Carole Maldonado-Codina

Agreement and repeatability of central thickness measurement in normal corneas using ultrasound pachymetry and the OCULUS Pentacam

Purpose: To compare the accuracy and repeatability of the OCULUS Pentacam (a new Scheimpflug-based imaging system) with ultrasound pachymetry in the measurement of central corneal thickness (CCT). Methods: CCT was measured in 21 subjects (21 normal corneas) on 2 separate occasions by the same examiner, using an Allergan-Humphrey 850 ultrasonic pachymeter and an OCULUS Pentacam instrument. Results: Mean values of CCT for both visits for each instrument were 534 ± 47 μm and 528 ± 45 μm using the ultrasonic pachymeter and the Pentacam, respectively. Plots of differences against means displayed relatively good agreement (limits of agreement were −13.0 to +26.6 μm). The repeatability (limits of agreement) of the ultrasound pachymeter was −18.3 to +17.7 μm, while for the OCULUS Pentacam it was −24.1 to +21.1 μm. Conclusions: Our data showed that the Pentacam instrument provided measurements that were slightly but systematically lower than the measurements provided by ultrasonic pachymetry, which is currently the clinical gold standard method. The results, coupled with a unique ability to image and analyze the anterior chamber in vivo, make the OCULUS Pentacam a promising new instrument for anterior eye evaluation.

The TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care Subcommittee

Jones, L., Brennan, N. A., Gonzalez-Meijome, J., Lally, J., Maldonado-Codina, C., Schmidt, T. A., … Nichols, J. J. (2013). The TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care Subcommittee. Investigative Opthalmology & Visual Science, 54(11), TFOS37. https://doi.org/10.1167/iovs.13-13215

Impact of manufacturing technology and material composition on the clinical performance of hydrogel lenses.

Purpose. To establish the clinical impact of three different methods of manufacture used to produce soft contact lenses. Methods. Clinical performance of five lens types was investigated by undertaking a prospective, double-masked, randomized, crossover study. Three of the lenses were made from poly(hydroxyethyl methacrylate) (pHEMA) by three different manufacturing processes (lathing, spin casting, and cast molding), and the remaining two lenses were cast molded from different materials—hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate (HEMA/GMA). All lenses were specially fabricated for this work at the same manufacturing plant. Thirty-four soft contact lens wearers wore each lens for 1 month on a daily-wear basis. Several clinical variables, such as ocular response, visual acuity, lens fitting, prelens tear film, lens surface dehydration, subjective response, and protein deposition, were measured. Results. In general, the spun-cast pHEMA lens performed inferiorly compared with the other pHEMA lenses. This lens induced significantly more limbal and conjunctival hyperemia than the cast-molded lens and provided poorer low contrast visual acuity (LCVA) than the other two lenses. It dehydrated more and had the least on-eye movement. However, the spun-cast lens deposited the least protein of the pHEMA lenses. In general, the HEMA/GMA lens performed inferiorly compared with the other cast-molded lenses. LCVA was worse with this lens, and subjective responses showed that this lens was thought to give the worst visual performance of the cast-molded lenses. It was also thought to be the most difficult lens to handle. Significantly more breakages occurred with this lens than any other. Conclusions. Overall, this work has shown that manufacturing method and material composition have a fundamental effect on many clinical properties of a lens. Therefore, method of manufacture is also an important consideration in the overall production of a soft lens.

Dynamic Contact Angle Analysis of Silicone Hydrogel Contact Lenses.

Contact angle measurements are used to infer the clinical wetting characteristics of contact lenses. Such characterization has become more commonplace since the introduction of silicone hydrogel contact lens materials, which have been associated with reduced in vivo wetting due to the inclusion of siloxane-containing components. Using consistent methodology and a single investigator, advancing and receding contact angles were measured for 11 commercially available silicone hydrogel contact lens types with a dynamic captive bubble technique employing customized, fully automated image analysis. Advancing contact angles were found to range between 20° and 72° with the lenses falling into six statistically discrete groupings. Receding contact angles fell within a narrower range, between 17° and 22°, with the lenses segregated into three groups. The relationship between these laboratory measurements and the clinical performance of the lenses requires further investigation.

Adverse events and discontinuations with rigid and soft hyper Dk contact lenses used for continuous wear.

Purpose. The purpose of this study was to assess the relative clinical success of hypertransmissible rigid and soft contact lenses in terms of the rates of adverse events and clinical discontinuations. Methods. One hundred subjects (50 experienced wearers and 50 neophytes) were fitted with either the Z-alpha lens (Menicon) or the Focus Night & Day lens (CIBA Vision), which were worn on a 30-day continuous wear basis. The rates of adverse events and clinical discontinuations were monitored over 12 months. Results. There were 20 adverse events that were categorized as being serious or significant—four with rigid lenses and 16 with soft lenses (p = 0.003). There was no significant difference between the experienced (10) and the neophyte (10) groups (p = 1.00). There were 23 clinical discontinuations—13 with rigid lenses and 10 with soft lenses (p = 0.46). Fewer experienced wearers (five) discontinued than neophytes (18) (p = 0.002). Conclusions. Practitioners should anticipate fewer adverse events with rigid versus soft lenses prescribed for continuous wear. Experienced wearers are less likely to discontinue compared with neophytes.

A hyper-Dk piggyback contact lens system for keratoconus.

Purpose To report the fitting of a hyper-Dk piggyback contact lens system in a case of keratoconus. Methods Case report. Results A patient with keratoconus, suboptimal visual acuity, corneal neovascularization, and marked conjunctival hyperemia, who was intolerant of rigid gas-permeable contact lenses, was fitted with a novel piggyback contact lens system that incorporated a hyper-oxygen transmissible hydrogel contact lens, on top of which was fitted a hyper-oxygen transmissible rigid gas-permeable lens. This novel contact lens system provided a significant improvement in visual acuity, comfort, and lens wear time. There was a marked reduction in corneal vascularization and ocular hyperemia. Conclusions This hyper-Dk piggyback contact lens system satisfied the ocular and visual requirements of this patient, for whom other nonsurgical options for vision correction had been unsuccessful. This system has potential application in the visual rehabilitation of other cases of corneal irregularity, including unsuccessful refractive surgery, ocular trauma, and keratoplasty. Piggyback contact lens systems require the same level of expertise to fit as basic forms of soft and rigid contact lenses. The hyper-oxygen transmissible lens materials available make these dual-lens systems a viable option for the compromised cornea.

Measurement errors related to contact angle analysis of hydrogel and silicone hydrogel contact lenses

This work sought to undertake a comprehensive investigation of the measurement errors associated with contact angle assessment of curved hydrogel contact lens surfaces. The contact angle coefficient of repeatability (COR) associated with three measurement conditions (image analysis COR, intralens COR, and interlens COR) was determined by measuring the contact angles (using both sessile drop and captive bubble methods) for three silicone hydrogel lenses (senofilcon A, balafilcon A, lotrafilcon A) and one conventional hydrogel lens (etafilcon A). Image analysis COR values were about 2 degrees , whereas intralens COR values (95% confidence intervals) ranged from 4.0 degrees (3.3 degrees , 4.7 degrees ) (lotrafilcon A, captive bubble) to 10.2 degrees (8.4 degrees , 12.1 degrees ) (senofilcon A, sessile drop). Interlens COR values ranged from 4.5 degrees (3.7 degrees , 5.2 degrees ) (lotrafilcon A, captive bubble) to 16.5 degrees (13.6 degrees , 19.4 degrees ) (senofilcon A, sessile drop). Measurement error associated with image analysis was shown to be small as an absolute measure, although proportionally more significant for lenses with low contact angle. Sessile drop contact angles were typically less repeatable than captive bubble contact angles. For sessile drop measures, repeatability was poorer with the silicone hydrogel lenses when compared with the conventional hydrogel lens; this phenomenon was not observed for the captive bubble method, suggesting that methodological factors related to the sessile drop technique (such as surface dehydration and blotting) may play a role in the increased variability of contact angle measurements observed with silicone hydrogel contact lenses.

Impact of manufacturing technology and material composition on the surface characteristics of hydrogel contact lenses.

Background: Our aim was to investigate the impact of manufacturing method and material composition on the surface characteristics of hydrogel contact lenses.

Characterization of the Surface of Conventional Hydrogel and Silicone Hydrogel Contact Lenses by Time-of-flight Secondary Ion Mass Spectrometry

Purpose. To characterize the surfaces of unworn conventional hydrogel and silicone hydrogel contact lenses. Methods. Near-identical formulations of poly(hydroxyethyl methacrylate) (pHEMA) were used to manufacture lathe-cut, spun-cast, and cast-molded contact lenses. The surfaces of two of each of these lens types and two of each of two commercially available silicone hydrogel lenses—balafilcon A (PureVision) and lotrafilcon A (Focus Night & Day)—were analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results. The ToF-SIMS spectra revealed the presence of the bulk polymer pHEMA at the surface of all three hydrogel lenses, along with other contaminants, such as poly(dimethyl siloxane), alkyl sulfates, alkyl-aryl sulfonates, dioctyl phthalate, Irgafos 168, sodium, chlorine, aluminum, potassium, calcium, copper, and fluorine, which are primarily derived from the various processing steps undertaken in lens manufacture, handling, and storage. The amount of bulk polymer detected at the surface of the PureVision lens was greater than that detected at the surface of the Night & Day lens. In addition, contaminants similar to those found on the surfaces of the conventional hydrogel lenses were detected. The Focus Night & Day lens appears to be coated with an organo-nitrogen material, which results from the plasma deposition of reactive precursors on the surface. Conclusions. We confirm that ToF-SIMS has the capacity to characterize the surface chemistry of contact lenses. The ongoing application of this technique can assist researchers and clinicians to understand the clinical performance of contact lenses. (Optom Vis Sci 2004;81:455–460)

Comfort response to rigid and soft hyper-transmissible contact lenses used for continuous wear.

Purpose. To assess subjective comfort during the first three months of continuous wear of hyper-transmissible soft and rigid contact lenses. Methods. One hundred subjects (50 experienced wearers and 50 neophytes) were fitted with either the Focus Night & Day lens (CIBA Vision, Duluth, GA) or the Z&agr; lens (Menicon, Nagoya, Japan). Comfort was monitored at regular intervals using a vertical analog comfort scale. Results. Good comfort scores (generally indicating very comfortable lenses) were recorded for the two soft lens groups (experienced and neophytes) and the experienced rigid lens group; these scores remained approximately constant throughout the study. Comfort reported by neophyte rigid lens wearers was initially recorded as being between slightly uncomfortable and comfortable; however, after 1 week of daily wear and 1 night of overnight wear, the mean comfort score of this group reached a level that was similar to that recorded by subjects in the other three study groups. Conclusion. The comfort data presented in this study can be used by clinicians to anticipate the subjective response of both new and existing lens wearers to new-generation hyper-transmissible soft and rigid contact lenses.