摘要:

Purpose.To develop a videokeratoscopic-based keratoconus detection scheme that avoids the ambiguity of dioptric power definitions and videokeratoscope design.Methods.Corneal height data obtained with a commercial videokeratoscope are decomposed into the set of orthogonal Zernike polynomials. Expansion coefficients of a “normal” group and a keratoconus group are compared to find significant differences. Elevated Zernike terms are used to detect the disease in these populations. The performance of this detection scheme is compared to other videokeratoscopic keratoconus indices.Results.Two low-order Zernike polynomial terms are identified as being elevated in keratoconus patients and combined to form a new detection index. This index performed at least as well as keratoconus detection schemes based on the inferior- superior (I-S) value, the steepest radial axes (SRAX), and the Surface Asymmetry Index (SAI) for the samples studied.Conclusion.The proposed Zernike scheme offers a potentially viable algorithm for detecting keratoconus that avoids the ambiguities of dioptric power definitions and is independent of videokeratoscope design.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

ABSTRACTDespite the wide variety of rigid contact lens fitting philosophies for the visual correction of keratoconus, questions remain, including which approach—flat, divided support, or steep—contributes the most toward the preservation of a clear cornea. One goal of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Pilot Study was to determine the feasibility of managing early keratoconus patients with apical clearance rigid contact lenses. Of 30 keratoconus patients identified with at least 1 nonscarred cornea, 17 patients (30 eyes) were randomly assigned to a steep lens fitting protocol. After trial fitting with a standardized lens design demonstrating minimum apical clearance, lenses were dispensed whose base curve was 0.2 mm steeper than the minimum apical clearance lens. Patients were re-evaluated on a quarterly schedule concluding at 12 months. Changes in keratometry between baseline and 12 months identified unequal steepening of the flat and steep corneal curvatures, suggestive of corneal molding. Best corrected rigid lens visual acuity measures illustrated no significant changes over the course of the study. Clinically significant corneal compromise pleting the pilot study and fitted with apical clearance developed mild corneal scarring.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

ABSTRACTThe influence of pupil size, lens centration, and translation on multifocal contact lens performance suggests that these parameters should be accounted for in the optical design of presbyopic contact lenses. The purpose of the present article is to complete the existing experimental data with clinical measurements of pupil diameter and lens position relative to the pupil in a group of presbyopic, with controlled target luminance, stimulus distance, gaze angle, and convergence. The experiments involve an infrared video-pupillometer and ring-marked contact lenses. Results on pupil aperture show that the effect of changing target distance is comparable in magnitude to that of varying luminance within the photopic range. The measured data on lens position confirm that soft contact lenses are generally decentered from the pupillary axis, usually in inferior temporal direction, and that their average translation between primary and downward gaze is very small. It is also found that the average relative position between lens and pupil centers is slightly modified by changes of luminance in far vision. All these results provide characteristic values which are helpful for the optical modeling of presbyopic contact lenses.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Background.Excessive numbers of the mite, Demodex folliculorum, in the eyelash follicles cause itching and is referred to as demodicosis. We evaluated 4% pilocarpine gel as a treatment for this condition.Methods.An advertisement was placed in a retirement home newsletter, requesting persons with ocular discomfort. Respondents were examined for Demodex and persons with abundant mites were invited to participate. One eye was treated with pilocarpine gel; the other eye was untreated. The relative abundance of mites was evaluated at baseline, after 1 and 2 weeks of treatment. Subjects kept a daily log of symptoms.Results.Eleven of 22 persons with ocular itching had abundant Demodex. Mites were reduced significantly by the treatment (p=0.017). The amount of mite reduction was closely correlated with the extent to which itching was alleviated (r=0.811, p=0.008).Conclusion.Abundant Demodex is an important cause of ocular itching in older persons. Mites can be reduced with pilocarpine gel and itching alleviated.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Contact lens patient discomfort has been linked to the pH of lens care solutions differing from that of tears. To determine if this is a potential problem with multi-purpose soft contact lens solutions, we used a Fisher Scientific Accumet 950 pH/ion meter (accuracy ±0.05 pH units) to measure the pH of 3 multi-purpose solutions—Alcon's Opti-One, Allergan's Complete, and Bausch & Lomb's ReNu. The resulting pH values were compared to the threshold for ocular awareness, which is outside the zone of 6.6 to 7.8, and the pH value of tears of 7.45. Each solution was dispensed and measured daily over a 23- to 36-day period using 15-ml increments to simulate the amount used on a daily basis. The average pH of solutions tested were 7.18 ± 0.02 for ReNu, 6.97 ± 0.02 for Opti-One, and 7.55 ± 0.02 for Complete. The highest and lowest pH values of all three multi-purpose solutions were found to be within the zone of ocular comfort and remained within a narrow value range throughout the testing period. Therefore, pH-induced discomfort is unlikely to occur when using these solutions on a daily basis. Nonetheless, practitioners should select lens care products carefully to ensure that the prescribed regimen meets the patient's needs.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The fitting characteristics of 1-day Acuvue disposable soft contact lenses (SCLs) [base curve (BC) 9.0 mm, diameter 14.2 mm] and 14-day Acuvue disposable SCLs (BC 8.8 mm, diameter 14.0 mm) were evaluated and compared with respect to lens centration and post-blink movement in primary gaze and in upgaze. In this double-blind study 25 successful daily wearers of either the 1-day lens or the 14-day lens with the same parameters were randomly fit with three 1 -day lenses and three 14-day lenses for a total of 6 lenses per eye. The lens fit was evaluated 5 min after insertion. Lens centration was assessed by measuring temporal, nasal, superior and inferior limbal coverage, and then comparing the net horizontal centration (temporal minus nasal coverage) and the net vertical centration (superior minus inferior coverage) of the 1-day and 14-day lenses. There was no significant difference between the two lenses in terms of temporal, superior, and inferior limbal coverage (p>0.05). However, the 1-day lens showed statistically more nasal coverage (p<0.05). No statistically significant difference in movement or in horizontal and vertical differences in centration were found (p>0.05). Although our findings indicate a subtle statistical difference in fitting characteristics, clinically the two lenses should provide similar fits.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID