) (Bausch & Lomb, USA) and AirOptix(®) (Alcon, USA); and four MFCLs: AirOptix(®) (Alcon, USA), Proclear(®) Distant and Near (Cooper Vision, USA), and PureVision(®) (Bausch & Lomb, USA). CLs had a distance prescription of -2.00D and for MFCLs, a +2.50D Add was selected. Five independent measurements were performed at field angles from -40° to +40° in 10° increments with both instruments. The COAS-HD measures were analyzed at 3mm pupil diameter. Results are reported as a change in the relative PR profile, as refractive power vector components: M, J180, and J45. Overall, at baseline, M, J180 and J45 measures obtained with SN and COAS-HD were considerably different only for field angles ≥±30°, which agreed well with previous studies. With respect to M, this observation held true for most SVCLs with a few exceptions. The J180 measures obtained with COAS-HD were considerably greater in magnitude than those acquired with SN. For SVCLs, the greatest difference was found at -40° for AirOptix SV (ΔCF=3.20D, ΔRB=1.56D) and for MFCLs it was for Proclear Distance at -40° (ΔCF=2.58D, ΔRB=1.39D). The J45 measures obtained with SN were noticeably different to the respective measures with COAS-HD, both in magnitude and sign. The greatest difference was found with AirOptix Multifocal in subject RB at -40°, where the COAS-HD measurement was 1.50D more positive. In some cases, the difference in the RPR profiles observed between subjects appeared to be associated with CL decentration. For most test conditions, distinct differences were observed between the RPR measures obtained with the two modified instruments. The differences varied with CL design and centration. Although the pilot study supports the interchangeable use of the two instruments for on- and off-axis refraction in unaided eyes or eyes corrected with low/no spherical aberration; we advocate the use of the COAS-HD over the SN for special purposes like refracting through multifocal CLs.

Ophthalmic Technologies XVI, 2006

Lid angles and aperture size are important factors for fitting and on-eye performance of contact ... more Lid angles and aperture size are important factors for fitting and on-eye performance of contact lenses. In particular, toric and translating bifocal lenses rely on predictable interaction with the eyelid for successful positioning and orientation. Traditionally, lid assessment and fitting evaluation is performed under slit lamp observation. Observations are limited to primary gaze and nasal or temporal directions. Quantification of

Ophthalmic Technologies X, 2000

ABSTRACT The pre-corneal tear layer provides an important optical as well as physiological functi... more ABSTRACT The pre-corneal tear layer provides an important optical as well as physiological function. Hence, the ability to assess the quality and behavior of tears, especially in dry-eye, marginal dry-eye and contact lens patients is important. While a large range of clinical tests exists for assessing tear quality, many are subjective and show poor repeatability. Since the tear meniscus is dependent on factors such as volume, viscosity and 'wettability,' we attempted to develop an optical system for imaging the tear meniscus. A basic prototype to test feasibility has been constructed. An algorithm for computing the profile of the meniscus was also developed. The methodology is described together with some examples of tear menisci imaged and analyzed.

Investigative Ophthalmology & Visual Science, 2015

Ophthalmic Technologies XIX, 2009

Ophthalmic Technologies XIX, 2009

Our aim was to fabricate a bench-top physical model eye that closely replicates anatomical and op... more Our aim was to fabricate a bench-top physical model eye that closely replicates anatomical and optical properties of the average human eye, and to calibrate and standardize this model to suit normal viewing conditions and subsequently utilize it to understand the optical performance of corrective lens designs; especially multifocal soft contact lenses. Using available normative data on ocular biometrics and Zemax ray-tracing software as a tool, we modeled 25, 45 and 55 year-old average adult human eyes with discrete accommodation levels and pupil sizes. Specifications for the components were established following manufacturing tolerance analyses. The cornea was lathed from an optical material with refractive index of 1.376 @ 589 nm and the crystalline lenses were made of Boston RGP polymers with refractive indices of 1.423 (45 & 55yr) and 1.429 (25yr) @ 589 nm. These two materials served to model the equivalent crystalline lens of the different age-groups. A camera, the acting retina, was hosted on the motor-base having translatory and rotary functions to facilitate the simulation of different states of ametropia and peripheral refraction respectively. We report on the implementation of the first prototype and present some simulations of the optical performance of certain contact lenses with specific levels of ametropia, to demonstrate the potential use of such a physical model eye. On completion of development, calibration and standardization, optical quality assessment and performance predictions of different ophthalmic lenses can be studied in great detail. Optical performance with corrective lenses may be reliably simulated and predicted by customized combined computational and physical models giving insight into the merits and pitfalls of their designs

Optometry and Vision Science, 2014

To measure the power profile across the optic zone (OZ) of four commercially available soft conta... more To measure the power profile across the optic zone (OZ) of four commercially available soft contact lenses and establish the impact on the peripheral refractive error of the eye. The power profiles of a spherical conventional hydrogel contact lens (etafilcon A, J&J Vistakon, Jacksonville, FL USA) and three spherical silicone hydrogel contact lenses (lotrafilcon A and B, CIBA Vision, Duluth, GA USA; enfilcon A, CooperVision, Pleasanton, CA USA) with a labeled power of -3.00 and -6.00 diopters were measured using a Shack-Hartmann wavefront sensor power mapping device. Central and peripheral refraction across the horizontal meridian (nasal and temporal visual field at 20, 30, and 40 degrees) was measured with an open-field autorefractor (Shin Nippon NVision K5001, Osaka Japan) with and without contact lenses in 26 myopic subjects. The relative peripheral refractive error on the eye was estimated and compared with and without contact lenses and between contact lenses. Differences in the distribution of the power profile across the OZ were apparent between contact lens types and powers. No significant differences (p > 0.05) were found between contact lens types for their effect on on-axis refraction. Significant differences (p < 0.05) were found at all peripheral retinal eccentricities between contact lens types. For a given central power, the four contact lenses exhibited variations in optical power across the OZ of the lens. The distribution of optical power across the OZ has an influence on the peripheral refractive error of the eye.

Proceedings of SPIE - The International Society for Optical Engineering

ABSTRACT

Journal of optometry, Jan 16, 2015

To determine if a fogging lens ameliorates accommodative effects driven by the closed-view design... more To determine if a fogging lens ameliorates accommodative effects driven by the closed-view design of the BHVI-EyeMapper (EM) instrument. We compared cycloplegic refraction and higher-order aberration measurements of the EM with those obtained with a fogging lens. Twenty-six, young, participants (15F, 25±5 years, range: 18-35 years, SE: +0.25D and -3.50D) with good ocular health were recruited. Five independent measurements of on- and off-axis refraction and higher-order aberrations were recorded across the horizontal visual field, under two conditions: non-cycloplegic measurements with +1.00D fogging lens and cycloplegia, always in the same sequence. The contralateral eye was occluded during the measurements. Two drops of 1% Tropicamide delivered within 5min facilitated cycloplegic measurements. All participants were refracted 30min after installation of the second drop. Mean spherical equivalent measures of the non-cycloplegic condition were significantly more myopic than their cyc...

Contact Lens and Anterior Eye, 2015

To assess visual performance of single vision and multifocal soft contact lenses. At baseline, fo... more To assess visual performance of single vision and multifocal soft contact lenses. At baseline, forty-four myopic participants (aged 18-35 years) were fitted bilaterally with a control lens (AirOptix Aqua). At the four follow-up visits, a total of 16 study lenses (5 single vision, 11 multifocal lenses) were fitted contralaterally. After 1h of lens wear, participants rated (scale 1-10) vision clarity (distance, intermediate and near), magnitude of ghosting at distance, comfort during head movement, and overall comfort. Distance high contrast visual acuity (HCVA), central refraction and higher order aberrations, and contact lens centration were measured. For single vision lenses, vision ratings were not significantly different to the control (p>0.005). The control outperformed Acuvue Oasys, Clariti Monthly and Night and Day in HCVA (mean VA: -0.10±0.07 logMAR, p<0.005). Most refraction and higher order aberration measures were not different between lenses. The Night and Day lens showed greatest differences compared to the control, i.e., C[4, 0] was more positive (p<0.005) at distance (Δ=0.019μm) and near (Δ=0.028μm). For multifocal lenses, the majority of vision ratings (84%) were better with the control (p<0.005). HCVA was better with the control (p<0.005). Proclear Multifocal lenses showed greatest differences for M, C[3, -1] and C[4, 0] at distance and near, and were inferiorly de-centered (p<0.005). Design differences between single vision lenses had a small impact on visual performance. Lenses featuring multifocality decreased visual performance, in particular when power variations across the optic zone were large and/or the lens was significantly de-centered.

Ophthalmic Technologies XV, 2005

ABSTRACT The ex vivo accommodation simulator stretches crystalline lenses radially under controll... more ABSTRACT The ex vivo accommodation simulator stretches crystalline lenses radially under controlled conditions, while monitoring the changes in zonular tension and lens diameter. A dual coaxial laser beam system was added for measuring changes in optical power as the lens is stretched. The EVAS instrument was fully characterized and calibrated. The results from 3 porcine eyes will be presented. Several crystalline lenses, similar in shape and size to porcine lenses, were cast molded in silicone gels of different stiffness. These lenses were evaluated using the EVAS instrument and custom made lens holding fixtures. With their well defined shape and material properties, results from these measurements will be useful for cross-validation of finite element models.

Journal of Medical Devices, 2010

Finite Element Modeling of Inverted (Inside Out) Soft Contact Lenses. [Journal of Medical Devices... more Finite Element Modeling of Inverted (Inside Out) Soft Contact Lenses. [Journal of Medical Devices 4, 024501 (2010)]. Fabian Conrad, Klaus Ehrmann, Jennifer D. Choo, Brien A. Holden. Abstract. Soft contact lenses (SCLs) can ...

Ophthalmic Technologies XXII, 2012

ABSTRACT Interest in measuring peripheral refraction rapidly and accurately has been stimulated b... more ABSTRACT Interest in measuring peripheral refraction rapidly and accurately has been stimulated by increasing evidence that the eye's peripheral refractive state can influence axial growth. In response to this, a new clinical instrument, the EyeMapper, was developed which performs quasi real-time global (central and peripheral) refraction measurements of the human eye. The EyeMapper is an aberrometer comprising a unique deflection system to permit an extremely rapid visual field scan. Refraction measurements are taken from -50° to +50° in 10° steps within 0.45 seconds. Multiple pupil imaging paths through the deflection system provide improved lateral and axial pupil alignment, and by rotating the instrument around its main optical axis, global power maps of the eye can be generated. Using a model eye with a pivoting and translating reflective surface to simulate the peripheral and central retina, the EyeMapper was cross-validated against a conventional aberrometer (COAS-HD, Wavefront Sciences, USA) and an autorefractor (Shin-Nippon NVision K5001, Japan). In addition, the right eyes of ten participants were measured across the horizontal visual field and in one eye, refraction measurements were performed globally. Overall, the EyeMapper showed good agreement and improved repeatability when compared to the other two instruments.

Ophthalmic Technologies XIX, 2009

ABSTRACT A new instrument has been developed and built to measure the spatially resolved optical ... more ABSTRACT A new instrument has been developed and built to measure the spatially resolved optical power of intra-ocular and contact lenses. Currently available instruments are based on either Hartmann Shack or Moiré Fringe techniques, which both have inherent limitations in terms of measurement range, sensitivity and achievable lateral resolution. Our new method uses a narrow laser beam which is scanned paraxially across the surface of the lens. The angle of the deflected beam is determined by capturing the lateral laser spot position at two different axial locations by means of a beam-splitter and two position sensitive, optical detectors. From the matrix of deflection angles, the spherical and cylindrical power components as well as higher order aberrations can be extracted and displayed as spatially resolved power maps. While measurement speed is compromised due to the scanning operation, the achievable lateral resolution can be as high as 20µm and the power accuracy in the order of milli-diopters. Soft contact lenses and foldable IOLs can be placed in wet cells to maintain hydration and form stability. Sample measurements of contact and intra ocular lenses are presented.

Ophthalmic Technologies XVIII, 2008

ABSTRACT Cataract surgery usually involves the replacement of the natural crystalline lens with a... more ABSTRACT Cataract surgery usually involves the replacement of the natural crystalline lens with a rigid or foldable intraocular lens to restore clear vision for the patient. While great efforts have been placed on optimising the shape and optical characteristics of IOLs, little is know about the mechanical properties of these devices and how they interact with the capsular bag once implanted. Mechanical properties measurements were performed on 8 of the most commonly implanted IOLs using a custom build micro tensometer. Measurement data will be presented for the stiffness of the haptic elements, the buckling resistance of foldable IOLs, the dynamic behaviour of the different lens materials and the axial compressibility. The biggest difference between the lens types was found between one-piece and 3-piece lenses with respect to the flexibility of the haptic elements

Ophthalmic Technologies XIV, 2004

ABSTRACT A new instrument was developed to simulate the accommodation of excised human and animal... more ABSTRACT A new instrument was developed to simulate the accommodation of excised human and animal crystalline lenses. The sclera is attached to 8 radially arranged translation stages and dissected into 8 segments. Change in accommodation is simulated by pulling and releasing the scleral segments, varying the load on the zonules and the capsular bag. Each translation stage is equipped with a sensitive force transducer for simultaneous recording of load and displacement. Additionally, changes in optical power, lens diameter, lens thickness and lens shape can be observed and quantified while the lens is stretched and released. The sensitivity and accuracy of the instrument was verified using steel springs and elastic bands. Preliminary results from sensitivity testing and instrument calibration are presented.

Ophthalmic Technologies XIX, 2009

We propose a novel theoretical design of gradient index (GRIN) multifocal contact lens (MFCL) to ... more We propose a novel theoretical design of gradient index (GRIN) multifocal contact lens (MFCL) to compensate presbyopia and make predictions regarding its performance on a schematic model eye and to compare its performance with conventional aspheric progressive MFCL.

Optometry and Vision Science, 2014

Optometry and vision science : official publication of the American Academy of Optometry, 2009

The recently discovered link between myopia development and peripheral refraction has triggered a... more The recently discovered link between myopia development and peripheral refraction has triggered a stream of clinical and animal investigations to confirm the theory and to understand the underlying mechanisms. For this, precise peripheral refractometry has now gained importance in myopia research. For more than 70 years, many researchers have measured off-axis refraction of the eye in horizontal and sometimes vertical meridians over a range of angles, using several modified refraction techniques. These techniques varied not only with respect to the instrumentation used, but also the modifications performed to enable off-axis refraction. Modifications included either head or eye turn of the participant with respect to the peripheral angle tested or rotation of the instrument itself around the center of the eye. The main focus of this study is to review and compare all refraction techniques for off-axis measurements including necessary modifications made to equipment or procedures. Be...

Ophthalmic Technologies X, 2000

ABSTRACT With the increasing complexity of contact lens designs and the demand on visual performa... more ABSTRACT With the increasing complexity of contact lens designs and the demand on visual performance required by wearers, the ability to assess the design and optical quality of a contact lens is an important capability. While more complex systems such as Hartmann-Shack devices exist, practitioners often call for a simple, quick and inexpensive system that can provide the above functions. A simple optical system based on modifying the knife-edge test has been developed for assessing design and optical quality. Incorporation of a Badal-type lens layout added lens power measurement capability. This system provides the practitioner with the ability to undertake rapid visual assessment of a contact lens's quality.

Journal of Optometry, 2015

To compare the contributions of single vision (SVCL) and multifocal contact lenses (MFCL) to the ... more To compare the contributions of single vision (SVCL) and multifocal contact lenses (MFCL) to the relative peripheral refraction (RPR) profiles obtained via an autorefractor and an aberrometer in a pilot study. Two instruments, Shin-Nippon NVision K5001 (SN) and COAS-HD, were modified to permit open field PR measurements. Two myopic adults (CF, RB) were refracted (cycloplegia) under eight conditions: baseline (no CL); three SVCLs: Focus Dailies(®) (Alcon, USA), PureVision(®) (Bausch & Lomb, USA) and AirOptix(®) (Alcon, USA); and four MFCLs: AirOptix(®) (Alcon, USA), Proclear(®) Distant and Near (Cooper Vision, USA), and PureVision(®) (Bausch & Lomb, USA). CLs had a distance prescription of -2.00D and for MFCLs, a +2.50D Add was selected. Five independent measurements were performed at field angles from -40° to +40° in 10° increments with both instruments. The COAS-HD measures were analyzed at 3mm pupil diameter. Results are reported as a change in the relative PR profile, as refractive power vector components: M, J180, and J45. Overall, at baseline, M, J180 and J45 measures obtained with SN and COAS-HD were considerably different only for field angles ≥±30°, which agreed well with previous studies. With respect to M, this observation held true for most SVCLs with a few exceptions. The J180 measures obtained with COAS-HD were considerably greater in magnitude than those acquired with SN. For SVCLs, the greatest difference was found at -40° for AirOptix SV (ΔCF=3.20D, ΔRB=1.56D) and for MFCLs it was for Proclear Distance at -40° (ΔCF=2.58D, ΔRB=1.39D). The J45 measures obtained with SN were noticeably different to the respective measures with COAS-HD, both in magnitude and sign. The greatest difference was found with AirOptix Multifocal in subject RB at -40°, where the COAS-HD measurement was 1.50D more positive. In some cases, the difference in the RPR profiles observed between subjects appeared to be associated with CL decentration. For most test conditions, distinct differences were observed between the RPR measures obtained with the two modified instruments. The differences varied with CL design and centration. Although the pilot study supports the interchangeable use of the two instruments for on- and off-axis refraction in unaided eyes or eyes corrected with low/no spherical aberration; we advocate the use of the COAS-HD over the SN for special purposes like refracting through multifocal CLs.

Ophthalmic Technologies XVI, 2006

Lid angles and aperture size are important factors for fitting and on-eye performance of contact ... more Lid angles and aperture size are important factors for fitting and on-eye performance of contact lenses. In particular, toric and translating bifocal lenses rely on predictable interaction with the eyelid for successful positioning and orientation. Traditionally, lid assessment and fitting evaluation is performed under slit lamp observation. Observations are limited to primary gaze and nasal or temporal directions. Quantification of

Ophthalmic Technologies X, 2000

ABSTRACT The pre-corneal tear layer provides an important optical as well as physiological functi... more ABSTRACT The pre-corneal tear layer provides an important optical as well as physiological function. Hence, the ability to assess the quality and behavior of tears, especially in dry-eye, marginal dry-eye and contact lens patients is important. While a large range of clinical tests exists for assessing tear quality, many are subjective and show poor repeatability. Since the tear meniscus is dependent on factors such as volume, viscosity and 'wettability,' we attempted to develop an optical system for imaging the tear meniscus. A basic prototype to test feasibility has been constructed. An algorithm for computing the profile of the meniscus was also developed. The methodology is described together with some examples of tear menisci imaged and analyzed.

Investigative Ophthalmology & Visual Science, 2015

Ophthalmic Technologies XIX, 2009

Ophthalmic Technologies XIX, 2009

Our aim was to fabricate a bench-top physical model eye that closely replicates anatomical and op... more Our aim was to fabricate a bench-top physical model eye that closely replicates anatomical and optical properties of the average human eye, and to calibrate and standardize this model to suit normal viewing conditions and subsequently utilize it to understand the optical performance of corrective lens designs; especially multifocal soft contact lenses. Using available normative data on ocular biometrics and Zemax ray-tracing software as a tool, we modeled 25, 45 and 55 year-old average adult human eyes with discrete accommodation levels and pupil sizes. Specifications for the components were established following manufacturing tolerance analyses. The cornea was lathed from an optical material with refractive index of 1.376 @ 589 nm and the crystalline lenses were made of Boston RGP polymers with refractive indices of 1.423 (45 & 55yr) and 1.429 (25yr) @ 589 nm. These two materials served to model the equivalent crystalline lens of the different age-groups. A camera, the acting retina, was hosted on the motor-base having translatory and rotary functions to facilitate the simulation of different states of ametropia and peripheral refraction respectively. We report on the implementation of the first prototype and present some simulations of the optical performance of certain contact lenses with specific levels of ametropia, to demonstrate the potential use of such a physical model eye. On completion of development, calibration and standardization, optical quality assessment and performance predictions of different ophthalmic lenses can be studied in great detail. Optical performance with corrective lenses may be reliably simulated and predicted by customized combined computational and physical models giving insight into the merits and pitfalls of their designs

Optometry and Vision Science, 2014

To measure the power profile across the optic zone (OZ) of four commercially available soft conta... more To measure the power profile across the optic zone (OZ) of four commercially available soft contact lenses and establish the impact on the peripheral refractive error of the eye. The power profiles of a spherical conventional hydrogel contact lens (etafilcon A, J&J Vistakon, Jacksonville, FL USA) and three spherical silicone hydrogel contact lenses (lotrafilcon A and B, CIBA Vision, Duluth, GA USA; enfilcon A, CooperVision, Pleasanton, CA USA) with a labeled power of -3.00 and -6.00 diopters were measured using a Shack-Hartmann wavefront sensor power mapping device. Central and peripheral refraction across the horizontal meridian (nasal and temporal visual field at 20, 30, and 40 degrees) was measured with an open-field autorefractor (Shin Nippon NVision K5001, Osaka Japan) with and without contact lenses in 26 myopic subjects. The relative peripheral refractive error on the eye was estimated and compared with and without contact lenses and between contact lenses. Differences in the distribution of the power profile across the OZ were apparent between contact lens types and powers. No significant differences (p > 0.05) were found between contact lens types for their effect on on-axis refraction. Significant differences (p < 0.05) were found at all peripheral retinal eccentricities between contact lens types. For a given central power, the four contact lenses exhibited variations in optical power across the OZ of the lens. The distribution of optical power across the OZ has an influence on the peripheral refractive error of the eye.