Ji C. He

Monochromatic Wavefront Aberrations in the Human Eye with Contact Lenses

Purpose. The aim of this study was to investigate the effect of contact lenses on the optical performance of the eye by measuring wavefront aberrations for the eyes with or without contact lenses. Method. A sensitive aberrometer was used to measure wavefront aberrations for 54 eyes in 27 subjects for three conditions: with no contact lens (non-CL), with soft-contact lenses (soft-CL) and with rigid gas permeable contact lenses (RGP-CL). The root mean square (RMS) value of the wavefront aberrations and Zernike aberrations were calculated. Results. A change in the RMS values of wavefront aberrations with CL wear was observed for every eye. The change in wavefront aberrations with CL wearing was found to vary substantially from individual to individual. Relative to the mean RMS value of the group for the non-CL condition, the mean RMS value was increased for the soft-CL condition and was significantly reduced for the RGP-CL condition. A significant increase in mean RMS for the soft-CL condition was found when astigmatisms were removed. Although soft-CL wearing resulted in significant increases in higher orders of Zernike aberrations (fourth, fifth, and higher), the RGP-CL condition led to a significant decrease in second-order Zernike aberrations. For the eyes with low wavefront aberrations in the non-CL condition, either soft-CL wearing or RGP-CL wearing results in increases in the RMS values. Conclusion. Contact lens wearing, either with soft lenses or the RGP lenses, causes changes in the wavefront aberrations of the eye. The changes in wavefront aberrations vary substantially from eye to eye. Although soft-CL wearing tends to induce more higher-order aberrations, RGP-CL effectively reduces the astigmatisms. Both soft-CL and RGP-CL induce more aberrations for the eyes that have low wavefront aberrations. The change in wavefront aberrations due to contact lens wearing may explain the changes in visual performance for contact lens wearers reported previously.

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.

On the compensation of horizontal coma aberrations in young human eyes.

The nature of the compensation of horizontal coma (Z31) between optical elements of the human eye has been studied and the compensative mechanism has been attributed to a passive process linked to angle kappa of the eye. We measured the horizontal coma in the anterior cornea, the whole eye and the internal optics for 221 young subjects. Thirty‐three eyes with minimum angle lambda and 53 eyes with relatively large angle lambda were selected from these eyes to test the hypothesis that horizontal coma compensation is linked to angle kappa. Significant horizontal coma in the anterior cornea was observed for the group with minimum angle lambda in both the right (−0.12 ± 0.07 μm) and left eyes (0.12 ± 0.10 μm), and this was well compensated by the internal optics so that the level of horizontal coma in the whole eye over a 6‐mm pupil size was very low (−0.05 ± 0.07 μm for OD and 0.02 ± 0.08 μm for OS). The horizontal coma in the anterior cornea was significantly correlated to the horizontal coma in the internal optics for both the right and the left eye. The results suggest that there is another source of horizontal coma, in addition to that linked to angle kappa, in the anterior cornea, and also a new compensative mechanism to balance the corneal coma, perhaps in the posterior cornea or the lens.

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.

The effects of monochromatic illumination on early eye development in rhesus monkeys.

PURPOSE Influence of longitudinal chromatic aberration (LCA) on emmetropization during early eye development has not been studied in primates. We investigated the effects of quasi-monochromatic lighting on refractive development and eye growth in rhesus monkeys. METHODS Infant rhesus monkeys were raised under one of three lighting conditions for 51 weeks: quasi-monochromatic blue light (peak 455 nm), red light (peak 610 nm), and white light (color temperature 5000 K). All animals underwent biometric measurements using cycloplegic streak retinoscope, keratometry, and A-scan ultrasonography for refraction, corneal power, and axial components, respectively, at designated time points. RESULTS At the 51st week, the mean difference in refraction of the white light and blue light groups, compared with that of the red light group, reached 1.71 diopters (D) and 1.43 D, respectively (both P < 0.001). Two monkeys in the red light group developed myopia at the 16th week, whereas the other seven remained hyperopic throughout the experiment. No significant difference in mean refraction was observed between the blue light group and white light group. CONCLUSIONS Illumination from long-wavelength light during early life could be a risk factor for the development of myopia in a small proportion of rhesus monkeys that are sensitive to L-cone stimulation.

Dynamic Changes in Ocular Zernike Aberrations and Tear Menisci Measured with a Wavefront Sensor and an Anterior Segment OCT

PURPOSE To measure dynamic change characteristics of spatial and temporal variations in the post-blink tear film of normal eyes. METHODS A wavefront sensor was used to measure dynamic changes in wavefront aberrations, up to the seventh order, for 10 seconds in a group of 33 normal young adults. Tear menisci were imaged with an anterior segment optical coherence tomography (AS-OCT) system and tear film break-up times (TFBUTs) were determined. RESULTS Systematic changes in main axis astigmatism (R(2) = 0.933, P < 0.0001), vertical coma (R(2) = 0.935, P < 0.0001) and spherical aberrations (R(2) = 0.879, P = 0.0002) occurred during the 10-second post-blink period. Both lower tear meniscus height and area increased by 10 seconds compared with the initial levels (P < 0.0001 for each). The change of vertical coma had significant correlation with the increase of lower tear meniscus areas during the 10-second post-blink period (R(2) = 0.181, P = 0.014). Subjects with TFBUTs < 15 seconds had significantly increased main axis astigmatism, vertical coma, and spherical aberrations by 10 seconds. Subjects with longer TFBUTs did not have any significant wavefront aberrations during that period. CONCLUSIONS Systematic changes in some Zernike aberrations after blinking are associated with the changes in tear menisci and TFBUT. There was a substantial individual variation in dynamic changes of Zernike aberrations, suggesting the necessity to explore individual differences in tear quality and tear performance. Dynamic wavefront measurement combined with anterior segment optical coherence tomography could provide a useful tool to understand spatial and temporal processes of the tear film in clinical practice.

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

The purpose of this study was to theoretically model the contributions of corneal asphericity (Q) and anterior chamber depth to peripheral wavefront aberrations.

The influence of intraocular pressure on wavefront aberrations in patients undergoing laser-assisted in situ keratomileusis.

PURPOSE To investigate the effect of intraocular pressure (IOP) on wavefront aberrations in the anterior cornea, the internal optics, and the whole eye for myopic patients undergoing laser-assisted in situ keratomileusis (LASIK) surgery. METHODS Fifty-seven myopic subjects were tested for wavefront aberrations in the anterior corneal surface and the whole eye using a corneal topographer and a wavefront analyzer, respectively, pre- and post-LASIK. The IOP and central corneal thickness (CCT) were measured with a noncontact tonometer and a pachymeter, respectively. Pre- and postoperative wavefront aberrations were compared, and the correlation between changes in the Zernike aberrations and the IOP was statistically tested. RESULTS The mean root mean square (RMS) values of the higher-order aberrations (HOAs) were significantly increased in the anterior cornea, the internal optics, and the whole eye. The mean RMS values for a majority of Zernike terms were significantly increased, and systematic increases in the spherical aberrations were found in both the cornea and the whole eye. The spherical aberrations after LASIK were significantly correlated to the IOP (r = 0.59, P < 0.01, for oculus dexter [OD, right eye] and r = 0.49, P < 0.01, for oculus sinister [OS, left eye] in the cornea; r = 0.38, P < 0.01, for OD and r = 0.46, P < 0.01, for OS in the whole eye). CONCLUSIONS IOP contributes to LASIK-induced HOAs, particularly spherical aberrations. To control the HOAs after LASIK, a new algorithm should include the IOP as a variable for laser surgery.

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

Citation information: Xu J, Bao J, Lu F & He JC. An indirect method to compare the reference centres for corneal measurements. Ophthalmic Physiol Opt 2012, 32, 125–132. doi: 10.1111/j.1475‐1313.2011.00880.x

Scheimpflug image-processing method for accurate measurement of ocular surfaces.

PURPOSE: To develop a method to process Scheimpflug images to estimate higher‐order variations in ocular surfaces. SETTING: New England College of Optometry, Boston, Massachusetts, USA. METHODS: Zernike polynomial functions were used rather than lower‐order surface functions to fit the ocular surfaces to evaluate higher‐order variations. A related ray‐tracing method was developed to correct optical distortion of the Scheimpflug image. RESULTS: The new method to process Scheimpflug images showed higher‐order variations in the posterior corneal surface. In a simulation, ignoring higher‐order variations in the anterior corneal surface, as in previous studies, produced an error as high as 202% for some estimated Zernike coefficients of the posterior corneal surface. CONCLUSION: The results indicate that it is necessary to correct refractive distortion in Scheimpflug images using higher‐order surface functions and that the method developed in this study can be used to process scheimpflug images for measurement of ocular wavefront aberrations. Financial Disclosure: Neither author has a financial or proprietary interest in any material or method mentioned.