Carol Lakkis

The new Richmond HRR pseudoisochromatic test for colour vision is better than the Ishihara test

Aim:  The Hardy‐Rand‐Rittler (HRR) pseudoisochromatic test for colour vision is highly regarded but has long been out of print. Richmond Products produced a new edition in 2002 that has been re‐engineered to rectify shortcomings of the original test. This study is a validation trial of the new test using a larger sample and different criteria of evaluation from those of the previously reported validation study.

Resistance of Pseudomonas aeruginosa isolates to hydrogel contact lens disinfection correlates with cytotoxic activity

ABSTRACT One of the most common pathogens in infection of hydrogel contact lens wearers is Pseudomonas aeruginosa, which can gain access to the eye via contamination of the lens, lens case, and lens care solutions. Only one strain per species is used in current regulatory testing for the marketing of chemical contact lens disinfectants. The aim of this study was to determine whether P. aeruginosa strains vary in their susceptibility to hydrogel contact lens disinfectants. A method for rapidly screening bacterial susceptibility to contact lens disinfectants was developed, based on measurement of the MIC. The susceptibility of 35 P. aeruginosa isolates to two chemical disinfectants was found to vary among strains. MICs ranged from 6.25 to 100% for both disinfectants at 37°C, and a number of strains were not inhibited by a 100% disinfectant concentration in the lens case environment at room temperature (22°C). Resistance to disinfection appeared to be an inherent rather than acquired trait, since some resistant strains had been isolated prior to the introduction of the disinfectants and some susceptible P. aeruginosa strains could not be made more resistant by repeated disinfectant exposure. A number of P. aeruginosa strains which were comparatively more resistant to short-term disinfectant exposure also demonstrated the ability to grow to levels above the initial inoculum in one chemical disinfectant after long-term (24 to 48 h) disinfectant exposure. Resistance was correlated with acute cytotoxic activity toward corneal epithelial cells and with exsA, which encodes a protein that regulates cytotoxicity via a complex type III secretion system. These results suggest that chemical disinfection solutions may select for contamination with cytotoxic strains. Further investigation of the mechanisms and factors responsible for resistance may also lead to strategies for reducing adverse responses to contact lens wear.

Categorical color naming of surface color codes by people with abnormal color vision.

Purpose. Past investigations of the ability of people with color vision deficiency (CVD) to name the colors of surface colors have been occupation-specific. This study was undertaken as a more generalized investigation to explore particularly the effects of stimulus size and shape. Methods. One hundred CVD observers and 20 color vision normal (CVN) subjects named the colors of two sets of surface colors, each set presenting the same 10 colors (red, orange, brown, yellow, green, blue, purple, white, gray, black). One set presented dot stimuli in three sizes (2.4°, 1.0°, 0.27°) and the other line stimuli with three widths (0.50°, 0.27°, 0.14°). Color vision was diagnosed using the Ishihara test, the Farnsworth D15 test, the Medmont C100, and the Nagel anomaloscope. Results. All CVN subjects and 37% of CVD subjects made no errors. Type of CVD and stimulus size were significant factors for probability of error and the effect of stimulus size is best described by 1/area. There were significant interactions between CVD type and 1/area and between shape and 1/area. Deuteranomals who passed the Farnsworth D15 test made significantly fewer errors than all other CVD types and 70% made no errors. Their common errors were to confuse red, orange, and brown. Protanomals who passed the Farnsworth D15 test made fewer errors than dichromats. Conclusions. Mild deuteranomals will make very few errors with a seven-color code that omits orange, brown, and purple and will make very few errors (approximately 0.3%) with a 10-color code when the stimuli are reasonably large (area >20 mm2).

Review of complications associated with contact lenses from unregulated sources of supply.

Objective: To review existing studies and case reports regarding complications associated with contact lenses (CLs) from unregulated sources of supply and to identify any relevant trends. Methods: A systematic literature search was performed to locate publications concerning complications associated with CLs obtained from unregulated sources of supply. Results: A total of 23 articles were identified that represent 70 individual cases. All 8 of the pre-2006 case reports originated from the United States and the United Kingdom, whereas from 2006 onwards, only 2 of the 15 reports came from these locations. Over-the-counter supply accounted for 73% (51/70) of cases, whereas 17% (12/70) were borrowed or shared lenses and 6% (4/70) lenses were obtained through the Internet. Nearly, three quarters of patients (30/42, 71%) waited longer than 48 hours after the onset of symptoms before seeking medical attention; 10 patients waited longer than a week, and 5 longer than a month. Microbial keratitis (MK) was reported in 43 (61%) patients, with permanent damage occurring in 72% (31/43) of patients followed to conclusion. Known risk factors associated for MK were present in all cases irrespective of whether the patients developed MK. Conclusions: There are various reasons to presume that the unregulated supply of CLs might result in the use of inappropriate lenses, increase the risk of poorer lens hygiene, and militate against the prompt treatment of any consequent complications. There is some indication that the introduction of regulations to control the supply of plano CLs has alleviated the level of complications.

Infection control guidelines for optometrists 2007.

Information from peer‐reviewed articles, guidelines from professional societies and manufacturers’ instructions were considered to determine the risk factors in optometric practice and to make recommendations for disinfection, sterilisation and reprocessing of instrumentation and other equipment used in practice and measures for personal protection.

Using clinical tests of colour vision to predict the ability of colour vision deficient patients to name surface colours

Purpose:  To determine the predictive power of commonly used tests for abnormal colour vision to identify patients who can or cannot name surface colours without error.

Clinical performance of microchannel contact lenses.

Purpose. It has been suggested that microchannels placed on the posterior surface of hydrogel contact lenses increase transverse lens movement and therefore increase tear mixing. Lens designs, which can improve tear exchange without adversely affecting lens performance, may play a significant role in improving the safety of contact lens wear. Our aim was to investigate the effect of posterior lens surface microchannels on contact lens performance. Methods. A randomized, single masked pilot study was conducted. Fifteen experienced hydrogel lens wearers were randomly assigned to wear a microchannel lens (MC) in one eye and a standard hydrogel lens design (STD) in the fellow eye over a period of 6 hours. A range of objective and subjective clinical performance measures were assessed, including visual acuity, lens movement, comfort and patient preference. Results. There were no significant differences between the MC and STD lenses with respect to vision measures, corneal staining, and bulbar and limbal redness (p > 0.05). The MC lenses produced significantly less conjunctival staining than the STD lenses and showed greater lens movement in primary gaze (p < 0.05). Lens distortion with blinking was evaluated through topographic assessment of the contact lenses on eye, and no significant differences were observed in central distortion levels between the two lens designs (p > 0.05). Subjective evaluation of the lenses with respect to comfort, vision, and overall satisfaction did not vary significantly between the two lens types (p > 0.05). Conclusions. The results of this study suggest that posterior lens surface microchannels do not adversely affect contact lens performance or subjective lens preference over a short-term wearing period. The MC lenses appear to produce less physiological impact on the conjunctival surface than STD lenses with less conjunctival staining observed with the MC lenses. Clinical investigation of the performance of this type of lens design in a larger group of subjects, over longer wearing periods, is warranted.

The efficacy of Acanthamoeba cyst kill and effects upon contact lenses of a novel ultraviolet lens disinfection system.

PURPOSE To assess the efficacy of a novel ultraviolet (UV) lens device on the killing of Acanthamoeba cysts and the impact of efficacious doses of UV upon soft contact lens parameter and material characteristics. DESIGN Prospective, in vitro, experimental study of a device. METHODS A UV lens device was constructed and used to expose Acanthamoeba cysts to various levels of UV irradiation. Once an efficacious dose, as defined by a greater than 3 log reduction, was determined (130 mJ/cm(2)), 6 soft contact lens materials (etafilcon A, senofilcon A, galyfilcon A, lotrafilcon A, polymacon, and comfilcon A) were exposed to that dose for 30 cycles and tested for visual parameters, mechanical parameters, and cytotoxicity. RESULTS The UV device produced an average log reduction of over 3.5 log of Acanthamoeba cysts when the lens and solution inside of the inset case was irradiated with 130 mJ per cm(2) of UV or greater. After 30 cycles of 130 mJ per cm(2) UV dose each, no gross changes were observed in mechanical properties or cytotoxicity tests in any soft contact lenses tested. In visual parameters, polymacon and lotrafilcon A exhibited a shift in sphere power and diameter, respectively. CONCLUSIONS The novel UV lens device was able to provide a marked log reduction to Acanthamoeba cysts, one of the most resistant ocular disease-causing organisms found in lens cases, without a detrimental effect on many lens materials.

Influenza A(H1N1) and infection control guidelines for optometrists.

The emergence of a novel influenza A virus (Influenza A[H1N1]), which has not circulated previously in humans, has led to the first global influenza pandemic in 41 years. Influenza A(H1N1), commonly called ‘swine flu’, is a novel influenza virus made up of porcine, avian and human genes, and preferentially infects younger people. Although Influenza A(H1N1) does not appear to be likely to cause as many fatalities as previous influenza pandemics, attempts to contain it are necessary because people whose health is already compromised through underlying chronic medical conditions are at risk of death if they contract the virus. In addition, pregnant women who become infected are at increased risk of complications.

Evaluation of the performance of photochromic spectacle lenses in children and adolescents aged 10 to 15 years

Background:  To compare the performance of clear and photochromic spectacle lenses in children and adolescents, with respect to visual acuity and satisfaction with day‐to‐day activities.