Topographic changes in contact lens-induced corneal warpage

Twenty-one eyes of 12 patients with contact lens-induced corneal warpage were followed prospectively using computer-assisted topographic analysis. Sixteen eyes had worn rigid contact lenses (13 eyes, polymethylmethacrylate; three eyes, gas-permeable), and five eyes had worn soft contact lenses. Initial corneal topographic patterns were characterized by the presence of central irregular astigmatism, loss of radial symmetry, and frequent reversal of the normal topographic pattern of progressive flattening of corneal contour from the center to the periphery. A correlation was noted between the initial corneal topography and the resting position of the contact lens on the cornea for nine of the 16 eyes with rigid contact lenses. Initial topography for each of these corneas showed relative flattening of the corneal contour underlying the resting position of a decentered contact lens. Superior-riding lenses produced a topography that simulated early keratoconus. After cessation of contact lens wear, 16 of 21 eyes had a change in corneal shape to a topography that was consistent with a normal pattern. Five corneas stabilized with an abnormal topographic pattern. A much longer time without contact lenses than had been previously reported, up to 5 months, was required for a return of a stable corneal topography in eyes with contact lens-induced corneal warpage caused by rigid lenses.     

Time to resolution of contact lens-induced corneal warpage prior to refractive surgery.

PURPOSE: To evaluate the resolution of contact lens-induced corneal warpage before keratorefractive surgery. METHODS: We prospectively studied the eyes of 165 consecutive contact lens-wearing patients evaluated for keratorefractive surgery. Significant contact lens-induced corneal warpage was detected by comeal topography in 20 eyes of 11 patients. Manifested refraction, keratometry, and cornea topography were subsequently recorded during weekly or biweekly reevaluations and were compared with previous measurements for stability. Effects of age, sex, type, and duration of contact-lens wear and the recovery time period to stabilization were analyzed. RESULTS: Overall, a 12% incidence of significant contact lens-induced corneal warpage was found. In patients demonstrating lens-associated warpage, the mean duration of prior contact lens wear was 21.2 years (range 10 to 30 years); lens use included daily wear soft (n=2), extended-wear soft (n=6), toric (n=4), and rigid gas-permeable contact lenses (n=8). Up to 3.0 diopter (D) refractive and 2.5D keratometric shifts accompanied by significant topography pattern differences were observed. The average recovery time for stabilization of refraction, keratometry (change within +/- 0.5D), and topography pattern was 7.8+/-6.7 weeks (range 1 to 20 weeks). Recovery rates differed between the lens types: soft extended-wear 11.6+/-8.5 weeks, soft toric lens 5.5+/-4.9 weeks, soft daily wear 2.5+/-2.1 weeks, and rigid gas-permeable 8.8+/-6.8 weeks. CONCLUSION: We observed a 12% incidence of significant contact lens-induced corneal warpage in patients undergoing evaluation for keratorefractive surgery. Warpage occurred with all types of contact lens wear but resolved at different rates. To optimize the quality and predictability of keratorefractive procedures, an appropriate waiting period is necessary for contact lens-induced corneal warpage to stabilize. We suggest that resolution of corneal warpage be documented by stable serial manifested refractions, keratometry, and corneal topographic patterns before scheduling patients for keratorefractive surgery.     

Differentiating contact lens induced warpage from true keratoconus using corneal topography.

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.     

Same PMMA contact lenses worn for over 30 years: A case report

Many, often asymptomatic, contact lens wearers have alterations of the corneal topography called corneal warpage. These topographic abnormalities are characterized by the presence of irregular astigmatism, loss of radial symmetry, and frequent reversal of the normal topographic pattern of progressive flattening of corneal contour from the center to the periphery. We describe a case in which the same pair of PMMA contact lenses was worn for over 30 years. The patient had no symptoms regarding her contact lenses, but on a visit for a posterior vitreous detachment, we found typical signs of corneal warpage, which resolved after 12 weeks of contact lens wear suspension     

正常戴角膜接触镜患者的角膜地形图变化

通过对戴角膜接触镜患者停镜后进行定期角膜地形图观察，发现戴角膜接触镜可引起角膜变形，如中心区不规则散光、缺乏正常角膜的由中心向周围逐渐变扁平和丧失辐射性对称。停镜后角膜恢复正常形态的时间为2～8周，平均为4．07±1．76周。最长时间为12周。停镜2周左右角膜变化较明显。提示屈光性角膜手术前，对戴角膜接触镜患者要定期检查角膜地形图，直至角膜形态恢复正常，才可进行手术治疗。     

Is abnormal focal steepening of the cornea related to persistent monocular diplopia?

PURPOSE: Some case reports have shown that abnormal focal steepening of the cornea appears to cause monocular diplopia by prismatic effect. The purpose of this study was to ascertain prospectively if the pattern of corneal distortion was related specifically to persistent monocular diplopia. METHODS: We selected 16 visually normal eyes (controls) and two groups of volunteers in which abnormal focal steepening of the cornea was expected to be found: 40 eyes of 20 volunteers who wore rigid gas-permeable contact lenses (RGP) for myopia and 10 eyes of seven patients with keratoconus. New charts that consisted of white dials on a black background were prepared for detection and measurement of secondary images. Any secondary image that could not be eliminated by any trial lens correction was defined as a persistent secondary image, using the charts. Corneal topography from all subjects was classified: round or oval, symmetric or asymmetric bowtie, abnormal focal steepening accompanied by contact lens-induced corneal warpage or keratoconus, or amorphous. We analyzed the relationship between the persistent secondary image and the corneal topographical patterns. RESULTS: A persistent secondary image was detected from seven eyes of RGP wearers and all keratoconus eyes. All corneal topographies of the seven RGP eyes with a persistent secondary image showed abnormal focal steepening related to contact lens-induced corneal warpage. The direction of the persistent secondary image was approximately consistent with the location of the focal steepening as seen on the corneal topography. CONCLUSION: Abnormal focal steepening of the cornea that appeared to produce a prismatic difference between two parts of the cornea was specifically related to persistent monocular diplopia.     

Predicting time to refractive stability after discontinuation of rigid contact lens wear before refractive surgery

PURPOSE: To determine whether discontinuing rigid contact lenses for 3 weeks is sufficient to achieve refractive stability and if not, to identify factors, including indicators of corneal warpage, that are associated with prolonged corneal instability. SETTING: University-based refractive surgery practice. METHODS: Charts of patients seen for refractive surgery consultation from January 1999 to March 2001 were reviewed. Patients with a history of rigid gas-permeable (RGP) contact lens use were identified and instructed to discontinue wearing lenses 3 weeks before the initial examination. Patients were examined at 3-week intervals until a stable refraction was achieved (within +/-0.25 diopter [D] sphere and 0.25 D cylinder with less than 25 degrees of axis orientation). Visual acuity, subjective refraction, and corneal topography were obtained at each visit. RESULTS: Of 55 eyes of 28 patients, 31 eyes achieved refractive stability by the second visit (early-stability group) and 24 eyes required more than 2 visits to achieve stability (late-stability group). No statistically significant between-group difference was observed in age, sex, refractive cylinder, topographic cylinder, difference between refractive and topographic cylinders, surface regularity index, surface asymmetry index, or spherical equivalent at the initial examination. The number of years of contact lens wear was significantly different between the groups (P = .05). CONCLUSIONS: The time for contact lens-induced corneal changes to reach a steady state after cessation of lens wear is highly variable. Among the variables examined, including those indicating corneal warpage, the factor that correlated with the required time to refractive stability after discontinuation of RGP wear was the length of time of contact lens use. Patients who are long-term RGP wearers should be counseled that multiple visits will likely be required before a stable refraction is obtained.     

Contact lens selection for keratoconus using a computer-assisted videophotokeratoscope

We used the Corneal Modeling System, a digital videophotokeratoscope, as an aid in selecting the initial base curve and lens diameter for contact lenses in keratoconus patients. With this instrument we studied corneal topography in 24 keratoconus patients (33 eyes) who were being fit for the first time or who had not worn contact lenses for at least one month prior to our examination. For the purposes of fitting contact lenses, the corneas were classified according to the topographic patterns observed, and appropriate fitting strategies were adopted for each subgroup. Diagnostic lenses and their fluorescein patterns were analyzed for the desired cornea-lens relationship. Topographic analysis of the cornea provided a rational basis for selecting appropriate trial contact lenses for our patients.     

A summary of the findings from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. CLEK Study Group.

BACKGROUND: This summary of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study includes the study design and results to date. METHODS: The CLEK Study is a longitudinal, observational study of 1,209 patients with keratoconus. The study's main outcome measures are corneal scarring, visual acuity, corneal curvature, and quality of life. RESULTS: These patients' mean age at baseline was 39.3 +/- 10.9 years, and they had moderate to severe keratoconus. Ninety-five percent of the patients had steep keratometric readings of at least 45 D, and 78% had best-corrected visual acuity of 20/40 or better in both eyes. Sixty-five percent of the patients wore rigid gas-permeable contact lenses in both eyes, and most of those (73%) reported that their lenses were comfortable. Most rigid gas-permeable contact lens wearers were fitted with apical touch (88%). Fifty-three percent had corneal scarring in one or both eyes, and corneal scarring was associated with corneal staining, contact lens wear, age, the presence of a Fleischer's ring, and a steeper cornea. Corneal scarring was associated with decreased high- and low-contrast visual acuity. CONCLUSIONS: These results characterize keratoconus patients as rigid gas-permeable contact lens wearers with moderately steep corneas. Corneal scarring is associated with decreased vision in keratoconus.     

Contact lens manipulation of corneal topography after penetrating keratoplasty: a preliminary study.

We conducted a preliminary retrospective study of five eyes that had undergone penetrating keratoplasty (PK) to determine if rigid gas permeable (RGP) contact lenses could be used as splints or molds to improve postoperative corneal topography. RGP lenses were fit 3-6 months (mean: 4.1 months) after PK and 3-4 months (mean: 1.8 months) after removal of the 10-0 nylon suture. Lenses were fit to attain a contact lens resting position centered on the corneal graft. After 4 to 8 months (mean: 6.2 months) of contact lens wear, analysis of corneal topography showed a decrease in simulated keratometry cylinder from 4.7 +/- 0.6 D (mean +/- 1 standard deviation) to 1.8 +/- 0.8 D (P = 0.02) and an improvement in anterior corneal surface regularity (surface regularity index: initial = 1.40 +/- 0.2; final = 1.0 +/- 0.2; P = 0.04). Three eyes were fit with a well-centered RGP lens; two eyes were fit with lenses that rode off-center. Increased irregular astigmatism in the two eyes with decentered contact lenses suggests the importance of centering RGP lenses with respect to corneal grafts. The best corrected spectacle visual acuity either improved or remained unchanged in four of five eyes after contact lens wear. One eye demonstrated a decrease in best corrected spectacle acuity by one Snellen line after 3 months of lens wear. Further clinical studies are needed to determine the potential of postoperative use of RGP lenses to improve corneal surface regularity, to decrease astigmatism, and to optimize visual results.     

New diagnostic methods for imaging the anterior segment of the eye to enable treatment modalities selection

New diagnostic instruments for imaging the anterior segment of the eye have been developed using the corneal topographer, wavefront sensor, and anterior segment optical coherence tomography (OCT). Data obtained from these instruments can be used to choose treatment modalities by providing information that is complementary to slit-lamp examination and visual acuity measurements. Zernike vector analysis was used to evaluate the corneal higher-order aberrations to quantify the effects of the corneal shape on the optical quality of the eye. The analyses showed the optical characteristics of the anterior and posterior surfaces of the cornea in patients with keratoconus or pellucid marginal corneal degeneration. The association between the deterioration of optical quality during rigid gas-permeable contact lens wear in patients with keratoconus and the residual coma due to posterior corneal shape was suggested by the findings made with this method. Zernike vector analyses also revealed the differences in the ocular higher-order aberrations between conventional Laser in situ keratomileusis (LASIK) and custom LASIK. Serial measurements of the ocular higher-order aberrations by a wavefront sensor enabled us to evaluate the effects of tear fluid dynamics on the optical quality of the eye. The findings clarified the characteristics of serial alterations of higher-order aberrations in normal eyes, dry eye with tear deficiency and dry eye with tear evaporation. The effects of internal lubricating agents on the soft contact lenses were also evaluated objectively. In addition, these results suggest that the effects of serial fluctuations in the ocular higher-order aberrations on refractive surgery should be considered. To observe the cornea at the cellular level with anterior segment OCT, a prototype machine of full-field OCT was developed. This made it possible to show epithelial edema in human donor corneas as well as the alterations in the epithelial layer and stromal layer associated with intraocular pressure elevation in ex vivo porcine eyes. An OCT-based corneal topographer was developed using a three-dimensional anterior segment OCT with the swept-source principle. Corneal topographic analyses of the anterior and posterior surfaces either in eyes with keratoconus or following keratoplasty was possible even in where it was difficult for conventional corneal topographers to analyze accurately. Also, OCT-based corneal topographer analyzed the host and donor cornea separately following Descemet stripping automated endothelial keratoplasty by recognizing the host-graft interface. The results from these new diagnostic methods for imaging the anterior segment of eye will be useful for the diagnosis of corneal disorders and the planning of treatment by evaluating the effects of corneal topographic abnormalities and tear fluid dynamics on visual function, by observing the abnormalities of the corneal tissue at the cellular level, and by showing corneal topography in diseased corneas more accurately and non-invasively.     

Rigid contact lens fitting relationships in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group.

PURPOSE: Although the influence of flat-fitting contact lenses on corneal scarring in keratoconus is frequently debated, the current standard of care with regard to the apical fitting relationship in keratoconus remains undocumented. METHODS: Patients were examined at baseline in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study (N = 1209). Patients wearing a rigid contact lens in one or both eyes (N = 808) had their habitual rigid contact lenses analyzed, and the fluorescein patterns and base curves were compared to the first definite apical clearance lens (FDACL). The FDACL is the flattest lens in the CLEK Study trial lens set that exhibits an apical clearance fluorescein pattern. For patients wearing a rigid contact lens in both eyes, one eye was selected randomly for analysis. RESULTS: Twelve percent of the rigid contact lens-wearing eyes were wearing lenses fitted with apical clearance based upon the clinician's fluorescein pattern interpretation. The remainder (88%) was wearing lenses fitted with apical touch. For mild (steep keratometric reading <45 D) keratoconus corneas, the mean estimate of the base curve to cornea-fitting relationship was 1.18 D flat (SD +/- 1.84 D); moderate (steep keratometric reading: 45 to 52 D) corneas were fitted on average 2.38 D flat (SD +/- 2.56 D); and severe (steep keratometric reading > 52 D) corneas were fitted an average of 4.01 D flat (SD +/- 4.11 D). CONCLUSIONS: Despite the potential risk for corneal scarring imposed by flat-fitting rigid contact lenses, most CLEK Study patients wear flat-fitting lenses. Overall, rigid lenses were fitted an average of 2.86 D (SD +/- 3.31 D) flatter than the FDACL.     

Bitoric rigid gas permeable contact lens fitting for the management of a corneal scar caused by herpes zoster ophthalmicus

Empirical fitting of a bitoric rigid gas permeable contact lens for the management of a scarred irregular cornea caused by herpes zoster ophthalmicus is described. Two corneal scars, which affect the pupil axis, caused an irregular cornea and produced low visual acuity and anisometropia. Two contact lenses were necessary to complete the fitting. Visual acuity improved from 0.2 to 1.0. The rigid gas permeable lenses can be a good alternative in the management of patients with irregular corneas caused by herpes zoster ophthalmicus.     

Rigid gas-permeable contact lens fitting in LASIK patients for the correction of multifocal corneas

BACKGROUND: Laser in situ keratomileusis (LASIK) has recently become the most commonly performed refractive surgery procedure. Results are promising in correcting low to moderate myopia. Most complications occur during the surgeon's learning curve. One of the complications is a decentration of the ablated area that causes monocular diplopia and a nocturnal halo phenomenon due to a multifocality of the corneal surface overlying the entrance pupil. The corneal shape is significantly altered after LASIK. We evaluate the efficacy of rigid gas-permeable contact lens designs and fitting techniques used in eight eyes with multifocal LASIK ablations to correct haloes and impaired night vision complaints. METHODS: We used large-diameter tetra-curved rigid gas-permeable (RGP) contact lenses for visual recovery in eight eyes of seven LASIK patients. We used the power on the transition zone of the corneal topographic map, 0.2 mm outside the ablated refractive area, for selection of the back optic zone radius of the RGP contact lenses. Procedures for lens fitting are described. Visual acuity (high-contrast logarithm of the minimum angle of resolution, LogMAR) was measured before- and 6 months after contact lens fitting. RESULTS: Large-diameter tetra-curve RGP lenses with a mean diameter of 11.85 (SD 0.16) mm were successfully used in LASIK patients with multifocal corneas. Mean best spectacle-corrected visual acuity was +0.3 LogMAR (SD 0.19; in Snellen equivalent, 20/40) and improved significantly with the contact lenses to +0.08 LogMAR (SD 0.11; in Snellen equivalent, 20/25, P=<0.01). During the follow-up period of 16.7 months, the average daily wearing time of the lenses was 12.5 h. Contact lenses with a standard geometry were not useful due to excessive movement and inadequate centration. CONCLUSIONS: Contact lenses with large diameters, in combination with selection of the back optic zone radius 0.2 mm peripheral of the refractive ablation zone, facilitate contact lens fitting to restore best-corrected visual acuity in LASIK patients with multifocal corneas.     

The relationship between long-term contact lens wear and corneal thickness.

PURPOSE: The purpose of this study is to assess the effects of long-term contact lens wear on corneal thickness and to compare differences based on rigid versus soft lens material. METHODS: This analysis included scanning slit topographic imaging (Orbscan, Bausch & Lomb, Rochester, NY) performed on 124 consecutive patients (248 eyes), who underwent comprehensive evaluations in consideration of refractive surgery by one surgeon. RESULTS: Sixty-two 62 patients (124 eyes) who had not previously worn contact lenses had a least-squares mean pachymetry of 546.4 microm +/-3.5 SE. Thirty-nine patients (78 eyes) who had previously worn soft contact lenses for an average of 16 years had a least-squares mean pachymetry of 543.2 microm +/-3.8 SE. Twenty-three patients (46 eyes) who had worn rigid contact lenses for an average of 19 years had a least-squares mean pachymetry of 509.4 microm +/-6.9 SE. Mean pachymetry differed significantly between eyes wearing rigid lenses versus no lenses (P<0.0001) and between eyes wearing rigid lenses versus soft lenses (P=0.0002). CONCLUSION: Long-term rigid contact lens wear is associated with a decrease in the average central-corneal thickness (CCT) by an average of 37 microm, in this group of otherwise healthy eyes, compared to no contact lens wear. Long-term soft contact lens wear did not appear to significantly change corneal thickness compared to no contact lens wear. Caution should be exercised when screening patients with a history of long-term rigid contact lens wear for possible excimer-laser photoablative correction.     

The challenges of the corneal graft

Indications for post-graft contact lens fitting are primarily therapeutic (healing/suture problems, leaking wound, graft dehiscence) or optical (high/irregular astigmatism, anisometropia, poor vision with spectacles, lens worn on fellow eye). In therapeutic application, 'soft' lenses of varying thickness and water content are generally indicated and for relatively short-term use. For optical management, rigid gas permeable corneal lenses are the mainstay although scleral lenses may be required in certain situations such as the highly irregular cornea where retention of smaller devices is problematic . There are numerous variations from the normal when considering contact lenses for the grafted cornea including physiological/metabolic (thickness variations, reduction in sensitivity, endothelial changes) and topographical (astigmatism, profile, position of graft). For example, in a patient with reduced corneal sensitivity where keratitis is a potential problem, optimising corneal oxygenation and reducing lens wear is recommended. Topographic peculiarities of the cornea can make the fitting of contact lenses a challenge – in extreme cases at best a compromise with the likelihood of limited wearing time and comfort, at worst potentially dangerous with the risk of corneal trauma and graft rejection. Liaison with the corneal surgeon in improving corneal topography by suture manipulation is essential.The practitioner must have access to a wide range of contact lens options and be mindful of lens dimensions and geometry and also material characteristics – this will give the optimal chance of success in dealing with the challenges posed.     

Irregular astigmatism after radial and astigmatic keratotomy

Eleven eyes of six patients, who had been referred for management of irregular astigmatism after receiving crossed incisions for myopic astigmatism, had moderate to marked irregular corneal astigmatism with marked flattening in the meridians of intersecting incisions. All six patients had a decrease in best-corrected visual acuity with spectacles after surgery. Visual acuity with spectacles was 20/40 in five of 11 eyes; with contact lenses it reached 20/40 in ten of 11 eyes. However, two patients could not wear the contact lenses because of lens decentration caused by the marked distortion in corneal topography. Even with contact lenses, visual acuity could only be improved to 20/25 or better in six of 11 eyes.     

Contact lens wear enhances adherence of Pseudomonas aeruginosa and binding of lectins to the cornea

Extended wear soft contact lenses are associated with an increased incidence of Pseudomonas aeruginosa keratitis. Because the first step in the pathogenesis of this disease is adherence of the microorganism to the corneal surface, we studied the effect of soft contact lens wear on the adherence of P. aeruginosa to the cornea. Rabbits were fitted for extended wear soft contact lenses in the left eye, and the right eye served as a control. Both eyes were then closed with a partial tarsorrhaphy. After 1-5 days of wear, the lenses were removed and the corneas of the left and right eye were removed. Differences in the number of adherent Pseudomonas and in lectin binding to lens-wearing corneas and non-lens-wearing corneas were determined. After 1, 3, and 5 days of soft contact lens wear, there was a significant increase in the number of P. aeruginosa adherent to the lens-wearing cornea. Three to eight times as many bacteria adhered to the lens-wearing eye as compared with the control eye (p less than 0.05). In addition, a soft contact lens placed in the eye followed by the immediate application of P. aeruginosa resulted in an eightfold increase in adherence of bacteria to the lens-wearing cornea (p less than 0.05). Lens wear also led to an increase in binding of concanavalin A (Con A), wheat germ agglutinin (WGA), and Maclura pomifera agglutinin (MPA) to surface epithelium covered by the lens. These corneal epithelial changes induced by extended wear soft contact lenses may provide some insight as to why soft contact lens wearers are predisposed to Pseudomonas keratitis.     

Treatment of ocular surface disorders and dry eyes with high gas-permeable scleral lenses.

Extreme corneal surface disorders and dry-eye conditions cannot be adequately treated with corneal contact lenses. For these cases a scleral lens with a diameter of between 21 and 25 mm could be prescribed. In this study, high oxygen-permeable scleral contact lenses were fitted onto 50 eyes, of which 32 had a deviant corneal topography and 18 had dry-eye syndrome. A significant improvement of visual acuity and good lens tolerance were found. The large lens successfully created a moist atmosphere in front of the cornea with dry-eye circumstances. No signs of oxygen shortage were recorded. In three dry eyes (16.7%) immediate failure in fitting was found, due to lens binding. The new scleral lens provides a physiological condition of the cornea, which allows a revival in the application of such lenses.     

Silicone-acrylate contact lenses for myopia control: 3-year results

One hundred myopic children between the ages of 8 and 13 years were fitted with Paraperm O2plus silicone-acrylate contact lenses. After 3 years of lens wear, the mean increase in myopia for the 56 subjects remaining in the study was 0.48 D (+/- 0.70) D as compared with 1.53 (+/- 0.81) D for a group of spectacle-wearing myopes matched for initial age and initial refractive error. The mean change in corneal refracting power for the contact lens wearers was a decrease (corneal flattening) of 0.37 (+/- 0.32) D. Assuming that little or no corneal change would have occurred in the absence of the contact lenses, we may conclude that corneal flattening (as measured by the keratometer) accounts for less than half of the effect of contact lenses in controlling myopia progression. A possible explanation for this disparity is that although the keratometer provides a valid measurement of corneal refracting power for a "normal" cornea, it fails to provide a valid measurement for a cornea that has been flattened by wearing a contact lens.