Ahmed Elsheikh - Academia.edu (original) (raw)

Papers by Ahmed Elsheikh

Medicine in Novel Technology and Devices, 2021

1Osteoarthritis (OA) is a whole joint disease that affects all knee joint tissues. Ligaments, a m... more 1Osteoarthritis (OA) is a whole joint disease that affects all knee joint tissues. Ligaments, a matrix-rich connective tissue, play an important mechanical function that stabilises the knee joint and yet their role in OA is not well studied. Recent studies have shown that ligament extracellular matrix (ECM) structure is compromised in the early stages of OA, but it remains unclear how this affects ligament function and biomechanics. In this study, the aim was to investigate the structural, cellular and viscoelastic changes in the anterior cruciate ligament (ACL) in a murine non-invasive post-traumatic OA (PTOA) model. Non-invasive mechanical loading of the knee joint of C57BL/6J mice (10-week-old) was used as a PTOA model. Knee joints were analysed for joint space mineralisation and the ACLs were assessed with histology and mechanical testing. PTOA knee joints had a 33-46% increase in joint space mineralisation and PTOA knee joint ACLs exhibited ECM modifications, including collagen...

PLOS ONE, 2021

PurposeTo investigate the stress-strain behaviour of 9 soft contact lens materials, that are comm... more PurposeTo investigate the stress-strain behaviour of 9 soft contact lens materials, that are commonly used in the market, under uniaxial compression loading.MethodsSeven types of hydrogel and two types of silicone-hydrogel soft contact lens materials were hydrated in phosphate-buffered saline (PBS) solution then subjected to uniaxial compression loads. The load rate was set to 16.0 N/min starting with two consecutive initial 5.0 N loading cycles followed by three relaxation periods of 4.0 min within which there were two more 5.0 N loading cycles and eventually, a full loading cycle that stopped at a load of 49.0 N. The load and contraction data obtained experimentally were analysed to derive the stress-strain behaviour. Finite Element (FE) analysis was then utilised to evaluate the performance of soft contact lenses on the human eye and handling lenses off the eye.ResultsUnlike tensile tests, all tested materials showed nonlinear behaviour when tested under compression. When fitted ...

Journal of Refractive Surgery

PURPOSE To evaluate the effect of the implantation of intracorneal ring segments (ICRS) in kerato... more PURPOSE To evaluate the effect of the implantation of intracorneal ring segments (ICRS) in keratoconus on the dynamic corneal response (DCR) parameters obtained with the Corvis ST (Oculus Optikgeräte GmbH). METHODS This prospective clinical study included patients who underwent ICRS implantation for keratoconus over a period of 1 year. On the day of the surgery and at least 1 month after ICRS implantation, the following measurements were made: corrected and uncorrected distance visual acuity, corneal tomography indices with the Pentacam (Oculus Optikgeräte GmbH), biomechanically corrected intraocular pressure (bIOP), Corvis ST DCR parameters, integrated inverse concave radius (1/R), deformation amplitude ratio (DA ratio), stiffness parameter at first applanation (SP-A1), stress-strain index (SSI), and highest concavity radius (HRC). RESULTS Fifty-one eyes of 40 patients were included with a median follow-up time of 3 months (interquartile ratio [IQR]: 2 to 6 months). Statistical analysis showed that ICRS implantation did not affect corneal biomechanical measurements evaluated with the Corvis ST, which was demonstrated by non-significant changes in the SP-A1 (P = .637), 1/R (P = .647), HRC (P = .177), DA ratio (P = .735), and SSI (P = .501). Additionally, the results showed that bIOP measurements were not significantly affected by ICRS implantation (P = .113). CONCLUSIONS ICRS implantation does not affect corneal biomechanical measurements in early follow-up. [J Refract Surg. 2022;38(4):264-269.].

International Journal of Environmental Research and Public Health, Nov 25, 2019

Optical Coherence Tomography (OCT) images have the potential to provide quantitative measurements... more Optical Coherence Tomography (OCT) images have the potential to provide quantitative measurements of the entire anterior segment of the eye. A new threedimensional (3D) segmentation framework founded on level set based shape prior segmentation model has been developed for automatic segmentation of the entire cornea in 3D anterior segment OCT (AS-OCT). A three step algorithm was developed. The first step was to pre-process the image to reduce noise. The next step was to obtain a coarse segmentation of the front eye by using an entropy filter and the Otsu’s thresholding technique. The final step used the new level set based shape prior segmentation model under cylindrical coordinates to evolve the contour initialised from the coarse segmentation and achieve the final segmentation. Initial results on synthetic image and real 3D AS-OCT images show promising results.

Introduction Corneal microstructure Corneal topography Corneal biomechanical behaviour Numerical ... more Introduction Corneal microstructure Corneal topography Corneal biomechanical behaviour Numerical modeling of ocular biomechanics Conclusion Index.

IOP Conference Series: Materials Science and Engineering, 2018

With the advent of research it was identified that material properties are responsible for errors... more With the advent of research it was identified that material properties are responsible for errors in tonometry pressure (referred to as Goldmann IOP or IOPG) with the stiffening of a composite structure of corneal tissue in particular. Strip tensile tests are conducted to determine their stress–strain relationship for the purpose to study the behaviour of material properties of cornea. Specimens are taken from the superior–inferior (vertical) and temporal– nasal (horizontal) directions. Testing is performed on an Instron machine, under different rate of loading conditions. First set of experiment, with single strain rate, is executed on eyes having random population. While the second set of experiment is executed on eyes of the same animal in both directions, and different strain rates are applied each specimen. Relatively, the first set of experiment is found to be slightly different and less accurate. In general, it is found that the vertical specimen is 34% on an average stiffer ...

SSRN Electronic Journal, 2021

Journal of Refractive Surgery, 2020

Current Eye Research, 2019

Journal of refractive surgery (Thorofare, N.J. : 1995), 2018

To determine the relationship between mechanical behavior in cross-linked corneas and changes in ... more To determine the relationship between mechanical behavior in cross-linked corneas and changes in the corneal ultrastructure after corneal cross-linking (CXL). Porcine corneas were treated following the "Dresden" protocol, the current gold standard for clinical treatment, consisting of dropwise application of 0.1% riboflavin in 20% dextran followed by 30 minutes of ultraviolet-A (UVA) irradiation. The effect of CXL was assessed using uniaxial tensile testing, transmission electron microscopy, and Fourier transform infrared spectroscopy, with results compared against corneas treated with each of the treatment solution components individually. UVA/riboflavin cross-linked corneas displayed 28% ± 17% increase in the material tangent modulus compared with dextran treatment alone, and altered collagen architecture within the first 300 µm of stromal depth consisting of 5% increase in the thickness of collagen fibrils, no significant changes to interfibrillar spacing, and an 8% to ...

Journal of refractive surgery (Thorofare, N.J. : 1995), 2018

To evaluate whether different corneal cross-linking (CXL) irradiances, all with the same delivere... more To evaluate whether different corneal cross-linking (CXL) irradiances, all with the same delivered total energy, achieve similar increases in corneal material stiffness. One hundred twenty-six healthy white Japanese rabbits were randomly divided into seven groups (n = 18 each). After removing the epithelium of the left corneas, six groups were exposed to riboflavin (0.22% concentration by volume) and ultraviolet-A (370 nm) at different CXL irradiations, all with the same total dose (5.4 J/cm2), ranging from 3 mW/cm2 for 30 minutes to 90 mW/cm2 for 1 minute. The left corneas of the seventh group were exposed to riboflavin without irradiation. Twelve corneas of each group were prepared for inflation testing, where they were subjected to internal hydrostatic pressure simulating intraocular pressure, whereas the other six specimens were processed for electron microscopy measurements of fibril diameter and interfibrillar spacing. The inverse modeling process was used to estimate the tang...

Essentials in Ophthalmology, 2016

Keratoconus, the occurrence and development of which is associated with corneal thinning and coni... more Keratoconus, the occurrence and development of which is associated with corneal thinning and conical protrusion causing irregular astigmatism, is a bilateral non-inflammatory degenerative corneal disease. With the disruption of the collagen organisation, the cornea loses its shape and function resulting in progressive visual degradation. Currently, corneal topography remains the most important tool for the diagnosis of keratoconus. However, this approach may lead to false negatives among the patient population in the subclinical phase. It is now hypothesised that biomechanical destabilisation of the cornea may take place ahead of the topographic evidence of keratoconus. Therefore, accurate characterisation of in vivo biomechanical properties could possibly be used to assist with diagnosis and management, particularly in the early stages of the disease. This chapter provides a summary of the definition, diagnosis and management strategies for keratoconus based on corneal biomechanics.

Medicine in Novel Technology and Devices, 2021

1Osteoarthritis (OA) is a whole joint disease that affects all knee joint tissues. Ligaments, a m... more 1Osteoarthritis (OA) is a whole joint disease that affects all knee joint tissues. Ligaments, a matrix-rich connective tissue, play an important mechanical function that stabilises the knee joint and yet their role in OA is not well studied. Recent studies have shown that ligament extracellular matrix (ECM) structure is compromised in the early stages of OA, but it remains unclear how this affects ligament function and biomechanics. In this study, the aim was to investigate the structural, cellular and viscoelastic changes in the anterior cruciate ligament (ACL) in a murine non-invasive post-traumatic OA (PTOA) model. Non-invasive mechanical loading of the knee joint of C57BL/6J mice (10-week-old) was used as a PTOA model. Knee joints were analysed for joint space mineralisation and the ACLs were assessed with histology and mechanical testing. PTOA knee joints had a 33-46% increase in joint space mineralisation and PTOA knee joint ACLs exhibited ECM modifications, including collagen...

PLOS ONE, 2021

PurposeTo investigate the stress-strain behaviour of 9 soft contact lens materials, that are comm... more PurposeTo investigate the stress-strain behaviour of 9 soft contact lens materials, that are commonly used in the market, under uniaxial compression loading.MethodsSeven types of hydrogel and two types of silicone-hydrogel soft contact lens materials were hydrated in phosphate-buffered saline (PBS) solution then subjected to uniaxial compression loads. The load rate was set to 16.0 N/min starting with two consecutive initial 5.0 N loading cycles followed by three relaxation periods of 4.0 min within which there were two more 5.0 N loading cycles and eventually, a full loading cycle that stopped at a load of 49.0 N. The load and contraction data obtained experimentally were analysed to derive the stress-strain behaviour. Finite Element (FE) analysis was then utilised to evaluate the performance of soft contact lenses on the human eye and handling lenses off the eye.ResultsUnlike tensile tests, all tested materials showed nonlinear behaviour when tested under compression. When fitted ...

Journal of Refractive Surgery

PURPOSE To evaluate the effect of the implantation of intracorneal ring segments (ICRS) in kerato... more PURPOSE To evaluate the effect of the implantation of intracorneal ring segments (ICRS) in keratoconus on the dynamic corneal response (DCR) parameters obtained with the Corvis ST (Oculus Optikgeräte GmbH). METHODS This prospective clinical study included patients who underwent ICRS implantation for keratoconus over a period of 1 year. On the day of the surgery and at least 1 month after ICRS implantation, the following measurements were made: corrected and uncorrected distance visual acuity, corneal tomography indices with the Pentacam (Oculus Optikgeräte GmbH), biomechanically corrected intraocular pressure (bIOP), Corvis ST DCR parameters, integrated inverse concave radius (1/R), deformation amplitude ratio (DA ratio), stiffness parameter at first applanation (SP-A1), stress-strain index (SSI), and highest concavity radius (HRC). RESULTS Fifty-one eyes of 40 patients were included with a median follow-up time of 3 months (interquartile ratio [IQR]: 2 to 6 months). Statistical analysis showed that ICRS implantation did not affect corneal biomechanical measurements evaluated with the Corvis ST, which was demonstrated by non-significant changes in the SP-A1 (P = .637), 1/R (P = .647), HRC (P = .177), DA ratio (P = .735), and SSI (P = .501). Additionally, the results showed that bIOP measurements were not significantly affected by ICRS implantation (P = .113). CONCLUSIONS ICRS implantation does not affect corneal biomechanical measurements in early follow-up. [J Refract Surg. 2022;38(4):264-269.].

International Journal of Environmental Research and Public Health, Nov 25, 2019

Optical Coherence Tomography (OCT) images have the potential to provide quantitative measurements... more Optical Coherence Tomography (OCT) images have the potential to provide quantitative measurements of the entire anterior segment of the eye. A new threedimensional (3D) segmentation framework founded on level set based shape prior segmentation model has been developed for automatic segmentation of the entire cornea in 3D anterior segment OCT (AS-OCT). A three step algorithm was developed. The first step was to pre-process the image to reduce noise. The next step was to obtain a coarse segmentation of the front eye by using an entropy filter and the Otsu’s thresholding technique. The final step used the new level set based shape prior segmentation model under cylindrical coordinates to evolve the contour initialised from the coarse segmentation and achieve the final segmentation. Initial results on synthetic image and real 3D AS-OCT images show promising results.

Introduction Corneal microstructure Corneal topography Corneal biomechanical behaviour Numerical ... more Introduction Corneal microstructure Corneal topography Corneal biomechanical behaviour Numerical modeling of ocular biomechanics Conclusion Index.

IOP Conference Series: Materials Science and Engineering, 2018

With the advent of research it was identified that material properties are responsible for errors... more With the advent of research it was identified that material properties are responsible for errors in tonometry pressure (referred to as Goldmann IOP or IOPG) with the stiffening of a composite structure of corneal tissue in particular. Strip tensile tests are conducted to determine their stress–strain relationship for the purpose to study the behaviour of material properties of cornea. Specimens are taken from the superior–inferior (vertical) and temporal– nasal (horizontal) directions. Testing is performed on an Instron machine, under different rate of loading conditions. First set of experiment, with single strain rate, is executed on eyes having random population. While the second set of experiment is executed on eyes of the same animal in both directions, and different strain rates are applied each specimen. Relatively, the first set of experiment is found to be slightly different and less accurate. In general, it is found that the vertical specimen is 34% on an average stiffer ...

SSRN Electronic Journal, 2021

Journal of Refractive Surgery, 2020

Current Eye Research, 2019

Journal of refractive surgery (Thorofare, N.J. : 1995), 2018

To determine the relationship between mechanical behavior in cross-linked corneas and changes in ... more To determine the relationship between mechanical behavior in cross-linked corneas and changes in the corneal ultrastructure after corneal cross-linking (CXL). Porcine corneas were treated following the "Dresden" protocol, the current gold standard for clinical treatment, consisting of dropwise application of 0.1% riboflavin in 20% dextran followed by 30 minutes of ultraviolet-A (UVA) irradiation. The effect of CXL was assessed using uniaxial tensile testing, transmission electron microscopy, and Fourier transform infrared spectroscopy, with results compared against corneas treated with each of the treatment solution components individually. UVA/riboflavin cross-linked corneas displayed 28% ± 17% increase in the material tangent modulus compared with dextran treatment alone, and altered collagen architecture within the first 300 µm of stromal depth consisting of 5% increase in the thickness of collagen fibrils, no significant changes to interfibrillar spacing, and an 8% to ...

Journal of refractive surgery (Thorofare, N.J. : 1995), 2018

To evaluate whether different corneal cross-linking (CXL) irradiances, all with the same delivere... more To evaluate whether different corneal cross-linking (CXL) irradiances, all with the same delivered total energy, achieve similar increases in corneal material stiffness. One hundred twenty-six healthy white Japanese rabbits were randomly divided into seven groups (n = 18 each). After removing the epithelium of the left corneas, six groups were exposed to riboflavin (0.22% concentration by volume) and ultraviolet-A (370 nm) at different CXL irradiations, all with the same total dose (5.4 J/cm2), ranging from 3 mW/cm2 for 30 minutes to 90 mW/cm2 for 1 minute. The left corneas of the seventh group were exposed to riboflavin without irradiation. Twelve corneas of each group were prepared for inflation testing, where they were subjected to internal hydrostatic pressure simulating intraocular pressure, whereas the other six specimens were processed for electron microscopy measurements of fibril diameter and interfibrillar spacing. The inverse modeling process was used to estimate the tang...

Essentials in Ophthalmology, 2016

Keratoconus, the occurrence and development of which is associated with corneal thinning and coni... more Keratoconus, the occurrence and development of which is associated with corneal thinning and conical protrusion causing irregular astigmatism, is a bilateral non-inflammatory degenerative corneal disease. With the disruption of the collagen organisation, the cornea loses its shape and function resulting in progressive visual degradation. Currently, corneal topography remains the most important tool for the diagnosis of keratoconus. However, this approach may lead to false negatives among the patient population in the subclinical phase. It is now hypothesised that biomechanical destabilisation of the cornea may take place ahead of the topographic evidence of keratoconus. Therefore, accurate characterisation of in vivo biomechanical properties could possibly be used to assist with diagnosis and management, particularly in the early stages of the disease. This chapter provides a summary of the definition, diagnosis and management strategies for keratoconus based on corneal biomechanics.