Was Dürer 500 years ahead of science?

Brewster's dark patch is a simple optical effect in the environment. It is easily seen, but apparently it has not been formally noticed or explained until quite recently. Nevertheless, some artists appear to have represented it in paintings without, of course, knowing its optical origins. A case can be made that a watercolor by Albrecht Dürer from around 1497 illustrates the phenomenon.

Isolation and Composition Analysis of Bioactive Glycosaminoglycans from Whelk.

Glycosaminoglycans (GAGs) are found covalently attached to proteins, which create conjugates known as proteoglycans. GAGs have remarkable biological activity as co-receptors for a variety of growth factors, cytokines, and chemokines. The present study identifies the key compositional differences between the GAGs isolated from whelk and mammalian GAGs. This polysaccharide represents a new, previously undescribed GAG with cytotoxic activity on cancer cells. Disaccharides were obtained by sample digestion with heparinases I, II, and III and chondroitinase ABC. The resistant oligosaccharides from whelk GAGs treated with heparinase I, II, and III and chondroitinase ABC were retained by the filter due to their larger size. Disaccharide analysis was performed using Glycan Reduction Isotope Labeling (GRIL LCQ-MS). The amounts of filter-retained fragments, as assessed by monosaccharides analysis, suggested that a proportion of the whelk GAG chains remained resistant to the enzymes used in the disaccharide analysis. Thus, the proportions of individual disaccharide produced in this analysis may not truly represent the overall proportions of disaccharide types within the intact whelk GAGs chain. However, they do serve as important descriptors for the classification and make-up of the anti-cancer GAGs chains. Furthermore, these data represent clear evidence of the compositional differences between whelk GAGs and commercial mammalian GAGs.

Antiproliferative Activity of Glycosaminoglycan-Like Polysaccharides Derived from Marine Molluscs.

Despite the increasing availability of new classes of cancer treatment, such as immune- and targeted therapies, there remains a need for the development of new antiproliferative/cytotoxic drugs with improved pharmacological profiles that can also overcome drug resistant forms of cancer. In this study, we have identified, and characterised, a novel marine polysaccharide with the potential to be developed as an anticancer agent. Sulphated polysaccharides isolated from the common cockle (Cerastoderma edule) were shown to have antiproliferative activity on chronic myelogenous leukaemia and relapsed acute lymphoblastic leukaemia cell lines. Disaccharide and monosaccharide analysis of these marine polysaccharides confirmed the presence of glycosaminoglycan-like structures that were enriched in ion-exchange purified fractions containing antiproliferative activity. The antiproliferative activity of these glycosaminoglycan-like marine polysaccharides was shown to be susceptible to heparinase but not chondrotinase ABC digestion. This pattern of enzymatic and antiproliferative activity has not previously been seen, with either marine or mammalian glycosaminoglycans. As such, our findings suggest we have identified a new type of marine derived heparan sulphate/heparin-like polysaccharide with potent anticancer properties.

Polarization optics of the Brewster's dark patch visible on water surfaces versus solar height and sky conditions: theory, computer modeling, photography, and painting.

When the sun is near the horizon, a circular band with approximately vertically polarized skylight is formed at 90° from the sun, and this skylight is only weakly reflected from the region of the water surface around the Brewster's angle (53° from the nadir). Thus, at low solar heights under a clear sky, an extended dark patch is visible on the water surface when one looks toward the north or south quarter perpendicular to the solar vertical. In this work, we study the radiance distribution of this so-called Brewster's dark patch (BDP) in still water as functions of the solar height and sky conditions. We calculate the pattern of reflectivity R of a water surface for a clear sky and obtain from this idealized situation the shape of the BDP. From three full-sky polarimetric pictures taken about a clear, a partly cloudy, and an overcast sky, we determine the R pattern and compose from that synthetic color pictures showing how the radiance distribution of skylight reflected at the water surface and the BDPs would look under these sky conditions. We also present photographs taken without a linearly polarizing filter about the BDP. Finally, we show a 19th century painting on which a river is seen with a dark region of the water surface, which can be interpreted as an artistic illustration of the BDP.

Preliminary identification of differentially expressed tear proteins in keratoconus.

PURPOSE: To examine the proteins differentially expressed in the tear film of people with keratoconus and normal subjects. METHODS: Unstimulated tears from people with keratoconus (KC) and controls (C) were collected using a capillary tube. Tear proteins from people with KC and controls were partitioned using a novel in-solution electrophoresis, Microflow 10 (ProteomeSep), and analyzed using linear ion trap quadrupole fourier transform mass spectrometry. Spectral counting was used to quantify the individual tear proteins. RESULTS: Elevated levels of cathepsin B (threefold) were evident in the tears of people with KC. Polymeric immunoglobulin receptor (ninefold), fibrinogen alpha chain (eightfold), cystatin S (twofold), and cystatin SN (twofold) were reduced in tears from people with KC. Keratin type-1 cytoskeletal-14 and keratin type-2 cytoskeletal-5 were present only in the tears of people with KC. CONCLUSIONS: The protein changes in tears, that is, the decrease in protease inhibitors and increase in proteases, found in the present and other previously published studies reflect the pathological events involved in KC corneas. Further investigations into tear proteins may help elucidate the underlying molecular mechanisms of KC, which could result in better treatment options.

A proposed methodology for conducting a remote rigid gas permeable contact lens consultation.

PURPOSE: COVID-19 spread to numerous countries, overwhelming healthcare systems and economies worldwide. COVID-19 restrictions have prevented patients from attending consultations in person and led to the further development of telemedicine to provide health care. The situation also applies to contact lens (CL) practitioners and their patients; telemedicine enables practitioners to provide patients with regular and continuing care. This study aimed to investigate available tools to enable continuing care for rigid gas permeable (RGP) CL wearers who are unable to attend face-to-face consultations. METHODS: The study consists of three components. Firstly, an approach to enable the assessment of a patient's CL fitting and cornea remotely. Secondly, to find an affordable and reliable method to obtain a patient's visual acuity (VA), and thirdly, to develop a questionnaire to provide practitioners with information to deliver optimal patient care. RESULTS: The use of a macro lens, smartphone, and auxiliary materials enables high-quality images of the anterior eye and RGP CL to be obtained. Two free and validated smartphone applications (apps) for VA measurements were identified which are available on Android and iOS systems. Two questionnaires were also developed to enable practitioners to obtain additional patient information to facilitate optimal patient care. CONCLUSION: This study has developed the components of a remote CL consultation to enable patients who cannot attend scheduled appointments to receive care and advice to ensure the safety of their RGP CL wear. The tools involved in this study are low-cost, affordable, and an adjunct, not a substitute, for face-to-face consultations.

A Systematic Literature Review of the Career Choice of Helping Professionals Who Have Experienced Cumulative Harm as a Result of Adverse Childhood Experiences.

The pervasive effects of cumulative harm resulting from adverse childhood experiences influence all aspects of an individual's life course. Research highlights a relationship between early trauma and career choice; however, there is a dearth of research pertaining specifically to cumulative harm and the influence on career choice in the helping professions. A systematic literature review was conducted to explore the associations of cumulative harm and childhood trauma on career decision making in people in the helping professions. A search was conducted across databases between February 1990 and February 2019 relevant to searches combining three areas of interest: (a) "childhood trauma," (b) "career choice," and (c) "helping professionals." Database searches and further manual searches yielded a total of 208 articles, and 28 studies satisfied all inclusion criteria. Only studies that were peer-reviewed and published between February 1990 and February 2019 were included. The evidence from the review indicated that family of origin dysfunction, parentification, individual characteristics, and traits developed through adversity, and experiential motivations were associated with the career choice in the helping professions. Further research is required to explore different professional cohorts and the utility of life themes as both a source of data for research and reflexive practice in helping professionals.

Clinical indicators for diabetic eyecare delivered by optometrists in Australia: a Delphi study.

CLINICAL RELEVANCE: Valid and updated clinical indicators can serve as important tools in assessing and improving eyecare delivery. BACKGROUND: Indicators for diabetic eyecare in Australia were previously developed from guidelines published before 2013 and then used to assess the appropriateness of care delivery through a nationwide patient record card audit (the iCareTrack study). To reflect emerging evidence and contemporary practice, this study aimed to update clinical indicators for optometric care for people with type 2 diabetes in Australia. METHODS: Forty-five candidate indicators, including existing iCareTrack and new indicators derived from nine high-quality evidence-based guidelines, were generated. A two-round modified Delphi process where expert panel members rated the impact, acceptability, and feasibility of the indicators on a 9-point scale and voted for inclusion or exclusion of the candidate indicators was used. Consensus on inclusion was reached when the median scores for impact, acceptability, and feasibility were ≥7 and >75% of experts voted for inclusion. RESULTS: Thirty-two clinical indicators with high acceptability, impact and feasibility ratings (all median scores: 9) were developed. The final indicators were related to history taking (n = 12), physical examination (n = 8), recall period (n = 5), referral (n = 5), and patient education/communication (n = 2). Most (14 of 15) iCareTrack indicators were retained either in the original format or with modifications. New indicators included documenting the type of diabetes, serum lipid level, pregnancy, systemic medications, nephropathy, Indigenous status, general practitioner details, pupil examination, intraocular pressure, optical coherence tomography, diabetic retinopathy grading, recall period for high-risk diabetic patients without retinopathy, referral of high-risk proliferative retinopathy, communication with the general practitioner, and patient education. CONCLUSION: A set of 32 updated diabetic eyecare clinical indicators was developed based on contemporary evidence and expert consensus. These updated indicators inform the development of programs to assess and enhance the eyecare delivery for people with diabetes in Australia.

Levels of lactoferrin, secretory IgA and serum albumin in the tear film of people with keratoconus.

Keratoconus is a degenerating disease of the eye which causes an irregularly shaped cornea leading to severe impairment of vision. Tear proteomics in keratoconus has been a topic of substantial discussion and speculation over many years. This study was designed to examine the levels of total protein, lactoferrin, secretory IgA and serum albumin in the tear film of people with keratoconus. Basal tears were collected using a capillary tube and corneal curvature was mapped using a topographer. Total protein in tears was estimated. The amount of regulated protein lactoferrin, constitutive protein sIgA and serum protein albumin was measured using specific ELISAs. The changes in protein concentrations in tears were correlated to the degree of corneal asphericity. There was a two-fold (p<0.0001) decrease in total protein levels between keratoconus (3.86 ± 1.62 mg/ml) and normal (7.00 ± 1.58 mg/ml) tears. The amount of lactoferrin (0.67 ± 0.28 vs. 1.13 ± 0.29 mg/ml) and secretory IgA (0.78 ± 0.36 vs. 1.70 ± 0.66 mg/ml) were significantly (p<0.0001) reduced in keratoconus tears. Variation in serum albumin levels between keratoconus (8.18 ± 4.72 µg/ml) and normal tears (11.66 ± 8.20 µg/ml) were not significant. The differences in total protein, lactoferrin and secretory IgA were not associated with contact lens wear, age, gender or atopy of subjects. The keratometry reading was negatively correlated to tear levels of total protein (r = -0.59, p < 0.01) lactoferrin (r = -0.40, p < 0.05) and secretory IgA (r = -0.34, p < 0.05). The tears of keratoconus subjects appear to have an altered protein profile, and one that might change with the severity of the disease. These findings may lead the way to understanding or monitoring disease progression.

A clinical method for estimating the modulus of elasticity of the human cornea in vivo.

BACKGROUND: To develop a method, using current clinical instrumentation, to estimate the Young's modulus of the human cornea in vivo. METHODS: Central corneal curvature (CCC), central corneal thickness(CCT), intraocular pressure (IOP) was measured with the Goldmann tonometer (IOPG) and the Pascal Dynamic Corneal Tonometer(PDCT) in one eye of 100 normal young human subjects (21.07 ± 2.94 years) in vivo. The Orssengo and Pye algorithm was used to calculate the Young's modulus of the corneas of these subjects. RESULTS: The Young's modulus(E) of the corneas of the subjects using the PDCT and IOPG results (Ecalc) was 0.25 ± 0.10MPa, and without the PDCT results (Eiopg) was 0.29 ± 0.06MPa. The difference in these results is due to the difference in tonometry results between the two instruments, as the mean PDCT result for the subjects was 16.89 ± 2.49mmHg and the IOPG result 15.06 ± 2.71mmHg. E was affected by the CCC of the subjects but more particularly by the CCT and IOP measurements. Corneal stiffness results are also presented. CONCLUSION: Two methods have been developed to estimate the Young's modulus of the human cornea in vivo using current clinical instrumentation. One method (Ecalc) is applicable to the general corneal condition, and Eiopg to the normal cornea, and these results can be used to calculate corneal stiffness.

Phase I trial of a CD8+ T-cell peptide epitope-based vaccine for infectious mononucleosis.

A single blind, randomized, placebo-controlled, single-center phase I clinical trial of a CD8(+) T-cell peptide epitope vaccine against infectious mononucleosis was conducted with 14 HLA B*0801-positive, Epstein-Barr virus (EBV)-seronegative adults. The vaccine comprised the HLA B*0801-restricted peptide epitope FLRGRAYGL and tetanus toxoid formulated in a water-in-oil adjuvant, Montanide ISA 720. FLRGRAYGL-specific responses were detected in 8/9 peptide-vaccine recipients and 0/4 placebo vaccine recipients by gamma interferon enzyme-linked immunospot assay and/or limiting-dilution analysis. The same T-cell receptor Vbeta CDR3 sequence that is found in FLRGRAYGL-specific T cells from most EBV-seropositive individuals could also be detected in the peripheral blood of vaccine recipients. The vaccine was well tolerated, with the main side effect being mild to moderate injection site reactions. After a 2- to 12-year follow-up, 1/2 placebo vaccinees who acquired EBV developed infectious mononucleosis, whereas 4/4 vaccinees who acquired EBV after completing peptide vaccination seroconverted asymptomatically. Single-epitope vaccination did not predispose individuals to disease, nor did it significantly influence development of a normal repertoire of EBV-specific CD8(+) T-cell responses following seroconversion.

Goldmann tonometry correction factors based on numerical analysis.

With the world's aging population, it is expected that the number of people affected by glaucoma, the second most common cause of irreversible blindness, will increase considerably. Current knowledge on glaucoma progression relates elevation of the intraocular pressure (IOP) to optic nerve damage and hence visual impairment. For this reason, IOP measurement in tonometry has become an essential part of routine eye examinations needed for the diagnosis and management of the disease. The accuracy of the current reference standard in tonometry, the Goldmann applanation tonometer, is known to be affected by the natural variations in corneal thickness, curvature, and material properties. Earlier studies attempted to quantify these effects and produced correction factors that considered the variations in each one of these parameters separately, and no guidance was given as to how to combine the effects of variations in more than one parameter. The present research attempted to address this gap by conducting a multidimensional numerical study that considered variations in thickness, curvature, material properties, and IOP, and used the results to develop a single correction equation that considered these parameters simultaneously. The results of the analysis and the correction equation were validated successfully against the outcome of earlier clinical and mathematical studies on the effect of individual parameters, and the correction equation was presented in a simple form suitable for clinical application.

Structural studies of heparan sulfate hexasaccharides: new insights into iduronate conformational behavior.

There is a growing opinion that the conformational dynamics within HS chains is critical to their observed biological activities. Investigations into HS conformational dynamics are problematic, given the structural complexity and heterogeneity of HS chains. However, this goal will be more obtainable once we understand the important roles HS sequence/sulfation patterns play in determining the conformational dynamics of iduronate units. This is the first study to compare isomers of N-sulfated oligosaccharides, with respect to the conformational versatility of their internal iduronates. Characterization by NMR spectroscopy of two HS oligosaccharides derived from porcine mucosal HS enabled the measurement of iduronate coupling constants, while under the influence of different flanking saccharide sequences. By fitting our coupling constant data to a new set of theoretical coupling constants, calculated using explicit water molecular dynamic simulations, we are able to offer new insights into the role sequence/sulfation patterns play in influencing iduronate conformational behavior. Fitting of experimental data, using our new theoretically derived coupling constants, suggests that replacement of the N-sulfate group to the reducing side of IdoUA by an N-acetyl group has little effect on the balance of IdoUA conformational equilibrium. Fitting of coupling constants for sequences GlcNS-IdoUA(2S)-GlcNS and GlcNS(6S)-IdoUA(2S)-GlcNS suggests that the flanking 6-O-sulfate group alters the balance of the IdoUA(2S) equilibrium more toward the (2)S0 conformation. There is also the suggestion that a cooperative effect may exist for N- and 6-O sulfation. These observations could be the key to understanding the important regulatory function attributed to 6-O-sulfation within HS chains.

Determination of the modulus of elasticity of the human cornea.

PURPOSE: To determine the material behavior of the human cornea in the form of simple relationships between the modulus of elasticity and intraocular pressure (IOP) and to establish the effect of age on the material behavior. METHODS: Human corneal specimens with age between 50 and 95 years were tested under inflation conditions to determine their behavior. The corneas were subjected to two extreme load rates to represent dynamic and static loading conditions. The pressure-deformation results were analyzed using shell theory to derive the relationship between the modulus of elasticity and IOP. RESULTS: The corneas demonstrated a nonlinear hyperelastic behavior pattern with an initial low stiffness stage and a final high stiffness stage. Despite the nonlinearity of the pressure deformation results, the relationship between the modulus of elasticity and the applied pressure was almost linear. A considerable increase was noted in the values of the modulus of elasticity associated with both age and load rate. General equations were derived to calculate the values of the secant and tangent moduli of elasticity in terms of IOP for any age greater than 50 years, and these equations are presented in a simple form suitable for use in numerical simulations. CONCLUSIONS: Adequate representation of corneal material behavior is essential for the accurate predictive modeling of corneal biomechanics. The material models developed in this work could be implemented in numerical simulations of refractive surgery procedures, corneal shape changes due to contact lens wear, and other applications.

Diurnal variation of central corneal thickness and Goldmann applanation tonometry estimates of intraocular pressure.

PURPOSE: To determine whether there is a temporal relationship between the diurnal variation of central corneal thickness (CCT) and intraocular pressure (IOP) by Goldmann applanation tonometry in young normal human participants in vivo. METHODS: Twenty-five eyes of 25 young healthy normal participants were examined in a prospective observational cross-sectional study. IOP, CCT and corneal curvature were measured using standard clinical techniques over a 24-hour period, and the temporal interrelationships between these parameters were examined. RESULTS: The overnight change in IOP measured by Goldmann tonometry was 3.1+/-2.4 mm Hg (P<0.001), CCT was 20.1+/-10.9 mum (P=0.016), with no statistical change in central corneal curvature (0.05 mm, P=0.477, paired t test with Bonferroni correction). Both IOP and CCT were highest on awakening at 7:00 then dropped rapidly to baseline levels by 9:00 (linear mixed models), and these two parameters were highly correlated (r=0.978, P<0.001). After 9:00, there was no correlation between these parameters (r=-0.453, P=0.260). CONCLUSIONS: The results of this study have highlighted a potential link between the diurnal variation of CCT and the accuracy of Goldmann tonometry estimates of IOP during the first 2 hours after awakening. Clinicians should be wary of using Goldmann tonometry to estimate IOP until the overnight increase in CCT has resolved.

The effect of contact lens induced corneal edema on Goldmann applanation tonometry measurements.

AIM: To determine the effect of small increases in corneal hydration on the accuracy of Goldmann applanation tonometry estimates of intraocular pressure (IOP). MATERIALS AND METHODS: Twenty-five young healthy subjects presented on 3 separate days approximately 1 week apart. On 2 visits, subjects were required to wear a hydrogel contact lens with either a center thickness of 0.3 and 0.7 mm (HEMA 38% water content, parallel surface curve) in 1 eye only under closed-eye conditions for 2 hours to induce corneal swelling. The third visit acted as a control. IOP, corneal thickness, and corneal curvature were measured in both eyes before and after contact lens wear on all visits. RESULTS: There was a statistically significant increase in corneal thickness of 40.2+/-14.4 microm (P<0.001) and 41.9+/-16.4 microm (P<0.001) after wearing the 0.3 and 0.7 mm thick contact lenses, respectively (2-tailed paired t test). There was an increase in IOP of 2.8+/-2.2 mm Hg (P<0.001) after wearing the 0.3 mm thick contact lens, and a statistically insignificant difference of 1.3+/-3.0 mm Hg (P=0.058) after wearing the 0.7 mm thick contact lens (2-tailed paired t test). There was a statistically significant Pearson correlation between the change in corneal thickness and the change in IOP after lens wear (r=0.500, P<0.001, 0.3 mm lens and r=0.399, P<0.001, 0.7 mm lens). The corneal hydration-induced measurement error was 0.46 mm Hg per 10 microm change in corneal thickness (0.3 mm lens) and 0.35 mm Hg per 10 microm change in corneal thickness (0.7 mm lens). CONCLUSION: A small increase in corneal hydration and thickness may cause a clinically significant overestimation of IOP when measured using Goldmann applanation tonometry.

Assessment of corneal biomechanical properties and their variation with age.

PURPOSE: The aim of this study was to determine the stress-strain behavior of corneal tissue and how the behavior was affected by age. METHODS: Human corneal specimens ranging in age between 50 and 95 years were tested under inflation conditions to determine their stress-strain behavior. The corneas were subjected to two load rates that represent dynamic and static loading conditions. The pressure-deformation results were analyzed using shell theory to derive the stress-strain behavior. RESULTS: The corneas demonstrated clear nonlinear behavior with an initial low stiffness stage and a final high stiffness stage. The transition between the two stages coincided with intraocular pressures between 12 and 20 mmHg. There was a considerable increase in stiffness associated with both age and load rate. Equations were derived to describe the nonlinear stress-strain relationship of corneal tissue for any age between 50 and 95 years, and these equations are presented in a form suitable for use in numerical simulations. CONCLUSIONS: The cornea demonstrates considerable stiffening with age with the behavior closely fitting an exponential power function typical of collagenous tissue. The increase in stiffness could be related to the additional age-related nonenzymatic cross-linking affecting the stromal collagen fibrils.

Effects of eye rubbing on the levels of protease, protease activity and cytokines in tears: relevance in keratoconus.

BACKGROUND: Proteases, protease activity and inflammatory molecules in tears have been found to be relevant in the pathogenesis of keratoconus. We sought to determine the influence of eye rubbing on protease expression, protease activity and concentration of inflammatory molecules in tears. METHODS: Basal tears were collected from normal volunteers before and after 60 seconds of experimental eye rubbing. The total amount of matrix metalloproteinase (MMP)-13 and inflammatory molecules interleukin (IL)-6 and tumour necrosis factor (TNF)-α in the tear samples were measured using specific enzyme-linked immunosorbent assays (ELISA). Tear collagenase activity was investigated using a specific activity assay. RESULTS: The concentrations of MMP-13 (51.9 ± 34.3 versus 63 ± 36.8 pg/ml, p = 0.006), IL-6 (1.24 ± 0.98 versus 2.02 ± 1.52 pg/ml, p = 0.004) and TNF-α (1.16 ± 0.74 versus 1.44 ± 0.66 pg/ml, p = 0.003) were significantly increased in normal subjects after eye rubbing. The experimental eye rub did not alter significantly the collagenase activity (5.02 ± 3 versus 7.50 ± 3.90 fluorescent intensity units, p = 0.14) of tears. CONCLUSION: Eye rubbing for 60 seconds increased the level of tear MMP-13, IL-6 and TNF-α in normal study subjects. This increase in protease, protease activity and inflammatory mediators in tears after eye rubbing may be exacerbated even further during persistent and forceful eye rubbing seen in people with keratoconus and this in turn may contribute to the progression of the disease.

Correction factors for Goldmann Tonometry.

PURPOSE: The purpose of the study was to evaluate the in vitro accuracy of correction factors in decreasing the error in the intraocular pressure (IOP) measurements obtained using the Goldmann Applanation Tonometer (GAT). METHODS: Nineteen donor corneas, from individuals aged between 57 and 99 years (mean 75.7 years, standard deviation±11.4 years) were subjected to posterior pressure simulating in vivo true IOP (IOPT) using an inflation test rig. Central corneal thickness and corneal curvature were measured. The posterior pressure was set at 25 different pressure levels between 5 and 45 mm Hg and IOP was measured using the GAT. Five different correction equations were applied to the IOP measurements obtained using the GAT to determine corrected IOP. The multiparameter correction equations applied were derived by Elsheikh, Ehlers, Chihara, Shimmyo et al, and Orssengo and Pye. The differences between IOPT and the IOP measured using the GAT were recorded as uncorrected errors, whereas the differences between IOPT and each of the corrected IOP were the tonometry errors after correction. RESULTS: The mean and standard deviation of error in tonometry before correction was +2.25±0.62 mm Hg. The mean errors in tonometry after correction using the Elsheikh and Chihara equations were +0.78±0.62 and +1.08±0.61 mm Hg, respectively. The mean errors in tonometry for the Ehlers, Shimmyo et al, and Orssengo and Pye equations were negative, indicating an overcorrection; the values were -0.75±2.28, -1.27±1.85, and -0.77±1.83 mm Hg, respectively. CONCLUSIONS: The Elsheikh and the Chihara et al's equations considerably decreased error in IOP measurements obtained by the GAT when compared with IOPT and were more consistent than other correction equations. The 2 equations may be of clinical utility in obtaining estimates of IOPT.