Peer-reviewed Articles

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


Begley,C. G., Chalmers,R. L., Mitchell,G. L., Nichols,K. K., Caffery,B., Simpson,T., DuToit,R., Portello,J., Davis,L. Characterization of ocular surface symptoms from optometric practices in North America. Cornea 2001;20,6:610-618. [ Show Abstract ]

Purpose. This study characterized ocular symptoms typical of dry eye in an unselected optometric clinical population in the United States and Canada. Methods. Self-administered dry eye questionnaires, one for non-contact lens wearers (dry eye questionnaire) and one for contact lens wearers (contact lens dry eye questionnaire), were completed at six clinical sites in North America. Both questionnaires included categoric scales to measure the prevalence, frequency, diurnal severity, and intrusiveness of nine ocular surface symptoms. The questionnaires also asked how much these ocular symptoms affected daily activities and contained questions about computer use, medications, and allergies. The examining doctors, who were masked to questionnaire responses, recorded a nondirected dry eye diagnosis for each patient, based on their own diagnostic criteria. Results. The dry eye questionnaires were completed by 1,054 patients. The most common ocular symptom was discomfort, with 64% of non-contact lens wearers and 79% of contact lens wearers reporting the symptom at least infrequently. There was a diurnal increase in the intensity of many symptoms, with symptoms such as discomfort, dryness, and visual changes reported to be more intense in the evening. The 22% percent of non-contact lens wearers and 15% of contact lens wearers diagnosed with dry eye (most in the mild to moderate categories) reported symptoms at a greater frequency than those not diagnosed with dry eye. Conclusions. Our results show that symptoms of ocular irritation and visual disturbances were relatively common in this unselected clinical population. The intensity of many ocular symptoms increased late in the day, which suggested that environmental factors played a role in the etiology of the symptoms.

Du Toit,R., Simpson,T. L., Fonn,D., Chalmers,R. L. Recovery from hyperemia after overnight wear of low and high transmissibility hydrogel lenses. Current eye research 2001;22,1:68-73. [ Show Abstract ]

Purpose. To measure the limbal vascular response after 8 hours of eye closure while wearing high and low permeability lenses compared to control eyes without lenses. Method. Twenty neophyte participants wore lotrafilcon A silicone hydrogel lenses (HDk; Dk = 140) or etafilcon A hydrogel lenses (LDk; Dk = 18). On two different nights the lenses were randomly worn for 8 hours during sleep in the right eyes only. Left eyes were non-lens wearing controls. Biomicroscopic images of the temporal limbal area were videotaped at baseline, on eye opening and every 20 minutes for 3 hours. A masked observer graded digitized images of the limbal area. Results. On waking and after lens removal there were no differences in hyperemia between the HDk and LDk lens wearing eyes. There were also no differences at any time between the HDk lens wearing eyes and their control eyes (p > 0.05). On waking the eyes wearing the LDk lens were more hyperemic compared to baseline (p < 0.001) and compared to their control eyes at 20 (p < 0.001) and 180 minutes (p = 0.01), indicating slower recovery from hyperemia. The HDk lens wearing eyes recovered to their baseline levels by 180 minutes (p = 0.99), compared to the LDk lens wearing eyes, which had not recovered to baseline levels by 180 minutes (p = 0.04). Conclusion. The reduction in hyperemia over time of the HDk lens wearing eyes was the same as the controls. The LDk lens wearing eyes were more hyperemic than the controls on waking and the reduction in hyperemia over time was slower. This suggests that the slower recovery from hyperemia may be affected by the lower oxygen transmissibility of the LDk lens.

Du Toit,R., Situ,P., Simpson,T., Fonn,D. The effects of six months of contact lens wear on the tear film, ocular surfaces, and symptoms of presbyopes. Optometry and Vision Science 2001;78,6:455-462. [ Show Abstract ]

Purpose. To assess the tear film, ocular surfaces, and symptoms of ocular discomfort in a presbyopic population before and after contact lens wear. Methods. A total of 150 presbyopes (49% were previous soft contact lens wearers) participated in a clinical trial in which they wore either monovision (single vision Acuvue lenses) or Acuvue Bifocal contact lenses. Clinical measurements of tear film, biomicroscopy, and corneal sensitivity as well as subjective ratings using the Dry Eye Questionnaire were collected at the initial visit and repeated after 6 months. Comparisons were made between age groups (40 to 51 years and 52 to 71 years) and genders before and after contact lens wear. Associations between objective and subjective tests were sought. Results. After 6 months of contact lens wear, clinical signs had worsened by less than one-half of a grade, and tear break up time (TBUT) worsened by 3 s. Only TBUT was lower for the older age group. Females had less bulbar hyperemia, more sensitive eyes, more lissamine green staining, and lower TBUT and phenol red thread measurements (all p lt; 0.04). Twenty-eight percent experienced dryness before contact lens wear, but this figure increased to 68% when wearing contact lenses. There were no age differences, but almost twice as many females as males reported dryness. Reporting symptoms of dryness was associated with gender, corneal sensitivity, and type of corneal staining. Conclusions. These results provide a representation of the ocular surface condition and symptoms of ocular discomfort in the middle-aged population and seem similar to reports of younger populations. Wearing contact lenses seems to influence dry eye symptoms more than age or gender. Therefore, presbyopes should not be excluded from consideration for contact lens fitting.

Dumbleton,K. A., Chalmers,R. L., Richter,D. B., Fonn,D. Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability. Optometry and Vision Science 2001;78,3:147-151. [ Show Abstract ]

Purpose. The purpose of this study was to determine the impact of extended wear of high and low oxygen permeability (Dk) lenses on the development or resolution of limbal hyperemia and corneal neovascularization in a randomized prospective clinical trial. Methods. Adapted daily-wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group (N = 23) wore etafilcon A lenses (Dk/t = 40) for up to 7 days and 6 nights, and the high-Dk group (N = 39) wore lotrafilcon A lenses (Dk/t = 175) for up to 30 days and nights. Limbal hyperemia and neovascularization were assessed and graded during 9 months of extended wear. A stratified analysis to determine how change in ocular redness depended on initial presentation was also conducted. Results. On a 0 to 100 scale, extended wear of low-Dk lenses resulted in a 16-point increase in limbal hyperemia (p < 0.0001); no significant change occurred with the high-Dk lenses. The difference was greatest for low-Dk participants who initially presented with lower levels of hyperemia (N = 18). There was a slight resolution of redness in participants who initially presented with higher levels of hyperemia (N = 10) after wearing the high-Dk lenses. Neovascularization increased by an average of 0.5 on a scale of 0 to 4 in low-Dk lens wearers (p < 0.0001) but remained unchanged in the high-Dk lens wearers. The increase was most marked for the low-Dk group with lower levels of neovascularization at baseline. Conclusions. Subjects who wore lenses with higher oxygen permeability for 9 months of extended wear exhibited a lower vascular response of the ocular surface compared with subjects who wore lenses of lower oxygen permeability for the same period. This result was found both for the surface limbal vessels and in the deeper neovascular stromal vessels. Moderate neovascularization also developed after 3 months of extended wear of low-Dk hydrogels, whereas high-Dk lenses caused no neovascularization.

Feng,Y., Varikooty,J., Simpson,T. L. Diurnal variation of corneal and corneal epithelial thickness measured using optical coherence tomography. Cornea 2001;20,5:480-483. [ Show Abstract ]

PURPOSE: To determine the feasibility of optical coherence tomography (OCT) measurement of overnight corneal swelling and de-swelling and, specifically, to examine overnight changes in the corneal epithelium and recovery during the day. METHODS: Ten healthy volunteers were recruited. Corneal OCT imaging was performed at 10:00 PM (baseline), 8:30 AM, and every 2 hours thereafter until 4:30 PM. Either the right or left eye was taped shut (using a gauze pad and surgical tape) until the 8:30 AM session of the next day. Measurements were made along a 1-mm strip centered on the visual axis. RESULTS: At baseline, there were no differences in corneal or epithelial thickness between control and experimental eyes (all p > 0.05). Immediately after patch removal, corneal and epithelial thicknesses of patched eyes were higher than the baseline (all p < 0.05). In patched eyes, the cornea and epithelium swelled 5.5% and 8.1% overnight, respectively (p > 0.05). Two hours later, the epithelial thickness of the experimental eyes recovered to baseline level (p > 0.05), but corneal thickness did not reach to baseline level until 4 hours after patch removal. For control eyes, there were no differences compared with baseline (all p > 0.05). CONCLUSION: Both cornea and corneal epithelium experience proportionately similar amounts of overnight swelling. Recovery of overnight swelling may be slower for the cornea than for the epithelium. OCT provides valuable information about anterior segment morphometry.

Jones,L. W., Jones,D. A. Non-inflammatory corneal complications of contact lens wear. Contact Lens and Anterior Eye 2001;24,2:73-79. [ Show Abstract ]

Contact lenses can induce changes in the epithelium, stroma and endothelium of the cornea, all of which can be observed clinically using the slit-lamp biomicroscope. These complications include epithelial microcysts, vacuoles and staining, stromal oedema and vascularization, and endothelial polymegethism and blebs. Each complication can be attributed to one or more aetiological factors such as hypoxia, hypercapnia, tissue acidosis, trauma, hypersensitivity and toxicity. This review outlines the way in which these complications manifest clinically, and consideration is given to management strategies and likely prognoses. Early detection of these conditions and appropriate action can usually prevent more serious ocular complications.

Lu,F., Tang,S., Zhu,X., Zhang,J., Zheng,H. Experimental study on the effect of perfluorodecalin on rabbit corneas.. Eye science 2001;17,1:16-20. [ Show Abstract ]

PURPOSE: To study the effects of perfluorodecalin on the cornea of the rabbit eyes. METHODS: Perfluorodecalin (0.05 ml/each) was injected into the anterior chambers of eighteen rabbit eyes. Corneal morphology and endothelial cells were monitored clinically by slit-lamp biomicroscope and specular microscope for 26 weeks. Animals were sacrificed in 1st, 2nd, 4th, 10th, 16th, 22nd, and 26th week after injection, respectively, and the corneas were examined under the light microscope. RESULTS: Perfluorodecalin droplets looking like "fish eggs" were found at about 1/4-1/2 of the corneal height in the inferior anterior chamber. Corneal opacification on the area contacted with perfluorodecalin was observed in five eyes five weeks after injection, and all in the 22nd week. Mutton fat KPs in one eye were seen in the 6th week firstly, and in all eyes in the 7th week. Corneal pannus formation in one eye was present in the 4th week, two eyes in the 5th week and three eyes in the 6th week. Retrocorneal fibrous membrane in one eye was detected at the 6th week and 3 eyes at the 7th week respectively. After injection of perfluorodecalin, endothelial cell density was significantly decreased (2,789 +/- 192 vs. 2,341 +/- 658, P < 0.01) and corneal thickness was increased. CONCLUSIONS: Perfluorodecalin injected into anterior chamber can lead to corneal damage and inflammatory reaction.

Tonge,S., Jones,L., Goodall,S., Tighe,B. The ex vivo wettability of soft contact lenses. Current eye research 2001;23,1:51-59. [ Show Abstract ]

Purpose. To investigate the ex vivo wettability of Etafilcon A contact lenses over an eight hour period of wear and observe the influence of surfactant pre-treatment. Methods. Etafilcon A hydrogel lenses, comprising poly[2-hydroxyethyl methacrylate-co-methacrylic acid] and 58% water, were soaked for 12 hours in either 0.9% saline (control) or a 1% aqueous solution of poloxamine 1107 (treated). The advancing and receding contact angles were subsequently determined ex vivo after various periods of wear in six adapted contact lens wearers using a single-blind, randomised protocol. Contact angles were measured with a dynamic contact angle tensiometer, using the Wilhelmy plate technique. Patient comfort scores were recorded and the static surface tensions of the probe fluids assessed. Results. Control lenses exhibited no change in wetting angles over time, indicating a lack of surface modification by components within the tear film. Treated lenses exhibited a significantly reduced advancing angle (p > 0.001) and hysteresis angle (p < 0.001) when compared with control lenses. In addition, treated lenses were consistently rated as being more comfortable than control lenses (p = 0.04). Conclusions. This study has shown clearly that new Etafilcon A lenses do not exhibit significant changes in wettability during the initial four hour wearing period. Pre-treatment of such lenses with a polymeric surfactant results in wetting of the lenses due to the adsorption of surfactant. The surfactant is retained by the lens for at least eight hours of wear, resulting in significant improvements in subjective comfort, especially over the first 30 minutes of wear.