The 75th anniversary of the Tuohy corneal contact lens: A review.

The aim of this review is to mark the 75th anniversary of the introduction of the original corneal contact lens of Tuohy in 1948. American documents in the public domain, such as census records and draft registration cards, were consulted in order to provide a more comprehensive biography of Kevin M Tuohy, inventor of the corneal contact lens, than those previously published. Perhaps due to a failure to consult original sources concerning the Tuohy corneal lens, some historical accounts have provided incomplete or incorrect information about its design and dimensions. The back surface specification of the bi-curve Tuohy lens in its standard diameter of 11.50 mm has been tabulated and edge lift and edge clearance values calculated. A colour photograph illustrates the fluorescein pattern of a Tuohy lens. Patients wearing Tuohy lenses were able to achieve a much longer wearing time compared to those wearing sealed scleral lenses since they eliminated corneal epithelial oedema, a frequent problem which necessitated removal of lenses after a few hours of wear due to cloudy vision. Only some of Tuohy lens wearers exhibited an adverse corneal response such as fluorescein staining after 12, or more, hours of wear. The clinical success of the Tuohy lens and the fact that its fitting procedure was simpler and quicker than that for scleral lenses encouraged optometrists to commence contact lens practice and to implement improvements in the design of the corneal lens.

Contact lens wear by Royal Air Force aircrew in World War II.

PURPOSE: To provide an overview of the use of contact lenses by RAF aircrew in World War II by identifying some of the fitters and wearers and appraising the clinical results that they achieved. METHODS: A wide-ranging literature search was undertaken that encompassed peer-reviewed journals, non-refereed publications, books, official publications, newspapers and archived documents. RESULTS: Thirty-one aircrew are known to have worn sealed scleral lenses in order to meet the required visual standards. Of these, only two were considered to be completely unsuccessful, one of whom was unilaterally aphakic. One additional case of undisclosed contact lens wear was found and the identity of this officer was established. Brief biographies of a few pilots establish the context of their contact lens wear. CONCLUSION: Overall, the results of scleral lens wear were variable reflecting those achieved by civilian patients of the period. While three men complained of discomfort due to heat and glare, one pilot experienced no photophobia when flying above white clouds in brilliant sunshine and another found no difficulty caused by altitude or tropical climate. Wearing time ranged from about 2h to 16, or more, hours. In about a third of the cases, wearing time was limited due to the onset of a form of contact lens induced-epithelial oedema known as Sattler's veil and effective solutions to this problem were not implemented until after the war.

The refractive index of contact lens saline solutions.

PURPOSE: The aim of this study was to measure the refractive index of three readily available contact lens saline solutions in order that these values could be used in a calculation to convert back vertex power measured in saline to its corresponding power in air. METHOD: Using an automatic digital refractometer, measurements were made daily for 31 days at 20°C and at a wavelength of 589.3nm of the refractive index of fifteen bottles from different manufacturing batches of each of the three saline solutions. RESULTS: For AMO LENS PLUS™ OcuPure™, BAUSCH & LOMB Sensitive Eyes™ Plus Saline Solution and Sauflon saline, the mean values of refractive index were 1.33458, 1.33465 and 1.33470, respectively. The standard deviation for each solution was 0.00001 and the range of the measured values of refractive index of the three solutions over the test period did not exceed 0.00005. CONCLUSIONS: It is proposed that when calculating back vertex power in air from measurements made in a wet cell that refractive index values for AMO LENS PLUS™ OcuPure™, BAUSCH & LOMB Sensitive Eyes™ Plus Saline Solution and Sauflon saline of 1.3347, 1.3348 and 1.3348, respectively be used for focimeters operating at a wavelength of 587.56nm and values of 1.3361, 1.3362 and 1.3362, respectively when a wavelength of 546.07nm is used.

A comparison of in-air and in-saline focimeter measurement of the back vertex power of spherical soft contact lenses.

PURPOSE: To compare the repeatability and validity of measurements of the back vertex power (BVP) of spherical soft contact lenses made in-air using the method specified in the International Standard (ISO 18369-3:2006) with the corresponding values when BVP was calculated from measurements made using a wet cell and focimeter method that is not approved by this Standard. METHODS: The BVP of 20 hydrogel and 20 silicone hydrogel lenses, with labelled powers ranging from +8.00 to -12.00 D, were measured with a focimeter by two operators on two occasions in-air in accordance with the relevant International Standard. Equivalent sets of measurements were made with the lenses immersed in-saline within a wet cell and their BVPs in-air were calculated. The validity of each method was assessed by comparing their results with an instrument that used the Hartmann method. RESULTS: The reliability results were generally a little better for the in-saline measurements than for the in-air measurements, although all reliability data demonstrated absolute values of mean errors (inter-operator and inter-session) that were <0.05 D for hydrogel lenses and <0.07 D for silicone hydrogel lenses. The in-air 95% confidence intervals were <0.45 D and <0.40 D for hydrogel and silicone hydrogel lenses, respectively and in-saline <0.39 and <0.31 D for hydrogel and silicone hydrogel lenses, respectively. The validity data revealed a relationship between measurement error and BVP for the in-air data (the focimeter overestimates the power of high plus and high minus lenses compared with the Hartmann instrument) and possibly a more complex relationship for the in-saline data. The 95% limits of agreement indicate better agreement for the in-saline validity data (-0.55 to +0.48 D for hydrogel lenses and -0.42 to +0.54 D for silicone hydrogel lenses) than those obtained in-air (-0.64 to +0.68 D for hydrogel lenses and -0.57 to +0.44 D for silicone hydrogel lenses). CONCLUSIONS: Using equipment readily available in a clinical setting, the wet cell method of measurement of the BVP of spherical soft contact lenses has been shown to provide results for reliability and validity that were at least as good as those obtained with the in-air method approved by the International Standard.

A review of the limitations of the first hydrogel contact lenses.

BACKGROUND: It is generally believed that the clinical performance of the original Czechoslovakian hydrogel contact lenses was poor but historical reviews provide very little explanation regarding their failings. There is a lack of information in the literature about their dimensions and, in particular, thickness, which is essential for the calculation of oxygen transmissibility. Until now no measurements on Czechoslovakian lenses have been reported. METHODS: A literature search on Czechoslovakian lenses was made that spanned the first decade of their use and included peer-reviewed journals, non-refereed publications and a number of archived documents. In addition, the water content and dimensions of five Geltakt and four Spofa lenses were measured. RESULTS: Lens packaging, lens lifetime, hygienic care, visual acuity, nominal lens dimensions, flexure, failure to correct astigmatism, corneal oedema, oxygen transmissibility, complications and wearing time are reviewed. Measurements on Czechoslovakian lenses indicate that the total diameter was similar to that of the cornea, the back optic zone radius was steep and the centre thickness was large. CONCLUSION: Problems associated with the Czechoslovakian lenses included packaging and an initial failure to require daily disinfection. Few complications of lens wear were reported, probably due to the comparatively small number of patients fitted and the limited wearing time that they achieved. Delayed disclosure of lens dimensions handicapped the development of a fitting technique. An acceptable visual acuity was attained in selected cases, while reduced acuity may sometimes have been due to uncorrected astigmatism or to poor lens quality. The most serious disadvantage was the very low oxygen transmissibility that could result in marked corneal oedema.

The Sämisch case and the Müllers of Wiesbaden.

PURPOSE: There are significant inconsistencies in accounts in textbooks of the fitting in 1887 of a device resembling a scleral contact lens. The aim of this study was to establish the facts of this case and to provide an overview of the subsequent clinical performance of blown scleral shells and lenses. METHODS: A literature search was conducted that included the original report published in 1910 of the fitting of the patient. The dimensions and back vertex power of a blown scleral shell were measured. RESULTS: In 1887, the right eye of a patient with lagophthalmic keratitis as a sequel to cancerous destruction of the lower eyelid was fitted with a protective blown scleral shell. His left eye was effectively blind. The referring ophthalmologist was Professor Theodor Sämisch of Bonn and the fitting was undertaken by the firm of F Ad Müller & Söhne of Wiesbaden, Germany. With periodical replacement, a shell was worn for at least 21 years. Müller scleral shells were principally fitted in keratoconus providing markedly improved visual acuities and wearing times of up to 14 h a day. There were instances of continuous wear. CONCLUSIONS: Failure to consult original sources is responsible for errors in descriptions of the Sämisch case that is of historical importance because it represents both the first use of a therapeutic contact shell and the first instance of continuous wear. Blown scleral shells and lenses played an important part in the optical correction of keratoconus and the management of other ocular conditions during the first quarter of the 20th century.

Rigid gas permeable lens tolerance limits and their possible effect on mode of fit.

BACKGROUND: Rigid gas permeable corneal lenses should be manufactured according to the tolerance limits specified in the International Standard ISO 18369-2: 2006. The purpose of this study was to model and quantify the central and edge fit provided by lenses with manufacturing errors that are at the limits of these dimensional tolerances. METHODS: A spreadsheet was used to design a tri-curve lens that provided specified values for apical tear layer thickness and axial edge clearance on corneas with three different apical radii and six different p values. The lens radii and diameters were then varied by amounts that were at the limit of the corresponding tolerances to ascertain the resultant central and edge fit of the lens. RESULTS: Rigid gas permeable lenses made with manufacturing errors at the limits of tolerances in either the back optic zone radius (BOZR) or back optic zone diameter (BOZD) are unlikely to provide an acceptable apical tear layer thickness. When the BOZR is 0.05 mm steep and the BOZD is 0.20 mm large, a lens intended to have an apical tear layer thickness (ATLT) of 5 microm will provide an actual value between 12.3 and 19.4 microm, depending on corneal radius and shape. When the BOZR is 0.05 mm flat and the BOZD is 0.20 mm small, the value of ATLT will be zero. Lenses in which all radii and diameters have been made with such errors may allow a clinically acceptable edge clearance in most cases. CONCLUSION: Current tolerance limits for RGP lenses may allow the ATLT to differ significantly from that intended but the edge fit may be acceptable. While the full specifications of a RGP lens should be verified prior to its supply to a patient, it is particularly important to measure the BOZR and desirable to measure the BOZD, to ensure that resultant ATLT does not differ significantly from that intended. Minimally blended transitions, especially on trial lenses, should allow the back surface dimensions to be measured in accordance with International Standard ISO 18369-3: 2006. Ideally, the practitioner should be aware of any differences between nominal and actual specifications of both trial lenses and those supplied to patients.

Aspects of wet cell measurement of back vertex power of contact lenses.

BACKGROUND: The back vertex power of soft contact lenses can be measured when they are immersed in saline within a wet cell. Six equations have been published for the purpose of converting the power measured in saline to its corresponding power in air. Results provided by these equations have not been compared and the consequences of inaccuracies in the variables used in them have not been quantified. METHODS: Sample data were used to solve these equations and inaccuracies were simulated in each of the variables required for their solution to determine the resultant magnitude of error in the calculated power in air. RESULTS: Three equations gave identical results. Inaccuracies in the lens specification, distance of the back vertex of the lens from the cell wall, refractive index of the cell and its wall thickness were of very little consequence in the calculation of power in air. In the case of a high water content lens, immersed power must be measured to 0.02 D and its refractive index and that of saline must be known to +/-0.001 to prevent errors in the calculated power in air exceeding tolerance limits. CONCLUSION: Measured power in saline can be converted to power in air using the original equation published by Wichterle in 1965. While the nominal specification of the lens can be used in this equation, it is essential to know its actual refractive index and that of the saline. Reproducibility of wet cell measurement of power using a suitable focimeter is unknown and should be established to allow this method to be used by practitioners and research laboratories.

An appraisal of the optics of the hydrodiascope.

The hydrodiascope is a simple optical device that was introduced in 1896 and for the next 20 years, represented a potentially superior alternative to contact shells as an effective means of optical correction in keratoconus. Previous historical accounts of the hydrodiascope have failed to quantify those optical characteristics that are essential to an understanding of its clinical performance. The results of this study confirm the validity of the inventor's original equations to determine the focal length of the hydrodiascope lens and show that for powers between +25.00 and +40.00D: * The spectacle magnification ranges from 1.49 up to 5.37. * For a reading distance of one third of a metre from the device, there is a substantial increase in accommodative demand of between 2.81 and 13.90 D. * A decrease in vertex distance of the hydrodiascope lens from 10 to 9 mm, reduces its effective power between 0.90 and 6.79 D. It is evident that the ability of the hydrodiascope to improve visual acuity to a normal level was due to both neutralisation of irregular astigmatism and the considerable spectacle magnification inherent in the system. The principal disadvantages of the hydrodiascope were its poor cosmetic appearance and the high demand that it placed upon accommodation. It fell into disuse as contemporary blown scleral shells were gradually replaced by ground scleral lenses. The latter ultimately proved to be capable of improving visual acuity significantly in keratoconus without imposing excessive accommodation and offering the aesthetic advantage of being 'invisible'.

Karl Otto Himmler, manufacturer of the first contact lens.

In 1889 August Müller (1864-1949) reported the correction of his own high myopia with a ground scleral contact lens that had been manufactured in Berlin two years earlier. This paper provides the first conclusive identification, based upon primary sources, of the manufacturer of these lenses. They were made by an optical engineer, Karl Otto Himmler (1841-1903), whose firm enjoyed, until the outbreak of World War II, an international reputation for the manufacture of microscopes and their accessories.

Chronic upper limb pain: an exploration of the biopsychosocial model.

OBJECTIVE: To model pain intensity and consequent disability by independent physical, psychological, and social variables in a group of patients with chronic upper limb pain. METHODS: We studied a group of 73 hospital outpatients with either chronic work related diffuse upper limb pain or carpal tunnel syndrome. We assessed pain intensity, disability, and personality by self-rated questionnaires; and psychiatric morbidity by a standardized interview. We measured illness behavior by assessing coping strategies, illness beliefs, financial benefits, and movements of the most affected limb. RESULTS: In both pain conditions, disability was positively correlated with present pain intensity, depression, helpless coping style, and receipt of state financial benefits; and was negatively correlated with age. This explained 43% of the variance and correctly classified 85% of all patients. Present pain intensity was positively correlated with both depression and the number of arm movements at night. This model explained 15% of the variance and correctly classified 75% of all patients. Inclusion of diagnostic group has no effect on these models. CONCLUSION: The correlations between disability and pain intensity with both psychosocial and physical factors support the biopsychosocial model of disability in particular, and pain to a lesser extent, irrespective of the diagnosis.

Illness behavior and psychosocial factors in diffuse upper limb pain disorder: a case-control study.

OBJECTIVE: To compare behavioral and other psychosocial factors in patients with diffuse upper limb pain disorder (ULPD) and patients with carpal tunnel syndrome (CTS). METHODS: We compared 37 hospital outpatients with diffuse ULPD with 36 hospital outpatients with CTS, matched by sex, pain intensity, and duration of illness. We assessed psychiatric morbidity by a standardized interview, and both symptoms and personality by self-rated questionnaires. We measured illness behavior by assessing financial benefits and compensation, coping strategies, illness beliefs, treatments received, and 24 hours of monitoring movements of the most affected arm and the body as a whole. RESULTS: There were no significant differences in the prevalence of either current or premorbid psychiatric disorders, personality scores, symptom amplification, disability, or treatments received. Subjects with ULPD had significantly lower self-rated scores for depression, somatic distress, sleep disturbance, and physical fatigue than subjects with CTS, although there were more than normal levels of anxiety, fatigue, and sleep disturbance in both groups. There were no significant differences in the numbers of arm or body movements by day and night. Significantly more ULPD subjects had been involved in litigation, but litigating patients were a minority. CONCLUSION: The primary etiology of endemic diffuse ULPD, presenting in secondary care, is no more psychiatric, psychological, behavioral, or related to personality than is the case with a similarly chronic and painful condition of known pathology. We cannot exclude either a specific role for psychosocial factors at work, or a more general role for psychosocial factors in maintaining disability in patients with chronic pain.