Optical properties of ocular tissues in the near infrared region

Dragonfly algorithm-support vector machine approach for prediction the optical properties of blood

Knowledge of the optical properties of blood plays important role in medical diagnostics and therapeutic applications in laser medicine. In this paper, we present a very rapid and accurate artificial intelligent approach using Dragonfly Algorithm/Support Vector Machine models to estimate the optical properties of blood, specifically the absorption coefficient, and the scattering coefficient using key parameters such as wavelength (nm), hematocrit percentage (%), and saturation of oxygen (%), in building very highly accurate Dragonfly Algorithm-Support Vector Regression models (DA-SVR). 1000 training and testing sets were selected in the wavelength range of 250-1200 nm and the hematocrit of 0-100%. The performance of the proposed method is characterized by high accuracy indicated in the correlation coefficients (R) of 0.9994 and 0.9957 for absorption and scattering coefficients, respectively. In addition, the root mean squared error values (RMSE) of 0.972 and 2.9193, as well as low mean absolute error values (MAE) of 0.2173 and 0.2423, this result showed a strong match with the experimental data. The models can be used to accurately predict the absorption and scattering coefficients of blood, and provide a reliable reference for future studies on the optical properties of human blood.

Influence of endotamponade on anterior chamber depth and refractive outcome after combined phacovitrectomy: case-control study

PURPOSE

To compare the changes in the anterior chamber depth (ACD) and in the refractive outcomes after combined phacovitrectomy with respect to the endotamponade (balanced salt solution, air, sulfur hexafluoride [SF 6 , gas]).

SETTING

Department of Ophthalmology, University Hospital Ulm, Ulm, Germany.

DESIGN

Retrospective, longitudinal case-control study.

METHODS

160 eyes of 160 patients were included in the study. 120 eyes underwent phacoemulsification with in-the-bag implantation combined with vitrectomy and were divided into 3 groups according to tamponade (balanced salt solution, air, gas). 40 control eyes with cataract surgery only were included. Further inclusion criteria were uneventful surgery, no postoperative complications and absence of corneal pathology. Endpoints were ACD as measured by swept-source optical coherence tomography-based biometry (IOLMaster 700) preoperatively, 1 to 2 days and 6 weeks postoperatively and refractive prediction error (PE) using the Barrett and Haigis formulas.

RESULTS

Within the first 2 days after surgery the ACD was shallower in the eyes left with gas or air tamponade, when compared with balanced salt solution or cataract surgery alone ( P < .001). This effect diminished 6 weeks later, and all eyes reached comparable ACD ( P = .396). The refractive PE was slightly, but statistically significantly higher in the gas group when compared with cataract surgery alone ( P = .012 for Barrett, P = .006 for Haigis).

CONCLUSIONS

The resulting ACD after combined phacovitrectomy was independent of the tamponade used, but a gas-tamponade was associated with a higher refractive PE.

Experimental imaging and Monte Carlo modeling of ultrafast pulse propagation in thin scattering slabs

SIGNIFICANCE

Most radiative transport problems in turbid media are typically associated with mm or cm scales, leading to typical time scales in the range of hundreds of ps or more. In certain cases, however, much thinner layers can also be relevant, which can dramatically alter the overall transport properties of a scattering medium. Studying scattering in these thin layers requires ultrafast detection techniques and adaptations to the common Monte Carlo (MC) approach.

AIM

We aim to discuss a few relevant aspects for the simulation of light transport in thin scattering membranes, and compare the obtained numerical results with experimental measurements based on an all-optical gating technique.

APPROACH

A thin membrane with controlled scattering properties based on polymer-dispersed TiO2 nanoparticles is fabricated for experimental validation. Transmittance measurements are compared against a custom open-source MC implementation including specific pulse profiles for tightly focused femtosecond laser pulses.

RESULTS

Experimental transmittance data of ultrafast pulses through a thin scattering sample are compared with MC simulations in the spatiotemporal domain to retrieve its scattering properties. The results show good agreement also at short distances and time scales.

CONCLUSIONS

When simulating light transport in scattering membranes with thicknesses in the orders of tens of micrometer, care has to be taken when describing the temporal, spatial, and divergence profiles of the source term, as well as the possible truncation of step length distributions, which could be introduced by simple strategies for the generation of random exponentially distributed variables.

Complex refractive index of freshly excised human breast tissue as a marker of disease

We report differences in the refractive index of healthy and tumorous freshly excised human breast tissue as determined from reflectance profile measurements at five wavelengths (432 nm, 532 nm, 633 nm, 964 nm, 1551 nm) in the visible and near-infrared using a standard prism-coupling refractometer. These refractive index differences, particularly in the near-infrared, can be used to distinguish fibroadenomas and cancerous growths not only from normal breast tissue but also from each other.

Biomimetic models of the human eye, and their applications

Replicating the functionality of the human eye has been a challenge for more than a century, creating a great wealth of biomimetic and bioinspired devices, and providing ever improving models of the eye for myriad research purposes. As improvements in microelectronics have proceeded, individual components of the eye have been replicated, and models of the optical behaviour of the eye have improved. This review explores both work developed for improving medical components, with an ultimate aim of a fully functioning prosthetic eye, and work looking at improving existing devices through biomimetic means. It is hoped that this holistic approach to the subject will aid in the cross pollination of ideas between the two research foci. The review starts by summarising the reported measurements of optical parameters of various components of the eye. It then charts the development of individual bionic components. Particular focus is put on the development of bionic and biomimetic forms of the two main adaptive components of the eye, namely the lens and the iris, and the challenges faced in modelling the light sensitive retina. Work on each of these components is thoroughly reviewed, including an overview of the principles behind the many different approaches used to mimic the functionality, and discussion of the pros and cons of each approach. This is concluded by an overview of several reported models of the complete or semi-complete eye, including details of the components used and a summary of the models' functionality. Finally, some consideration is given to the direction of travel of this field of research, and which existing approaches are likely to bring us closer to the long term goal of a fully functional analogue of the eye.

Refractive outcomes after vitrectomy combined with phacoemulsification of idiopathic macular holes

AIM

To report the refractive outcomes after vitrectomy combined with phacoemulsification and intraocular lens (IOL) implantation (phaco-vitrectomy) in idiopathic macular holes (IMH).

METHODS

A total of 56 eyes with IMH (IMH group) that underwent phaco-vitrectomy and 44 eyes with age-related cataract (ARC group) that underwent cataract surgery were retrospectively reviewed. The best corrective visual acuity (BCVA), predicted refractive error (PRE), actual refractive error (ARE), axial length (AL), were measured in both groups before and 6mo after operation. The power calculation of IOL and the predicted refractive error (PRE) were calculated according to the SRK/T formula. The difference of PRE and ARE between the two groups were compared and analyzed.

RESULTS

In the IMH group, the diameters of macular holes were 271.73±75.85 µm, the closure rate was 100%. The pre- and post-operative BCVA were 0.80±0.35 and 0.40±0.35 logMAR. The PRE of A-ultrasound and IOL Master in the IMH group was -0.27±0.25 and 0.10±0.66 D. The postoperative mean absolute prediction error (MAE) was observed to be 0.58±0.65 and 0.53±0.37 D in the IOL Master and A-ultrasound (P=0.758). The PRE and ARE of the IMH group were 0.10±0.66 D and -0.19±0.64 D (P=0.102). The PRE and ARE of the ARC group was -0.43±0.95 and -0.31±0.93 D (P=0.383). The difference between PRE and ARE was -0.33±0.81 and 0.09±0.64 D in the IMH and ARC groups (P=0.021). The proportion of myopic shift was 67.9% in the IMH group and 27.3% in the ARC group (P=0.004).

CONCLUSION

The myopic shift can be observed in patients with IMH after phaco-vitrectomy.

Label-free adaptive optics imaging of human retinal macrophage distribution and dynamics

Microglia, a type of macrophage, were discovered a little more than a century ago by Pío del Río-Hortega. Since that time, we have gained an immense amount of knowledge on their origin and multifaceted function with the aid of labeling techniques and animal models, among other tools. Only recently have macrophage cells been imaged in living humans. Here we characterize macrophage spatial distribution and temporal dynamics in live human eyes using a label-free adaptive optics imaging approach. This investigation lays a foundation to better understand the body’s immune response not only to ocular diseases like glaucoma, but also to a vast array of neurological diseases with ocular manifestations, including Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis.

Microglia are resident central nervous system macrophages and the first responders to neural injury. Until recently, microglia have been studied only in animal models with exogenous or transgenic labeling. While these studies provided a wealth of information on the delicate balance between neuroprotection and neurotoxicity within which these cells operate, extrapolation to human immune function has remained an open question. Here we examine key characteristics of retinal macrophage cells in live human eyes, both healthy and diseased, with the unique capabilities of our adaptive optics–optical coherence tomography approach and owing to their propitious location above the inner limiting membrane (ILM), allowing direct visualization of cells. Our findings indicate that human ILM macrophage cells may be distributed distinctly, age differently, and have different dynamic characteristics than microglia in other animals. For example, we observed a macular pattern that was sparse centrally and peaked peripherally in healthy human eyes. Moreover, human ILM macrophage density decreased with age (∼2% of cells per year). Our results in glaucomatous eyes also indicate that ILM macrophage cells appear to play an early and regionally specific role of nerve fiber layer phagocytosis in areas of active disease. While we investigate ILM macrophage cells distinct from the larger sample of overall retinal microglia, the ability to visualize macrophage cells without fluorescent labeling in the live human eye represents an important advance for both ophthalmology and neuroscience, which may lead to novel disease biomarkers and new avenues of exploration in disease progression.

Numerical Computational Study of Photoacoustic Signals from Eye Models to Detect Diabetic Retinopathy

Introduction:

Detection of Diabetic Retinopathy (DR) is essential in clinical ophthalmology as it may prevent sight degradation. In this paper, a complete Photoacoustic (PA) analysis is implemented to detect DR in three different eye models representing a healthy eye as well as two abnormal eyes exhibiting Non-Proliferative Retinopathy (NPDR), and Proliferative Retinopathy (PDR)

Methods & Materials:

Monte Carlo method was used to simulate the interaction of a 0.8 ns duration laser pulse with eye tissues at 750 nm wavelength. Thermal, structural and acoustical analyses were performed using the Finite Element Method (FEM).

Results:

The results showed that there is a significant change in the amplitude of the detected PA signal for abnormal eye tissues in the retina (P < 0.05) as compared to healthy eye tissues. The maximum amplitude of the received PA signal in the NPDR and the PDR eye models is 5% and 33%, respectively, which are greater than those observed in the healthy eye.

Conclusion:

These results may provide insights into using PA imaging to detect DR.

Modeling retinal detachment associated with hemorrhage by Monte Carlo simulation

In this work we study fundus reflection in the case of retinal detachment. Vitreous humor builds up beneath the retina through a break in the retina or when there is traction on the retina. Further, we assume that this detachment is associated with hemorrhage in regions both above and below the retina. To investigate hemorrhage, we assume erythrocytes to be spheres of different radii. Then we apply Mie scattering theory to these spheres and calculate the scattering coefficient, the absorption coefficient, and the anisotropy factor. Using these parameters, we apply Monte Carlo simulation to calculate reflection. In order to model fundus reflection under retinal detachment, we define three types of reflection: reflection from the vitreous body, retinal reflection where photons are reflected from the retinal vitreous interface once, and retinal reflection where photons are reflected many times from the retinal vitreous interface.

Prospective Comparison of Intraocular Lens Dynamics and Refractive Error between Phacovitrectomy and Phacoemulsification Alone

PURPOSE

To compare intraocular lens (IOL) dynamics and refractive prediction errors between eyes that underwent phacovitrectomy and eyes that underwent phacoemulsification alone.

DESIGN

Prospective, nonrandomized, comparative, observational study.

PARTICIPANTS

Sixty eyes of 60 patients who underwent 25-gauge phacovitrectomy without gas injection for macular pathology and 60 eyes of 60 patients who underwent phacoemulsification alone for cataract were enrolled.

METHODS

Preoperative optical biometry was performed using the IOLMaster 700 (Carl Zeiss Meditec, Inc, Dublin, CA) to calculate the IOL power with the Barrett Universal II formula. Monofocal, nontoric, single-piece foldable aspherical IOLs were implanted in each patient. Comprehensive ocular examinations, including CASIA2 (Tomey Corp, Nagoya, Japan) evaluations of the preoperative crystalline lens and postoperative IOL positions (i.e., decentration, tilt, and aqueous depth), were performed before and 3 days, 1 month, and 3 months after surgery.

MAIN OUTCOME MEASURES

Refractive prediction errors and IOL dynamics.

RESULTS

Mean refractive prediction errors at 3 days, 1 month, and 3 months after phacovitrectomy were 0.51±0.59 diopters (D), 0.11±0.40 D, and 0.05±0.41 D, respectively, whereas those after phacoemulsification alone were 0.43±0.38 D, 0.11±0.37 D, and 0.07±0.34 D, respectively. There was no significant difference in the refractive error between the 2 groups at any time point. A myopic shift of -0.50 D or more negative refractive error occurred in 4 (6.7%) of 60 eyes with phacovitrectomy and 3 (5.0%) of 60 eyes with phacoemulsification alone; there was no significant between-group difference. At 3 months postoperatively, refractive errors within ±0.50 D and ±1.00 D were achieved in 49 (81.7%) and 58 (96.7%) of 60 eyes in the phacovitrectomy group and 52 (86.7%) and 60 (100.0%) of 60 eyes in the phacoemulsification alone group, again without any significant between-group differences. There were no significant differences in the preoperative lens and postoperative IOL positions between the 2 study groups, except for a significantly deeper mean aqueous depth at 3 days after surgery in the phacovitrectomy group.

CONCLUSIONS

Neither myopic shift nor IOL displacement occurs after 25-gauge phacovitrectomy with a single-piece IOL without gas injection for macular pathology compared with phacoemulsification alone.

Determination of optical parameters of the porcine eye and development of a simulated model

The eye is a very sophisticated system of optical elements for the preeminent sense of vision. In recent years, the number of laser surgery to correct the optical aberration such as myopia or astigmatism has significantly increased. Consequently, improving the knowledge related to the interactions of light with the eye is very important in order to enhance the efficiency of the surgery. For this reason, a complete optical characterization of the porcine eye is presented in this study. Kubelka-Munk and Inverse Adding-Doubling methods were applied to spectroscopy measurement to determine the absorption and scattering coefficients. Furthermore, the refractive index has been measured by ellipsometry. The different parameters were obtained for the cornea, lens, vitreous humor, sclera, iris, choroids and eyelid in the visible and infrared region. Thereafter, the results are implemented in a COMSOL Multiphysics® software to create an eye model. This model gives a better understanding of the propagation of light in the eye by adding optical parts such as the iris, the sclera or the ciliary bodies. Two simulations show the propagation of light from the cornea to the retina but also from the sclera to the retina. This last possibility provides a better understanding of light propagation during eye laser surgery such as, for example, transscleral cyclophotocoagulation. Figure: Eye simulation models allow the development of new laser treatments in a simple and safe way for patients. To this purpose, the creation of an eye simulated model based on optical parameters obtained from experimental data is presented in this study. This model will facilitate the understanding of the light propagation inside the porcine eye.

Noninvasive Assessment of Corneal Crosslinking With Phase-Decorrelation Optical Coherence Tomography

Purpose

There is strong evidence that abnormalities in corneal biomechanical play a causal role in corneal ectasias, such as keratoconus. Additionally, corneal crosslinking (CXL) treatment, which halts progression of keratoconus, directly appeals to corneal biomechanics. However, existing methods of corneal biomechanical assessment have various drawbacks: dependence on IOP, long acquisition times, or limited resolution. Here, we present a method that may avoid these limitations by using optical coherence tomography (OCT) to detect the endogenous random motion within the cornea, which can be associated with stromal crosslinking.

Methods

Phase-decorrelation OCT (PhD-OCT), based in the theory of dynamic light scattering, is a method to spatially resolve endogenous random motion by calculating the decorrelation rate, Γ, of the temporally evolving complex-valued OCT signal. PhD-OCT images of ex vivo porcine globes were recorded during CXL and control protocols. In addition, human patients were imaged with PhD-OCT using a clinical OCT system.

Results

In both the porcine cornea and the human cornea, crosslinking results in a reduction of Γ (P < 0.0001), indicating more crosslinks. This effect was repeatable in ex vivo porcine corneas (change in average Γ = −41.55 ± 9.64%, n = 5) and not seen after sham treatments (change in average Γ = 2.83 ± 12.56%, n = 5). No dependence of PhD-OCT on IOP was found, and correctable effects were caused by variations in signal-to-noise ratio, hydration, and motion.

Conclusions

PhD-OCT may be a useful and readily translatable tool for investigating biomechanical properties of the cornea and for enhancing the diagnosis and treatment of patients.

Effect of Nd:YAG Laser Capsulotomy on Anterior Segment Parameters in Patients with Posterior Capsular Opacification after Phacovitrectomy

Purpose

To compare changes in anterior segment parameters after Nd:YAG laser capsulotomy in eyes that underwent either combined phacovitrectomy or cataract surgery.

Methods

This retrospective study enrolled 37 eyes of 35 patients with posterior capsular opacification treated with combined phacovitrectomy (group A), and 35 eyes of 32 patients with posterior capsular opacification treated with cataract surgery (group B). Anterior segment parameters, including anterior chamber depth (ACD), anterior chamber angle, and anterior chamber volume, were measured by a Pentacam before Nd:YAG laser capsulotomy and 1 hour, 1 day, 1 week, 1 month, and 3 months after this treatment.

Results

In the cataract surgery group, the ACD was significantly lower 1 day (3.75 ± 0.74 mm), 1 week (3.73 ± 0.24 mm), and 3 months (3.74 ± 0.33 mm) after Nd:YAG laser capsulotomy compared with the pretreatment value (4.20 ± 0.62 mm, p = 0.002). By contrast, the ACD did not change significantly over time in the combined phacovitrectomy group. The ACD differed significantly between the two groups at 1 week, 1 month, and 3 months after capsulotomy. There were no significant changes in the anterior chamber volume, anterior chamber angle, central corneal thickness, or pupil size from before to after capsulotomy in either group. A non-significant trend toward myopic shift was observed in group A (p = 0.072) and B (p = 0.055).

Conclusions

The results of the present study may help determine the power of the intraocular lens in patients who underwent combined surgery or cataract surgery and who will receive Nd:YAG laser capsulotomy.

Post-operative Refractive Prediction Error After Phacovitrectomy: A Retrospective Study

Introduction

Many authors have reported on a myopic post-operative refractive prediction error when combining phacoemulsification with pars plana vitrectomy (phacovitrectomy). In this study we evaluate the amount of this error in our facility and try to elucidate the various factors involved.

Methods

This was a retrospective study which included 140 patients who underwent phacovitrectomy (39 with macular holes, 88 with puckers, and 13 with floaters). Post-operative refractive error was defined as the difference between the actual spherical equivalent (SEQ) and expected SEQ based on the SRK/T and Holladay-II formulas. Both univariate (paired t test, independent t test, one-way analysis of variance, or Mann–Whitney test) and multivariate (regression analysis) statistical analyses were performed.

Results

Overall, a refractive error of − 0.13 dpt (p = 0.033) and − 0.26 dpt (p < 0.01) were found in the SRK/T and Holladay-II formulas, respectively. For the independent diagnoses, only macular holes showed a myopic error with the SRK/T (− 0.31 dpt; p < 0.01) and Holladay-II (− 0.44 dpt; p < 0.01) formulas. In univariate analysis, significant factors involved in myopic refractive error were macular hole as diagnosis (p < 0.01 for SRK/T and Holladay-II), gas tamponade (SRK/T p = 0.024; Holladay-II p = 0.025), pre-operative myopia (p < 0.01 for SRK/T), and optical technique for axial length measurement (SRK/T and Holladay-II p < 0.01). In the multivariate analysis, pre-operative axial length (p = 0.026), optical technique for axial length measurement (p < 0.01), and pre-operative SEQ (p < 0.01) were independent predictors for myopic refractive error in the SRK/T formula. For the Holladay-II formula, optical technique for axial length measurement (p < 0.01) and pre-operative SEQ (p = 0.04) were predictive.

Conclusion

Various factors are involved in determining the myopic refractive error after phacovitrectomy. Not every factor seems to be as important in each individual patient, suggesting a more tailored approach is warranted to overcome this problem.

Postoperative refractive error after phacovitrectomy for epiretinal membrane with and without macular oedema

PURPOSE

This study was initiated to investigate whether the presence of macular oedema influenced intraocular lens (IOL) power calculation in eyes with epiretinal membrane.

METHODS

The files of patients undergoing combined phacoemulsification were retrospectively reviewed. Two groups were defined according to presence of macular oedema. The main outcome measure was the IOL power prediction error (PE). Secondary outcome measures were the correlation between preoperative macular thickness, absolute change of macular thickness and dioptric shift. The mean postoperative PE achieved with the Haigis formula was compared with the PE that would have been obtained had the SRKII and HofferQ formulas been used.

RESULTS

We investigated 47 eyes of 47 consecutive patients. Regardless of the IOL formula used, the PE was on average higher in eyes without macula oedema (group 1). The myopic dioptric shift was dependent on preoperative macular thickness and absolute change of macular thickness. This association was more markedly pronounced in group 1.

CONCLUSIONS

Increased retinal thickness is the main cause for underestimation of the cornea-photoreceptor layer distance, and therefore could contribute to inaccuracy in IOL power calculations. The current results show that a myopic shift tends to be less pronounced in cases where a macula oedema is present. Eyes with pure traction have less predictable refractive results in terms of higher PE and dioptric shift.

Refractive change after vitrectomy for epiretinal membrane in pseudophakic eyes

PURPOSE

To report the change in refraction in pseudophakic eyes following 23-gauge vitrectomy for epiretinal membrane (ERM), without use of silicone oil, intraocular gas or scleral buckling.

METHODS

Retrospective review of the records of 28 pseudophakic eyes in 28 patients undergoing 23-gauge pars plana vitrectomy for ERM. All 28 eyes had a measured preoperative refraction in their records and were seen minimum 2 months after vitrectomy for measuring their refraction. Fellow eyes (28 eyes) were used as controls.

RESULTS

The mean preoperative refraction was -0.15 ± 0.85 dioptre (D), and the mean postoperative refraction was -0.41 ± 0.93 D. Thus, a myopic shift was observed following vitrectomy with a mean change in refraction of -0.26 ± 0.60 D (range +0.75 to -2.13 D, p = 0.032). The postoperative change in refraction was within ±0.25, ±0.50 and ±1.00 D in 39%, 68% and 96% of the eyes, respectively. The mean absolute refractive error was 0.47 ± 0.44 D. The change in refraction in fellow eyes was +0.01 D (p = 0.82).

CONCLUSION

The change in refraction following 23-gauge pars plana vitrectomy for ERM in pseudophakic eyes was -0.26 D.

Reproducibility of a long-range swept-source optical coherence tomography ocular biometry system and comparison with clinical biometers

OBJECTIVE

To demonstrate a novel swept source optical coherence tomography (SS-OCT) imaging device using a vertical cavity surface-emitting laser (VCSEL) capable of imaging the full eye length and to introduce a method using this device for noncontact ocular biometry. To compare the measurements of intraocular distances using this SS-OCT instrument with commercially available optical and ultrasound biometers. To evaluate the intersession reproducibility of measurements of intraocular distances using SS-OCT.

DESIGN

Evaluation of technology.

PARTICIPANTS

Twenty eyes of 10 healthy subjects imaged at the New England Eye Center at Tufts Medical Center and Massachusetts Institute of Technology between May and September 2012.

METHODS

Averaged central depth profiles were extracted from volumetric SS-OCT datasets. The intraocular distances, such as central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), crystalline lens thickness (LT), vitreous depth (VD), and axial length (AL), were measured and compared with a partial coherence interferometry device (IOLMaster; Carl Zeiss Meditec, Inc., Dublin, CA) and an immersion ultrasound (IUS) A-scan biometer (Axis-II PR; Quantel Medical, Inc., Cournon d'Auvergne Cedex, France).

MAIN OUTCOME MEASURES

Reproducibility of the measurements of intraocular distances, correlation coefficients, and intraclass correlation coefficients.

RESULTS

The standard deviations of the repeated measurements of intraocular distances using SS-OCT were 6 μm (CCT), 16 μm (ACD), 14 μm (AD), 13 μm (LT), 14 μm (VD), and 16 μm (AL). Strong correlations among all 3 biometric instruments were found for AL (r > 0.98). The AL measurement using SS-OCT correlates better with the IOLMaster (r=0.998) than with IUS (r=0.984). The SS-OCT and IOLMaster measured higher AL values than ultrasound (175 and 139 μm, respectively). No statistically significant difference in ACD between the optical (SS-OCT or IOLMaster) and ultrasound methods was detected. High intersession reproducibility of SS-OCT measurements of all intraocular distances was observed with intraclass correlation coefficients >0.99.

CONCLUSIONS

The SS-OCT using VCSEL technology enables full eye length imaging and high-precision, noncontact ocular biometry. The measurements with the prototype SS-OCT instrument correlate well with commercial biometers. The SS-OCT biometry has the potential to provide clinically useful comprehensive biometric parameters for pre- and postoperative eye evaluation.

Optical and spectroscopic properties of human whole blood and plasma with and without Y₂O₃ and Nd³⁺:Y₂O₃ nanoparticles

The optical properties of human whole blood and blood plasma with and without Y₂O₃ and Nd³⁺:Y₂O₃ nanoparticles are characterized in the near infrared region at 808 nm using a double integrating sphere technique. Using experimentally measured quantities of diffuse reflectance and diffuse transmittance, a computational analysis was conducted utilizing the Kubelka-Munk, the Inverse Adding Doubling, and Magic Light Kubelka-Munk and Monte Carlo Methods to determine optical properties of the absorption and scattering coefficients. Room temperature absorption and emission spectra were also acquired of Nd³⁺:Y₂O₃ nanoparticles elucidating their utility as biological markers. The emission spectra of Nd³⁺:Y₂O₃ were taken by exciting the nanoparticles before and after entering the whole blood sample. The emission from the ⁴F(3/2) → ⁴I(11/2) manifold transition of Nd³⁺:Y₂O₃ nanoparticles readily propagates through the blood sample at excitation of 808 nm and exhibits a shift in relative intensities of the peaks due to differences in scattering. At 808 nm, in both whole blood and plasma samples, a direct relationship was found with absorption coefficient and Y₂O₃ nanoparticle concentration. Results for the whole blood indicate a small inverse relationship with Y₂O₃ nanoparticle concentration and scattering coefficient and in contrast a direct relation for the plasma.

Agreement between retinal nerve fiber layer measures from Spectralis and Cirrus spectral domain OCT

PURPOSE

An assessment of the retinal nerve fiber layer (RNFL) provides important information on the health of the optic nerve. There are several non-invasive technologies, including spectral domain optical coherence tomography (SD OCT), that can be used for in vivo imaging and quantification of the RNFL, but often there is disagreement in RNFL thickness between clinical instruments. The purpose of this study was to investigate the influence of scan centration, ocular magnification, and segmentation on the degree of agreement of RNFL thickness measures by two SD OCT instruments.

METHODS

RNFL scans were acquired from 45 normal eyes using two commercially available SD OCT systems. Agreement between RNFL thickness measures was determined using each instrument's algorithm for segmentation and a custom algorithm for segmentation. The custom algorithm included ocular biometry measures to compute the transverse scaling for each eye. Major retinal vessels were identified and removed from RNFL measures in 1:1 scaled images. Transverse scaling was also used to compute the RNFL area for each scan.

RESULTS

Instrument-derived global RNFL thickness measured from the two instruments correlated well (R(2) = 0.70, p < 0.01) but with significant differences between instruments (mean of 6.7 μm; 95% limits of agreement of 16.0 μm to -2.5 μm, intraclass correlation coefficient = 0.62). For recentered scans with custom RNFL segmentation, the mean difference was reduced to 0.1 μm (95% limits of agreement 6.1 to -5.8 μm, intraclass correlation coefficient = 0.92). Global RNFL thickness was related to axial length (R = 0.24, p < 0.01), whereas global RNFL area measures were not (R(2) = 0.004, p = 0.66). Major retinal vasculature accounted for 11.3 ± 1.6% (Cirrus) or 11.8 ± 1.4% (Spectralis) of the RNFL thickness/area measures.

CONCLUSIONS

Sources of disagreement in RNFL measures between SD-OCT instruments can be attributed to the location of the scan path and differences in their retinal layer segmentation algorithms. In normal eyes, the major retinal vasculature accounts for a significant percentage of the RNFL and is similar between instruments. With incorporation of an individual's ocular biometry, RNFL area measures are independent of axial length, with either instrument.

Influence of anterior segment power on the scan path and RNFL thickness using SD-OCT

PURPOSE

Retinal nerve fiber layer (RNFL) thickness measures with spectral domain-optical coherence tomography (SD-OCT) provide important information on the health of the optic nerve. As with most retinal imaging technologies, ocular magnification characteristics of the eye must be considered for accurate analysis. While effects of axial length have been reported, the effects of anterior segment optical power on RNFL thickness measures have not been described fully to our knowledge. The purpose of our study was to determine the influence of the optical power change at the anterior corneal surface, using contact lenses, on the location of the scan path and measurements of RNFL thickness in normal healthy eyes.

METHODS

We recruited 15 normal subjects with less than 6 diopters (D) of ametropia and no ocular pathology. One eye of each subject was selected randomly for scanning. Baseline SD-OCT scans included raster cubes centered on the optic nerve and macula, and a standard 12-degree diameter RNFL scan. Standard 12-degree RNFL scans were repeated with 10 separate contact lenses, (Proclear daily, Omafilcon A/60%) ranging from +8 to -12 D in 2-D steps. The extent of the retinal scan, and RNFL thickness and area measures were quantified using custom MATLAB programs that included ocular biometry measures (IOL Master).

RESULTS

RNFL thickness decreased (0.52 μm/D, r = -0.33, P < 0.01) and the retinal region scanned increased (0.52%/D, r = 0.97, P < 0.01) with increase in contact lens power (-12 to +8). The normalized/percentage rates of change of RNFL thickness (-0.11/mm, r = -0.67, P < 0.01) and image size (0.11/mm, r = 0.96, P < 0.01) were related to axial length. Changes in the retinal region scanned were in agreement with transverse scaling, computed with a three surface schematic eye (R(2) = 0.97, P < 0.01). RNFL area measures, that incorporated the computed transverse scaling, were not related significantly to contact lens power (863 μm(2)/D, r = 0.06, P = 0.47).

CONCLUSIONS

Measurements of RNFL thickness by SD-OCT are dependent on the optics of the eye, including anterior segment power and axial length. The relationships between RNFL thickness measures and optical power are a direct reflection of scan path location with respect to the optic nerve head rim, caused by relative magnification. An incorporation of transverse scaling to RNFL area measures, based on individualized ocular biometry, eliminated the magnification effect.

Optical absorption and scattering of bovine cornea, lens, and retina in the near-infrared region

The optical properties of bovine ocular tissues have been determined at laser wavelengths in the near-infrared (NIR) region. The inverse adding doubling (IAD), Kubelka-Munk (KM), and inverse Monte Carlo (IMC) methods were applied to the measured values of the total diffuse transmission, total diffuse reflection, and collimated transmission to determine the optical absorption and scattering coefficients of the bovine cornea, lens and retina from 750 to 1,000 nm using a CW Ti:sapphire laser. The optical properties obtained from these three methods have been compared and are discussed.

Optical absorption and scattering of bovine cornea, lens and retina in the visible region

Optical properties of bovine ocular tissues were determined at laser wavelengths in the visible region. The inverse adding doubling (IAD), Kubelka-Munk (KM), and inverse Monte Carlo (IMC) methods were applied to the measured values of the total diffuse transmission, total diffuse reflection, and collimated transmission to determine the optical absorption and scattering coefficients of the bovine cornea, lens and retina at 457.9 nm, 488 nm, and 514.5 nm laser lines from an argon ion laser. The optical properties obtained from these three methods were compared, and their validity is discussed.

Optical Clearing of Cranial Bone

We present experimental results on optical properties of cranial bone controlled by administration of propylene glycol and glycerol. Both transmittance and reflectance spectra of human and porcine cranial bone in vitro were measured. For estimation of absorption and reduced scattering coefficients of the bone, the inverse adding-doubling method was used. The decrease of reflectance of the samples under action of the immersion agents was demonstrated. The experiments have shown that administration of the immersion liquids allows for effective controlling of tissue optical characteristics that makes bone more transparent, thereby increasing the ability of light penetration through the tissue. The presented results can be used in developing of functional imaging techniques, including OCT.