角膜接触镜对眼屈光的影响

目的探讨角膜接触锐对眼屈光的影响。方法利用SEED自动电脑验光仪观察测定160名（320眼）近视患者戴软性及送气性硬性角膜接触镜一年之中角膜屈率半径、角膜激光度及眼球镜度的变化。结果戴软性角膜接触镜一年后，眼屈光状态与裁镜前比较，无显著性变化。戴透气性硬性角膜接触镜一年后，眼屈光状态与戴镜前比较，有显著性变化；角膜曲车半径值平均增加0．12mm（P＜0．0005），角膜散光度平均降低0．65D（P＜0．0005），眼球镜度近视降低0．49D（0．005＜P＜0．01）。结论由此推断透气性硬性角膜接触锐对近视、散光有一定防治效果。     

Corneal refraction: relative effects of each corneal component

The refractive power of the cornea may change after wearing contact lenses and as a result of disease or surgery. Each corneal component that contributes to the refractive power was analyzed and their relative significance was determined by comparing the refractive effects of a 10% change. In order of magnitude, the effect of a 10% change in each component was as follows: anterior corneal curvature (4.87 D), index of refraction (1.87 D), depth of anterior chamber (1.20 D), posterior corneal curvature (0.62 D) and corneal thickness (0.01 D). Refractive changes are the result of increases and decreases of each component and the total effect is the sum of the individual changes in each component.     

Intraocular lens calculations in patients with corneal scarring and irregular astigmatism

PURPOSE: To compare various methods of estimating corneal power for intraocular lens (IOL) calculation in patients with irregular corneal astigmatism. SETTING: Pepose Vision Institute, St. Louis, Missouri, USA.Case reports and review of the medical literature. RESULTS: Two patients with irregular corneal astigmatism had an IOL exchange after a "surprise" post-cataract-surgery refraction. In the first case, the patient had a post-cataract-surgery refraction of +5.50 -0.75 x 69 and in the second case, a refraction of -7.00 -1.00 x 180. The central corneal power before IOL exchange was assessed using manual keratometry, various computerized videokeratography curvature and power maps, and contact lens overrefraction. The total axial power map (Orbscan(R), Bausch & Lomb), total optical power map (Orbscan), and contact lens overrefraction method provided the most accurate estimates of central corneal power in these 2 patients. CONCLUSION: Computerized scanning-slit videokeratography, which analyzes the anterior and posterior surfaces of the cornea, and the contact lens overrefraction method gave good estimations of corneal power in patients with irregular corneal astigmatism. This type of analysis may improve the accuracy of IOL calculation in patients with corneal pathology and irregular astigmatism.     

Infectious keratitis in orthokeratology

Orthokeratology is a method of changing refraction in myopic patients by using rigid contact lenses to reduce the curvature of the cornea. This treatment was in use in the two cases of corneal ulcer described in this paper and appears to have contributed to the development of their disease. As with extended wear contact lenses, patients undergoing orthokeratology treatment are frequently advised to wear the orthokeratology lenses overnight increasing the risk of corneal ulceration and infection. Patients should be adequately warned of the associated risks and advised that any envisaged benefits of the procedure are temporary.     

Apical clearance rigid contact lenses induce corneal steepening.

PURPOSE: Anecdotal reports suggest that steeply fitted rigid contact lenses can induce corneal steepening and myopic shifts in refraction. This study investigated changes in corneal topography, corneal thickness, and refraction after short-term wear of apical clearance lenses. METHODS.: Ten young adults participated in the study in which apical clearance lenses (Conoid, Hydron Pty. Ltd., Frenchs Forest, NSW, Australia), fitted approximately 0.3 mm steeper than the flattest keratometric reading, were worn for 4 h. A polymethyl methacrylate (PMMA) lens was worn in one eye, and a Boston XO lens (Bausch & Lomb, Rochester, NY) was worn in the other. Lenses were nonfenestrated in the first trial, and a single midperipheral fenestration was incorporated for a second trial. Corneal topography was monitored using the EyeSys topographic analysis system (EyeSys Vision, Inc., Houston, TX); central corneal thickness was quantified using ultrasonic pachometry; and refraction and anterior ocular response were also monitored. RESULTS: Significant central corneal edema (8.2 +/- 2.2%) was demonstrated in the PMMA lens-wearing eye only. Fenestration did not reduce the edema response. We found significant corneal steepening over a 5- to 6-mm central zone, which was more pronounced in the PMMA lens-wearing eye and was modified by lens fenestration. The curvature changes altered central corneal shape from prolate (Q = -0.06 +/- 0.10) to oblate (Q = -0.26 +/- 0.31). A slight myopic shift in refraction (-0.38 +/- 0.60 D) was found with the PMMA lenses only. CONCLUSIONS.: Apical clearance lenses induce corneal steepening after short-term wear. Although corneal molding is implicated as the primary factor driving the shape change, corneal edema and postlens tear film pressures can modify this response.     

Ocular effects of hard gas-permeable-lens extended wear

Thirty-five myopic subjects were fitted with rigid gas-permeable lenses for 6 months of extended wear (EW). These lenses had an average oxygen transmissibility of 37 x 10(-9) (cm x ml x O2)/(s x ml x mm Hg). For six monthly morning visits subjects reported with one eye patched; corneal thickness, corneal curvature, refractive error, endothelial photomicroscopy, and slitlamp examinations were done on both eyes. The average morning corneal swelling was 5.9 +/- 3.3%. Corneal curvature showed 0.24 +/- 0.44 D flattening in the steep meridian and 0.20 D steepening in the flat meridian. Spectacle refraction and corrected visual acuity changes were small in the spherical and cylindrical components. Complications that were important clinically included 10% lens adherence syndrome, 20% superficial limbal keratitis, 6.5% epithelial microcysts, and some increase in endothelial polymegathism. No infections, red eye responses, or infiltrative keratitis were observed during the 6-month follow-up period. These results suggest that hard-lens EW is feasible and that lenses with this Dk/L value will meet oxygen requirements for many patients; however, some patients will require lenses of higher oxygen transmissibility to avoid undesirable complications.     

Changes in corneal curvature and subjective refraction of soft contact lens wearers.

Changes in corneal curvature and subjective refraction were found to occur in some wearers of N & N lathe-cut soft contact lenses. These changes appear to be the result of any one of a number of factors, including a relatively steep lens-cornea relationship, over-wearing of lenses and inadequate blinking habits.     

Changes in corneal curvature and refractive error upon refitting with flatter hydrophilic contact lenses.

Eight subjects who wore hydroxy-ethylmethacrylate (HEMA) contact lenses showed a steepening in corneal curvature and an increase of minus in their post-wear refraction after three months of wear. After one year or more of wear, with the previously noted changes still present, these patients were fitted with a flatter series lenses which they wore for three months. Significant results are noted in corneal curvature and post-wear refractive error.     

多焦软性角膜接触镜对周边屈光度及周边角膜屈光力的影响

目的：:观察配戴多焦软性角膜接触镜引起的周边屈光度及周边角膜屈光力的变化,研究二者之间的关系。方法：:自身对照研究。于2020年10月1─15日在温州医科大学收集成年近视受检者18例,在配戴单焦软性角膜接触镜（简称单焦软镜）和多焦软性角膜接触镜（简称多焦软镜）状态下分别采用红外自动验光仪和角膜地形图测量周边屈光度及周边...     

High gas permeability contact lens effects on the cornea: A comparative study

The aim of this paper is to compare the physiological responses, degree of comfort, vision quality, and acceptance of two types of high gas permeable contact lenses over a period of 3 months usage. Both contact lens materials were initially unknown to the authors; once the study was concluded, the manufacturing laboratories were consulted to determine the chemical composition of both materials. The lens types were fluoropolymer (Equalens) (lens A) and siloxane acrylate (lens B).Ocular responses of 30 patients to these lenses were studied. Fifteen of these patients were veteran contact lens wearers; the rest of the patients were new contact lens wearers. Each patient was fitted with lens A on one eye, and lens B, on the other eye. The degree of comfort experienced with both lens types as well as any changes in the corneal thickness, anterior corneal curvature, ocular refraction, and ocular physiology were noted.Lens A produced more discomfort than did lens B, due possibly to its wetting angle and edge design. No significant change in corneal curvature was found for either type of lens. Although lens B produced a greater increase in corneal thickness than did lens A, it is important to point out that, from the first week of contact lens usage through the 3 months of usage, corneal edema caused by both lenses was within the physiological limits of adaptation.     

后曲率实测法计算准分子激光角膜原位磨镶术后角膜屈光力的准确性

目的 探讨后曲率实测法计算准分子激光原位角膜磨镶术(LASIK)后角膜屈光力的准确性.方法 多种测量角膜屈光力方法的比较性研究.回顾性分析按后曲率实测法计算人工晶状体度数的LASIK术后人工晶状体植入眼8例(11只眼,10只为超声乳化白内障吸除及人工晶状体植入术,1只为人工晶状体置换术),计算术后稳定屈光状态与目标屈光度的差异,并据此推导实际角膜屈光力.分析其他角膜曲率法(自动曲率计、角膜地形图、球镜当量法、前曲率法、Pentacam提供的EKR曲率)计算人工晶状体度数可能造成的届光偏差.对LASIK术后6个月随访眼23例行详细屈光检查,根据术前角膜屈光力及手术前后眼屈光度改变推导术后理论角膜屈光力.分析后曲率实测法计算所得角膜屈光力与理论角膜屈光力的差异,并与其他角膜曲率法作比较.结果 采用后曲率实测法计算的人工晶状体植入眼术后平均裸眼视力0.8±0.2,与目标屈光度绝对偏差平均为(0.36±0.36)D(-0.63～+0.85 D),绝对偏差≤0.25 D、≤0.50 D、≤1.00 D的眼比例数分别为55%、73%和91%.其屈光偏差显著低于自动曲率计[(2.50±1.08)D]、角膜地形图[(1.90±0.88)D]、球镜当量法[(2.09±1.62)D](P<0.01)及前曲率法[(1.45±1.10)D](P<0.05)的预期结果;与EKR曲率法比较差异无统计学意义,但其偏差范围(-1.13～0.85 D)小于后者(-1.10～1.80 D).23例单纯LASIK术后眼的角膜屈光力测算同样显示后曲率实测法计算所得角膜屈光力与理论角膜屈光力偏离程度最小,绝对偏差为(0.67±0.45)D.结论 后曲率实测法计算LASIK术后角膜屈光力,可行性准确性俱佳.     

角膜塑形术控制近视发展的临床观察

目的观察角膜塑形术控制近视发展的临床效果。方法106例患者（212眼），平均等效球镜度（-3．85±1．43）D，按照角膜塑形术的验配程序给予配戴角膜塑形镜，采取过夜配戴形式,平均配戴3年后停戴角膜塑形镜1个月，测量屈光度、角膜曲率的变化，并与本院同样条件的渐进镜、框架镜屈光度、角膜曲率变化结果进行对比分析，评价角膜塑形术控制近视进展的作用。结果戴镜3年后停戴1个月时，等效球镜度为（-4．34±1．43）D，等效屈光度增幅（0．49±0．68）D，平均每年增幅0．15D，与戴镜前比较差异有统计学意义（t=9．75，P〈0．01）。戴镜3年后停戴1个月，平均角膜曲率为（43.30±1．42）D，较配戴前扁平（0．09±0．34）D，但两者比较差异无统计学意义（t=1．95,P〉0．05）。结论配戴角膜塑形镜后每年近视加深约0．15D，角膜塑形术在一定程度上可控制近视加深，但其具体作用机制尚需进一步研究。     

Evaluation of corneal changes induced by orthokeratological contact lenses

The authors have studied a response of the cornea (a change in its thickness, shape, refraction, and endothelium) to nocturnal orthokeratotology - a procedure for temporarily diminishing or removing myopic refraction, which is accomplished by wearing rigid gas-permeability contact lenses that change corneal shape and optical strength. The orthokeratological technique has been ascertained to be an effective modality for the temporary reversible reduction of mild and moderate myopic refraction. In some cases, the refractive effect of the technique may run up to 7.5 diopters. The mechanism of action of orthokeratological contact lenses is to form an epithelial diverging biolens onto the corneal surface by transferring epithelial cells from the center to the paracentral parts. Wearing of orthokeratological contact lenses does not cause clinically significant symptoms of damages to the epithelium and corneal stroma or lead to altered endothelial cell density.     

Overnight orthokeratology.

PURPOSE: Orthokeratology is defined as the temporary reduction in myopia by the programmed application of rigid gas-permeable contact lenses. New reverse geometry contact lens designs and materials have led to a renewed interest in this field. The purpose of this study is to assess visual, refractive, topographic, and corneal thickness changes in subjects undergoing overnight orthokeratology. METHODS: Ten myopic subjects (mean age, 25.9+/-3.9 years) were recruited for a 60-day trial of overnight orthokeratology using reverse geometry rigid contact lenses. After commencing lens wear, subjects were examined on days 1, 7, 14, 30, and 60 at several times throughout the day. High- and low-contrast logarithm of the minimum angle of resolution (logMAR) visual acuity, monocular subjective refraction, autorefraction, autokeratometry, corneal topography, corneal thickness, and slit lamp examinations were performed at each session. RESULTS: Eight subjects completed the study. Both high- and low-contrast uncorrected visual acuity improved significantly by day 7. The mean change in uncorrected high contrast visual acuity at day 60 was -0.55+/-0.20 logMAR (mean at day 60, -0.03+/-0.16; Snellen equivalent, 20/19). The mean change in uncorrected low-contrast visual acuity at day 60 was -0.48+/-0.26 logMAR (mean at day 60, +0.22+/-0.23; Snellen equivalent, 20/33). The mean subjective refraction and autorefraction were significantly reduced from baseline at day 60 (mean change in subjective refraction, +1.83+/-1.23 D; mean change in autorefraction, +0.64+/-0.52 D). Corneal topography showed significant central flattening (mean change in apical radius, +0.20+/-0.9 mm; mean change in shape factor, -0.11+/-0.18 at day 60). The central cornea also showed significant thinning (mean change, -12+/-11 microm at day 60). All visual, refractive, and topographic outcomes were sustained over the course of an 8-h day. CONCLUSIONS: Overnight orthokeratology is an effective means of temporarily reducing myopia. The possible mechanism of corneal remodeling through central corneal thinning is discussed.     

Contact lens wear after photorefractive keratectomy: comparison between rigid gas permeable and soft contact lenses.

PURPOSE: To determine if rigid gas permeable (RGP) or soft contact lenses can be successfully worn after photorefractive keratectomy (PRK) to correct residual refractive errors. METHODS: Patients with residual stable ametropia after PRK were fit with RGP or soft lenses. Manifest refraction, corneal topography, and keratometry were performed, and post-PRK corneal haze was graded during the study visits. Contact lens fit characteristics and comfort were assessed. Lens centration, visual quality, and ocular surface status were graded, and visual acuity with contact lenses was charted. RESULTS: Eighteen patients were recruited for RGP lens fitting. The mean refractive error post-PRK was +0.80 D +/- 2.03 (range: -3.50 to+3.00 D). The mean contact lens power was -3.90 D +/- 2.03 (range: 0 to -7.00 D), and the mean contact lens base curve was 7.88 mm +/-0.16. A significant positive tear film at the site of the central ablation was noted, contributing to excessive minus lens power in all cases. Despite mild to moderate lens instability and de-centration, 14 patients reported excellent visual quality with the lenses, and pre-PRK best-corrected acuity was achieved in all patients. Twenty-five percent (4 of 16) of the patients were able to wear the lenses all day. Eleven patients were recruited for soft contact lens fitting-five from the RGP trial. The mean refractive error post-PRK was -0.64 D +/- 2.01 (range: -3.50 to +1.75D). The mean contact lens power was -0.60 D +/- 2.07 (range: -3.75 to +2.5 D), and the mean contact lens base curve was 8.33 mm +/- 0.42. Eight patients were corrected with lenses to their pre-PRK best-corrected acuity, and nine patients reported excellent visual quality with the lenses. All the patients had excellent lens centration. Thirty-six percent (four of 11) of patients were wearing the lenses all day. CONCLUSIONS: Fitting RGP lenses after PRK results in good visual acuity but may be associated with mild to moderate lens instability and decentration. Soft contact lens fitting also results in good visual acuity. Soft lenses were better tolerated by the subjects in our study because of improved lens centration and stability.     

Changes in corneal structure with continuous wear of high-Dk soft contact lenses: a pilot study.

PURPOSE: Despite numerous studies that have considered the effects of extended wear of high-Dk soft contact lenses on ocular physiology, little attention has been paid to the impact of such lenses on central or peripheral corneal thickness and curvature. The present study aims to report the time course of changes in corneal thickness and curvature that accompanies the 30-night continuous wear of new silicone hydrogel soft contact lenses in a neophyte population in a longitudinal study. METHODS: Six subjects wore high-Dk lotrafilcon (Dk = 140) on a 30-night replacement schedule for 12 months. Only measurements from the right eye were considered for analysis. Topographical measurements of corneal thickness and curvature were taken. The same parameters were monitored for an additional period of 3 months after lens removal. RESULTS: An almost homogenous increase in corneal radius of curvature was detected for all the locations studied, being statistically significant for the 4-mm cord diameter area. This effect was associated with a progressive thinning effect for the central cornea, whereas midperipheral and peripheral areas did not display such a thinning effect during continuous wear. These effects were still evident for the central cornea 3 months after contact lens wear discontinuation. CONCLUSIONS: Continuous wear of high-Dk silicone hydrogel contact lenses is associated with clinically appreciable changes in topographical corneal curvature, whereas only a reduction in corneal thickness is appreciated in the central area. This effect seems to be a result of mechanical pressure induced by these hybrid hyperpermeable materials, characterized by a higher modulus of elasticity. The small sample size compromises the conclusions addressed from this study, and further work will be necessary to confirm the present results.     

Refractive and biometric changes with silicone hydrogel contact lenses.

PURPOSE: This study reports data from an 18-month longitudinal study of neophyte contact lens wearers and compares changes in ocular refraction and biometry induced by daily wear and continuous wear of two different silicone hydrogel (SiH) materials. METHODS: Forty-five subjects were enrolled in the study and randomly assigned to wear one of the two silicone hydrogel materials: Lotrafilcon A or Balafilcon A lenses on either a daily or continuous wear basis. Measurements of objective refraction, axial length, anterior chamber depth, corneal curvature, and the rate of peripheral corneal flattening were performed before and 1, 3, 6, 12, and 18 months after initial fitting. RESULTS: Mean spherical equivalent refractive error increased in the myopic direction in all contact lens groups across time (p < 0.001). Axial length was the main biometric contributor to the development of myopia. After 18 months of lens wear, subjects in the Lotrafilcon A group showed the greater mean increase in myopia (i.e., -0.50 D). CONCLUSIONS: The results of this study show that increases in myopia, similar if not higher than those found to occur normally in young adult noncontact lens wearers, still occur with silicone hydrogel contact lens wear. The main biometric contributor to the progression of myopia was an increase in axial length. Differences between our results and those of previous studies with silicone hydrogel contact lenses could be attributed to the differing populations used in which both age and occupation may have played a role.     

Comparison of changes in manifest refraction and corneal power after photorefractive keratectomy

PURPOSE: To determine which corneal curvature values most closely correlate to change in manifest refraction after excimer laser photorefractive keratectomy. METHODS: In a prospective study at the Cullen Eye Institute, excimer laser photorefractive keratectomy was performed on 27 eyes of 27 patients (mean age, 38.07+/-6.65 years). Preoperative refractive errors ranged from -2.25 diopters to -8.75 diopters (mean, -5.74+/-2.09 diopters). Preoperatively and 1 month postoperatively, we determined the spherical equivalent of the subjective manifest refraction (corrected for a 12-mm vertex distance) and measured corneal power using standard keratometry (Bausch & Lomb Keratometer; Rochester, New York) and computerized videokeratography (EyeSys Corneal Analysis System; Premier Laser Systems Inc, Houston, Texas). We collected 15 corneal values: standard keratometry and 14 computerized videokeratography values calculated using the axial, instantaneous, and refractive formulas. All calculations were performed with 1.3375 and 1.376 for the refractive index of the cornea. For each of the corneal values, we subtracted the change in corneal power from the change in manifest refraction and calculated for this difference the means, SDs, correlations, and regressions. RESULTS: Mean differences between change in refraction and change in corneal power were lower when for a refractive index of 1.376 than for 1.3375, were lowest for the most central measurement points, and displayed a high SD. A value of 1.408 for the refractive index would be required to optimize the correlation between change in manifest refraction and effective refractive power of the central 3 mm of the cornea. CONCLUSIONS: For individual patients who have undergone photorefractive keratectomy, changes in corneal values determined by computerized videokeratography or by standard keratometry do not reliably predict change in manifest refraction.     

胰岛素对幼年豚鼠及远视性光学离焦幼年豚鼠眼球正视化发育的影响

目的研究胰岛素对幼年豚鼠及远视性光学离焦幼年豚鼠眼球正视化发育的影响。方法实验研究。将22只3周龄体重100 g左右豚鼠随机分为2组：负透镜组（-4.00 D、12只、双眼戴镜）和不戴镜组（10只）。实验开始后第1天、第6天,右眼玻璃体腔注射胰岛素12.5 μl（0.5 U）、左眼玻璃体腔注射等量生理盐水。于实验开始时和实验开始2周后分别检测其屈光度、角膜曲率半径、前房深度、晶状体厚度、玻璃体腔长度以及眼轴长度变化。结果用析因分析及配对样本t检验进行分析。结果实验开始时2组基线资料差异无统计学意义;实验2周后,负透镜组右、左眼屈光度变化值分别为（-3.56±1.69）D和（-3.69±1.08）D,角膜曲率半径变化值分别为（0.04±0.04）mm和（0.06±0.04）mm,眼轴变化值分别为（0.22±0.11）mm和（0.20±0.16）mm;不戴镜组右、左眼屈光度变化值分别为（-2.24±1.07）D和（-2.05±0.77）D,角膜曲率半径变化值分别为（0.15±0.05）mm和（0.13±0.05）mm,眼轴变化值分别为（0.23±0.13）mm和（0.19±0.08）mm。2组屈光度均向远视度数减少的方向发展,相对于不戴镜组,负透镜组形成明显的相对性近视,且差异具有统计学意义（F=15.99,P<0.01）;2组角膜曲率半径均增大,相对于不戴镜组,负透镜组增长幅度略低,角膜屈光力相对较大,且差异具有统计学意义（F=37.38,P<0.01）。组内左右眼各参数差异无统计学意义,即无论有无远视性光学离焦的处理,胰岛素注射眼和生理盐水注射眼各参数差异均无统计学意义。结论远视性光学离焦使幼年豚鼠形成相对性近视;胰岛素对幼年豚鼠及远视性光学离焦幼年豚鼠眼球正视化发育无影响。     

Changes in corneal curvature after wearing the orthokeratology lens

IntroductionThe orthokeratology lens (OK lens) is designed to reshape the cornea and correct refraction error. Owing to the convenience of ceasing the use of glasses during the day, the use of the OK lens is increasing in myopic children. In this study, changes in corneal curvature and astigmatism after wearing the OK lens were analyzed.MethodsThis retrospective cohort study included 65 children (130 eyes) who underwent full and regular examinations. None of the participants had any ocular disease other than myopia and astigmatism. The OK lenses used in this study were four-zone, reverse-geometry lenses. The corneal curvature of each patient was checked annually after the patients discontinued daily wearing of the OK lens for 10 days. Student t test and repeated measures analysis of variance (ANOVA) analyses were performed to compare the results.ResultsThe radius of corneal curvature showed a progressive annual increase with significant differences, both in the steepest and flattest radius of the corneal curvature (p < 0.001 and p = 0.001, respectively). The mean radius of the steepest and flattest corneal curvature increased significantly from baseline to the following years consecutively (all p < 0.001). Nevertheless, astigmatism did not change significantly in any of the tests.ConclusionCorneal curvature changed as the patients grew older. There was a statistically significant increase in the radius of the corneal curvature in the myopic children studied. For correct fit of OK lenses, the radius of the corneal curvature should be regularly checked prior to dispensing a new set of lenses.