The CLAO journal : official publication of the Contact Lens Association of Ophthalmologists, Inc最新文献

Purpose: While most clinicians agree that fitting of rigid gas permeable (RGP) lenses is the preferred treatment strategy for some types of patients, many patients have difficulty adapting to full-time daily wear of these lenses. The Contact Lens Extended Wear Study (CLEWS) is a randomized, controlled clinical trial in which subjects are first adapted to full-time RGP daily wear prior to randomization to either high or medium oxygen transmissibility (Dk/L) RGP lenses for 12 months of extended wear. The CLEWS pre-randomization data provide an opportunity to examine the reasons some patients fail to adapt to RGP daily wear and to determine whether a patient's demographic, historical, and ocular characteristics can be used to predict RGP daily wear success.

Methods: From 1,809 individuals who expressed interest in RGP lenses, 411 subjects passed the CLEWS screening criteria and were fit with high Dk lenses (mean Dk = 92 x 10(-11) [cm2/sec][mL 02/mL x mmHg]). The fitting strategy included minimum apical alignment, lid attachment, centration, and average lens diameters of 9.2 mm. Success was defined as a minimum of 14 hours per day without adverse ocular responses that would contraindicate either full-day daily wear or extended wear.

Results: Of the 411 subjects, 286 (69.6%) were successful with RGP extended wear. Among the 125 failures, 50 were based on clinician findings (e.g., cornea, vision, compliance), while 75 subjects chose to discontinue wear because of unacceptable comfort or poor vision. Multivariate linear logistic regression modeling shows that younger patients with greater corneal curvature (K) and less predicted residual astigmatism have a higher probability of RGP daily wear success.

Conclusions: Our study showed that RGP lenses can be fit with a relatively high rate of success and that many of those patients who elect to discontinue RGP daily wear report unacceptable comfort as the primary reason. We propose a Bayesian statistical method that will assist clinicians in selecting those candidates for RGP daily wear who are most likely to adapt successfully.

Purpose: To simplify the fitting of bitoric rigid gas permeable (RGP) contact lenses.

Methods: We prescribed bitoric RGP lenses using two kinds of diagnostic lenses at random. One type of lens was a diagnostic polymethylmethacrylate (PMMA) spherical lens and the other was a diagnostic RGP bitoric lens.

Results: The bitoric RGP lenses that were prescribed using a diagnostic bitoric lens required fewer parameter changes compared with the bitoric RGP lens prescribed using a diagnostic PMMA spherical lens.

Conclusions: The diagnostic RGP bitoric lens simplifies the prescription of bitoric RGP lenses and is very useful in fitting astigmatic corneas.

Purpose: We conducted a retrospective study of 47 patients who wore frequent replacement contact lenses on a daily-wear basis to determine the incidence of giant papillary conjunctivitis (GPC) and to assess the potential risk factors that may predispose frequent replacement contact lens wearers to develop GPC.

Methods: We reviewed the records of patients with no prior contact lens experience who were fit with frequent replacement contact lenses from September 1993 to February 1997.

Results: Forty-seven of 260 patients met the requirements for inclusion in the study. Ten (21.27%) patients had developed GPC. The incidence varied with the frequency of contact lens replacement. The contact lens replacement schedule ranged from 1 day to 12 weeks. In those patients replacing their contact lenses every 4 weeks or at a longer interval, the incidence of GPC was 36%, while for patients who replaced their lenses more frequently, the incidence was 4.5%. Coated contact lenses were also more common among patients who replaced their lenses at 4 weeks or longer (P = 0.23). A significantly greater number of patients in the GPC group incorporated enzymatic cleaning into their contact lens care system (P = .0004). A history of allergy was more prevalent in patients who developed GPC and was statistically significant (P = .012). There was no significant difference found between the groups for age, gender, average daily wearing time, FDA classification of contact lens material, time in contact lenses from fitting to diagnosis or last follow-up period, or the parameters and fitting characteristics of the contact lenses.

Conclusion: The frequency at which patients replace their contact lenses appears to be an important variable in developing GPC. Although frequent replacement contact lenses do not eliminate GPC, patients on a 1-day to 3-week replacement cycle had a significantly lower risk of developing GPC than patients who replaced their lenses at longer intervals. Lens coating was present less often on contact lenses replaced daily and up to 3 weeks. For patients who are at high risk for GPC, replacing lenses at intervals ranging of one day to two weeks appears to offer a better strategy for avoiding GPC than incorporating enzymatic cleaning into their lens care system.

Purpose: To assess the penetration of topical ciprofloxacin by a presoaked medicated disposable soft contact lens without topical drop administration.

Methods: Disposable soft contact lenses were presoaked in 0.3% topical ciprofloxacin (Ciloxan, Alcon Laboratories, Fort Worth,TX) for 10-12 hours. Presoaked lenses were placed on the eyes of patients with senile cataracts for 3 hours in group A, 5-6 hours in group B, and 8-12 hours in group C prior to their scheduled lens extraction surgery. Aqueous humor samples were drawn by paracentesis during the operation. Ciprofloxacin concentrations were determined by high pressure liquid chromatography-fluorescence detection.

Results: The mean ciprofloxacin concentration was 2.70 +/- 0.98 microg/mL in group A, 1.22 +/- 1.0 microg/mL in group B, and 0.5 +/- 0.2 microg/mL in group C.

Conclusions: Penetration of topical ciprofloxacin is enhanced through a presoaked disposable soft contact lens, and at 3 hours therapeutic levels are obtained. Significant levels of ciprofloxacin are retained through 8-12 hours. This mode of treatment may increase patient compliance compared to frequent topical drop administration, and as a consequence, assure efficient treatment of keratitis, at least for the first 3 hours.

Purpose: To study the effect of rigid contact lens oxygen transmissibility on cell proliferation of the corneal, limbal, and conjunctival epithelium in vivo following 2 days of extended wear in the rabbit model.

Methods: Fourteen adult New Zealand White rabbits were divided equally into two groups. Each group was assigned to one of two test rigid gas permeable (RGP) contact lenses (Dk/Ltotal = 10 and 97) with uniform thickness (0.15 mm) and diameter (14.0 mm). One eye of each rabbit randomly received a contact lens for two days (48 hrs) extended wear, and the fellow eye was used as a control. Rabbits were injected intravenously with 5-bromo-2-deoxyuridine (200 mg/kg) in sterile phosphate buffered saline (pH 7.4) 24 hours before being killed. Corneas with a limbal rim of episclera and overlying conjunctiva were fixed in situ and excised. Nuclei labeled with BrdU were detected with a monoclonal anti-BrdU antibody and an FITC-conjugated secondary antibody. Digital images were collected and BrdU-labeled nuclei of whole-mount corneas were counted from superior limbus to inferior limbus using epifluorescence microscopy.

Results: Twenty-four hours after intravenous injection of BrdU, labeled nuclei were confined to and appeared as pairs in the basal epithelial layer. The density of BrdU-labeled nuclei were found to be 258 +/- 42, 167 +/- 43, 372 +/- 64, and 310 +/- 46 (pairs/mm2, mean +/- SD, n = 14) in normal controls for adjacent conjunctiva, limbus, peripheral cornea, and central cornea, respectively. By contrast,there was significant 81.35% (low Dk)and 22.46% (ultra-high Dk) suppression of cell proliferation in the central cornea after two days lens wear (n = 7). In addition, significant increases in the labeling of limbal and conjunctival epithelium were also noted.

Conclusions: Significantly less BrdU labeling of epithelial cells at the normal rabbit limbus was noted as compared to the peripheral and central cornea (P < 0.05) and is consistent with the presence of slow-cycling limbal basal cells and the limbal stem cell theory; however, this is the first report of up-regulation of limbal cell proliferation induced by contact lens wear. This study also revealed, for the first time, that short-term extended wear of RGP lenses inhibits central corneal epithelial cell proliferation. This effect was significantly more pronounced for a low-oxygen vs. a hyper-oxygen transmissible test lens. This data also suggests that corneal epithelial layer thinning seen following extended contact lens wear may be explained, in part, by suppression of basal epithelial cell proliferation. Further study is clearly necessary to validate and extend these preliminary findings.

Purpose: Superior corneal flattening associated with inferior corneal steepening is a videokeratoscopic topography pattern that usually describes both keratoconus and contact lens induced warpage. To differentiate these two conditions topographically, we analyzed ten different corneal topographic shape variables and found that two distinct conditions were described. Three unique measurements of corneal geometry: shape factor (SF), irregularity (CIM), and apical toricity (TKM) were analyzed and evaluated as an additional method for differentiating these two conditions.

Methods: A retrospective series of 100 eyes with a medical diagnosis of either contact lens induced warpage or true keratoconus were mapped using the Humphrey Atlas Corneal Topographer (San Leandro, CA) and their individual topographic indices were analyzed in an attempt differentiate the two conditions with videokeratoscopy. Variables included Flat Keratometry Reading, Maximum Axial Curvature, Maximum Tangential Curvature, Corneal Astigmatism, Corneal Shape Factor, Reference Sphere, Corneal Irregularity Measure (CIM), Maximum Elevation, and Mean Reference Toric K (TKM). All patients wore rigid gas permeable contact lenses.

Results: True keratoconic eyes had steeperflat K readings (46.9+/-3.7 D vs. 43.04+/-1.18 D; P<6.3E-13) with greater variations in maximum axial curvature (54.1+/-4.76 D vs. 43.6+/-1.5 D; P<2.4E-15) and maximum tangential curvature (55.1 7+/-4.56 D vs. 47.7+/-1.5 D; P<5.4E-16) than did eyes with contact lens induced warpage. The amount of corneal toricity (-3.43+/-2.29 D vs. -1.33+/-0.88 D; P<1.5E-07) was also greater for true keratoconus. True keratoconic eyes had larger and more variable shape factors (0.61+/-0.26 vs. 0.02+/-0.13; P<2.5E-19) and CIM's (2.30+/-1.16 vs. 1.03+/-0.37; P<7.5E-10) than those with contact lens induced warpage. Steeper reference spheres (47.58+/-3.55 D vs. 43.6+/-0.37 D; P<2.2E-10), greater maximum elevation over their respective reference spheres (15.51+/-9.91 microns vs. 6.2+/-3.0 microns; P<8.1E-08) and steeper, more variable toric mean reference spheres (51.88+/-4.01 D vs. 43.82+/-1.82 D; P<3.9E-17) are also present in true keratocon us. True keratoconic eyes can be separated from contact lens induced warpage eyes with a sensitivity of 98%, while identification of contact lens induced warpage demonstrates 94% specificity using corneal topography.

Conclusions: While contact lens induced warpage and true keratoconus exhibit similar corneal topography patterns (superior flattening and inferior steepening), they demonstrate two uniquely different geometric shapes that can be readily differentiated using the various corneal shape indices of videokeratoscopy with a high degree of accuracy and specificity.

Purpose: This study evaluates the effect of hypoxic and hypercapnic stress on bacterial adherence to surface corneal epithelial cells, as well as tear LDH levels, surface cell desquamation, and corneal swelling in normal human subjects.

Methods: Sixteen eyes of eight human volunteers were successively exposed to three gas mixtures (air, 100% N2, 95% N2-5% CO2) through tightly fitted goggles for six hours at two-week intervals. Exfoliated epithelial cells were collected and counted using a modified corneal irrigation chamber. Bacterial binding was determined by measuring Pseudomonas aeruginosa (PA) adherence to exfoliated corneal epithelial cells. The effects of hypoxic or hypercapnic stress on the corneal surface were also assessed by tear LDH measurement, and quantification of surface epithelial cell size and epithelial and stromal thickness were determined by in vivo confocal microscopy.

Results: Short-term precorneal hypoxia significantly decreased corneal epithelial cell desquamation. Both short-term hypoxia alone and combined with hypercapnia induced significant corneal stromal swelling (7 to 8%) but did not significantly enhance PA adherence to exfoliated human corneal epithelial cells.

Conclusions: This study demonstrates, for the first time, that short-term precorneal hypoxia downregulates corneal epithelial cell desquamation in humans. These results also demonstrate that short-term hypoxia alone or combined with hypercapnia does not significantly increase PA adherence to exfoliated epithelial cells from the human cornea. The results reveal that either longer hypoxic exposure or other interactive factor(s), including but not limited to the mechanical effect of the contact lens itself, may be required for promotion of increased epithelial cell-PA binding following lens wear in humans.

Purpose: The purpose of this study was to compare the lactate dehydrogenase (LDH) activities in the tears of patients wearing different types of contact lenses with each other and to individuals who have never worn contact lenses (controls).

Methods: Tear LDH activities were determined in 13 normal subjects who had never worn contact lenses, 12 daily wear and ten extended wear soft contact lens wearers, and 14 daily wear and eight extended wear rigid gas permeable (RGP) contact lens wearers(Dk125). Tear samples were collected from all subjects at the same time of day from the inferior meniscus by using a microcapillary tube. The measurements were determined using a Sigma diagnostic LDH reagent and a spectrophotometer.

Results: There was no statistically significant difference in the LDH activities between soft and RGP contact lenses--used either as daily or extended wear--when compared with each other. However, individuals wearing extended wear soft contact lenses had significantly higher tear LDH activities than the control group.

Conclusion: Tear LDH activity may be a useful method in evaluating the physiologic response of extended soft contact lens wear.

Purpose: To describe a case of bilateral corneal ulcers caused by Pseudomonas in a disposable soft contact lens wearer. This case study discusses the role of patient examination, contact lens care instruction, and adequate patient supervision in reducing the risk of serious potential complications.

Methods and results: A 17 year old student who had been using disposable soft contact lenses on an extended wear basis for 6 months presented complaining of pain in the left eye. When he was examined, a corneal ulcer with surrounding infiltrate was observed in the superior middle periphery of the left eye. Samples were collected for culture, and treatment with fortified cefalotin and gentamicin was started. After 8 hours the patient returned, now complaining of pain in the right eye. Examination of the right eye revealed a diffused keratitis with a mucopurulent discharge. A culture was taken, and the same treatment was instituted. The laboratory tests revealed Pseudomonas in both eyes. The bilateral corneal ulcers responded to therapy after 1 week of treatment.

Conclusions: We discuss the factors involved in the occurrence of infectious keratitis in contact lens wearers, and stress that even disposable contact lens wear can be associated with serious complications. This case also highlights extended wear as one of the main risk factors for complications in disposable soft contact lens wear.