M.Phil. (Optometry) / The primary aim of this research was to investigate whether the Icare® rebound tonometer may be used in place of the Goldmann tonometer to obtain accurate and reliable intraocular pressure measurements on a sample of the general population seeking eye care, in a South African context. Due to the portability of the Icare®, lack of dependency on other instrumentation and power source, together with the ease of use with minimal training, and without the use of topical anaesthetic favourable results of the instrument may lead to its widespread use. This could aid in earlier diagnosis of glaucoma where intraocular pressure remains the only modifiable risk factor. In the South African context, where a high prevalence of undiagnosed primary open angle glaucoma has been found, access and accuracy of intraocular pressure measurement could save and extend functional vision in this country. Patients presenting at the Department of Optometry for routine eye examinations were selected utilizing convenience sampling. The right and left eyes of 113 patients were assessed using both the Icare® TA01i and the Goldman applanation tonometer by independent examiners for each method, all readings of intraocular pressure with the Goldman being taken by the same experienced examiner. The age of the patients ranged from 20 to 89 years with a mean age 50.29 ±20.97 years. Using the Oculus Pachycam® when it became available, central corneal thickness was obtained on 71 patients (142 eyes). Analysis of data using descriptive statistics from SPSS (Statistical Programs for the Social Sciences) was performed in addition to the Bland-Altman method of comparative analysis for sets of data of corrected and uncorrected measurements between the instruments...

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 177-186).

Purpose: We evaluate solutions for an applanating surface modification to the Goldmann tonometer prism, which substantially negates the errors due to patient variability in biomechanics. Methods: A modified Goldmann or correcting applanation tonometry surface (CATS) prism is presented which was optimized to minimize the intraocular pressure (lOP) error due to corneal thickness, stiffness, curvature, and tear film. Mathematical modeling with finite element analysis (FEA) and manometric lOP referenced cadaver eyes were used to optimize and validate the design. Results: Mathematical modeling of the optimized CATS prism indicates an approximate 50% reduction in each of the corneal biomechanical and tear film errors. Manometric lOP referenced pressure in cadaveric eyes demonstrates substantial equivalence to GAT in nominal eyes with the CATS prism as predicted by modeling theory. Conclusion: A CATS modified Goldmann prism is theoretically able to significantly improve the accuracy of lOP measurement without changing Goldmann measurement technique or interpretation. Clinical validation is needed but the analysis indicates a reduction in CCT error alone to less than +/- 2 mm Hg using the CATS prism in 100% of a standard population compared to only 54% less than +/- 2 mm Hg error with the present Goldmann prism. Translational Relevance: This article presents an easily adopted novel approach and critical design parameters to improve the accuracy of a Goldmann applanating tonometer.

The purpose of this thesis was to investigate the effect of corneal swelling on the accuracy of Goldmann tonometry estimates of intraocular pressure (IOP). In the first experiment, central corneal thickness (CCT, ultrasonic pachymetry), IOP (Goldmann tonometry) and corneal curvature (keratometry) was measured in one eye of 25 subjects every two hours for 24 hours, except for 8 hours overnight (no measurements taken), and for the first two hours after awakening (measurement frequency 20 minutes). CCT (+20.1??10.9 pm) and IOP (+3.1??2.4 mmHg) peaked on eye opening, and then decreased at a similar rate (r=0.967, p<0.001) for the next two hours. Corneal swelling may have influenced the accuracy of Goldmann IOP measurements during this time. In the second and third studies, the CCT, IOP and corneal curvature were measured in both eyes of two groups of 25 subjects before and after the induction of corneal swelling, resulting from two hours of monocular closed eye contact lens wear. The increase in IOP was correlated to the increase in CCT at a rate of 0.33 to 0.48 mmHg per 10 pm, which signified an overestimation error in Goldmann IOP measurement. However, the change in IOP could not be accounted for solely by the change in CCT. In the fourth study, CCT, IOP and corneal curvature were used in conjunction with the Orssengo-Pye algorithm to determine the range of Young's modulus in the normal population, which was 0.29??0.06 MPa. Physiological variations in Young's modulus had a similar effect on Goldmann tonometry to CCT. In the fifth study, the data collected for studies 2 and 3 was used to calculate the Young's modulus changes associated with corneal swelling, again with the assistance of the Orssengo-Pye algorithm. No systematic change in Young's modulus was recorded after contact lens wear, but the model suggested that corneal biomechanical changes were responsible for the remainder of the change in IOP. All experimental results were combined to develop a model to calculate the diurnal variation of Goldmann IOP errors. The likely error in IOP due to overnight corneal swelling was 0.6 to 1.4 mmHg, which may explain as much as 45% (1.4 mmHg) of the 3.1 mmHg diurnal variation of IOP. In summary, small amounts of corneal swelling were shown to have a clinically significant impact on the accuracy of Goldmann tonometry. This may interfere with the measurement of the diurnal variation of IOP, particularly if measurements are taken prior to the resolution of overnight corneal swelling.

No description available.

The purpose of this thesis was to investigate the effect of corneal swelling on the accuracy of Goldmann tonometry estimates of intraocular pressure (IOP). In the first experiment, central corneal thickness (CCT, ultrasonic pachymetry), IOP (Goldmann tonometry) and corneal curvature (keratometry) was measured in one eye of 25 subjects every two hours for 24 hours, except for 8 hours overnight (no measurements taken), and for the first two hours after awakening (measurement frequency 20 minutes). CCT (+20.1??10.9 pm) and IOP (+3.1??2.4 mmHg) peaked on eye opening, and then decreased at a similar rate (r=0.967, p<0.001) for the next two hours. Corneal swelling may have influenced the accuracy of Goldmann IOP measurements during this time. In the second and third studies, the CCT, IOP and corneal curvature were measured in both eyes of two groups of 25 subjects before and after the induction of corneal swelling, resulting from two hours of monocular closed eye contact lens wear. The increase in IOP was correlated to the increase in CCT at a rate of 0.33 to 0.48 mmHg per 10 pm, which signified an overestimation error in Goldmann IOP measurement. However, the change in IOP could not be accounted for solely by the change in CCT. In the fourth study, CCT, IOP and corneal curvature were used in conjunction with the Orssengo-Pye algorithm to determine the range of Young's modulus in the normal population, which was 0.29??0.06 MPa. Physiological variations in Young's modulus had a similar effect on Goldmann tonometry to CCT. In the fifth study, the data collected for studies 2 and 3 was used to calculate the Young's modulus changes associated with corneal swelling, again with the assistance of the Orssengo-Pye algorithm. No systematic change in Young's modulus was recorded after contact lens wear, but the model suggested that corneal biomechanical changes were responsible for the remainder of the change in IOP. All experimental results were combined to develop a model to calculate the diurnal variation of Goldmann IOP errors. The likely error in IOP due to overnight corneal swelling was 0.6 to 1.4 mmHg, which may explain as much as 45% (1.4 mmHg) of the 3.1 mmHg diurnal variation of IOP. In summary, small amounts of corneal swelling were shown to have a clinically significant impact on the accuracy of Goldmann tonometry. This may interfere with the measurement of the diurnal variation of IOP, particularly if measurements are taken prior to the resolution of overnight corneal swelling.

Thesis (M.Phil.) - University of Queensland, 2004. / Includes bibliographical references.

Orientador: Vital Paulino Costa / Tese (doutorado)- Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-14T22:24:08Z (GMT). No. of bitstreams: 1 Silva_MarceloJordaoLopesda_D.pdf: 4720767 bytes, checksum: e65a7faa1b4b7b160cef41acf6f4b989 (MD5) Previous issue date: 2009 / Resumo: Os objetivos deste trabalho são comparar a pressão intra-ocular (PIO), medida com tonometria de contorno dinâmica (TCD) e tonometria de aplanação de Goldmann (TAG), analisar a influência da espessura central da córnea (ECC) e idade, em ambas as medições, bem como a influência do índice de qualidade sobre as leituras da TCD. Foram avaliados 500 indivíduos saudáveis (1000 olhos), sem história prévia de glaucoma ou hipertensão ocular (idade: 7 a 86 anos) recrutados consecutivamente. TAG, TCD e ECC foram obtidos de ambos os olhos de cada indivíduo, nessa ordem, por três observadores. A média de cinco medidas da ECC foi utilizada para análise. As medições da TCD foram aceitas quando o escore de qualidade variou entre 1 (qualidade superior) e 3 (menor qualidade). A média das PIOs obtidas com TCD foram superiores em 3,2 mmHg às medições com TAG. A análise de Bland-Altmann revelou má concordância entre as leituras de TCD e TAG, com intervalos de confiança de 95% de ± 6,98 mmHg. Os valores da ECC variaram entre 449 e 653 µm. As PIOs medidas com TAG mostraram-se fortemente correlacionadas à ECC (r? = 0,28, p <0,001), enquanto as PIOs obtidas com TCD apresentaram fraca correlação com a ECC (r2 = 0,01, p = 0,017). Tanto as medidas de TCD (r2 <0,01, p = 0,044) quanto as obtidas com TAG (r2 = 0,01, p <0,001) apresentaram fraca correlação com a idade. Os escores de qualidade das medidas de TCD foram 1 (n = 369, 36,9%), 2 (n = 340, 34,0%) e 3 (n = 291, 29,1%). As leituras de medida com TCD com escore de qualidade 3 (18,8 ± 3,4 mmHg) foram significativamente maiores do que aquelas com escore 1 (16,7 ± 2,9 mmHg) e 2 (17,4 ± 2,9 mmHg) (p <0,001). Concluiu-se que a medida com TCD não é influenciada pela ECC, ao contrário daquela com TAG. As medidas de PIO tomadas com TCD e com TAG não são influenciados pela idade. Finalmente, medidas de TCD com qualidade inferior apresentam valores maiores que as de qualidade superior. / Abstract: The purposes of this study are to compare the IOP measurements obtained with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT), and to analyze the influence of central corneal thickness (CCT) and age on both measurements, and the influence of the quality score on DCT readings. 500 healthy subjects with no previous history of glaucoma or ocular hypertension (ages: 7 to 86 years old) were consecutively recruited. GAT (Haag Streit R900, Switzerland), DCT (SMT Swiss Micro Technology, Switzerland), and CCT (Sonomed Micropach 200P+, USA) measurements were obtained from both eyes of each individual, in this order, by three observers. The mean of five CCT measurements was used for analysis. DCT measurements were accepted when quality scores varied between 1 (higher quality) and 3 (lower quality). In our series, the mean DCT measurements were 3.2 mmHg higher than GAT readings. CCT values varied between 449 and 653 µm. IOP measured by GAT correlated strongly with CCT (r2=0.28, p<0.001), whereas DCT readings correlated poorly with CCT (r2=0.01, p=0.017). Both DCT (r2<0.01, p=0.044) and GAT (r2=0.01, p<0.001) measurements correlated poorly with age. Bland-Altmann analysis revealed disagreement between DCT and GAT readings, with 95% confidence intervals of ± 6.98 mmHg. Quality scores for DCT measurements were 1 (n=369, 36.9%), 2 (n=340, 34.0%) and 3 (n=291, 29.1%). DCT readings with quality score of 3 (18.77±3.35 mmHg) were significantly higher than those with quality scores of 1 (16.61±2.91 mmHg) and 2 (17.44±2.93 mmHg) (p<0.001). In conclusion, DCT is not influenced by CCT, unlike GAT. Both DCT and GAT measurements are not influenced by age. DCT measurements with lower quality scores are associated with higher readings. / Doutorado / Doutor em Ciências Médicas

Ocular disease is one of the most common problems encountered in sea lions at various zoos and aquariums around the world.1 The California sea lion (Zalophus californianus) is one of the most common marine mammals maintained in zoos and is also the most commonly afflicted with ocular disease. Studies have shown that pinnipeds housed in captivity manifest an array of ocular lesions.2 Eye disease can range from a pinpoint corneal opacity to loss of vision due to keratopathy, cataracts and secondary glaucoma. Glaucoma is a disease that has not been extensively studied in the sea lion.3 Observation of clinical signs and determination of intraocular pressures (IOP) are critical for early diagnosis. IOP measurement may elucidate intraocular disease and provides information on the balance between aqueous humor production and outflow. The objective of this study is to measure IOP in California sea lions that have clinically normal eyes as well as those with varying degrees of ocular diseases, and to evaluate the incidence of secondary glaucoma in this species.

Yes / Ophthalmologists rely on a device known as the Goldmann applanation tonometer to make intraocular pressure (IOP) measurements. It measures the force required to press a flat disc against the cornea to produce a flattened circular region of known area. The IOP is deduced from this force using the Imbert-Fick principle. However, there is scant analytical justification for this analysis. We present a mathematical model of tonometry to investigate the relationship between the pressure derived by tonometry and the IOP. An elementary equilibrium analysis suggests that there is no physical basis for traditional tonometric analysis. Tonometry is modelled using a hollow spherical shell of solid material enclosing an elastic liquid core, with the shell in tension and the core under pressure. The shell is pressed against a rigid flat plane. The solution is found using finite element analysis. The shell material is anisotropic. Values for its elastic constants are obtained from literature except where data are unavailable, when reasonable limits are explored. The results show that the force measured by the Goldmann tonometer depends on the elastic constant values. The relationship between the IOP and the tonometer readings is complex, showing potentially high levels of inaccuracy that depend on IOP.