Hydrogen peroxide disinfection of hydrogel contact lenses: An overview

Many hydrogen peroxide systems have recently been introduced to the contact lens market. No two systems are identical, and practitioners are confronted with a great deal of information from the various solution companies. When considered en musse, this information is complex and often contradictory. Here, we review the principles of hydrogen peroxide disinfection and neutralization, and critically examine the major differences in the systems with a view to the development of guidelines for the safe and effective use of this disinfecting agent. Attention is drawn to a number of important issues which are yet to be resolved.     

Bifocal contact lenses today.

Bifocal contact lenses produced today are far from perfection; however, there are several different types produced, one of which should work out for most presbyopic patients who can be successfully fit with single vision contact lenses. This paper looks at the products we have available now. It is not designed to be a cookbook that the optometric practitioner can follow from A to Z and come up with the ideal contact lens bifocal fit. It is pointed at making the optometrist aware of the growing population of contact lens wearers that the health professions are now creating, and a resume of the products and fitting techniques now available to the eye care field.     

Rigid lenses: an overview.

New gas permeable rigid contact lens materials, by allowing direct transmission of oxygen, provide significant advantages over PMMA. Edema resulting from oxygen deprivation with PMMA lenses is eliminated and comfort is increased. Three types of gas permeable materials are described: CAB, silicone, and a combination of CAB and silicone.     

Contact lenses in South Africa: an overview

Contact lenses were introduced into South Africa over three decades ago. Within the past 15 years, interest in the lenses has increased tremendously among practitioners and wearers, and this interest has influenced contact lens commercial activities in the country. Most contact lens companies in the country were established during this period.The standard of contact lens practice in South Africa is considered to be among the best in Africa. Lenses and solutions are readily available in the country. Major contact lens companies either have branches in South Africa or are represented by local agents. Hard lenses are generally manufactured locally, whereas soft lenses are imported.With the improvement in the social and economic situations of many South Africans, the prospect for contact lens wear in the country is considered to be good.This article is a synopsis of the history, education, practice profile, and commercial activities relating to contact lenses in South Africa.     

Cleaning hydrophilic contact lenses: an overview.

The composition of the major, critical component of the amorphous deposits forming on hydrophilic lenses during wear was identified and reported by Karageozian as basically proteinaceous in nature. The research surrounding the identification has produced animal and laboratory models for testing the parameteres involved in the protein deposition, as well as in its removal. A standardized system for classifying the protein deposits during and after formation, along with the experimental animal and laboratory models allows a relatively complete development of the predictive tests required for a compound or a product intended for use as a cleaner of hydrophilic lenses. These predictive tests have been run on several available cleaning systems as well as on a new one; the results indicate clearly that, unlike the available systems, the new system will safely remove deposits from hydrophilic lenses. The laboratory predictive test results have been borne out by clinical trial; the clinical results indicate the suitability of the new formulation and the predictive capability of the test models developed.     

Bifocal contact lenses as a correction method in presbyopia

A study aimed at assessing the efficiency of presbyopia correction by bifocal contact lenses (BCL) was undertaken; it envisaged a comprehensive evaluation of subjective data provided by patients and measurements of a number of functional parameters of the visual quality for far and near, including mono- and binocular measurements with BCL of different constructions versus a maximal sphero-cylindrical spectacle correction for far and for near. Soft Acuvue Bifocal BCL as well as soft and rigid BCL manufactured in the optical-and-mechanical laboratory of the Research Institute for Eye Disease of the Russian Academy of Medical Sciences and Russian-made and imported bifocal soft and rigid lenses, respectively, were made use of in the study. A reduced contrast sensitivity (mainly in high frequencies) to 7% with Russian-made BCL, to 12.5% with Acuvue Bifocal BCL, to 8.7% with monofocal BCL and to 13.4% with the "mono-vision" system was registered. A decreased visual working ability to 13% with soft bifocal Russian-made BCL, to 17.3% with Acuvue Bifocal BCL and to 20.7% with the "mono-vision" system was detected versus the spectacle correction. A reduction by 25% was noted in the stereoscopic vision indices with the "mono-vision" system. A study of sensitivity to dazzling did not show any statistically reliable differences between various correction types.     

Phakic intraocular lenses: An overview

Phakic intraocular lenses (pIOLs) are a common solution for the surgical correction of high myopia and myopia in thin corneas. Global trends result in increasing rates of patients with high myopia which will result in increased rates of pIOL implantation. Three types of lenses can be distinguished: anterior chamber angle-supported, anterior chamber iris-fixated, and posterior chamber phakic IOLs. The efficacy of phakic intraocular lenses is generally very good, but pIOLs have undergone many changes over the years to improve the safety profile and decrease pIOL-related complications such as endothelial cell loss, corneal decompensation and cataract formation. This article describes the efficacy and safety profiles of the most recent pIOLs, as well as suggests gaps of knowledge that are deserve additional research to optimize the results of pIOLs.     

Comfort of fenestrated hydrogel lenses

A controlled, double-masked, randomized study was conducted on ten subjects to determine the effect of fenestration size on the initial comfort of hydrogel contact lenses. Four fenestrated lenses were tested, each lens containing four mid-peripheral fenestrations of the same size. The diameter of the fenestrations used in the four lenses ranged from 0.39 to 0.96 mm. An unfenestrated lens was also tested. All lenses were made of HEMA and were ordered with the following specifications: -3.00 D, 14.0 mm diameter, 8.4 mm back central optic radius and 0.06 mm centre thickness. There was a significant negative correlation between comfort and fenestration size, indicating that larger fenestrations are less comfortable. Even the lens with the smallest fenestrations (0.39 mm) was significantly less comfortable than the unfenestrated lens. The implication of this finding is that fenestrations may not be clinically efficacious in view of the poor comfort (and presumably increased mechanical effect of the fenestration edges on the tarsal conjunctiva) of fenestrated lenses.     

A comparative study of biweekly disposable contact lenses: silicone hydrogel versus hydrogel

Background: Our aim was to compare the clinical performance of a biweekly (second generation) silicone hydrogel lens and a biweekly hydrogel lens worn for daily wear modality. Methods: We used a double‐masked study, in which non‐presbyopic, asymptomatic and adapted soft lens wearers were recruited. Subjects wore a silicone hydrogel lens in one eye and a hydrogel lens in the other (lens types and eyes were randomly assigned) for one month. Lenses were replaced every two weeks. Contact lens fitting, pre‐lens tear film thinning time, vision, corneal integrity and lens deposits were assessed before and every fortnight after delivery of new lenses. A questionnaire was used to compare the subjective performance of the two lens types. Results: Thirty of the 33 subjects completed the study. There were no significant differences in lens fitting (centration and movement), pre‐lens tear film thinning time, vision or corneal integrity between the two lens types. Statistically, there was no significant difference in lens deposits between the two lens types but silicone hydrogel lenses tended to have more Grade 3 to 4 lipid deposits than hydrogel lenses. Subjects found no significant differences between the two lens types in terms of vision and comfort. Preference for silicone hydrogel lenses increased from 33 at the first after‐care visit to 50 per cent at the second after‐care visit. Conclusion: This short‐term study demonstrates that the performance of silicone hydrogel and hydrogel lenses is comparable but the former tends to build up more lipid deposits than the latter. We did not find better performance in terms of ocular integrity of silicone hydrogel lenses compared to the hydrogel lenses, probably because the subjects were adapted asymptomatic contact lens wearers before commencing the study. Contact lens wearers having hypoxia‐related problems are likely to benefit from using silicone hydrogel lenses, as these lenses provide at least three times more oxygen than conventional hydrogel lenses.     

Surface hydration of hydrogel contact lenses

A hand refractometer was used to measure the surface hydration of soft contact lenses of three different water contents, in a randomized, double masked study conducted on nine subjects. No statistically significant difference was found after 30 minutes of lens wear between the hydration levels at the front and back surfaces of Permathin (42.5 % nominal water content) and Snoflex 50 (50% nominal water content) hydrogel lenses; however, there was a significant difference for Gelfiex 60 (60% nominal water content) lenses, the back surface being more hydrated than the front surface. These findings suggest that there may be a water gradient between the front and back surfaces of higher water content hydrogel lenses during wear. Whilst the magnitude of the difference between surface hydration levels is small and of little consequence in the routine clinical measurement of water content using a hand refractometer, this phenomenon could be of aetiological significance with respect to the occurrence of multiple corneal erosions observed in patients wearing very thin, high water content lenses.     

Tinted hydrogel lenses permanency of tint

The spectral transmittances of a sample group of tinted hydrogel contact lenses were analyzed to assess the reproducibility of tinted lenses of a given density. Transmittance data were used to assess permanency of the tint after a 14-day cycle of daily cleaning, sterilization, and storage using a variety of cleaning and sterilization treatments. One-way analysis of variance of the transmittance data has demonstrated significant variations in the density of tint for Cibasoft lenses of a given color and density. However, these variations are smaller than the manufacturer's stated criterion for acceptable differences in tint density at a given tint level, i.e., light, medium, or dark. The Cibatint is stable when the lenses are cleaned with the Septicon and Miraflow systems. However, tinted hydrogel lenses from other manufacturers demonstrated changes of tint which were dependent upon the cleaning and sterilization methods used.