Peer-reviewed Articles

Please use the archived list on the right to look at past peer-reviewed articles.


Begley,C. G., Chalmers,R. L., Abetz,L., Venkataraman,K., Mertzanis,P., Caffery,B. A., Snyder,C., Edrington,T., Nelson,D., Simpson,T. The relationship between habitual patient-reported symptoms and clinical signs among patients with dry eye of varying severity. Investigative Ophthalmology and Visual Science 2003;44,11:4753-4761. [ Show Abstract ]

PURPOSE. To investigate symptom profiles and clinical signs in subjects with dry eye and normal subjects in a cross-sectional multicenter study. METHODS. Subjects aged 35 to 65 were recruited according to dry eye diagnostic codes and telephone interview and completed the Dry Eye Questionnaire 2001, among others, and underwent dry eye clinical tests. RESULTS. Subjects (122) included 28 control subjects (C), 73 with non-Sjögren's keratoconjunctivitis sicca (non-SS KCS) and 21 with Sjögren's syndrome (SS). Subjects with SS or non-SS KCS reported discomfort and dryness most frequently and that many symptoms worsened over the day and were quite bothersome. Groups were significantly different in corneal fluorescein staining, conjunctival lissamine green staining, Schirmer 1 tear test, and tear break-up time (TBUT; X2 and Kruskal-Wallis, P 0.0001). CONCLUSIONS. Subjects with SS or non-SS KCS reported frequent and intense ocular surface symptoms in the evening, some of which correlated moderately with clinical test results. The global clinician grade of dry eye correlated more highly with patient symptoms than did clinical signs, suggesting that patient symptoms influence dry eye diagnosis and grading of dry eye more than clinical test results.

Du Toit,R., Vega,J. A., Fonn,D., Simpson,T. Diurnal variation of corneal sensitivity and thickness. Cornea 2003;22,3:205-209. [ Show Abstract ]

Purpose. To measure the diurnal variation of central corneal sensitivity and thickness over 24 hours. Methods. A noncontact pneumatic esthesiometer to measure central corneal sensitivity and an optical pachymeter to measure central corneal thickness were used on 20 noncontact lens wearers. These measurements were performed at 22:00 before 8 hours of sleep and on the following day on eye opening and at hourly intervals between 7:00 and 22:00. Results. Central corneal sensitivity varied by 35% over the 24 hours. Sensitivity was significantly lower by 17.1 ± 2.1% on eye opening and recovered to the level of the previous night after 4 hours. Corneal sensitivity continued to increase throughout the day but was not significantly higher. Central corneal thickness varied by 3.9% over the 24 hours. The mean overnight corneal swelling was 2.9 ± 0.31%, and 2 hours after eye opening, the cornea had deswelled to the same thickness as the previous night. The cornea thinned further throughout the day, but there were no statistically significant differences between the values after 14:00. There was a high correlation between corneal sensitivity and thickness over time (r = 0.8; p < 0.05). Discussion. Corneal sensitivity correlated with corneal thickness: both were higher on awakening and then decreased and remained below the levels measured the previous night. This may be due to physiological and/or environmental factors. The lack of significant differences between the values after 14:00 suggests that baseline may be measured at any time from 7 hours after eye opening.

Dumbleton,K. Noninflammatory silicone hydrogel contact lens complications.. CLAO Journal 2003;29,1 Suppl:S186-189; discussion S190-191, S192-194. [ Show Abstract ]

High Dk silicone hydrogel lenses have overcome many of the hypoxic problems associated with traditional extended wear, and the popularity of continuous wear with these lens types is increasing. Despite the elimination of hypoxia, several noninflammatory clinical complications have been reported to occur as a result of mechanical disturbances or trauma when wearing silicone hydrogel lenses. This article reviews the origin and presentation of mucin balls, superior epithelial arcuate lesions, contact lens papillary conjunctivitis, and corneal erosions in silicone hydrogel lens wearers. A number of management strategies and approaches to minimize the occurrence of these clinical complications are also discussed.

Feng,Y., Simpson,T. L. Nociceptive sensation and sensitivity evoked from human cornea and conjunctiva stimulated by CO2. Investigative Ophthalmology and Visual Science 2003;44,2:529-532. [ Show Abstract ]

PURPOSE. To compare sensation and sensitivity evoked from human cornea and conjunctiva stimulated by CO2. METHODS. Twenty healthy participants were recruited for the study. Central corneal and temporal conjunctival chemical sensation and sensitivity of only one eye of each subject were evaluated. Air mixed with different concentrations of CO2 was delivered by a modified Belmonte pneumatic esthesiometer. The ascending method of limits was used to determine the sensitivity and subjects were required to characterize the sensation at threshold. RESULTS. The sensations evoked by CO2 in the cornea and conjunctiva were stinging or burning. The sensation evoked by mechanical stimulation was that of irritation. The corneal and conjunctival chemical thresholds were 31% ± 2% and 54% ± 5% CO2 (mean ± SE), respectively. The corneal and conjunctival mechanical thresholds were 80 ± 6 and 140 ± 10 mL/min (mean ± SE), respectively. The corneal sensitivity was significantly higher for both mechanical and chemical stimuli (P < 0.05). CONCLUSIONS. The results suggest that CO2 stimulates similar corneal and conjunctival nociceptors in that the interpretations were the same (i.e., nociceptive). The central cornea had a higher sensitivity to CO2 than the temporal conjunctiva, which may reflect a different peripheral innervation, such as different nerve density or different receptor characteristics. Sensations evoked by mechanical and chemical stimulation were different, which suggests that at the peripheral level, the two modalities stimulate two different kinds of molecular receptors or channels and that this information is somehow retained within the nociceptive system.

Fonn,D., Dumbleton,K. Dryness and discomfort with silicone hydrogel contact lenses.. Eye & contact lens 2003;29,1 Suppl:S101-104; discussion S115-118, S192-194. [ Show Abstract ]

PURPOSE: The purpose of this study was to determine whether symptoms of dryness and discomfort are experienced differently with silicone hydrogel lenses compared to conventional hydrogels, in symptomatic and asymptomatic subjects. METHODS: Thirty-nine symptomatic and asymptomatic subjects wore four types of lenses: Focus NIGHT & DAY (CIBA Vision), Focus DAILIES (CIBA Vision), ACUVUE 2 (Johnson & Johnson Visioncare) and Proclear Compatibles (CooperVision) contralaterally for 7 hours and rated comfort and dryness on a zero-to-100 point visual analog scale at 0, 1, 3, 5 and 7 hours. RESULTS: In both groups, no lens differences were found for comfort and dryness, but the comfort and dryness ratings of the symptomatic group decreased significantly (became worse) over the 7-hour period. CONCLUSIONS: These results demonstrate that dryness and comfort is the same over time with silicone hydrogel as with the other three lenses.

Hrynchak,P., Hutchings,N., Jones,D., Simpson,T. A comparison of cup-to-disc ratio evaluation in normal subjects using stereo biomicroscopy and digital imaging of the optic nerve head. Ophthalmic and Physiological Optics 2003;23,1:51-59. [ Show Abstract ]

The cup-to-disc (CD) ratio evaluated using stereoscopic biomicroscopy was compared with that evaluated by viewing a non-stereo digital image of the optic nerve head. Twenty normal subjects (mean age 26 +/- 4 years) were evaluated by two observers. The average CD ratio was 0.29 with a range of 0-0.80. The intra-class correlations between the observers ranged from 0.82 to 0.96, when comparing horizontal and vertical CD ratios for both evaluation techniques. The mean CD ratio was significantly smaller when viewing the digital image (0.25 +/- 0.01) compared with stereoscopic observation (0.33 +/- 0.03, p < 0.0001). Although the mean differences between the two techniques were small, the percentage of CD ratios that differed by >or=0.2 were between 5 and 25% of evaluations. Caution should be exercised when using stereoscopic and non-stereo digital evaluations of CD ratio interchangeably to assess longitudinal progression in a multi-clinician setting.

Jones,L., Senchyna,M., Glasier,M. A., Schickler,J., Forbes,I., Louie,D., May,C. Lysozyme and lipid deposition on silicone hydrogel contact lens materials.. Eye Contact Lens 2003;29,1 Suppl:S75-79; discussion S83-84, S192-194. [ Show Abstract ]

PURPOSE: We sought to determine whether there were differences in lysozyme (quantity and conformation) and lipid deposition on in vivo worn conventional (etafilcon) and silicone hydrogel (balafilcon and lotrafilcon) contact lenses. METHODS: After extraction, lysozyme concentration in each extract was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Lysozyme activity was determined by the rate of lysis of Micrococcis lysodeikticus cells. Lipid deposition was determined by high-performance liquid chromatography. RESULTS: Lysozyme deposition on etafilcon lenses was significantly greater than that measured on silicone hydrogel (SH) lenses (985 microg per lens versus 10 and 3 microg per lens for balafilcon and lotrafilcon materials, respectively; P<0.001). The degree to which lysozyme was denatured was influenced by the lens material, with the lowest degree of denaturation (22%) seen on the conventional lens material, as compared with 50% for balafilcon and 80% for lotrafilcon (P<0.001). Lipid deposition was greatest on the SH materials, with up to 600 microg per lens of certain lipid classes being deposited on balafilcon, as compared with 20 microg per lens on etafilcon (P<0.001). CONCLUSION: The quantity and conformation of lysozyme and the quantity of lipid deposited on hydrogel contact lenses is significantly influenced by the composition of the lens material. SH contact lens materials deposit low levels of lysozyme and high levels of lipid deposition compared with ionic contact lens materials. Although SH materials deposit only small amounts of lysozyme, the degree of lysozyme denaturation that occurs is higher relative to that seen on ionic lens materials.

Karlgard,C. C. S., Jones,L. W., Moresoli,C. Ciprofloxacin interaction with silicon-based and conventional hydrogel contact lenses. Eye and Contact Lens 2003;29,2:83-89. [ Show Abstract ]

Purpose. Hydrogel contact lenses can be used as bandage lenses to protect the corneal surface after injury. The use of novel silicon-based hydrogel lens materials as bandage lenses has not gained widespread acceptance. As a first step toward advocating their usefulness as bandage lenses, their interaction with ocular pharmaceuticals must be understood because topical agents are often administered in conjunction with bandage lenses. Methods. The in vitro uptake and release of ciprofloxacin from silicone-based hydrogel (SH) and conventional pHEMA-based (CH) hydrogel contact lenses was examined by spectrophotometric evaluation of the drug concentration in saline solution. Results. The hydrogel contact lenses tested showed similar drug uptake (average 1800 μg/lens) but different levels of drug release. Multiphoton laser microscopy indicated that ciprofloxacin was distributed throughout the lens thickness, with higher levels of drug at the surface owing to drug precipitation. The drug adsorption onto the lenses was partially reversible. The SH lenses released a lower amount of drug than CH lenses (72 vs. 168 μg/lens). Ionic lenses released less drug than non-ionic lenses (127 vs. 151 μg/lens). Conclusions. The differences in ciprofloxacin uptake and release between SH and CH materials may not be clinically significant because the amount of drug released from all lenses would be above the MIC90 of ciprofloxacin for common ocular pathogens. These results indicate that material properties have a significant impact on drug-lens interactions. © 2003 Contact Lens Association of Ophthalmologists, Inc.

Karlgard,C. C. S., Wong,N. S., Jones,L. W., Moresoli,C. In vitro uptake and release studies of ocular pharmaceutical agents by silicon-containing and p-HEMA hydrogel contact lens materials. International journal of pharmaceutics 2003;257,1-2:141-151. [ Show Abstract ]

The in vitro uptake and release behaviour of cromolyn sodium, ketotifen fumarate, ketorolac tromethamine and dexamethasone sodium phosphate with silicon-containing (lotrafilcon and balafilcon) and p-HEMA-containing (etafilcon, alphafilcon, polymacon, vifilcon and omafilcon) hydrogel contact lenses indicated that both drug and material affected the uptake and release behaviour. Rapid uptake and release (within 50min) was observed for all drugs except ketotifen fumarate which was more gradual taking approximately 5h. Furthermore, the maximum uptake differed significantly between drugs and materials. The highest average uptake (7879±684μg/lens) was cromolyn sodium and the lowest average uptake (67±13μg/lens) was dexamethasone sodium phosphate. Partial release of the drug taken up was observed for all drugs except dexamethasone sodium phosphate where no release was detected. Sustained release was demonstrated only by ketotifen fumarate. Drug uptake/release appeared to be a function of lens material ionicity, water and silicon content. The silicon-containing materials released less drug than the p-HEMA-containing materials. The lotrafilcon material demonstrated less interactions with the drugs than the balafilcon material which can be explained by their different bulk composition and surface treatment. © 2003 Elsevier Science B.V. All rights reserved.

Situ,P., Du Toit,R., Fonn,D., Simpson,T. Successful monovision contact lens wearers refitted with bifocal contact lenses. Eye and Contact Lens 2003;29,3:181-184. [ Show Abstract ]

Purpose. Should successful monovision contact lens wearers be refitted with bifocal lenses? Methods. Fifty current monovision lens wearers were fitted with ACUVUE Bifocal contact lenses (Johnson & Johnson Vision Care, Jacksonville, FL). Visual function and subjective vision ratings were assessed with habitual monovision lenses at the first visit and then were repeated at the end of 6 months while wearing bifocal lenses. Lens preference was determined at the end of the 6-month study, and the subjects were called 1 year later to repeat the lens preference questionnaire. Results. Forty (80%) subjects completed the 6-month study; nine discontinued for visual reasons. At the end of 6 months of wear, 68% preferred bifocal lenses and 25% preferred monovision. Of the subjects who were contacted a year later, 53% were still wearing bifocal lenses. High-contrast visual acuity and letter contrast sensitivity at distance was the same for monovision and bifocal lenses, but low-contrast acuity was better with monovision. Intermediate low- and high-contrast acuity and 3-meter and near stereoscopic acuity were better with bifocal lenses. Near high- and low-contrast acuity were better with monovision. All subjective ratings, except near vision in poor lighting, were significantly greater with bifocal lenses. Conclusions. It is possible to refit successful monovision lens wearers with simultaneous vision bifocal lenses, and these lenses should be considered as an alternative method for the correction of presbyopia. In addition, subjective responses to bifocal lenses may not be reflective of visual function measurements. © 2003 Contact Lens Association of Ophthalmologists, Inc.

Wang,J., Fonn,D., Simpson,T. L. Topographical thickness of the epithelium and total cornea after hydrogel and PMMA contact lens wear with eye closure. Investigative Ophthalmology and Visual Science 2003;44,3:1070-1074. [ Show Abstract ]

PURPOSE. To determine changes in topographical thickness of the epithelium and total cornea after hydrogel (2-hydroxyethyl methacrylate; HEMA or soft lens) and PMMA rigid contact lens wear with eyes closed, as measured by optical coherence tomography (OCT). METHODS. Epithelial and total corneal thickness in 18 neophyte eyes was measured with OCT at intervals of 10° across a 10-mm zone of the horizontal meridian of the cornea, before and after 3 hours of soft and rigid contact lens wear with the eye closed. These measurements were repeated 20 minutes after removal of the lenses. RESULTS. Lens type, time, and location were found to be significant main influences (P < 0.0001) on corneal swelling in patched eyes, by three-way ANOVA, and there was a significant three-way interaction among lens type, time, and location (F(16,272) = 1.78, P = 0.033). However, there was no significant main effect and interaction of epithelial thickness (F(16, 272) = 0.33, P = 0.99). Immediately after removal of the lenses, total corneal thickness in the horizontal meridian was significantly greater with both soft and PMMA lenses (P < 0.001) at each location with each lens, compared with the baseline measurements. With both lenses, the increase in actual thickness and percentage of corneal swelling at the center was greater than at each peripheral point (excluding the first 10° points; P < 0.005). HEMA lenses caused greater corneal swelling than the PMMA lenses at each location immediately after removal of the lenses (P < 0.005). CONCLUSIONS. This study shows that corneal swelling is dependent on lens type and corneal location when eyes are closed, but epithelial thickness across the horizontal corneal meridian does not change during lens wear with eyes closed. OCT is an efficient method of measuring topographical corneal and epithelial thickness in response to contact lens wear.

Wang,J., Fonn,D., Simpson,T. L., Jones,L. Precorneal and pre- and postlens tear film thickness measured indirectly with optical coherence tomography. Investigative Ophthalmology and Visual Science 2003;44,6:2524-2528. [ Show Abstract ]

PURPOSE. To demonstrate the feasibility of indirectly measuring the precorneal tear film thickness and pre- and postlens tear film (PLTF) thickness using optical coherence tomography (OCT). METHODS. Central corneal thickness (C1) which includes the tear film (T) of both eyes of 40 non-contact lens wearers was measured using OCT after calibration. The mean age of the 40 subjects was 31.2 ± 9.3 years with a mean horizontal K-reading of 7.87 mm. Rigid contact lenses with base curves 0.3- to 0.5-mm steeper than the flattest K of the eye were fitted to measure real corneal thickness (C2), independently of the postlens tear film. T was calculated by T = C1 - C2. To measure pre- and postlens tear film thickness, Focus Night & Day and Acuvue lenses (Vistakon, Johnson & Johnson Vision Care, Jacksonville, FL) were fitted on both eyes. Central soft lens thickness (L1), which includes the prelens tear film (P), was measured by OCT in situ and in saline in a wet cell (L2). P was calculated by P = L1 - L2. Thickness of the central cornea plus the postlens tear film (C3) was measured during lens wearing. Postlens tear film (PLTF) was calculated by PLTF = C3 - C2. RESULTS. The mean ± SD precorneal tear film thickness was 3.3 ± 1.5 μm (range, 0-6.9) before lens insertion and 4.7 ± 2.3 μm (range, 0.7-11.0) after lens fitting, which was significantly thicker (paired t-test: P < 0.01). The prelens tear film thickness was 3.9 ± 2.6 and 3.6 ± 2.1 μm (mean ± SD; paired t-test: P = 0.52) and the postlens tear film thickness was 4.5 ± 2.3 and 4.7 ± 3.1 μm (paired t-test: P = 0.08) on and under Focus Night & Day and Acuvue lenses, respectively. Post hoc tests showed that precorneal (baseline) and prelens tear films were equivalent, and each was different (thinner; Tukey honestly significant difference P < 0.05) from the postlens tear film. CONCLUSIONS. OCT can noninvasively measure the thickness of the precorneal and prelens tear film as well as the postlens tear film. The thickness of the normal precorneal tear film is approximately 3 μm and becomes thicker after lens fitting. The postlens tear film is thicker than the precorneal and prelens tear films with soft contact lenses. The thickness of both preand postlens tear films appears to be independent of the investigated lens types.