Rigid contact lens fitting relationships in keratoconus.
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Contact Lenses↗
Biomedical subjects
C W McMonnies
Publications and source records attributed to C W McMonnies.
Letter legibility and chart equivalence.
INTRODUCTION: We tested the appropriateness of the assumption that charts, which only vary in having different sequences of five letters per line, chosen from the same 10 letter set, can be regarded as equivalent for the purpose of making valid comparisons of visual acuity. METHOD: Visual acuity findings from samples of 400 patients, for each of two nominally equivalent Bailey-Lovie charts, have been used to determine the relative legibility of individual letters and lines, using the percentage incorrect method of analysis. RESULTS: The chance of error for the hardest letter is approximately 13 times greater than for the easiest letter on each chart. Significant between-chart differences in error rates for the hardest letters ('F' and 'H') were found. Some letters that have adjacent ranks on the legibility scale were found to have significantly different legibility. Significant differences in difficulty can occur for the same nominal line on apparently equivalent charts because of chance combinations of easier or harder letters in that line. Uneven line-to-line scale intervals have been confirmed for the charts examined, by showing corresponding differences in the distributions of lines of threshold acuity. CONCLUSIONS: The use of varying examination distances may be inappropriate for Bailey-Lovie (or similar) charts that depart from their nominal interval scaling. When different versions of these charts are assumed to be equivalent, the discrepancy between repeated measurements may be significantly increased. There is the possibility of increasing measurement precision using charts having different sequences of the same 10 letters in each line to achieve equal scaling of line intervals. Equivalent charts can be validly constructed using different sequences of the same 10 letters in each line.
Equipment Design↗
Chart construction and letter legibility/readability.
Variation in legibility/readability between charts letters may be due to differences in chart construction and/or examination protocols and/or subject selection. An examination of legibility/readability of letters that are common to two chart constructions was undertaken. Identical examination and subject selection protocols for both charts were employed. It was found that ranking of error frequencies for some letters varied between the Bausch & Lomb Compact Acuity Projector and Bailey-Lovie charts. Despite many similarities in ranking, the differences found for the letters D and E indicate that caution should be observed before assuming that legibility/readability determined with one letter chart would apply when using another. Lack of standardisation for chart construction, as well as measurement methods and conditions of measurement, invalidate inter-practice comparisons for visual acuity.
Adolescent↗
Use of a 'contract' in the management of the child contact lens patient.
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Letter↗
Visuo-spatial discrimination and mirror image letter reversals in reading.
This review compares visuo-spatial and linguistic mechanisms for discriminating between mirror image letters. The conclusion is drawn that both processes play a role in efficient reading, their relative contributions varying with reading experience and ability. It is shown that arguments used to reject visuo-spatial theories in mirror image letter reversals are flawed. Attention is drawn to the importance of visuo-spatial discrimination of mirror image letters, based on confident left/right body awareness, for beginning readers and for older children who are deficient in compensatory linguistic skills. When confused left/right body awareness is found in association with reversal problems, there is an indication to provide remediation that includes the promotion of mirror image letter discrimination based on confident left/right body awareness. Early intervention (pre-school and infants class) programs that teach left/right body awareness as a pre-reading skill are justified when the progress of beginning readers is facilitated and the need for remedial intervention is reduced in later years.
Child↗
Conjunctival hyperaemia in non-contact lens wearers.
Conjunctival hyperaemia was assessed in noncontact lens wearers using a photographic reference scale. The study was carried out on a sample of 252 females and 227 males within the age range of 1 to 89 years. The results show increasing levels of hyperaemia with age and higher levels of hyperaemia in males than in females. The differences in hyperaemia level for age and sex, however, were small and were insignificant clinically.
Adolescent↗
Assessment of conjunctival hyperemia in contact lens wearers. Part I.
A photographic reference scale representing six levels of conjunctival hyperemia has been developed for the assessment of responses to contact lenses. The scale has been found to be capable of detecting statistically significant differences in conjunctival hyperemia responses between samples of hard, soft, and noncontact lens wearers. For experienced observers, inter- and intraobserver reliability was found to be high and the conclusion is drawn that this type of scale is potentially useful in research and clinical applications.
Adult↗
Assessment of conjunctival hyperemia in contact lens wearers. Part II.
A photographic reference scale has been used to grade conjunctival hyperemia in contact lens wearers. A sample of hard lens wearers, included as a control, has been found to have significantly less conjunctival hyperemia (p less than 0.01) than either of two soft lens wearing groups (one using preserved storage solutions and the other using unpreserved storage solutions). Because both soft lens samples were found to have more hyperemia, it is concluded that factors other than storage solution preservative contribute to increase conjunctival hyperemia in soft lens wearers. However, the preserved storage soft lens wearers had significantly more hyperemia than the unpreserved storage solution group (p less than 0.01). The conclusion is that, apart from acute and subacute responses, there may be a relatively benign chronic response to soft lens storage solution that is associated with minimal symptoms.
Conjunctival Diseases↗
Patient history in screening for dry eye conditions.
A dry eye history questionnaire was completed by 500 patients who presented for the correction of refractive errors (normals), and 68 patients with previously diagnosed sicca syndrome. Subsamples of females over 45 years were extracted for comparison, and discriminant analysis yielded correct classification for 62 of 63 sicca subjects and 36 of 37 normals, representing 98% sensitivity and 97% specificity. An equivocal classification that warranted supplementary diagnostic procedures was indicated for 5% of subjects. The results indicated that the use of the questionnaire will obviate the need for supplementary ocular sicca examination procedures for the majority of patients presenting for an ocular examination.
Aged↗
Responses to a dry eye questionnaire from a normal population.
A dry eye questionnaire was completed by 500 patients who presented for the correction of refractive error. A sample of non-contact lens wearers was extracted (N = 177) and responses were compared between males and females, and between three subgroups according to age. Females responded at a significantly higher rate in regard to 4 of 24 questionnaire segments. Differences according to age were found for 5 of 24 questionnaire segments. Except for the question concerning arthritis, increased prevalence of dry eye findings in over-45-year-old females was not found in this normal population. These results, combined with those reported previously, validate the use of the questionnaire as a screening instrument that will enable ocular sicca cases to be identified.
Adult↗
Noncontact tonometry through soft contact lenses.
Under some circumstances it is advantageous to measure intraocular pressure (IOP) without removing soft contact lenses. In this study comparisons have been made between IOP measurements [using a noncontact tonometer (NCT)] with and without soft contact lenses on the eye. The influence of lenses of different water content, lens design, lens power, method of manufacture, and lens center thickness was examined. The most important parameter affecting the results was center thickness. It was shown that reliable and valid IOP findings can be obtained using a NCT with soft lenses on the eye when center thickness is less than 0.15 mm. In glaucoma screening readings obtained with lenses thicker than 0.15 mm may be convenient and useful although such results would be achieved with increased sensitivity and concomitant reduced specificity.
Contact Lenses, Hydrophilic↗
Key questions in a dry eye history.
The literature has been reviewed to derive a dry eye history questionnaire. The questions included examine for primary and secondary symptoms as well as assess for increased risk associated with age, sex, contact lens wear, medication use, and systemic and ocular factors that may be associated with dry eye syndromes. At the risk of obtaining responses of reduced validity, the questionnaire, administered by an assistant, may be preferred to direct interrogation for routine screening. Apart from serving as an indication of the presence of a dry eye condition, the questionnaire results may successfully identify individuals who are at risk for developing dry eye problems at a later time, especially those individuals exposed to provocative factors such as contact lens wear. A screening based on questionnaire results will help identify patients requiring further examination for dry eye conditions and associated differential diagnosis.
Age Factors↗
The vascular response to contact lens wear.
The ocular limbal blood vessels were studied in daily wearers of soft contact lenses and hard contact lenses, and in eyes of subjects who had never worn a contact lens. The degree of filling of vessels and the number of vessels crossing the limbus were measured photographically at the inferior limbus. The extent to which vessel filling in contact lens wearers could be considered as capillary injection, as apposed to new vessel growth, was estimated by comparing the degree of injection in lens wearers to that found in nonwearers given a vasodilating stimulus. It was found that soft lens wearers showed greater limbal injection than hard lens wearers. The limbal vasculature of hard lens wearers was indistinguishable from that of nonwearers. The vascular response to soft lens wear was similar in magnitude to that produced by vasodilating agents in noncontact lens wearers, and was therefore considered to be due to the filling of preexisting capilliaries rather than new vessel growth. The chronic level of vessel dilation in soft lens wearers is cause for concern, as sustained dilation of the limbal vessels may be a precursor to new vessel growth.
Adult↗
Contact lens intolerance in association with epithelial dystrophy.
Refractile changes in corneal transparency that are associated with epithelial basement membrane dystrophy have been detected in contact lens wearers who show a wide range of contact lens tolerance. In some of these cases, contact lens wear precipitates an episode of recurrent epithelial erosion. In other cases excellent contact lens tolerance is observed. The cases described indicate that pure bleb forms of epithelial basement membrane dystrophy may not be of benign significance when contact lenses are worn.
Adult↗
Endothelial bedewing of the cornea in association with contact lens wear.
Endothelial bedewing is described as either a cluster of oedematous droplets or a constellation of leucocytes deposited on the surface of the corneal endothelium. The use of marginal retroilumination in biomicroscopy is described for the detection of endothelial bedewing. Some of the clinical characteristics of endothelial bedewing are outlined, and its occurrence in patients who are chronically endothelial bedewing may be indicative of a limited anterior uveal response associated with contact lens wear.
Adolescent↗