The demographics and contact lens wearing history of two groups, each of 100 patients were examined, one grouphaving been assessed as suitable for photorefractive keratectomy (PRK) treatment but electing not to go ahead, the othergroup having proceeded with PRK treatment. Although only minor differences were found between the two groups in terms of demographics, the group that elected to be treated comprised a large number of contact lens-intolerant individuals. A breakdown is given of the contact lens-related reasons for opting to undergo PRK, emphasising the importance of the role of the contact lens practitioners in the preselection of patients for PRK.
Infrared thermography was employed to measure the change in ocular surface temperature on eye opening within agroup of 11 dry-eye patients and seven control subjects. Qualitatively, the colour coded thermograms were found to be disorganised and irregular in the dry-eye group. Quantitatively, the decrease in temperature was found to be much more rapid in the dry-eye group (0.88 ± 0.23°C in 7s) compared with the control group (0.21 ± 0.27°C) (P<0.0001). This faster rate of cooling can be explained in terms of a greater evaporation rate and the increased ocular surface temperature on eye opening in a dry eye. This observation, if confirmed on a larger study group, potentially offers a new, objective, non-invasive system for analysis of the tear-film and dry-eye therapies.
A prospective, single-centre, controlled, double-masked randomised study was conducted to determine the benefits, ifany, of regular replacement of daily-wear rigid gas permeable (RGP) contact lenses. Forty-one subjects, divided into two groups, wore Quantum 2 lenses (Bausch & Lomb, Rochester, New York, USA; Dk=120) for 12 months on a daily-wear basis; subjects in group I replaced lenses every 3 months, whereas those in group II were not scheduled to replace lenses. All subjects were existing RGP lens wearers without any contact lens-induced pathology (>grade 1). The integrity of the lenses and the ocular responses to lens wear were monitored in both groups every 3 months. Compared with lenses worn by subjects in group II, lenses worn by subjects in group I displayed significantly less surface drying (at 9 months), less mucus coating (at 12 months), less surface deposition (at 12 months), and less surface scratching (at 9 and 12 months) (p 0.05, ANOVA). Compared with the ocular response of subjects in group II, the ocular response of subjects in group I displayed significantly less corneal staining at 12 months (p<0.05,- ANOVA). No significant differences between the groups were observed with respect to comfort, vision, or any of the other variables assessed. We advocate that, in order to maintain optimal lens integrity and ocular health, RGP lenses used for daily wear should be replaced every 6 months.
A formula is developed to give the true thickness of a lens at various distances, measured radially, from the optical axiswhen the centre thickness, index of refraction and the power of the lens are known.
Therapeutic contact lenses have been advocated as an important component of anterior segment ophthalmic careregimes since the late 1960s. Despite favourable reviews in the ophthalmic literature, the perception remains, among contact lens and corneal specialists alike, that the benefits associated with this type of treatment should be considered only as a last resort. The results obtained in 46 consecutive cases fitted with either hydrogel or silicone therapeutic lenses, over an 18-month period are reviewed. Results indicate that successful therapeutic lens programmes can be achieved through a combination of appropriate patient and lens selection, and the initiation of a suitable management strategy. Approximately 25% of patients were fitted successfully with a conventional hydrogel low water content therapeutic lens. Twenty-five per cent of patients required alternative hydrogel lenses of differing parameters. Thirty per cent required silicone lenses to overcome ocular surface and lid abnormalities which had rendered hydrogel lens wear inappropriate. Almost 80% of patients fitted achieved some success with therapeutic lenses. Virtually all of those fitted on the basis of ocular pain achieved relief during the course of the treatment. Results highlight the need for a management protocol for the provision of therapeutic bandage contact lenses on a regional basis.
Using a non-invasive tear break-up time (NITBUT) technique, we measured the tear stability of 22 asymptomatic Hong Kong (HK)-Chinese before and after performance of the phenol red thread (PRT) test. One eye was used as the test eye while the fellow eye acted as control. The effect of performing the PRT test before NITBUT measurements on NITBUT values was analysed by comparing the pre- and post PRT test NITBUT values of the test eye, and by comparing the post-PRT test NITBUT values of the test eye with the NITBUT values of the control eye. The median pre- and post-PRT test NITBUT values for the test eye were 129s and 10.4s, respectively; for the control eye, the NITBUT values were 17 7s and 14.7s, respectively. The mean±SD PRT value was 19.6±6.8mm/15s. PostPRT test NITBUT values may be longer or shorter than prePRT test NITBUT values. Similar findings were observed for the control eye between the first and second measurement. Performance of the PRT test before NITBUT measurement does not affect the NITBUT values of asymptomatic HK-Chinese. The performance of the PRT test in one eye also does not affect the NITBUT value of the fellow eye. The same procedures were repeated on 14 subjects using the fluorescein-instillation tear break-up time (TBUT) test instead of the NITBUT test. Performing the PRT test did not affect the TBUT values. The median pre- and post-PRT test TBUT values for the test eye were 3.8s and 4.2s, respectively,- for the control eye, the TBUT values were 5.4s and 4.1s, respectively. The mean±SD PRT value was 19.0±5.Omm/15s. The performance of the PRT test before NITBUT measurements does not appear to affect the locations of tear defects in the NITBUT test; the location of tear defects is not random but is most frequent in the inferior periphery of the cornea.
Tear volumes of 15 normal Hong Kong (HK-Chinese were measured using a cotton thread test (CM and the phenol red thread (PRT) test on 6 different days. The results showed that both CTT and PRT tests performed on normal subjects were reliable over time. The mean CTT and PRT values were 11.8 (±4.4)mm/15s and 15.4 (±4.9)mm/15s respectively. There is a significant difference between the CTT values and the PRT values so the two tests cannot be used interchangeably. There is a day-to-day variation in both tests which may be clinically significant for some subjects and we suggested that more than one measurement be taken when an accurate tear volume measurement is important for the management of the patient. We also compared our PRT results with those of previous investigators and found that the mean PRT value is significantly lower in HK-Chinese subjects than in Caucasian subjects, while no difference was found between HK-Chinese and Japanese subjects.
A case is described of a patient fitted with contact lenses to correct myopic astigmatism following regression of refractive effect post photorefractive keratectomy. Rigid gas permeable lens tolerance was limited by lid sensation so the patient was refitted with daily-wear soft lenses. Successful lens wear was achieved with minimal corneal curvature change and epithelial disturbance. Corneal changes following PRK and subsequent contact lens fitting are discussed.
Twenty-five Quantum II rigid gas permeable corneal lenses, in a range of five negative back vertex powers but otherwise of identical nominal specification, were immersed in distilled water for up to 6 weeks and the back optic zone radius of each lens was measured periodically to determine the magnitude and time course of curvature changes during hydration. Changes in back optic zone radius were of small magnitude and were less than the tolerance limits of ±0.05mm listed in British Standard BS7208: Part 1: 1992 (‘Specification for Rigid Corneal and Scleral Contact Lenses’) for rigid gas-permeable corneal lenses.
Several authors investigated the use of standard microwave ovens as an alternative method for soft contact lens disinfection. However, none of these studies tested whether or not repeated exposure to microwave irradiation could alter the properties of crofilcon A or tinted polymacon soft contact lenses. The purpose of this study was to evaluate the effects of microwave disinfection on optical properties of unworn lenses from group 1 of the FDA material classification. Afocal lenses including clear and aqua Hydron Z6 and CSI DW were used. Each lens was placed in a Ciba AOSept case, filled with unpreserved saline. All the lenses were disinfected together for 120s in a standard microwave oven with a rotating plate. Lens variables (back vertex power, back optic zone radius (BOZR) and water content) were measured at baseline and after 30, 60 and 90 cycles of microwave disinfection. The results indicated that there were no statistically or clinically significant changes in the refractive power and BOZR after 90 disinfection cycles. But our results showed a statistically significant change in water content for every lens type (range −0.1% to +0.9%). However, these differences are within experimental error and are not clinically significant. Microwave disinfection is a feasible alternative to current disinfection methods in group 1 lenses at least when its effects on optical properties are considered. Further studies on the effects of microwave irradiation on worn soft lenses are needed.
The Nidek KM-500 is a recently introduced hand-held automatic keratometer. If the accuracy and reliability of thisinstrument are good then it offers a number of benefits to contact lens practitioners and other clinicians. This study investigated the repeatability and reproducibility of readings taken using the hand-held Nidek KM-500, the Topcon RK-3000A and the Bausch & Lomb keratometer. The Nidek KM-500 was found to be reliable when used according to the manufacturer's instructions and the readings equated well with those obtained with the table-mounted Topcon KR-3000A. The repeatability of the Bausch & Lomb keratometer can be improved by taking the mean of three readings. Clinicians should consider conducting a simple repeatability study of the keratometer used in their own practice. The results may help to pinpoint a weakness in technique when using a non-automated instrument, and will establish the criterion for a true change in corneal radius.
Two separate international ring tests were carried out to assess the measurement capability of the focimeter and the Moiré deflectometer as applied to the power-related parameters of toric soft contact lenses. The results show that in order to measure the sphere and cylinder powers and axis direction using the focimeter a high number of replicate measurements are required to be confident of the test to within reasonable tolerance limits. The availability of the deflectometer provides lens manufacturers with measurement technology which is objective and reproducible and can be used to measure the power-related parameters of toric soft lenses with increased reproducibility using relatively few replicate measurements.
To investigate the effect of various oxygen transmissibilities (Dk/t) of scleral lenses and corneal thickness recovery time from overnight eye closure with patching on corneal edema during 5 h lens wear.Scleral lenses (hofocon A, 15.6 mm diameter) were worn bilaterally with three different Dks (100, 140, and 160 Barrer). Central and peripheral corneal thickness (CCT and PCT) were measured using optical coherence tomography. Four subjects were randomly selected for one additional visit and asked to patch one eye before night sleeping. The patch was not removed until lens insertion to avoid corneal deswelling. Then CCT of both eyes was measured.Ten neophytes with healthy eyes participated in the study. Mean [95% CI] Dk/t of the study lenses was 32.0 [29.2, 34.7] hBarrer/cm. Mean [95% CI] CCT immediately upon lens insertion and after 5 h of lens wear were 532.4 [520.3, 544.5] μm and 538.7 [526.5, 551.0] μm, respectively. Mean [95% CI] percentage change (%Δ) in CCT was 1.2% [0.9%, 1.5%], 1.2% [0.9%, 1.4%], and 0.8% [0.6%, 1.1%] for CCT, nasal PCT, and temporal PCT, respectively. There was an inverse relationship between temporal Dk/t and %ΔPCT (p < 0.05) while Dk/t was not found significantly associated with either CCT or nasal PCT. The patched eyes maintained a relatively stable CCT and showed progressive deswelling, starting and ending with 2.8% and 0.6%, respectively. In contrast, the unpatched eyes swelled, starting with nearly 0% and ending with 0.7% with a maximum swelling of 1.8%.There was limited amount of corneal edema induced by short-term scleral lens wear with lens Dk/t ranging from 21 to 47 hBarrer/cm and lenses with lower lens Dk/t did not induce significantly higher corneal swelling. Scleral lens insertion soon after overnight eye closure with patching did not introduce additional swelling for young and healthy eyes.
This study explores the conceptualization of investigative journalism by Malaysian media practitioners through in-depth interviews. Their conceptualizations were stimulated by various values and factors affecting their practice. Using qualitative analysis software Nvivo, this study found four major themes that characterized the conceptualization of investigative journalism among Malaysian media practitioners. Although the stimuli are different from other countries, their perception on investigative journalism still concurred with general understanding, but they alter the practice to suit local media environment, values and culture.
A multicentre, controlled, masked and randomised trial was conducted to evaluate the benefits of proactive contactlens recommendation by optometrists on prescribing trends. From 1st January 1995, patients presenting for routine eye examination to the practices of three optometrists were selected according to the study criteria. The first 150 patients satisfying this criterion were prescribed contact lenses only if they specifically asked to try them. The next 150 suitable patients had the option of contact lens correction presented to them. Every patient trying contact lenses was offered a ‘free trial’ of 1.Day Acuvue, or Acuvue or Surevue (Vistakon, Johnson & Johnson). The practitioners had the freedom to use products of other manufacturers if this was clinically necessary. Patient-initiated trials resulted in 17% of patients being fitted with lenses, whereas practitioner-initiated trials resulted in significantly more patients being-fitted with lenses (31%; P < 0.0125). Presbyopic patients were less likely to try contact lenses than pre presbyopes (10% and 34% respectively; P < 0.0001); however, whether or not the patient was Presbyopic had no effect on the success of trials (nonpresbyopes = 90% presbyopes = 78%). Eighty-eight per cent of all patients in the trials were successfully fitted with lenses. The results of this study demonstrate that a proactive approach to contact lens fitting is likely to have a positive impact on increasing the number of contact lens wearers.
