Ka Yin Chan

Microbial adherence to cosmetic contact lenses

AIM To investigate whether cosmetic contact lenses (CCL) with surface pigments affect microbial adherence. METHOD Fifteen brands of CCL were purchased from optical, non-optical retail outlets, and via the Internet. A standardized rub-off test was performed on each CCL (five lenses per brand) to confirm the location of the pigments. The rub-off test comprised gentle rubbing on the surfaces of each CCL with wetted cotton buds for a maximum of 20 rubs per surface. A new set of CCL (five lenses per brand) were incubated in Pseudomonas aeruginosa overnight. Viable counts of adhered bacteria were determined by the number of colony-forming units (CFU) on agar media on each lens. The adherence of P. aeruginosa as well as Staphylococcus aureus and Serratia marcescens to three brands of CCL (A-C) (five lenses per brand) were also compared to their adherences on their clear counterparts. RESULTS Only two of the 15 brands of CCL tested (brands B and C) had pigments that did not detach with the rub-off test. The remaining 13 brands of CCL all failed the rub-off test and these lenses showed higher P. aeruginosa adherence (8.7 × 10(5)-1.9 × 10(6) CFU/lens). Brands B and C lenses showed at least six times less bacterial adhesion than the other 13 brands. Compared to their clear counterparts, bacterial adherence to brands B and C lenses did not differ significantly, whereas brand A lenses showed significantly higher adherence. CONCLUSION Surface pigments on CCL resulted in significantly higher bacterial adherence.

Corneal sublayer thickness measurements with the Nidek ConfoScan 4 (z Ring).

Purpose. To determine the repeatability of corneal sublayer thickness measurements using the Nidek ConfoScan 4 (CS4) with the z ring on a group of young adult subjects. Methods. Thirty subjects aged 18 to 30 years were invited to have thickness measurements with the CS4 (z ring) on two different days, at similar time of the day to avoid diurnal variation. Results. Only 22 subjects had valid measurements for analysis. The mean ± SD of central corneal thickness (CCT) was 534 ± 26 &mgr;m, epithelial thickness was 42 ± 8 &mgr;m, Bowmans layer thickness was 19 ± 7 &mgr;m, and stromal thickness (ST) was 472 ± 25 &mgr;m. There was no significant difference in the between-visit thickness measurements of each layer with the CS4 (z ring) (paired t-tests, p > 0.05). The limits of agreement of between-visit measurements were −41 (8%) to 37 &mgr;m (7%) for CCT, −21 (50%) to 19 &mgr;m (45%) for epithelial thickness, −13 (68%) to 17 &mgr;m (89%) for Bowman layer thickness, and −46 (10%) to 37 &mgr;m (8%) for ST. Conclusions. Measurements of CCT and ST with the CS4 (z ring) showed reasonably good repeatability (7 to 10%). However, the repeatability of measurements of the thinner corneal layers, such as epithelium and Bowmans layer, was poor.

Clinical performance of an orthokeratology lens fitted with the aid of a computer software in Chinese children

PURPOSE To report the clinical performance of the orthokeratology (ortho-k) lens fitted with computer assisted system after 1-month of lens wear, in a group of children undergoing ortho-k treatment in a 2-year randomized myopic control study. METHOD Children aged 6-11 years old were fitted with the ortho-k lenses using computerized fitting. The initial myopia was 4.00-0.50 D and the initial refractive astigmatism was within 1.25 D. Lens performance, in terms of centration, myopic reduction, vision, ocular health status and lens binding incidence, was evaluated at one night, one week and one month after lens wear. Only data from the right eye was presented. RESULTS The initial spherical equivalent refraction (SER) for the 51 subjects was -2.29 ± 0.81 D. The first fit success rate was 90%. The reduction of SER after one night and one week aftercare visit were 57% and 81%, respectively. At the one month visit, the mean reduction in SER was 89% with unaided logMAR visual acuity of 0.03 ± 0.11. Mild central corneal staining was found in 9-20% of the subjects at the aftercare visits. The incidences of lens binding at one night, one week and one month aftercare visits were 17%, 39% and 30%, respectively. CONCLUSIONS Computer assisted system for Menicon Z Night lens fitting gave a high first fit success rate. Menicon Z Night lens was effective in myopic reduction and provided stable vision after one week of lens wear. Ocular health of the subjects after lens wear was generally unremarkable.

Corneal epithelial cell viability of an ex vivo porcine eye model

Purpose The aim was to assess the consistency of corneal epithelial cell viability of an ex vivo porcine eye model. Method Six porcine eye models (four test and two control) were prepared for each experiment. The model has a computer-controlled mechanical arm, which could move the eyelid of the porcine eye and apply phosphate buffered saline to simulate blinking and lacrimation. The four test eyes were set up to simulate evaporative dry eyes with simulated lacrimation and blinking (one blink and one drop of buffered saline per minute) over three hours. Control A models were set up to collect pre-experimental baseline data, while those of control B were the same as the test eyes but without lacrimation and blinking simulation. All porcine eyes were kept in a closed chamber with temperature and humidity well controlled. After three hours, the cells of all eyes (except control A, which were assessed immediately before commencement of the experiment) were assessed. The eyes were first dipped into 0.4 per cent trypan blue solution. Following the dissection and separation of the cells, the number of dead cells were then counted under the microscope with a field size of 0.25 mm2. The experiment was repeated 11 times. Results No significant differences were found in the number of dead cells among the four test eyes in both the central and peripheral cornea. There were significantly more dead cells in the test eyes compared to control A but significantly less when compared to control B. More dead cells were found in the central cornea than the peripheral cornea in the test eyes but the difference was not observed in controls A and B. Conclusion Epithelial cell viabilities among the four porcine eye models with simulated lacrimation and blinking were consistent. The majority of cells were viable before the experiment and simulated lacrimation and blinking maintained more viable cells over time.The aim was to assess the consistency of corneal epithelial cell viability of an ex vivo porcine eye model.

Orthokeratology for slowing myopic progression in a pair of identical twins.

PURPOSE To compare the axial length elongation and change in refractive errors in a pair of identical twins wearing orthokeratology (ortho-k) and single vision lenses (SVLs), respectively. CASE REPORT Identical Twin A and B, who were 8 years of age, with the same amount of near activities, were assigned to wear ortho-k and SVLs randomly and they were monitored for two years for myopic progression. Twin A and B were assigned to wear ortho-k and SVLs, respectively. Myopic progression was evaluated by the change in axial length and in refractive errors. A faster axial length elongation was observed in each eye of Twin B during the two-year study period. The overall change in axial length was 0.52mm (OD) and 0.70 (OS) in Twin A and 0.77mm (OD) and 0.82mm (OS) in Twin B. In terms of cycloplegic refractive errors (SER), one month after ceasing lens wear (after completion of the two-year study), the increase (from baseline) were 11% (OD) and 48% (OS) in Twin A and 87% (OD) and 67% (OS) in Twin B. CONCLUSIONS Ortho-k is more effective in controlling myopic progression in terms of axial elongation than wearing SVLs in this pair of identical twins.

Nidek ConfoScan 4 (z-ring) measurements over soft contact lenses.

Objective The aim was to compare the thickness of each corneal sublayer and the visualization of superficial epithelial cells measured with the ConfoScan 4 (CS4) z-ring with and without the use of a soft contact lens and to evaluate the recovery rate of corneal staining after measurement with the CS4 (z-ring) with and without the application of artificial tears (ATs). Methods Twenty-eight subjects aged 18 to 35 years were recruited to have measurements with the CS4 (z-ring) on 2 different days. The measurements were performed over soft contact lenses (hydrogel lens or silicone hydrogel lens) on the first day and on the naked cornea on the second day. The recovery rates of the corneal staining induced by the measurements at the second visit were monitored for 5 hrs after measurements, one eye with the application of ATs and one eye without. Results No significant differences were found in the thicknesses of the central cornea and the sublayers measured with or without soft contact lenses. The intensity of epithelial cell images was improved with measurement made over hydrogel lenses, and on average, grade 3 (coverage) staining was observed in the corneas immediately after measurements without contact lenses. The recovery rate of the corneal staining did not improve with the application of ATs. Conclusions Thickness measurements with the CS4 (z-ring) were not affected if made over soft contact lenses. The use of a soft lens to buffer the cornea during measurements was effective in eliminating corneal dehydration, preventing staining induced by the z-ring without affecting the corneal thickness measurement. It also enhanced epithelial image brightness, which may improve the accuracy in pachymetry.

Corneal parameters of six‐ to 12‐year‐old Chinese children

Purpose:  The aim was to determine the corneal parameters in low to moderate myopic Chinese children and to investigate the differences in these corneal parameters between male and female subjects.

Corneal epithelial cell viability of anex vivoporcine eye model: Porcine corneal epithelial cell viability

Purpose The aim was to assess the consistency of corneal epithelial cell viability of an ex vivo porcine eye model. Method Six porcine eye models (four test and two control) were prepared for each experiment. The model has a computer-controlled mechanical arm, which could move the eyelid of the porcine eye and apply phosphate buffered saline to simulate blinking and lacrimation. The four test eyes were set up to simulate evaporative dry eyes with simulated lacrimation and blinking (one blink and one drop of buffered saline per minute) over three hours. Control A models were set up to collect pre-experimental baseline data, while those of control B were the same as the test eyes but without lacrimation and blinking simulation. All porcine eyes were kept in a closed chamber with temperature and humidity well controlled. After three hours, the cells of all eyes (except control A, which were assessed immediately before commencement of the experiment) were assessed. The eyes were first dipped into 0.4 per cent trypan blue solution. Following the dissection and separation of the cells, the number of dead cells were then counted under the microscope with a field size of 0.25 mm2. The experiment was repeated 11 times. Results No significant differences were found in the number of dead cells among the four test eyes in both the central and peripheral cornea. There were significantly more dead cells in the test eyes compared to control A but significantly less when compared to control B. More dead cells were found in the central cornea than the peripheral cornea in the test eyes but the difference was not observed in controls A and B. Conclusion Epithelial cell viabilities among the four porcine eye models with simulated lacrimation and blinking were consistent. The majority of cells were viable before the experiment and simulated lacrimation and blinking maintained more viable cells over time.The aim was to assess the consistency of corneal epithelial cell viability of an ex vivo porcine eye model.

Prevalence of papillary changes and folliculosis of the palpebral conjunctiva in asymptomatic Chinese children

PURPOSE To determine the prevalence of papillary changes of the upper palpebral conjunctiva and folliculosis of the lower palpebral conjunctiva in Chinese children with no history of contact lens wear. METHOD Ninety-nine subjects (aged 6-15 years old) who were interested in a myopia control study were screened for papillary changes and folliculosis of the palpebral conjunctiva. Photodocumentation was performed under white and blue light (after the application of fluorescein) with a yellow filter and the photographs were graded by a group of practitioners according to a pre-set grading scale. Analysis was performed with the subjects divided into groups according to gender and age. RESULTS More than 48% of the subjects had clinically significant (≥Grade 3) papillary changes in the upper palpebral conjunctiva. The prevalence of significant folliculosis in the lower lid was about 33%. The prevalence of significant papillary changes and folliculosis were similar between genders. No differences were observed between younger (age≤10 years old) and older (age>10 years old) in papillary changes but younger subjects showed a higher prevalence of folliculosis. CONCLUSIONS The prevalences of clinically significant papillary changes and folliculosis of unknown aetiology are high in Chinese children.