Diagnostic Contact Research Articles

Kontaktoptische Rehabilitation eines Auges mittels Sklerallinse nach einer Schwefelsäureverletzung

Purpose. The case report describes the optical rehabilitation of one eye by scleral lens fitting after a sulfuric acid related occupational accident. Material and Methods. Based on the corneal topography determined by Pentacam and other slit-lamp examinations relevant for contact lens fitting, a custom-made scleral lens was fitted on the basis of diagnostic contact lenses. The fit assessment of the diagnostic contact lens was performed by interpreting the fluorescein image as well as the centration behavior of the lens. Results. With the help of the fitted scleral lens a sufficient visual acuity of 20/25 in the right eye with a stereopsis in connection with a good subjective and objective acceptance could be achieved. This was associated with a professional reintegration. Conclusion. In many cases of complex ocular injuries, con- tact lens fitting with scleral lenses is the means of choice for optical rehabilitation of the affected eye. The fitting of scleral lenses requires an experienced practitioner both in the evaluation of the issues relevant for the contact lens design and in the evaluation of the anterior segment of the eye and here in particular the cornea. Keywords acid burn, corneal erosion, irregular cornea, mini scleral lens, scleral lens, sulfuric acid

Technical Report: Guidelines for Handling of Multipatient Contact Lenses in the Clinical Setting

Standardized guidelines that are clinically practical are needed to assist the prescriber in minimizing the risk of conveying infection through multiuse diagnostic contact lens use and reuse.Contact lens prescribers face the specter of transferring potential pathogens from one patient to another when reusing diagnostic (trial) contact lenses on multiple patients because infectious organisms have been recovered from worn contact lenses, although there is no evidence of transmission through this mechanism. These pathogens can be introduced into the system from one patient to another, or they may be introduced by clinician lens handling, storage, or both. These pathogens can cause acute or chronic systemic or ocular infection that can lead to significant morbidity (temporary or permanent) that includes vision loss.

Materials and Applications of Smart Diagnostic Contact Lens Systems.

Contact lenses were originally developed for the purpose of vision correction, but they have recently been used for various purposes. Because contact lenses are minimally invasive, they are used in diagnostic and drug delivery applications. In particular, interest in using contact lenses for the purpose of diagnosing diseases by fusing contact lenses with information technology (IT), nanotechnology (NT), and biotechnology (BT) is increasing. These contact lens-based platforms are getting more attention as Google and Novartis develop contact lenses for diabetes diagnosis. Therefore, this chapter introduces materials that can be used for contact lens materials and diagnostic contact lenses, and discusses future prospects.

RGP contact lens fitting in keratoconus using FITSCAN technology

To assess and compare the base curve (BC) of rigid gas permeable contact lens (RGP) that were calculated by FITSCAN using corneal topography (Orbscan IIz) and the diagnostic contact lens fitting method in keratoconus eyes. A prospective comparative study of 85 keratoconus eyes was conducted. Two masked observers calculated the contact lens parameters of RGP lens by diagnostic fitting method and using FITSCAN technology. The base curves calculated by two methods were compared using Wilcoxon signed rank test and agreement between two methods were analysed using Bland-Altman plot. Eighty-five eyes from 55 keratoconus patients were included in the study. The mean age was 17.63±2.78 (range: 12-23) years and among them 46 were males. The keratoconus was graded into mild, moderate and severe based on average keratometry values. The base curve calculated by the FITSCAN is on average 0.22mm higher than that calculated by diagnostic method (P value <0.0001, 95% CI=0.155, 0.245, Wilcoxon signed rank test) and the bias between the two methods was found to be 2.7% (Bland-Altman plot), indicating systematic bias between the two modalities. By single linear regression analysis, the base curve of RGP contact lens could calculated by using the formula, base curve (BC)=(FITSCAN calculated BC×0.86563)+0.78738. Our study showed that selecting the BC of the initial trial lens 0.22mm steeper than the FITSCAN calculated base curve, may help to reduce the complexity of RGP contact lens fitting in keratoconus.

Evaluation of anterior segment parameter changes using the Pentacam after uneventful phacoemulsification

This study set out to evaluate the influences of uneventful phacoemulsification on the anterior segment parameters obtained with the Pentacam rotating Scheimpflug camera and intraocular pressure (IOP). A total of 42 eyes of 34 patients (26 men, eight women) were evaluated preoperatively, and at 1, 3 and 6 months postoperatively with the Pentacam. Intraocular pressure was measured with the Goldmann applanation tonometer. The non-parametric paired t-test was used to compare preoperative and 1-, 3- and 6-month postoperative measurements of anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA) width, central corneal thickness (CCT), the central 3-, 5- and 7-mm corneal volume (CV), pupil size, and IOP. Pearson's correlation test was used to evaluate the relationships between IOP and ACD, ACV and ACA width. The differences between ACD, ACV, ACA and IOP values taken preoperatively and those taken postoperatively at 1, 3 and 6 months were statistically significant (p<0.05). The differences between CCT, central 3-, 5- and 7-mm CV, and pupil size measurements taken preoperatively and those taken postoperatively at 1, 3 and 6 months were not statistically significant (p>0.05). The decrease in IOP was not correlated with the changes in ACD, ACV and ACA (p>0.05). Uneventful phacoemulsification significantly reduced IOP, increased ACD and ACV, and widened the ACA. However, alterations in CV, CCT and pupil size values were not statistically significant. Alterations in ACD, ACV, ACA and IOP remain stable after the first month of surgery.

The Level Of Contact Lens Practice In Port Harcourt, Rivers State Of Nigeria.

The level of contact lens practice in Port Harcourt, Rivers State of Nigeria was investigated. The instruments of research were field work/direct observation, oral interviews of eye care practitioners, andthe assessment of clinical records of the contact lens patients from 2003 to 2006. Thirty five eye care practices were studied. The level of contact lens practice was assessed based on the number of clinics offering contact lens services, the number of eye care practitioners involved in contact lens services, the availability of essential instruments required for contact lens care, the percentage of patients prescribed contact lenses, and the annual contact lens patient flow in those clinics. Results showed that eleven(31.43%) of the eye care practices offer contact lens services, and seventeen (36.96%) eye care practitioners were involved in contact lens services. The level of contact lens practice based on the availability of retinoscope, trial case, and diagnostic contact lenses was very high (100.00%), and it was also high based on the availability of slit lamp biomicroscope 72.73%) and keratometer (63.64%). The percentage of patients corrected with contact lenses was very low (7.60%). The annual contact lens patient flowincreased from244 in 2003 to 345 in 2006 (a 41.40%increase) Enthusiasmon the part of the eye care practitioners incontact lens practice, andcreatingthe proper awarenesswouldboost the level of contact lens practice.

Reverse geometry contact lens fitting in corneal scar caused by perforating corneal injuries

Purpose To describe a reverse geometry rigid gas permeable (RGP) contact lens fitting in corneal scar caused by perforating corneal injuries with intraocular strange body. Methods A reverse geometry RGP lens, with large diameter, was empirically fitted in a 38-year-old male patient who had previous open globe injuries due to work accident in right eye. Corneal suture, vitrectomy and lens extraction were performed. Irregular corneal surface with corneal scar in line with the visual axis were found with low uncorrected visual acuity. Results Snellen visual acuity improved from counterfinger to 0.8 with high contact lens acceptance, 6–9 h per day of wear. Only three diagnostic contact lenses, in two visits, were necessary. Orbscan simulated fluorescein pattern was different to definitive fluorescein pattern. Conclusions Reverse geometry RGP contact lens, with large diameters, could be a good alternative in irregular corneal surface with corneal scar. Fluorescein pattern analysis could be the proper fitting technique. This fitting could involve less time and fewer visits. Computer-aided fitting was of limited value in these cases.

Cellular retention on diagnostic contact lenses: an evaluation of current cleaning protocol

To compare cellular contamination of diagnostic contact lenses after two different cleaning methods. Twenty-five used diagnostic contact lenses were cleaned by two different methods and the material retained on their contact surface examined for cells. Two diagnostic contact lenses were examined using electron microscopy and surface debris was subjected to x-ray photoelectron spectroscopy. Significantly more cells were present on used lenses compared with controls (P<0.001). There was no significant difference in total cell count between the lenses subjected to the two cleaning strategies but the lenses simply wiped clean retained marginally more nucleated cells than controls (P=0.039). Electron microscopy showed the majority of the debris on or close to the rim of the lens. X-ray photoelectron spectroscopy confirmed the presence of proteinaceous material. Regardless of cleaning method, significant cellular debris is retained on the surface of diagnostic contact lenses after use.

Bitoric Gas-Permeable Contact Lens Application in Pellucid Marginal Corneal Degeneration

To evaluate the authors' experience fitting patients with pellucid marginal corneal degeneration (PMCD) with bitoric gas-permeable contact lenses. The records of 11 patients with a confirmed diagnosis of PMCD were retrospectively reviewed. The numbers of diagnostic contact lenses at the first visit, office visits, and lenses ordered to complete the fitting; uncorrected, spectacle-corrected, and contact lens-corrected Snellen visual acuities; contact lens success or failure; and complications encountered were all assessed. These data were compared to historic data for patients with other corneal irregularities (keratoconus, penetrating keratoplasty, and refractive surgery). The mean number of diagnostic contact lenses used at the first visit was 1.09 +/- 0.302, and the number of lenses ordered to complete the fitting was 1.82 +/- 1.33. The number of visits during 4 months was 6.18 +/- 2.14. Uncorrected visual acuity (logMAR) was 0.957 +/- 0.398 (20/181 in Snellen); the best-corrected spectacle visual acuity (logMAR) was 0.231 +/- 0.309 (20/34 in Snellen); and the best contact lens-corrected visual acuity (logMAR) was 0.0424 +/- 0.06275 (20/22 in Snellen). Corrected vision in eyes with PMCD improved approximately two lines with bitoric gas-permeable contact lenses compared to that achieved with spectacles. Ten (91) of the patients met the criteria of contact lens success during the 4-month follow-up period. Bitoric gas-permeable contact lenses achieved a comfortable and visually successful fit in most eyes with PMCD. Patients with PMCD used the fewest contact lenses and had the fewest lens exchanges, but required more office visits than other groups of patients with various corneal irregularities.

Photonic crystal glucose-sensing material for noninvasive monitoring of glucose in tear fluid.

We recently developed a photonic crystal glucose-sensing material, which consists of a crystalline colloidal array embedded within a polymer network of a polyacrylamide-poly(ethylene glycol) hydrogel with pendent phenylboronic acid groups. The aim of the present work was to improve this approach for application to noninvasive or minimally invasive monitoring of glucose. We used new boronic acid derivatives such as 4-amino-3-fluorophenylboronic acid and 4-carboxy-3-fluorophenylboronic acid as the molecular recognition elements to achieve sensing at physiologic pH values. The improved photonic glucose-sensing material sensed glucose in the range of the 100 mumol/L concentrations found in tear fluid. The detection limits were approximately 1 mumol/L in synthetic tear fluid. The visually evident diffraction color shifted across the entire visible spectral region from red to blue over the physiologically relevant tear-fluid glucose concentrations. This sensing material is selective for glucose over galactose, mannose, and fructose. These new glucose sensors have properties appropriate for use in such glucose-sensing applications as ocular inserts or diagnostic contact lenses for patients with diabetes mellitus.

Results of phototherapeutic keratectomy in the management of flap striae after LASIK

Objective To evaluate the efficacy of phototherapeutic keratectomy (PTK) in reducing or resolving visually significant surface irregularities resulting from flap striae after LASIK. Design Retrospective, noncomparative case series. Participants Twenty-three eyes of 22 patients with flap striae after LASIK and reduced best-corrected visual acuity or visual symptoms that resolved with diagnostic contact lens fitting treated between January 2001 and April 2002 with at least 1 month of follow-up. The mean follow-up interval was 134 days (range, 30–354 days). Intervention Transepithelial PTK. Main outcome measures Uncorrected visual acuity (UCVA), resolution or reduction of preoperative symptoms, corneal haze, and best spectacle-corrected visual acuity (BSCVA). Results Mean BSCVA and UCVA improved significantly from 20/32 and 20/48 to 20/22 and 20/33 ( P<0.0001 and P = 0.027), respectively, after PTK. There was a significant mean hyperopic shift of 0.88 diopters (D; P = 0.002, range, −1.38 to +3.88 D). Fourteen eyes (61%) were clinically clear, 6 eyes (23%) had trace haze, and 3 eyes (16%) had 1+ haze at the last follow-up visit. Mean spherical equivalent refractive error before LASIK was −7.23 D (range, −2.88 to −13.55 D). Twenty-two of 23 eyes had significant qualitative resolution or reduction of preoperative visual symptoms. Conclusions In cases of visually significant LASIK flap striae, PTK is effective in improving best-corrected visual acuity and reducing visual symptoms. High myopia may be a risk factor for development of visually significant microstriae. Development of anterior stromal haze did not exceed 1+ density and was not correlated to either the number of laser pulses or the length of the follow-up period.

Feasibility of contact lens fitting on keratoconus patients with INTACS inserts

Purpose: To demonstrate the feasibility of contact lens fitting in keratoconus patients with INTACS inserts. Methods: A chart review was conducted of all patients with bilateral keratoconus who were treated with INTACS inserts on one eye and who were subsequently referred for contact lens fitting in a university based contact lens practice between April 2000 and April 2002. The study was a retrospective, non-comparative case series. The uncorrected and best spectacle corrected visual acuity (BSCVA) after INTACS implantation surgery, postoperative best contact lens-corrected visual acuity (BCLVA), number of diagnostic contact lenses used, number of contact lenses ordered within a 4-month follow-up period, contact lens complications encountered, final base curves, final lens powers, and final wearing times were determined. Results: Three keratoconic patients meeting the selection criteria were found through the chart review. Prior to surgery, all patients had uncorrected visual acuity (UCVA) of 2.0 logMAR (counting fingers). This improved to a mean of 0.81±0.25 logMAR (20/125-1) after surgery. Mean BSCVA also improved from 0.51±0.30 logMAR (20/60-2) to 0.30±0.16 logMAR (20/40). The mean postoperative best contact lens-corrected visual acuity was 0.02±0.10 logMAR (20/20-1). The number of diagnostic lenses ranged from 1 to 7. The numbers of contact lenses ordered during the 4-month follow up period ranged from 1 to 3. Two eyes were fitted with larger than usual lens designs made of rigid gas-permeable material and one eye was fitted with a toric soft lens. The final lens power ranged from +1.25 to −21.0 D with a mean spherical equivalent of −7.46±11.89 D. Final wearing times ranged from 2.5 to 12.0 h. Conclusion: Fitting contact lenses on keratoconus patients who have INTACS inserts is feasible and has a role in augmenting their vision.

Contact lens care in keratoconus

Purpose: To quantify the complexity involved in fitting contact lenses on the eyes of patients with keratoconus. Methods: The contact lens care of one randomly selected eye each of 38 keratoconus patients was retrospectively analyzed and compared to that of 38 gender and age matched controls. We evaluated the number of diagnostic contact lenses used to establish the initial contact lens order, number of ordered rigid gas permeable (RGP) contact lenses needed to complete the fit, number of office visits during the initial 4 months of care, best spectacle and RGP contact lenses corrected Log MAR visual acuities, complications encountered, and whether or not the patient was successful in contact lens wear. Results: Keratoconic eyes statistically used more diagnostic lenses, more ordered lenses, and more office visits than did normal eyes. Visual acuities improved from an average of 20/40 with spectacles to an average of 20/20 by use of RGP contact lenses in keratoconic eyes. Visions were corrected to 20/20 with both spectacles and contact lenses in control eyes. Sixty nine percent (69%) of keratoconic eyes and 95% of controls were successful in contact lens wear. Conclusions: Contact lens care of keratoconic eyes is more challenging than care of normal eyes because of the need for more diagnostic and ordered contact lenses and the use of more professional time. Keratoconic eyes may suffer more complications than normals during contact lens care, but this does not affect the success rates, and such patients benefit from enhanced visual acuity with RGP contact lenses compared to that achieved with spectacles.

Complexity of contact lens fitting after refractive surgery

PURPOSE: To quantify and describe the complexity of contact lens correction on corneas altered by refractive surgery. DESIGN: A case-control study involving postrefractive surgery patients and controls from one multidisciplinary contact lens practice. METHODS: The contact lens care of one randomly selected eye of 30 postrefractive surgery patients (15 postincisional and 15 postlamellar refractive surgery cases) was retrospectively analyzed and compared with that of 30 age-and-gender matched nonrefractive surgery controls. We quantified the complexity by the number of diagnostic lenses used to establish the initial lens order, the number of ordered lenses required to complete the fit, and the number of office visits during the first 4 months of lens care. Final contact lens optical powers, corrected visual acuities, complications, and lens success/failure were also studied. The nonparametric Mann-Whitney U test was used for statistical analysis. RESULTS: Postrefractive surgery eyes utilized statistically more diagnostic lenses ( P = .048), ordered lenses ( P = .008), and office visits ( P < .0001). There were no statistical differences in the number of office visits, number of diagnostic contact lenses used, and number of ordered contact lenses between the postincisional and postlamellar refractive surgery patients. Although final contact lens optical powers were not significantly different ( P = .06) between the two groups, contact lens corrected LogMAR acuities were statistically worse ( P = .013) in the postrefractive surgery eyes than in the control group. Contact lens failures occurred in four postrefractive surgery eyes, while no eyes in the control group failed to tolerate contact lenses. CONCLUSIONS: Corneas altered by either incisional or lamellar refractive surgery techniques are more challenging to fit with contact lenses than nonsurgically altered eyes, requiring more lenses and chair time, while resulting in slightly poorer contact lens corrected visions and more failures.

Complexity of contact lens fitting following penetrating keratoplasty

The aim of this study was to quantify the complexity of contact lens (CL) fitting following penetrating keratoplasty (PKP). The CL care of 40 eyes following PKP was analyzed retrospectively and compared to that of 40 age-matched and gender-matched controls. We evaluated the numbers of diagnostic and ordered rigid gas permeable (RGP) CLs, office visits for 6-month follow-up, best spectacle and RGP CL-corrected logMar visual acuities (VAs), and RGP CL success and complication rates. Post-PKP corneas required more diagnostic CLs ( p = 0.009), ordered CLs ( p = 0.0003), and office visits ( p = 0.001) than did controls. Corrected logMAR VAs post-PKP improved from 0.31 ± 0.31 (mean ± SD) with spectacles (20/41) to 0.076 ± 0.19 (20/24) with RGP CLs ( p < 0.0001). Controls logMAR spectacle and CL-corrected VAs were 0.0043 ± 0.12 (20/20) and −0.023 ± 0.058 (20/19), respectively (no significant difference, p = 0.096). Ninety percent of PKP eyes and 100% of controls were successful, and 30% of PKP and 12.5% controls had CL-related complications; these differences did not reach statistical significance. Post-PKP eyes require more diagnostic CLs, ordered CLs, and professional office visits. They also have greater improvement of VAs with RGPs than normals compared to spectacles. CL wear post-PKP does not statistically increase the rate of CL complications or alter the success rate of CL wear.

Linkage between research sponsorship and patented eye-care technology

Purpose. To examine the linkage between the funding of ophthalmologic and related biomedical research and the development of patented eye-care technology using data on patents granted and the scientific literature cited by those patents. Methods. The United States patents granted during the 20-year period from 1975 through 1994 were screened using patent office classifications and key words to identity all eye-care-related patents. Each patent's nonpatent references (references to literature other than previously granted patents) were examined, and those references to scientific papers then were reviewed to determine the authors' institutions and acknowledged funding sources. Results. Major findings include the following : (1) Eye technology innovation has grown steadily, with a threefold increase in number of patents granted from 224 in 1975 to 662 in 1994. (2) The cited scientific base that supports this technology has grown even more rapidly, with a sixfold increase in the average number of nonpatent references, from fewer than 0.5 per patent in 1975 to more than 3.0 in 1994 ; as a result, the total number of nonpatent references has increased by a factor of 20, from 100 in 1975 to 2000 in 1994. (3) The National Eye Institute is the leading single institution in providing support for this research : 31% of all eye-care patents with science references cite papers that contain at least one acknowledgment to National Eye Institute (NEI) support ; and when NEI is combined with the rest of the National Institutes of Health (NIH), 41% of the patents with science references are linked to NIH-funded research. (4) Patent science dependence, as measured by science references, is greatest for technologies related to medical treatment, surgical instruments, and intraocular lenses ; moderate for diagnostic instruments and contact lens ; and least for eyeglasses. Conclusions. The NIH and other sponsored vision research is of direct and increasing relevance to the growing number of US patented eye-care technologies.

The use of computerized videokeratography as an aid in fitting rigid gas permeable contact lenses

To assess the efficacy of computerized corneal topography in (1) fitting cosmetic rigid gas permeable contact lenses on normal corneas and (2) patients who have keratoconus. In study 1, 26 patients were fitted with cosmetic contact lenses. In 13 patients, the first rigid gas permeable lens was chosen on the basis of corneal topography using the EyeSys videokeratoscope and contact lens software version 2.11w. Thirteen control patients were fitted with rigid gas permeable contact lenses by means of diagnostic contact lenses. The number of parameter changes required in each group to reach the best fit were compared. In study 2, the records of 28 patients (41 eyes) with keratoconus who had been successfully fit with rigid gas permeable lenses were reviewed. Topographic analysis using the EyeSys videokeratoscope was conducted. The following 8 data points were analyzed: maximum dioptric curvature with respect to the central visual axis, the power at the visual axis (VK), the average keratometry readings within the 3-mm zone, the average flat K at 3-mm central and 5-mm paracentral regions, and the K reading at 1.5, 2.0, and 2.5 mm superior to the visual axis. Study 1: In 10 eyes (38%) fitted with cosmetic contact lenses utilizing corneal topography and the EyeSys contact lens program, the first lens chosen by the computer program was correct with no additional changes in lens parameters required. In the other 16 eyes, 21 parameter changes were required. In the control group, 14 eyes (53%) required no additional change in parameters from the original contact lens that was fitted using diagnostic lenses. In the other 12 eyes, 12 parameter changes were required. Study 2: In the keratoconus group, of the 9 measurements analyzed, the final base curve of patients' rigid gas permeable lenses was correlated most closely with the average flat corneal curvature at the 3-mm central zone. Study 1: In fitting cosmetic rigid gas permeable contact lenses, the videokeratoscope with the EyeSys software 2.11w contact lens program proved to be inferior to diagnostic lenses in selecting the final correct contact lens parameters. However, it may be useful in selecting an initial diagnostic lens with which to begin rigid gas permeable fitting. Study 2: In patients with irregular corneas such as keratoconus, corneal topography is helpful in determining the initial base curve of the contact lens. In patients with keratoconus, it appears to be the average flat corneal curvature at the 3.0-mm zone.

The effect of repeated disinfection of rigid gas permeable lens materials using 3% hydrogen peroxide

The disinfection of diagnostic contact lenses has been advocated for the control of many organisms, including HIV. One of the suggested methods, a hydrogen peroxide soak, has been shown to be appropriate for soft contact lenses, but extensive study of its effects on rigid gas permeable contact lenses has not been performed. This study investigated the effects of hydrogen peroxide soaks on the base curves of different rigid contact lens materials and lens thicknesses. PMMA, Paraperm 02, Paraperm EW, Fluoroperm 60 and Fluoroperm 92 lenses, made into contact lenses of 0.12, 0.16, or 0.20 mm center thickness were subjected to repeated ten minute soaks in 3% hydrogen peroxide. The results of this study indicated a statistically significant flattening of base curves when subjected to hydrogen peroxide. However, the amount of flattening was not clinically significant. Some of the lenses warped, with thinner lenses warping more often than thicker lenses.

Refracting the corneal graft

Patients who have undergone penetrating keratoplasty have unique postoperative refractive requirements. These include irregular astigmatism, high corneal toricity, and anisometropia. We present a stepwise clinical approach for accurate, efficient refraction of these patients, utilizing visual acuity measurement, retinoscopy, subjective refraction, keratometry, photokeratoscopy, and diagnostic rigid contact lens application.

Rigid Lens Base Curve Stability upon Hydrogen Peroxide Disinfection

Because of the possibility of transmitting communicable diseases, in particular the HIV virus, it has been recommended that all diagnostic contact lenses, including rigid lenses, be disinfected after each use. Hydrogen peroxide is a recommended disinfection agent, but its effect on rigid lens polymers is relatively unknown. We soaked 50 lenses of 5 different polymers in 3% hydrogen peroxide for 10 min and measured the base curves to determine if any changes occurred. Our results showed no statistically significant change in base curve for the lenses measured, but 22% of the lenses did exhibit a small amount of warpage (mean 0.0382 mm) of the base curve. We were not able to determine what caused these lenses, and not all the lenses, to warp. Under the conditions of this study, hydrogen peroxide does not appear to cause clinically significant parameter changes, but lenses should be checked for warpage before use.