Correlation analysis and multiple regression formulas of refractive errors and ocular components

The multiple regression formulas and correlation of ocular components with refractive errors are presented by Gaussian optics. The refractive error changing rate for the cornea and lens power, the axial length, anterior chamber depth (ACD) and vitreous chamber depth (VCD) are calculated, including nonlinear terms for more accurate rate functions than the linear theory. Our theory, consistent with the empirical data, shows that the Pearson correlation coefficients for spherical equivalent (SE) and ocular components are highest for SE with axial length, ACD and VCD and weakest for corneal power, lens power and lens thickness. Moreover, our regression formulas show the asymmetric feature of the correlation that the axial length, ACD and VCD are more strongly correlated (with higher negative regression constants) with refractive errors in eyes with hyperopia than in eyes with myopia, particularly for severe hyperopia.     

巩膜环扎术后眼球的屈光改变及生物测量

目的 :观察环扎术后眼球屈光状态的改变。方法 :前瞻性研究了 35例孔源性视网膜脱离巩膜环扎术患者。分别在术前 1天、术后 1 0天测量屈光度、前房深度、晶状体厚度、眼轴长度、角膜水平及垂直曲率。结果 :巩膜环扎术后屈光度向负值偏移 (- 0 75± - 0 2 5)D。角膜水平曲率变大、前房变浅 (P <0 0 5)。而角膜垂直曲率和晶状体厚度变化不明显 (P >0 0 5)。控制环扎带平均 65mm长时 ,眼内嵴高 3～ 6D ,眼轴长度平均增加 1 36mm。结论 :巩膜环扎术后眼屈光度向负值偏移。眼轴长度的增加是偏移的主要原因     

The change in ocular refractive components after cycloplegia in children

PURPOSE: To study the change in ocular refractive components after cycloplegia in children. METHODS: Anterior chamber depth, lens thickness, vitreous chamber length, and ocular axial length were measured in 135 Chinese children (270 eyes) before and after cycloplegia. The corneal curvatures of 136 selected eyes were studied before and after cycloplegia with a computerized video keratoscope. RESULTS: Anterior chamber depth increased (P <.001) while both lens thickness and vitreous chamber length decreased (P <.001) significantly after cycloplegia regardless of the refractive state. However, axial length increased in hyperopic eyes (P =.027) but decreased in myopic eyes (P =.008) after cycloplegia. Mean corneal power of zones 3 mm (MD3, P =.009) and keratometer K1 readings increased (P =.025) in hyperopic eyes, while MD3 (P =.033), K1 (P =.039) and K2 (P =.003) readings decreased in myopic eyes significantly after cycloplegia. Similarly, mean corneal power of zones 5 mm and 7 mm in myopic eyes decreased dramatically (P 相似文献   

近视眼角膜厚度及相关因素分析

目的:探讨青年近视患者角膜厚度分布特点及其相关因素。方法:选取青年近视患者200例(400眼),按屈光度不同分为4组,应用OrbscanⅡ眼前节分析系统对患者的角膜中央点、最薄点、后表面平均屈光度最大点,以及距中心1.5,2.5mm上方、下方、颞上、颞下、鼻上、鼻下、颞侧、鼻侧部位的角膜厚度及相应的前房深度、后表面高度、后表面曲率、前表面曲率进行测量。结果:角膜厚度呈中心薄周边厚分布,最薄点位于距中心2.5mm范围内(86%),角膜颞下部位(50%)。后表面平均屈光度最大点、最薄点、中央点三个点的角膜厚度在不同近视组中差异无统计学意义(P>0.05)。不同部位的角膜厚度与其他因素相关分析。结果:中央点:角膜厚度与前房深度、前表面曲率负相关(r=-0.181,-0.103,P=0.000,0.039)。最薄点:角膜厚度与相应的前房深度、后表面高度、后表面曲率绝对值、前表面曲率呈负相关(r=-0.167,-0.113,-0.104,-0.109;P=0.001,0.024,0.038,0.03)。后表面屈光度最大点:角膜厚度与相应的前房深度、后表面高度、后表面曲率绝对值、前表面曲率呈负相关(r=-0.342,-0.138,-0.189,-0.159;P=0.000,0.000,0.000,0.001)。结论:角膜厚度最薄点多位于旁中心2.5mm颞下部位;角膜厚度与近视程度无关;角膜厚度与相应的前房深度、后表面高度、后表面曲率绝对值、前表面曲率为负相关关系。     

On the ocular refractive components: the Reykjavik Eye Study

PURPOSE: To study the correlation between ocular refraction and the refractive components (corneal power, lens power and axial length) in a population-based sample of normal subjects. METHODS: We analysed the refractive and biometric findings for 723 right eyes (325 males and 398 females) comprising a population-based random sample of citizens 55 years and older participating in the Reykjavik Eye Study. Measurements of refraction, corneal curvature (by keratometry), anterior chamber depth, lens thickness and axial length (all by ultrasound biometry) were used to calculate crystalline lens power. The correlation and regression between refraction and ocular refractive components (corneal power, anterior chamber depth, lens power and axial length) were studied by distributional statistical methods. RESULTS: Refraction (spherical equivalent) showed a significant negative correlation with axial length (r = -0.59, P < 0.0001), lens power (r = -0.26, P < 0.0001) and corneal power (r = -0.16, P < 0.0001). There were significant negative correlations between axial length and corneal power (r = -0.44, P < 0.0001) and between axial length and lens power (r = -0.44, P < 0.0001). Based on multiple linear regression analysis, refraction could be correlated with corneal power, lens power and axial length in combination with a correlation coefficient of 0.98 (P < 0.0001). CONCLUSION: This study confirms that ocular refraction is statistically significantly correlated with not only axial length but also lens power and (to a lesser extent) corneal power. The variation and correlations of crystalline lens power were considerable -- possibly indicating this component's modulatory effect on ocular refraction during growth. We conclude the refractive error of the eye to be a multifactorial condition involving a complex interplay between the cornea, the lens and the length of the eye.     

Changes in keratometric corneal power and refractive error after laser thermal keratoplasty

PURPOSE: To evaluate the effect of laser thermal keratoplasty (LTK) on corneal power and refractive error to develop a logical approach to calculating accurate intraocular lens (IOL) power for cataract surgery. SETTING: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. METHODS: Laser thermal keratoplasty was performed in 27 eyes of 23 patients. Preoperatively and postoperatively, the refractive error was measured and the corneal power obtained by manual keratometry and topography. The changes in keratometric corneal power and refractive error after LTK were compared. RESULTS: The mean age of the 15 women and 8 men was 45.0 years +/- 4.6 (SD) (range 43 to 61 years). The mean preoperative refractive error was +1.43 +/- 0.97 diopters (D) (range 0 to +3.63 D) at the spectacle plane and +1.46 +/- 1.01 D (range 0 to +3.79 D) at the corneal plane. The mean postoperative refractive error was -0.44 +/- 1.07 D (range -2.24 to +2.18 D) at the spectacle plane and -0.44 +/- 1.08 D (range -2.18 to +2.23 D) at the corneal plane. After surgery, corneal powers measured by manual keratometry were significantly smaller than those measured by topography (P<.001) and refractive error changes were significantly smaller than keratometric changes (P<.001). CONCLUSIONS: After LTK, corneal power measured by manual keratometry was smaller than that measured by corneal topography and changes in corneal power measured by conventional keratometric instruments were greater than changes in refractive error. This difference should be considered in calculating IOL power in post-LTK eyes to prevent undesirable hyperopia after cataract surgery.     

Ocular structure changes during vacuum by the Hansatome microkeratome suction ring

PURPOSE: To evaluate whether the vacuum of a microkeratome suction ring induces ocular structure changes. METHODS: A prospective case series using A-scan ultrasonography to measure anterior chamber depth, lens thickness, vitreous body, and axial length was performed. Measurements before and during application of a Hansatome microkeratome suction ring were performed on 69 eyes of 39 consecutive patients scheduled to undergo a first-time LASIK procedure with mechanical creation of a corneal flap. RESULTS: Mean patient age was 43 +/- 12.1 years. Of the 69 eyes, 63 (91.3%) had refractive myopia with a mean spherical equivalent refraction of -2.93 +/- 1.56 diopters (D) and 6 (8.7%) had refractive hyperopia with a mean spherical equivalent refraction of 1.37 +/- 0.31 D. Overall, the mean spherical equivalent refraction of all eyes was -2.56 +/- 1.94 D. Ultrasound measurements during suction revealed a decrease in the anterior chamber depth of -0.06 +/- 0.36 mm (P < .05) and lens thickness by -0.14 +/- 0.45 mm (P < .05) whereas the vitreous body increased 0.25 +/- 0.36 mm (P < .05). Although insignificant, a trend toward increasing axial length was noted. No measurements changed over time during the application of vacuum. CONCLUSIONS: Vacuum by a microkeratome suction ring induced a compression of the anterior chamber and lens with commensurate expansion of the vitreous body. The assessment of vacuum effects during LASIK suggests that measurements of intraocular compartments are more informative than axial length.     

Epithelial thickness in the normal cornea: three-dimensional display with Artemis very high-frequency digital ultrasound

PURPOSE: To characterize the in vivo epithelial thickness profile in a population of normal eyes. METHODS: An epithelial thickness profile was measured by Artemis 1 (ArcScan Inc) very high-frequency (VHF) digital ultrasound scanning across the central 10-mm diameter of the cornea of 110 eyes of 56 patients who presented for refractive surgery assessment. The average, standard deviation, minimum, maximum, and range of epithelial thickness were calculated for each point in the 10x10-mm Cartesian matrix and plotted. Differences between the epithelial thickness at the corneal vertex and peripheral locations at the 3-mm radius were calculated. The location of the thinnest epithelium was found for each eye and averaged. Correlations of corneal vertex epithelial thickness with age, spherical equivalent refraction, and average keratometry were calculated. RESULTS: The mean epithelial thickness at the corneal vertex was 53.4+/-4.6 microm, with no statistically significant difference between right and left eyes, and no significant differences in age, spherical equivalent refraction, or keratometry. The average epithelial thickness map showed that the corneal epithelium was thicker inferiorly than superiorly (5.9 microm at the 3-mm radius, P<.001) and thicker nasally than temporally (1.3 microm at the 3-mm radius, P<.001). The location of the thinnest epithelium was displaced on average 0.33 mm temporally and 0.90 mm superiorly with reference to the corneal vertex. CONCLUSIONS: Three-dimensional thickness mapping of the corneal epithelium demonstrated that the epithelial thickness is not evenly distributed across the cornea; the epithelium was significantly thicker inferiorly than superiorly and significantly thicker nasally than temporally with a larger inferosuperior difference than nasotemporal difference.     

Pilot study on the influence of corneal biomechanical properties over the short term in response to corneal refractive therapy for myopia

PURPOSE: To study the short-term corneal response to corneal refractive therapy for myopia and correlate it with corneal biomechanical properties as measured with the ocular response analyzer. METHODS: Eight eyes from 8 young subjects were fitted with a reverse geometry contact lens, attempting a myopic correction of -4.00 D. Corneal resistance factor and corneal hysteresis (CH) were measured before contact lens fitting with the ocular response analyzer. These parameters were correlated with the degree of change in apical curvature, simulated keratometry, and central corneal thickness after 3 hours of contact lens wear (effect) and 3 hours after lens removal (recovery). RESULTS: There was a trend toward a faster effect and faster recovery of the orthokeratologic effect for corneas with less resistance in terms of biomechanical properties. Corneal resistance factor did not correlate significantly, however, with any of the topographic and pachymetric parameters. Conversely, CH was significantly correlated with changes in steep keratometry (0.758; P = 0.029) and central corneal thickness (0.755; P = 0.030) during lens wear and with changes in steep keratometry (-0.835; P = 0.010) during recovery. Overall, higher values of CH meant slower effect and recovery of the orthokeratologic effect. CONCLUSIONS: Short-term response of human cornea to corneal refractive therapy is correlated with the biomechanical properties of the cornea. Of the different theories supporting such involvement of corneal response to reverse geometry contact lenses, the most likely one seems to be the one assuming a faster response and faster recovery for corneas with lower resistance. Larger sample studies would be needed to clarify the involvement of corneal biomechanical properties on corneal response to orthokeratology.     

Relationship between anterior chamber depth, refractive state, corneal diameter, and axial length

PURPOSE: Phakic intraocular lenses are being used increasingly to correct refractive errors. We studied the relationship between anterior chamber depth, refractive state of the eye, spherical equivalent refraction, axial length of the globe, corneal diameter, and keratometry. METHODS: Two hundred eleven eyes of 211 patients were enrolled. All eyes underwent the same protocol with a complete ocular examination that included slit-lamp microscopy, intraocular pressure, objective and subjective refraction, calculation of the spherical equivalent refraction, corneal pachymetry, anterior chamber depth, axial length of the globe, and keratometry. All results were analyzed statistically using SPSS statistics software. Correlations between different parameters were studied using the Pearson correlation test. RESULTS: The anterior chamber depth was found to correlate significantly with both the average corneal diameter and the axial length of the globe (0.744, 0.531, P < .01) and was also found to correlate through an inverse relation with both age and spherical equivalent refraction (-0.391, -0.623, P < .01). Corneal thickness and keratometric power did not correlate with the anterior chamber depth. CONCLUSION: Most parameters (axial length, corneal diameter, spherical equivalent refraction, patient age) affected anterior chamber depth and should be considered carefully when planning refractive procedures that employ phakic intraocular lenses.     

Transient hyperopia with lens swelling at initial therapy in diabetes.

The clinical courses of 10 eyes of five diabetic patients who exhibited bilateral transient hyperopia (maximum: 1:1-4.9 dioptres, spherical equivalent) after initiation of strict control of diabetes with or without insulin are reported. The hyperopia occurred within a few days after abrupt decrease in plasma glucose, progressed to maximum at days 7-14, and regressed gradually over 1 month thereafter. Transient cycloplegia had no effect on refractive error. During hyperopia, there were no significant changes in axial length or corneal curvature. However, thickened lens, decreased anterior chamber depth, and transient cataract were observed to significant degrees. It is suggested that the transient hyperopia, with lens swelling and opacity, was caused by decreased lens refractive index following water influx.     

基于儿童正视眼的眼光学模型构建

目的根据正视儿童眼部参数,构建正视儿童的眼光学模型。方法实验研究。基于“安阳儿童眼病研究”数据,包括角膜曲率半径、角膜厚度、前房深度、晶状体厚度、屈光度和眼轴长度,取右眼数据,应用ZEMAX光学设计软件构建一个符合我国儿童眼球特点的正视眼光学模型。正态性检验采用单样本K-S分析。结果共纳入正视儿童332名,年龄（7.1±0.4）岁,等效球镜度（SE）为（0.11±0.24）D。构建的正视儿童眼光学模型的光学参数为：角膜前表面曲率半径7.78 mm,非球面系数-0.18;后表面曲率半径6.4 mm,非球面系数-0.60;厚度0.54 mm,折射率1.376。前房深度3.00 mm,房水折射率1.336。晶状体前表面曲率半径12.4 mm,非球面系数-0.94;后表面曲率半径-8.1 mm,非球面系数0.96;厚度3.55 mm,折射率为梯度渐变折射率。玻璃体厚度15.94 mm,折射率1.336。视网膜曲率半径-12.3 mm,眼轴长度23.03 mm,总屈光力62.55 D。结论本研究构建了一个符合儿童正视眼特点的眼光学模型,该模型眼的总屈光力为62.55 D,眼轴长度23.03 mm,该模型可作为儿童眼正视化和近视研究的参考工具。     

A comparison of laser photocoagulation with cryotherapy for threshold retinopathy of prematurity at 10 years: part 2. Refractive outcome

OBJECTIVE: To compare the refractive outcome of eyes treated with cryotherapy for threshold retinopathy of prematurity (ROP) with eyes treated with laser photocoagulation. DESIGN: Extended follow-up of a randomized controlled clinical trial. PARTICIPANTS: One hundred eighteen eyes from 66 patients were randomly assigned to receive either cryotherapy or laser photocoagulation for threshold ROP. Twenty-five patients (44 eyes treated) were available for follow-up examination 10 years later. INTERVENTION: Cycloplegic autorefraction or retinoscopy was performed. Immersion ultrasound biometry (A-scan) was also performed, and an autokeratometer was used for keratometry. If an A-scan could not be tolerated or the patient was not cooperative, a B-scan through-the-lid biometry was performed. Corneal thickness was measured using optical coherence tomography. MAIN AND SECONDARY OUTCOME MEASURES: Refractive error. In addition, anterior chamber depth, lens thickness, and axial length were measured. Central corneal thickness measurements and keratometric readings were also obtained. RESULT: Eyes treated with cryotherapy were significantly more myopic than those treated with laser photocoagulation. When comparing patients with bilateral treatment, the mean spherical equivalent (SE) of eyes treated with laser was -4.48 diopters (D) compared with a mean SE of -7.65 D for eyes treated with cryotherapy (n = 15 pairs of eyes, P = 0.019). Cryotherapy-treated eyes had a mean axial length of 21.7 mm versus 22.9 mm for laser-treated eyes (P = 0.024, n = 12 pairs of eyes). The anterior chamber depth and lens thickness averaged 2.86 mm and 4.33 mm, respectively, in the cryotherapy-treated eyes compared with 3.42 mm and 3.95 mm in the laser-treated eyes (P < 0.001, n = 12 pairs for both measurements). There were no statistical differences in anterior corneal curvature and central corneal thickness between the two treatment modalities. Crystalline lens power bore the strongest correlation to refractive outcomes in both laser-treated (r = 0.885, P < 0.001) and cryotherapy-treated eyes (r = 0.591, P = 0.026). Although keratometric readings were higher than normal values in these eyes, there was no correlation to the degree of myopia. CONCLUSIONS: Laser-treated eyes were significantly less myopic than cyrotherapy-treated eyes. Lens power seemed to be the predominant factor contributing to the excess myopia.     

Comparison of symptomatic and asymptomatic, chronic, primary angle-closure glaucoma, open-angle glaucoma, and controls

PURPOSE: To determine the clinical features and anatomic parameters in asymptomatic (creeping) and symptomatic, chronic, primary angle-closure glaucoma (PACG) as compared with open-angle glaucoma (OAG) and with control subjects with normal eyes. METHODS: Forty consecutive patients with each of the following four types of eyes were studied (N = 160): eyes with symptomatic PACG, eyes with asymptomatic PACG, eyes with OAG, and the eyes of age-, sex-, and refraction-matched control subjects. The refractive status, keratometry, pachymetry, corneal diameter, anterior chamber depth, lens thickness, axial length, and relative lens position were noted. The groups were compared using a paired t test and analysis of variance. RESULTS: Patients with asymptomatic chronic PACG were older than patients in the symptomatic group, were more often men, and were more likely to have either diabetes mellitus or hypertension. Symptomatic chronic PACG eyes were more hypermetropic. Asymptomatic eyes had more iridotrabecular synechiae and minimal pupillary ruff atrophy as compared with the symptomatic eyes that had largely iridocorneal synechiae and large areas where the ruff was absent. All other clinical and anatomic parameters were statistically similar in the two groups, but differed significantly from OAG and control eyes. CONCLUSIONS: The ocular parameters of asymptomatic or creeping angle closure eyes show that these are significantly different from eyes having POAG. Asymptomatic and symptomatic chronic PACG eyes are structurally similar. Open-angle glaucoma eyes and normal eyes were comparable, but differed from both the chronic angle-closure glaucoma groups in having a larger corneal diameter, deeper anterior chamber, thinner lens, and a longer axial length. The symptomatic chronic PACG eyes showed more evidence of ischemic damage to the iris, and this could account for the symptoms reported by these patients.     

Precision of flap measurements for laser in situ keratomileusis in 4428 eyes

PURPOSE: To determine the factor(s) that influence the dimensions and predictability of the LASIK corneal flap with the Automated Corneal Shaper (ACS) or the Summit Krumeich Barraquer microkeratome (SKBM). METHODS: We performed a retrospective, comparative interventional case study of 4,428 eyes. Flap dimensions were measured using subtraction ultrasonic pachymetry during LASIK with one of two microkeratomes. RESULTS: Mean preoperative corneal thickness for all eyes was 555 +/- 35 microm. Corneal curvature and refractive astigmatism were inversely related to preoperative corneal thickness (P<.001). With an attempted flap thickness of 160 microm, the ACS flap thickness averaged 119.8 +/- 22.9 microm; SKBM flaps averaged 160.9 +/- 24.1 microm (P<.001). The coefficient of variation for central pachymetry compared to flap thickness was 6.4% vs. 22.1%. Flap thickness at enhancement was 10 to 17 microm thicker than at primary surgery. An increase in flap thickness was associated with thicker preoperative pachymetry (P<.001) and younger age for both instruments (P<.001) whereas increasing flap thickness was related to flatter preoperative mean keratometry for the ACS (P<.001) and steeper mean keratometry for the SKBM (P=.005). Less preoperative hyperopia or more myopia was related to an increase in flap thickness only for the SKBM (P<.001). CONCLUSIONS: Flap thickness varies significantly depending on the microkeratome used. Factors that influence flap thickness are primarily corneal thickness, patient age, preoperative keratometry, preoperative refraction including astigmatism, and corneal diameter. By understanding the factors that affect flap thickness, one can select a microkeratome system to allow maximum refractive correction while minimizing the risk of ectasia.     

Peripheral refraction and ocular shape in children

PURPOSE: To evaluate the relation between ocular shape and refractive error in children. METHODS: Ocular shape was assessed by measuring relative peripheral refractive error (the difference between the spherical equivalent cycloplegic autorefraction 30 degrees in the nasal visual field and in primary gaze) for the right eye of 822 children aged 5 to 14 years participating in the Orinda Longitudinal Study of Myopia in 1995. Axial ocular dimensions were measured by A-scan ultrasonography, crystalline lens radii of curvature by videophakometry, and corneal power by videokeratography. RESULTS: Myopic children had greater relative hyperopia in the periphery (+0.80 +/- 1.29 D), indicating a prolate ocular shape (longer axial length than equatorial diameter), compared with relative peripheral myopia and an oblate shape (broader equatorial diameter than axial length) for emmetropes (-0.41 +/- 0.75 D) and hyperopes (-1.09 +/- 1.02 D). Relative peripheral hyperopia was associated with myopic ocular component characteristics: deeper anterior and vitreous chambers, flatter crystalline lenses that were smaller in volume, and steeper corneas. Lens thickness had a more complex association. Relative peripheral hyperopia was associated with thinner lenses between refractive error groups but changed in sign to become associated with thicker lenses when analyzed within each refractive error group. Receiver operator characteristics analysis of the ocular components indicated that vitreous chamber depth was the most important ocular component for characterizing the myopic eye, but that peripheral refraction made a significant independent contribution. CONCLUSIONS: The eyes of myopic children were both elongated and distorted into a prolate shape. Thinner crystalline lenses were associated with more hyperopic relative peripheral refractions across refractive error groups, but failure of the lens to thin may account for the association between thicker lenses and more hyperopic relative peripheral refractions within a given refractive group. Increased ciliary-choroidal tension is proposed as a potential cause of ocular distortion in myopic eyes.     

Refractive changes in diabetic patients during intensive glycaemic control

AIMS: To evaluate the clinical course and the characteristics of transient refractive error occurring during intensive glycaemic control of severe hyperglycaemia. METHODS: 28 eyes of patients with persistent diabetes were included in this prospective study. During the observation period, patients underwent general ophthalmological examination and A-mode scan ultrasonography was performed at each examination-at days 1, 3, and 7, and then once every week or every other week until recovery of hyperopia. RESULTS: A transient hyperopic change occurred in all patients receiving improved control after hyperglycaemia. Hyperopic change developed a mean of 3.4 (SD 2. 0) days after the onset of treatment, and reached a peak at 10.3 (6. 1) days, where the maximum hyperopic change in an eye was 1.47 (0. 87) D (range 0.50-3.75 D). Recovery of the previous refraction occurred between 14 and 84 days after the initial assessment. There was a positive correlation between the magnitude of the maximum hyperopic change and (1) the plasma glucose concentration on admission (p<0.01), (2) the HbA(1c) level on admission (p<0.005), (3) the daily rate of plasma glucose reduction over the first 7 days of treatment (p<0.001), (4) the number of days required for hyperopia to reach its peak (p<0.001), and (5) the number of days required for the development and resolution of hyperopic changes (p<0.0001). There was a negative correlation between the maximum hyperopic change of an eye and baseline value of refraction (p<0.01). During transient hyperopia, no significant changes were observed in the radius of the anterior corneal curvature, axial length, lens thickness, or depth of anterior chamber. CONCLUSIONS: The degree of transient hyperopia associated with rapid correction of hyperglycaemia is highly dependent on the rate of reduction of the plasma glucose level. A reduction of refractive index in intraocular tissues, especially in lens, appears to be responsible for this hyperopic change.     

Ocular measurements throughout the adult life span of rhesus monkeys

PURPOSE: To examine the relationship of ocular components to refraction throughout the adult life span of the rhesus monkey (Macaca mulatta). METHODS: Cycloplegic retinoscopy, A-scan ultrasonography, slit lamp examination, indirect ophthalmoscopy, and keratometry were performed in a cross-sectional study of 111 monkeys, aged 5 to 31 years. Lens thickness and anterior and vitreous chamber depths were measured from the echograms. The intercorrelations of these variables were analyzed, as well as their association with age and sex. RESULTS: In monkeys aged 5 to 15 years, the mean refractive value of +1.5 D with an SD of 1.7 D was maintained near the previously established developmental asymptote of +2 D. In monkeys older than 15 years, there was greater interindividual variation (SD = 4.5 D), including extreme myopia and hyperopia. The cornea became steeper with age. The axial length of the eyes increased up to 12 years of age and began to shorten after 20 years. Changes also occurred in the other individual components that constitute eye length. These age-related changes were decreased vitreous chamber depth, decreased anterior chamber depth, and increased lens thickness. In general, males had longer eyes than females. The eyes of old monkeys were more likely to exhibit cataract and drusen, but age-related changes in focal atrophy of the retinal pigment epithelium did not achieve statistical significance. CONCLUSIONS: The components of the monkey eye change with age in a pattern similar to that reported in humans. Age-related changes in individual ocular components that could be detrimental to refraction appear to be compensated for by changes in other components.     

准分子激光角膜屈光术后人工晶状体度数计算的研究进展

曾行准分子激光角膜屈光手术的白内障患者,人工晶状体(IOL)度数的计算一直是个难题,如按常规方法计算,结果会产生较大误差,主要是术后出现不同程度的远视。本文就准分子激光角膜屈光术后角膜屈光力的测算、人工晶状体计算公式选择、前房深度测量、眼轴测量等影响人工晶状体度数计算的多种因素及其解决方法做一综述。     

调节对儿童屈光构成因素的影响

目的：通过分析调节对儿童屈光构成因素的影响，探讨调节与屈光不正、特别是与近视眼的关系。方法：检测135例（270只眼）儿童睫状肌麻痹前后的前房深度（AD）、晶状体厚度（LT）、玻璃体腔径（VL）、眼轴长度（AL）的变化以及睫状肌麻痹后的屈光状态。对其中136只眼行睫状肌麻痹前后角膜地形图检查。结果：不论远视眼、正视眼还是近视眼在睫状肌麻痹后胶房加深（P＜0．01），晶状体变薄（P＜0．01），玻璃体腔径缩短（P＜0．01），但远视眼睫状肌麻痹后眼轴增长（P＜0．05），近视眼眼轴缩短（P＜0．01）；远视眼睫状肌麻痹后，以角膜中心点中心，直径为3mm的环平均角膜屈光度（MD3，P＝0．009）和角膜曲率K1（P＜0．05）增加；近视眼睫状肌麻痹后除MD3（P＝0．033）、K1（P＜0．05），K2以及以角膜中心点为中心，直径为5mm,7mm的环平均角膜屈光度（MD5、MD7）均降低（P≤0．01）；角膜垂直径线下方的平均角膜屈光度（LMD）大于上方的平均角膜屈光度（UMD）而水平径线颞侧的平均角膜屈光度（LaMD)大于鼻侧的平均角膜屈光度（MMD）（P＜0．01）。结论：调节对眼的几乎所有屈光构成因素有着显著的影响；它本身不仅是传统意义上的晶状体本身屈光度增加，同时还伴有晶状体的相对前移；角膜的非球面性即便是在同一垂直或水平径线上的屈光分布也是非对称的。