Refractive Index Measurement of the Crystalline Lens in Vivo.

SIGNIFICANCE: This study provides a new method to measure the refractive index of crystalline lens in the human eye in vivo . PURPOSE: Accessing the refractive index of crystalline lenses in the human eye in vivo has long been a challenge. This study aimed to measure the refractive index of a lens in vivo using an anterior segment optical coherence tomography (AS-OCT) system combined with a Scheimpflug imaging system. METHOD: A ray-traceable Scheimpflug imaging was developed and integrated into an AS-OCT system. A theoretical study revealed that the combination of these two systems provides a unique solution for simultaneously measuring the refractive index and the thickness of the lens. The average lens refractive index along the ray pathway ( Nav ) and lens shape were measured for seven subjects. RESULTS: The lens Nav along the central ray varies from 1.383 to 1.419 between subjects. The lens refractive index function across the lens diameter varies from subject to subject. The lens Nav increases for accommodated eyes. The thicknesses and profiles of the lenses are also determined. CONCLUSIONS: The lens refractive index varies substantially from individual eye to individual eye, not only along the central ray pathway but also for the lens refractive index function across the lens diameter. Ray-traceable Scheimpflug imaging-equipped AS-OCT is useful for testing the refractive index of lenses in the human eye in vivo .

Refractive and biometrical characteristics of children with retinopathy of prematurity who received laser photocoagulation or intravitreal ranibizumab injection.

PURPOSE: To investigate the refractive and biometrical developments of children with retinopathy of prematurity (ROP) who received laser photocoagulation (LP) or intravitreal ranibizumab injection as treatment. METHODS: This case-control study involved cases with Zone II Stage 3 ROP. Fourteen children (28 eyes) who received single LP were included in the laser group, and 14 children (27 eyes) who received single intravitreal ranibizumab injection were included in the injection group. The mean age at operation was 37.00±1.72 and 36.36±1.66 weeks for the laser and injection groups, respectively (P=0.161), and refraction measurements and biometry were performed at the mean age of 5.00±1.63 and 5.00±0.94 years for the laser and injection groups, respectively (P=1.000). Spherical equivalent (SE) after mydriatic refraction and best corrected visual acuity (BCVA) were measured by refraction test. Central corneal thickness (CCT), anterior corneal surface curvature and curvature radius, anterior chamber depth (ACD), lens thickness (LT) and axial length (AL) were measured by biometry using the IOL Master700 biometric instrument (Carl Zeiss Meditec AG). The biometrical images were reanalysed using a self-developed program in MATLAB (R2016a, MathWorks, Inc.) to obtain additional eye parameters, including the curvatures of the posterior cornea and the anterior and posterior surfaces of the lens. SPSS (V.23.0) was used for statistical analysis. Independent sample t test was used to compare the eyeball biological and refractive state measures of the two groups, and Pearson correlation coefficient was used to evaluate the correlation between SE and the biological parameters. RESULTS: 1. (1) Cornea-related parameters: CCT (0.54±0.04mm vs 0.55±0.02mm, P>0.05), anterior corneal surface curvature radius (7.56±0.26 mm vs 7.67±0.43mm, P>0.05) and posterior corneal surface curvature radius (6.82±0.27mm vs 6.79±0.42mm, P>0.05). (2) ACD (3.21 ± 0.25mm vs 3.22 ± 0.19mm, P>0.05). (3) Lens-related parameters: anterior lens surface curvature radius (10.04±0.89mm vs 9.82±1.08mm, P>0.05), posterior lens surface curvature radius (5.49±0.55mm vs 5.92±0.73mm, P<0.05) and LT (3.80±0.14mm vs 3.59±0.16mm, P<0.05). (4) AL (21.82±1.07 vs 22.68±1.61, P<0.05). (5) Parameters related to refractive state: SE (-2.43±3.56 vs -0.53±3.12, P<0.05) and BCVA (log MAR, 0.17±0.14 vs 0.21±0.18, P>0.05). 2. (1) The SE of children in the laser group was positively correlated with LT (r=0.438, P<0.05), negatively correlated with ACD (r=-0.437, P<0.05) and had no significant correlation with other eyeball biological indicators (P>0.05). (2) The SE of children in the injection group was negatively correlated with AL (r=-0.537, P<0.05), positively correlated with CCT (r=0.455, P<0.05) and had no significant correlation with other eyeball biological indicators (P>0.05). CONCLUSION: LP and intravitreal ranibizumab injection as ROP treatments produce myopic refraction with increased degree of myopia in children who received LP than in children who received ranibizumab injection. The increased myopia after LP is due to the increases in LT and posterior lens curvature and a shallow ACD.

Effects of tilt and decentration of Visian Implantable Collamer Lens (ICL V4c) on visual quality: an observational study.

BACKGROUND: The central hole of the Visian Implantable Collamer Lens (ICL V4c) provides a reference to observe its tilt or decentration. This study aimed to investigate the tilt and decentration effects of ICL V4c on visual quality after implantation. METHODS: A total of 135 eyes from 69 patients who underwent ICL V4c implantation were included in this study. Evaluation of uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and aberrations were performed 6-months postoperatively. The anterior segment parameters were collected using CASIA2 anterior segment-optical coherence tomography, tilt and decentration of ICL V4c were analyzed using MATLAB software. All patients received questionnaires to investigate the visual quality postoperatively. RESULTS: The safety and effectiveness were 1.18 ± 0.17 and 1.11 ± 0.18, respectively. No significant changes were observed regarding higher-order and spherical aberrations after the operation; however, coma and trefoil significantly increased compared to preoperative values. The average total decentration and tilt was 0.21 ± 0.12 mm and 2.54 ± 1.00°, respectively. Horizontal, vertical, and total values of tilt and decentration were not significantly associated with postoperative CDVA, UDVA, and aberrations. The most common visual symptom was halo, and 97.04% of patients had a satisfaction score ≥ 8. The total or horizontal tilt was significantly positively correlated with the frequency, severity, and bothersome scores from the questionnaires. CONCLUSIONS: ICL V4c implantation can obtain high visual quality and patient satisfaction. Although the degree of tilt and decentration after ICL V4c implantation was small, a positive effect on subjective visual quality was observed.

A Model of the Effect of Lens Development on Refraction in Schoolchildren.

SIGNIFICANCE: The study provides a new theory on the mechanism underlying myopia development, and it could be useful in clinical practice to control myopia development in schoolchildren. PURPOSE: To model the effect of the crystalline lens on refractive development in schoolchildren. METHODS: The Zemax 13 was used to calculate Zernike aberrations and refractions across 50° horizontal visual fields. Optical effects of the anterior chamber depth, lens thickness, and radii of curvature of the lens surfaces on refractions were modeled. Refractive changes induced by lens development in emmetropic and myopic eyes, based on a previous longitudinal study from literature, were calculated. RESULTS: A lens thickness reduction with an anterior chamber depth deepening caused a hyperopic shift over the visual fields and even more at the periphery. Opposite effects were found when the lens was thinned without any change of the anterior chamber depth. While a flattening of the anterior lens surface produced hyperopic refractions overall, a posterior lens flattening caused a myopic shift at the periphery, but a hyperopic shift of the central refraction. In the myopic eye, lens development induced refractive change toward more hyperopic over the visual fields and more at the periphery. CONCLUSIONS: Lens thinning and lens axial movement participate in peripheral refractive development in schoolchildren, and lens development with a deeper anterior chamber depth and a flatter lens surface in the myopic eye could generate extra hyperopia over visual fields. The myopic lens development could be due to a backward movement of the lens, driven by a backward growth of the ciliary process, which might be a causative factor of myopia development.

Measurement of wavefront aberrations and lens deformation in the accommodated eye with optical coherence tomography-equipped wavefront system.

To quantitatively approach the relationship between optical changes in an accommodated eye and the geometrical deformation of its crystalline lens, a long scan-depth anterior segment OCT equipped wavefront sensor was developed and integrated with a Badal system. With this system, accommodation was stimulated up to 6.0D in the left eye and also measured in the same eye for three subjects. High correlations between the accommodative responses of refractive power and the radius of the anterior lens surface were found for the three subjects (r>0.98). The change in spherical aberration was also highly correlated with the change in lens thickness (r>0.98). The measurement was very well repeated at a 2nd measurement session on the same day for the three subjects and after two weeks for one subject. The novelty of incorporating the Badal system into the OCT equipped wavefront sensor eliminated axial misalignment of the measurement system with the test eye due to accommodative vergence, as in the contralateral paradigm. The design also allowed the wavefront sensor to capture conjugated sharp Hartmann-Shack images in accommodated eyes to accurately analyze wavefront aberrations. In addition, this design extended the accommodation range up to 10.0D. By using this system, for the first time, we demonstrated linear relationships of the changes between the refractive power and the lens curvature and also between the spherical aberration and the lens thickness during accommodation in vivo. This new system provides an accurate and useful technique to quantitatively study accommodation.

Theoretical model of the contributions of corneal asphericity and anterior chamber depth to peripheral wavefront aberrations.

PURPOSE: The purpose of this study was to theoretically model the contributions of corneal asphericity (Q) and anterior chamber depth to peripheral wavefront aberrations. METHODS: Ray-tracing was performed on a model eye using a customised MatLab program to calculate Zernike aberrations up to the 5th order across ±60° of the horizontal visual field. The corneal Q was varied from -0.5 to 0.8, and the anterior chamber depth was changed from 2.05 to 4.05 mm while axial length was held constant. Spherical equivalent refractive error derived from Zernike defocus was used to estimate peripheral refraction. RESULTS: Relative to axial Zernike aberrations, both defocus and astigmatism in the peripheral field increased with the corneal Q value, but the increases in relative peripheral astigmatism were much smaller in amplitude than relative peripheral defocus. Anterior chamber depth shortening caused the relative peripheral defocus and astigmatism to increase toward more positive values, although the changes in relative peripheral astigmatism with anterior chamber depth were small. Combination of the variations in both corneal Q and anterior chamber depth does not produce linear sum of the changes in relative peripheral defocus. The relative peripheral refractive error was more myopic when either the corneal Q was increased or the anterior chamber depth was shortened. The changes in relative peripheral x-axis coma, trefoil and spherical aberration with corneal Q value were complex but were barely changed with anterior chamber depth within the central 60° visual field. CONCLUSIONS: Both corneal asphericity and anterior chamber depth play important roles in determining peripheral wavefront aberrations. The two factors nonlinearly interact to affect peripheral aberrations. Higher corneal Q and/or shorter anterior chamber depth tend to produce relatively more myopic peripheral refraction. Increasing the Q value of the anterior surface of a contact lens might provide an interesting intervention to slow myopia progression.

Effects on radius of curvature and refractive power of the cornea and crystalline lens by atropine 0.01% eye drops.

PURPOSE: The morphological changes in the cornea and crystalline lens have not been closely evaluated after the administration of atropine 0.01%. This study aims to evaluate the radii of curvature and refractive power of the cornea and lens in myopic eyes during atropine 0.01% treatment. METHODS: Children aged 6-14 years with myopia <-6.0 D were randomized to receive atropine 0.01% once nightly with single vision lenses or simply wear single vision lenses. Ocular biometric parameters were measured using the IOLMaster 700 biometry and the radii of corneal and lenticular curvature were simulated using a customized program. RESULTS: At the 9-month visit, 69 atropine-treated eyes and 50 control eyes were included in the final analyses. In atropine-treated eyes, the posterior corneal surface steepened (-0.05 ± 0.13 mm) and the anterior lenticular surface flattened (0.20 ± 0.69 mm) significantly within 3-6 months, whereas the posterior corneal surface and anterior lenticular surface gradually flattened (0.07 ± 0.23 and 0.32 ± 0.80 mm respectively) in the control eyes over 9 months. The difference in the change of corneal refractive power was significant between groups (-0.03 ± 0.18 D vs. 0.11 ± 0.24 D, p = 0.001), while that in the change of lenticular refractive power was statistically insignificant (0.01 ± 0.92 D vs. -0.22 ± 0.86 D, p = 0.161). CONCLUSIONS: The administration of atropine 0.01% exhibited a clinically short and subtle impact on the cornea and lens, which may shed light on new targets of action for atropine in inhibiting myopia.

Corneal and lenticular biometry in Chinese children with myopia.

CLINICAL RELEVANCE: The measurement and simulation of corneal and lenticular curvature radii using a single swept-source biometry device enables a more thorough evaluation of the shape and refractive power of the cornea and lens during emmetropization or myopia progression in children. BACKGROUND: This study aimed to evaluate the distribution characteristics of corneal and lenticular parameters in Chinese children with myopia and explored their association with other ocular components. METHODS: In this cross-sectional study, all ocular biometric parameters were measured using a Zeiss IOLMaster 700 Biometry. Simulations of the corneal and lenticular curvature radii were implemented using a customised MATLAB program based on cross-sectional swept-source optical coherence tomography images obtained from the same device. The associations of the calculated and simulated refractive powers of the cornea and lens with other ocular parameters were evaluated. RESULTS: In total, 119 children with myopia were recruited. Boys had a deeper anterior chamber and longer axial length (AL) than girls, while girls had steeper anterior corneal and lenticular curvatures and greater corneal and lenticular power. Children aged 10 years and older showed a larger anterior lenticular radius of curvature (sRal) and less lenticular power (PL,OCT) than younger participants. There was a significant positive correlation between AL and the anterior corneal radius of curvature, regardless of sex or age. The sRal exhibited a significant increasing trend, and PL,OCT exhibited a declining trend with a longer AL only in children younger than 10 years. CONCLUSION: AL is the most influential factor in the determination of spherical equivalent refractive error, while decreases in both corneal and crystalline lens power are significantly inversely correlated with axial elongation.

An indirect method to compare the reference centres for corneal measurements.

PURPOSE: Corneal measurements are commonly presented with respect to a specific reference centre, but the location of the reference centre on the corneal surface could vary from one diagnostic modality to another. This study aimed to develop a method for comparing reference centres used by corneal measurement systems. METHODS: An indirect method was developed to compare reference centres by making use of the pupil centre and its offset from the reference centre. Reference centres in a Scheimpflug imaging system, the Pentacam HR, and a Placido-ring corneal topography system, the ATLAS Corneal Topography System, were compared for the right and left eyes of 30 subjects. The subjects all had similar pupil sizes when measured by the two systems. Differences and correlations of the pupil centre offsets between the two systems were statistically tested and compared by Bland-Altman analyses. RESULTS: There were no significant differences in mean pupil offsets between the two systems for either the right or left eyes (p > 0.05). There were strong correlations of the pupil centre offsets between the two systems for each eye (right eye x-axis: r = 0.95, p < 0.0001; right eye y-axis: r = 0.98, p < 0.0001; left eye x-axis: r = 0.96, p < 0.0001, left eye y-axis: r = 0.93, p < 0.0001). Bland-Altman analyses revealed no significant differences in pupil centre offsets between the two systems. CONCLUSIONS: The Pentacam HR system and the ATLAS system have very similar reference centres. Thus it is possible to directly analyze data from the Pentacam HR and other instruments using the corneal vertex or the pupil centre as the reference centres due to the similarity in the reference centre settings between the two systems.

Effects of lighting conditions and accommodation on the three-dimensional position of Visian implantable collamer lens.

BACKGROUND: To investigate the effects of lighting conditions and accommodation on the three-dimensional position of Visian implantable collamer lens (ICL V4c). METHODS: This observational study recruited 62 eyes of 31 myopia patients underwent ICL V4c implantation. Anterior segment optical coherence tomography (AS-OCT) assessed the anterior chamber depth (ACD), ACD-ICL (distance from the corneal endothelium to anterior surface of the ICL V4c), vault (distance between the posterior ICL V4c surface and anterior crystalline lens surface), and crystalline lens tilt under various lighting conditions and accommodation relative to the corneal topographic axis at one year after ICL V4c implantation. Baseline was defined as the scotopic condition, which was also the non-accommodative stimulus condition. The ICL V4c tilt was analyzed using MATLAB. The significance level was set at P < 0.05. RESULTS: The ACD-ICL values were similar under various lighting conditions (P = 0.978) but decreased during accommodation (P < 0.001). The vault was significantly smaller under mesopic and photopic conditions than the baseline (P = 0.044 and P < 0.001, respectively) but remained unchanged during accommodation (P = 0.058). The inferotemporal proportion of ICL V4c (88.7%, 55 eyes) and crystalline lens (74.2%, 46 eyes) tilts were not significantly different (P = 0.063). Crystalline lens under various lighting conditions and accommodation exhibited similar tilts. The vertical tilt of ICL V4c was significantly larger under photopic conditions than the baseline (P = 0.038). The horizontal and total tilts were significantly decreased during accommodation (P = 0.043 and 0.013, respectively). CONCLUSIONS: The axial position of ICL V4c in the anterior chamber was stable under various lighting conditions. Lighting conditions and accommodation may influence vertical, horizontal and total tilts of ICL V4c.

Comparison of lens refractive parameters in myopic and hyperopic eyes of 6-12-year-old children.

Background/aims: To evaluate the influence of cycloplegia on lens refractive parameters in 6-12-year-old children with myopia and hyperopia for exploring the pathogenesis of myopia. Methods: One hundred eyes of 100 patients (50 boys) were included. In the myopic group, 50 subjects (25 boys and 25 right eyes) were enrolled with a mean age of 9.20 ± 1.69 years. IOLMaster 700 measurements were performed pre- and post-cycloplegia. The pictures were marked using semi-automatic software. The lens curvature and power were obtained using MATLAB image processing software. Paired and independent sample t-tests were used for data analysis. Statistical significance was set at P < 0.05. Results: Anterior and posterior lens curvature radius in myopic eyes were larger than those in hyperopic eyes, both pre- and post-cycloplegia (both P < 0.001). The refractive power in myopic eyes was lower than that in hyperopic eyes without cycloplegia, both pre- and post-cycloplegia (both P < 0.001). The changes in anterior lens curvature and refractive power between pre- and post-cycloplegia in hyperopic eyes were larger than those in myopic eyes (both P < 0.05). No significant difference was found in the change in posterior lens curvature and refractive power after cycloplegia in hyperopic and myopic eyes (P > 0.05). Conclusion: Anterior and posterior surfaces of the lens were flatter, and the refractive power was lower in the myopia group than in the hyperopia group. Myopic and hyperopic patients showed a tendency for lens flattening and refractive power decrease after cycloplegia. Hyperopic patients had more changes in anterior lens curvature and refractive power after cycloplegia.

Effects of different monochromatic lights on refractive development and eye growth in guinea pigs.

We investigated whether different monochromatic lights with similar luminance or identical light quantum number produce predictable changes in refractive state and eye growth in early eye development in guinea pigs. In experiment I, three groups of guinea pigs (two weeks of age, n=18 in each group) were reared for 12 weeks under LED lighting of 430 nm (short-wavelength light, SL), 530 nm (middle-wavelength light, ML), and broad-band light (BL). The lighting conditions were set to provide equal levels of luminance. All animals underwent refraction and biometric measurements every 2 weeks. In experiment II, the lighting conditions were set at equal quantum number and another three groups of guinea pigs were raised and tested for 20 weeks. In experiment I, compared to the BL group, refraction of the ML group was less hyperopic (P<0.001) with a faster vitreous extension (P<0.001), while the SL group was more hyperopic with a slower vitreous elongation (P<0.001). The mean difference in refraction between the SL and ML groups reached about 4.5 D at maximum. The refractive changes and eye growth in experiment II were very similar to experiment I during the first 12 weeks, but the difference in refraction between the SL and ML groups reached 6.05 D after 20 weeks of treatment, which was greater than the longitudinal chromatic aberration (approximately 1.5 D) in the guinea pigs eyes. The results suggest that the guinea pigs' eyes overcompensated in response to narrow-band light, which resulted in an exaggerated and inaccurate refractive growth.

The effect of blur adaptation on accommodative response and pupil size during reading.

To study the effect of blur adaptation on accommodative variability, accommodative responses and pupil diameters in myopes (n = 22) and emmetropes (n = 19) were continuously measured before, during, and after exposure to defocus blur. Accommodative and pupillary response measurements were made by an autorefractor during a monocular reading exercise. The text was presented on a computer screen at 33 cm viewing distance with a rapid serial visual presentation paradigm. After baseline testing and a 5-min rest, blur was induced by wearing either an optimally refractive lens, or a +1.0 DS or a +3.0 DS defocus lens. Responses were continuously measured during a 5-min period of adaptation. The lens was then removed, and measurements were again made during a 5-min post-adaptation period. After a second 5-min rest, a final post-adaptation period was measured. No significant change of baseline accommodative responses was found after the 5-min period of adaptation to the blurring lenses (p > 0.05). Compared to the pre-adaptation level, both refractive groups had similar and significant increases in accommodative variability right after blur adaptation to both defocus lenses. After the second rest period, the accommodative variability in both groups returned to the pre-adaptation level. The results indicate that blur adaptation has a short-term effect on the accommodative system to elevate instability of the accommodative response. Mechanisms underlying the increase in accommodative variability by blur adaptation and possible influences of the accommodation stability on myopia development were discussed.

Effects of monochromatic aberration on visual acuity using adaptive optics.

PURPOSE: To investigate the effect on visual acuity of correcting specific Zernike aberrations. METHODS: Visual acuity was tested for 12 young subjects using a Freiburg Acuity Test procedure under conditions with wavefront aberrations corrected by an adaptive optics system. The adaptive optics system consists of a Hartmann-Shack wavefront sensor, a deformable mirror, relevant optical channels and closed loop control system. Five aberration correction paradigms were used to correct different Zernike terms. RESULTS: With the second order aberration fully corrected, a significant improvement in visual acuity was observed (0.056 logMAR, t = 2.79, p = 0.018). Further correction of third order Zernike aberrations resulted in an additional improvement of 0.041 logMAR (t = 2.63, p = 0.023). But an additional correction of spherical aberration did not produce a significant increase in visual acuity (t = 1.10, NS). Full correction of aberrations achieved the best visual acuity with an improvement of 0.022 logMAR (t = 2.46, p = 0.032). The visual acuity was found to increase with the root mean square values of the residual aberrations with a linear relationship (r = 0.63, p < 0.0001). CONCLUSIONS: Correction of monochromatic wavefront aberrations improves visual acuity for normal eyes and the improvement of visual acuity is proportional to the change of root mean square of wavefront aberrations.

Effect of flap thickness on higher order wavefront aberrations induced by LASIK: a bilateral study.

PURPOSE: To investigate the effect of flap thickness on wavefront aberrations induced by LASIK. METHODS: LASIK was performed on 56 eyes of 28 patients with refraction errors that were well matched between the right and left eyes. For each patient, a planned 160-microm flap was created for one randomly selected eye using the Moria M2 microkeratome (130-microm head; thick flap group), and a 110-microm flap was created for the contralateral eye with the same microkeratome (90-microm head; thin flap group). Flap thickness was measured using ultrasonic pachymetry. Wavefront aberrations were measured in the anterior cornea using the Orbscan II (Bausch & Lomb) and in the whole eye using the Wavefront Supported Custom Ablation (WASCA) aberrometer (Carl Zeiss Meditec) preoperatively and at 1 month and 1 year postoperatively. RESULTS: Mean flap thickness was 155 +/- 13 microm in the thick flap group and 112 +/- 11 microm in the thin flap group. Mean root-mean-square of higher order wavefront aberrations were changed for the different test times in the cornea (F = 29.9, P < .0001) and the whole eye (F = 48.0, P < .0001). There was no significant difference between the two flap groups for the cornea (F = 0.76) or for the whole eye (F = 0.07). Similar results were observed for higher order Zernike aberrations such as spherical aberration and comas. CONCLUSIONS: The results suggest higher order wavefront aberrations induced by LASIK are independent of flap thickness. Complications in visual outcome for patients with different flap thickness should be attributed to factors other than aberrations.

Changes in corneal wavefront aberrations in microincision and small-incision cataract surgery.

PURPOSE: To study the effect of incision size on the optical quality of the anterior cornea by comparing the changes in corneal wavefront aberrations between microincision cataract surgery (MICS) and small-incision cataract surgery (SICS). SETTING: Eye Hospital of Wenzhou Medical College, Wenzhou, Zhejiang, China. METHODS: This prospective randomized clinical study included 36 eyes having MICS (1.5 mm) and 38 eyes having SICS (3.0 mm). Anterior corneal topography was measured preoperatively and 3 to 6 months postoperatively. The data were used to calculate anterior corneal Zernike aberrations (through the 6th order) for a 6.0 mm central area. RESULTS: In the MICS group, 2 corneal Zernike aberrations (trefoil and tetrafoil) changed significantly from preoperatively to postoperatively (both P<.0001). In the SICS group, in addition to trefoil and tetrafoil, oblique astigmatism (P<.0001), secondary oblique astigmatism (P= .001), and vertical tetrafoil (P= .001) changed significantly. The SICS group had greater changes than the MICS group in oblique astigmatism (P= .0001), oblique trefoil (P= .0035), and vertical tetrafoil (P= .0023). The changes in the SICS group were significantly greater than in the MICS group in the total root mean square (RMS) (P= .007) and higher-order RMS (P= .023) of corneal wavefront aberrations. CONCLUSIONS: Cataract surgery-related changes in corneal wavefront aberrations were dependent on incision size. The MICS technique had advantages over the SICS technique in minimizing the effect of the incision size on the optical quality of the cornea.

Wavefront aberration and its association with intraocular pressure and central corneal thickness in myopic eyes.

PURPOSE: To investigate the association between intraocular pressure (IOP), central corneal thickness (CCT), or both and wavefront aberrations in the anterior cornea and the whole eye in myopia. SETTING: Wenzhou Medical College, Wenzhou, Zhejiang, China. METHODS: Seventy myopic subjects were tested with a Humphrey corneal topographer for wavefront aberrations in the anterior corneal surface and with a wavefront aberration-supported cornea ablation wavefront analyzer (Complete Ophthalmic Analysis System, Carl Zeiss Meditec) for wavefront aberrations in the whole eye. The IOP and CCT were measured with a noncontact Canon tonometer and a Tomey pachymeter, respectively. Relationships between the wavefront aberrations and the IOP and CCT were analyzed. RESULTS: Four corneal Zernike aberrations were significantly correlated with the IOP, including defocus (Z4) (r = 0.36, P<.01 for right eye; r = 0.31, P<.05 for left eye), y-axis coma (Z7) (r = 0.32, P<.05 for right eye), spherical aberration (Z12) (r = 0.34, P<.02 for both eyes), and secondary astigmatism (Z13) (r = -0.35, P<.01 for right eye; r = -0.37, P<.01 for left eye). In the whole eye, 3 Zernike aberrations were significantly correlated with IOP: trefoil (Z6) (r = 0.31, P<.05 for right eye), spherical aberration (Z12) (r = 0.34, P<.02 for right eye; r = 0.30, P<.05 for left eye), and secondary astigmatism (Z13) (r = -0.45, P<.01 for right eye; r = -0.30, P<.05 for left eye). However, only a single Zernike aberration (Z11) was significantly correlated with CCT (r = -0.29, P<.05 for right eye). CONCLUSIONS: Intraocular pressure was associated with wavefront aberrations in both the cornea and the whole eye, and its association was not limited to symmetrical aberrations but included asymmetric higher-order aberrations as well. In contrast, CCT was very weakly associated with wavefront aberrations.

Interocular Difference of Peripheral Refraction in Anisomyopic Eyes of Schoolchildren.

PURPOSE: Refraction in the peripheral visual field is believed to play an important role in the development of myopia. The purpose of this study was to investigate the differences in peripheral refraction among anisomyopia, isomyopia, and isoemmetropia for schoolchildren. METHODS: Thirty-eight anisomyopic children were recruited and divided into two groups: (1) both eyes were myopic (anisomyopic group, AM group) and (2) one eye was myopic and the contralateral eye was emmetropic (emmetropic anisomyopic group, EAM group). As controls, 45 isomyopic and isoemmetropic children were also recruited with age and central spherical equivalent (SE) matched to those of the AM and EAM groups. The controls were divided into three groups: (1) intermediate myopia group (SE matched to the more myopic eye of AM group), (2) low myopia group (SE matched to the less myopic eye of AM group and the more myopic eye of EAM group), and (3) emmetropia group (SE matched to the less myopic eye of EAM group). Peripheral refraction at 7 points across the central ±30° on the horizontal visual field with a 10° interval was measured with an autorefractor. Axial length (AL), corneal curvature (CC), and anterior chamber depth (ACD) were also determined by using the Zeiss IOL-Master. RESULTS: The relative peripheral spherical equivalent [RPR(M)] and relative peripheral spherical value [RPR(S)] of the more myopic eye was shifted more hyperopically than the contralateral eye in both the AM and the EAM groups (both p<0.0001). The RPR(M, S) of the less myopic eyes in the AM and EAM groups showed a relatively flat trend across the visual field and were not significantly different from the emmetropia group. The RPR(M, S) of less myopic eyes in the AM group were shifted less hyperopically than in the isomyopic low myopia group and the more myopic eye of the EAM group [RPR(M), p = 0.007; RPR(S), p = 0.001], although the central SEs of the three groups were not significantly different from each other. However, RPR(M, S) of the more myopic eyes were not different from the corresponding isomyopic groups. There was also no significant difference in the relative peripheral astigmatism [RPR(J0, J45)] between the more and the less myopic eyes in either the AM or the EAM group. CONCLUSION: Refraction of anisomyopia differs between the two eyes not only at the central visual field but also at the off-axis periphery. The relative peripheral refraction of the more myopic eye of anisomyopia was shifted hyperopically, as occurs in isomyopia with similar central subjective SE values. Less myopic eyes were much less hyperopically shifted in relative peripheral refraction than the corresponding isomyopic eyes, but are comparable to emmetropic eyes. This emmetropia-like relative peripheral refraction in less myopic eyes might be a factor responsible for slowing down the progression of myopia.

The association of wavefront aberration and accommodative lag in myopes.

Accommodative lags, induced by a target at 33 cm (distance-induced condition) and by a -3.0 D lens (lens-induced condition), and wavefront aberrations were measured in 27 young myopic eyes. The accommodative lags and Strehl ratios derived from the wavefront aberrations in myopes were compared with those from 57 emmetropes. Accommodation was measured using a Canon R-1 autorefractor, while aberrations were measured using a psychophysical ray-tracing technique. In accord with previous results, larger accommodative lags were found for the myopes than the emmetropes in both the lens-induced and distance-induced conditions. The mean Strehl ratio was smaller in the myopes (0.079) than the emmetropes (0.091); this difference approached significance (p = 0.055). In addition, for myopes the accommodative lag was significantly correlated with the Strehl ratio in the lens-induced condition (r = -0.45, p < 0.02) and approached significance in the distance-induced condition (r = -0.35, p = 0.07). No significant correlations were found for emmetropes. Possible reasons to account for these results are discussed.

A limitation of Hartmann-Shack system in measuring wavefront aberrations for patients received laser refractive surgery.

PURPOSE: To explore the relationship between ablation parameters of myopic laser surgery and measurement area of wavefront aberration (WA) with Hartmann-Shack wavefront sensor. METHODS: 58 subjects undergone myopic laser surgeries and 74 uncorrected myopic subjects were enrolled in this experiment. The laser ablation parameters were obtained from surgical records, which included spherical error (Rx), depth, and optical zone (OZ) of ablation. The measured area of WA was tested by the WASCA, and the real pupil size was tested by Pentacam. The corneal eccentricity (E value) and curvature was also measured with the Pentacam. All the measurements were performed under mydriatic condition. RESULTS: For uncorrected myopic eyes, the measured area of WA was similar with the real pupil size. But for the corrected eyes, the measured area of WA was smaller than the real pupil size with a mean difference of 0.66 ± 0.54 mm for moderate myopia (t = 6.45, p < 0.0001) and 1.76 ± 0.55 mm for high myopia (t = 18.92, p < 0.0001), but not for mild myopia. The Rx (t = -3.20, p = 0.0017), OZ (t = 64.4, p < 0.0001) and postoperative corneal E value (t = 2.52, p = 0.017) were the independent factors of measured area of WA. Measured area of WA = -0.81*Rx + 1.13*OZ + 0.49*postoperative corneal E value (r2 = 0.997). CONCLUSIONS: The WASCA has a limitation in measuring wavefront aberration over the whole pupil area when it's used for patients received myopic laser surgery. The measured area is smaller than the real pupil size and depends linearly on ablation depth, optical zone and corneal eccentricity.