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Dumbleton,K. A., Chalmers,R. L., Richter,D. B., Fonn,D. Changes in myopic refractive error with nine months' extended wear of hydrogel lenses with high and low oxygen permeability. Optometry and Vision Science 1999;76,12:845-849. [ Show Abstract ]
Background: A small but significant increase in myopia after extended wear of low oxygen permeability (Dk) hydrogel lenses has been previously reported; however, the specific impact of hypoxia on refractive status and corneal curvature with extended wear are not well documented. The purpose of this study was to compare the refractive changes induced over a period of 9 months' extended wear with high-Dk fluorosiloxane hydrogel lenses and low-Dk hydrogel lenses. Methods: Adapted daily wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group wore etafilcon A (Dk = 28) for up to 7 days and 6 nights and the high-Dk group wore Iotrafilcon A (Dk = 140) for up to 30 days and nights. Refractive error and corneal curvature were measured at 3-month intervals over 9 months of extended wear. Results: The etafilcon A group demonstrated an average increase in myopia of 0.30 D over the 9-month period; however, no change in spherical myopic correction was measured in the Iotrafilcon A group. The cylindrical component did not change in either group. A stratified analysis revealed a greater increase in myopia for low myopes than moderate myopes in the etafilcon A group but no difference in the Iotrafilcon A group. Keratometric analysis revealed no change in the etafilcon A group and a small degree of central corneal flattening in both major meridians of 0.35 D in the Iotrafilcon A group. Conclusions: Nine months of extended wear of low-Dk lenses is associated with a small degree of myopic progression in adult myopes that appears to be reversible. Wearing fluorosiloxane-hydrogel lenses of high-Dk had no impact on refractive error and may be associated with a small degree of central corneal flattening.
Fonn,D., Du Toit,R., Simpson,T. L., Vega,J. A., Situ,P., Chalmers,R. L. Sympathetic swelling response of the control eye to soft lenses in the other eye. Investigative Ophthalmology and Visual Science 1999;40,13:3116-3121. [ Show Abstract ]
PURPOSE. To compare central corneal swelling and light scatter after 8 hours of sleep in eyes wearing high- and low-Dk hydrogel lenses and to the contralateral control eyes. METHODS. Twenty neophyte subjects wore a Lotrafilcon A (Dk, 140; Ciba Vision, Duluth GA) silicone hydrogel lens and an Etafilcon A (Dk, 18; Acuvue; Vistakon, Jacksonville, FL) 58% water content hydrogel lens of similar center thickness in random order in the right eye only, for overnight 8-hour periods. The contralateral nonwearing left eyes served as controls. Central corneal thickness was measured using an optical pachometer and light scatter using a Van den Berg stray-light meter before lens insertion, after lens removal on waking, and every 20 minutes for the next 3 hours. RESULTS. Central corneal swelling induced by the Etafilcon A lens on eye opening was significantly higher than with the Lotrafilcon A lens (8.66% ± 2.84% versus 2.71% ± 1.91%; P < 0.00001). Light scatter induced by the Etafilcon A lens on eye opening was significantly higher than with the Lotrafilcon A lens (46.09 ± 5.62 versus 42.78 ± 6.07 Van den Berg units, P = 0.0078). The swelling of the control eyes paired with the Etafilcon A lens- wearing eyes was also slightly but significantly higher than that of the control eyes paired with the Lotrafilcon A lens-wearing eyes (2.34% ± 1.26% versus 1.44% ± 0.91%; P = 0.0002). Light-scatter measurements were not significantly different between control sets of eyes but showed the same trend. CONCLUSIONS. In neophyte subjects, corneal swelling of the contralateral control eyes appears to be influenced by the swelling of the fellow lens-wearing eyes - that is, the swelling of the contralateral control eye was significantly lower when there was less swelling of the fellow eye wearing the high-Dk lens. Although there was no statistically significant difference in light-scatter measurements between the control sets of eyes, a trend similar to the corneal swelling results was observed, which could be used to support the suggestion that this may he a sympathetic physiological response rather than an unusual sampling coincidence.
Fonn,D., Situ,P., Simpson,T. Hydrogel lens dehydration and subjective comfort and dryness ratings in symptomatic and asymptomatic contact lens wearers. Optometry and Vision Science 1999;76,10:700-704. [ Show Abstract ]
Purpose. To determine whether lens dehydration correlates with discomfort, dryness, and noninvasive tear break-up time in symptomatic and asymptomatic contact lens wearers and whether dehydration of the two lens types varies. Method. Twenty hydrogel contact lens wearers with dryness- related symptoms and 20 asymptomatic wearers wore an Etafilcon A lens (Acuvue; Vistakon, Inc., Jacksonville, Florida) in one eye and an Omafilcon A lens (Proclear; Biocompatibles, Norfolk, Virginia) in the contralateral eye for 7 h in a randomized, double-masked study. Lens water content was measured before and after 7 h of lens wear and prelens noninvasive tear film break-up time (NIBUT) was measured immediately after insertion and after 5 h of lens wear. Subjective comfort and dryness were rated at 0, 1, 3, 5, and 7 h of lens wear. Results. The symptomatic group had significantly reduced prelens NIBUT, decreased comfort, and increased dryness, but there was no difference between lenses for these variables. The Omafilcon-A lenses dehydrated significantly less than the Etafilcon A lenses, but there was no significant difference in lens dehydration between two subject groups. Conclusion. No correlation was found between lens dehydration and subjective dryness and comfort. Symptomatic hydrogel contact lens wearers with decreased wearing time had measurably decreased comfort, increased dryness ratings, and reduced NIBUT.
Fonn,D., Situ,P., Simpson,T. L. Oxygen and contact lens wear. Chin J Optom and Ophthalmol 1999;1,3:185-189.
Mathur,A., Jones,L., Sorbara,L. Use of reverse geometry rigid gas permeable contact lenses in the management of the postradial keratotomy patient: Review and case report. International Contact Lens Clinic 1999;26,5:121. [ Show Abstract ]
Radial keratotomy (RK) is a well-known procedure for reducing myopia. However, the complications associated with the procedure and the development of newer technologies, such as photorefractive keratectomy and laser-assisted in situ keratomileusis, has resulted in the technique of RK falling out of favor. A number of patients who received RK during the 1980s are now experiencing a shift in their prescription and are presenting to primary care practitioners for contact lens fitting. These patients pose a significant challenge to the contact lens practitioner, and novel methods frequently are required to fit corneas that exhibit such abnormal topography. This article reviews the potential problems associated with fitting patients who have received RK and describes a case in which a novel lens design was used to achieve a successful lens fit.
Vega,J. A., Simpson,T. L., Fonn,D. A noncontact pneumatic esthesiometer for measurement of ocular sensitivity: A preliminary report. Cornea 1999;18,6:675-681. [ Show Abstract ]
Purpose. The aim of this investigation was to evaluate a prototype noncontact pneumatic esthesiometer for measuring sensitivity of the eye. Methods. To evaluate the instrument's repeatability, central corneal sensitivity was recorded on two separate occasions with a 24-h interval between the two measures. In a separate experiment, corneal edema was induced with a thick hydrogel lens, and the eye was closed and patched. Corneal sensitivity was measured before wearing the lenses for 3 h, immediately after lens removal, and 15 min later. Corneal sensitivity also was measured before the instillation of a single drop of proparacaine (Alcaine, 0.5%) and at 2 and 18 min later. Sensitivity was measured at the corneal apex and at a temporal conjunctival location 3 mm from the limbus. Results. A high correlation was found between clays 1 and 2 (r = 0.90; p = 0.0001). The coefficient of repeatability (COR = 0.87 mm Hg) showed that 95% of the difference between test and retest measures were between ±0.87 mm Hg. Corneal sensitivity decreased by 55% after lens-induced corneal swelling and by 159% after instillation of the topical anesthetic. Central corneal sensitivity was found to be significantly higher than that of the temporal conjunctiva (p = 0.0001). Conclusion. We conclude that this pneumatic esthesiometer provides repeatable and reliable measures of ocular-surface sensitivity.