Lens Structures Research Articles

The effect of lens parameters on the development of the primary angle-closure glaucoma

Objective To investigate the role the lens dimensions played on the pathogenesis of primary angle-closure glaucoma. Methods 38 eyes of 20 patients with primary angle-closure glaucoma(PACG) and 35 eyes of 22 normal individuals without ocular abnormalities were examined. The anatomical parameters of the lens and other structures of the anterior segment were calculated using B ultrasound, computer image processing and ultrasound biomicroscopy(UBM). The parameters were compared between the patients and normal subjects. Correlation analysis was used to determine the relationship between the radii of curvature of the anterior lens surface(RCALS) and the other parameters of the anterior segment. Results Compared with the normal eyes, the eyes of PACG had thicker lens, steeper curvature of anterior lens surface, decreased depth of the anterior chamber, narrower chamber angle, and more anterior position of the ciliary bodies and lens. All these differences were significant( P <0.05 or P < 0.01). In the PACG group, the RCALS had significantly negative correlation with the central and peripheral lens thickness( P <0.01and P < 0.05 respectively), and had positive correlation with relative lens position, anterior chamber depth(ACD), angle-open distance at 500 um(AOD 500), trabecular iris angle(TIA) and trabecular ciliary processes distance(TCPD, P <0.05or P <0.01). Conclusion The occurrence of PACG is relevant to the abnormal anatomical structures of the anterior segment. Among all factors, the lens parameters play an important role in the pathogenesis. Increased lens thickness, relative more anterior position of lens, especially steepened curvature of anterior lens surface are predisposing factors of the pathologic phenomenon in PACG including pupillary blockage, shallow anterior chamber, secondary closure of chamber angle and elevation of intraocular pressure.

Morphological and optical properties of the corneal lens and retinal structure in the posterior large stemma of the tiger beetle larva

The morphological and optical features of the corneal lens and retina have been examined in the posterior large stemma of the larva of the tiger beetle ( Cicindela chinensis). A cup-shaped retina was positioned 55 ± 6 μm beneath the posterior margin of the corneal lens, which was 479 ± 20 μm in diameter and 391 ± 18 μm in thickness ( n = 41). A light path through an isolated corneal lens showed that the object at infinite distance was focused on the distal margin of the retina. Geometrical optics gave a value of 334 ± 15 μm ( n = 55) for the posterior focal length of the corneal lens. The refractive index of the corneal lens was estimated to be around 1.8, if the lens was considered to be homogenous in structure. The internal structure of the lens, including concentric lamellae, was presumed to contribute to such a high refractive index, because this was higher than that of insect cuticle. The retinal structure and how images were blurred at different focus levels were also examined. Data obtained for optics of the corneal lens and retinal structures are discussed with reference to the distinct visual behavior of the larva.

Cover Picture: Fabricating Microlens Arrays by Surface Wrinkling (Adv. Mater. 24/2006)

AbstractThe unique lateral confinement of a swelling polymer network leads to surface wrinkles that define a multitude of surface structures, including microlens arrays (background). The versatility of this approach, which is reported on p. 3238 by Crosby and Chan, allows for the realization of a variety of functional devices on both planar and nonplanar surfaces, such as synthetic compound lens structures (see inset).

Multistage Polymeric Lens Structures Integrated into Silica Waveguides

A waveguide lens, composed of multistage polymer-filled thin grooves in a silica planar lightwave circuit (PLC) is proposed and a low-loss structure has been designed. A waveguide lens in a silica slab waveguide has been fabricated using reactive ion etching (RIE) and formed by filling with polymer. Both an imagding optical system and a Fourier-transform optical system can be configured in a PLC using a waveguide lens. It renders the PLC functional and its design flexible. To obtain a shorter focal length with a low insertion loss, it is more effective to use a multistage lens structure. An imaging optical system and a Fourier-transform optical system with a focal length of less than 1000 µm were fabricated in silica waveguides using a multistage lens structure. The lens imaging waveguides incorporate a 16–24-stage lens, with insertion losses of 4–7 dB. A 4 ×4 optical coupler, using a Fourier-transform optical system, utilizes a 6-stage lens with losses of 2–4 dB.

A DoD Perspective on Left Handed Negative Index Materials and Potential Applications

AbstractIn the quest for ever smaller, lighter weight, and conformal components and devices for radar and communication applications, researchers in the RF community have increasingly turned to artificially engineered, composite structures (or “metamaterials”) in order to exploit the extraordinary electromagnetic response these materials offer. One particularly promising class of metamaterials that has recently received a great deal of attention are “left-handed” or negative index materials. Because these metamaterials exhibit the unique ability to bend and focus light in ways no other conventional materials can, they hold great potential for enabling a number of innovative lens and antenna structures for a broad range of commercial and DoD relevant applications. Exploring the possible implementation of negative index materials for such applications will require significant enhancements in the properties of existing Negative Index Materials (NIM) (bandwidth, loss, operational frequency, etc.), as well as improved understanding of the physics of their electromagnetic transport properties. For this reason the Defense Advanced Research Project Agency (DARPA) has initiated a program that seeks to further develop and demonstrate NIM for future DoD missions including, but not limited to, the following: 1) lightweight, compact lenses with improved optics; 2) sub wavelength/high resolution imaging across the electromagnetic spectrum; 3) novel approaches to beam steering for radar, RF, and/or optical communications; and 4) novel approaches for integrating optics with semiconductor electronics. A brief overview of the salient properties of NIM will be presented as well as a general discussion of a few of their potential applications.

A microfabricated capillary electrophoresis chip with multiple buried optical fibers and microfocusing lens for multiwavelength detection

We present a new microfluidic device utilizing multiwavelength detection for high-throughput capillary electrophoresis (CE). In general, different fluorescent dyes are only excited by light sources with appropriate wavelengths. When excited by an appropriate light source, a fluorescent dye emits specific fluorescence signals of a longer wavelength. This study designs and fabricates plastic micro-CE chips capable of performing multiple-wavelength fluorescence detection by means of multimode optic fiber pairs embedded downstream of the separation channel. For detection purposes, the fluorescence signals are enhanced by positioning microfocusing lens structures at the outlets of the excitation fibers and the inlets of the detection fibers, respectively. The proposed device is capable of detecting multiple samples labeled with different kinds of fluorescent dyes in the same channel in a single run. The experimental results demonstrate that various proteins, including bovine serum albumin and beta-casein, can be successfully injected and detected by coupling two light sources of different wavelengths to the two excitation optic fibers. Furthermore, the proposed device also provides the ability to measure the speed of the samples traveling in the microchannel. The developed multiwavelength micro-CE chip could have significant potential for the analysis of DNA and protein samples.

New method to correct eddy current in magnetic focusing-deflection system

Analysis and new structure is introduced to correct eddy current in electron beam focusing-deflection system. Maximum errors caused by eddy current are computed by changing permeability of the conductive materials at time t 0 ( t 0 = 0, μ = 0) and t ∞ ( t 0 = ∞, μ = μ r) with the aid of Munro’s software. The new double ferrite structure includes outer- and inner-layer ferrite rings which are spaced by ceramic spacer uniformly and staggered each other in radial direction. Basic principle for eddy current correction in this paper is that ferrite materials prevent the flow of magnetic flux from the deflection coil to the polepiece without perturbing the lens field. Magnetic flux of various lens structures and magnetic scalar equipotential lines of various deflectors illustrate the principle. Correction and performance versus the values of the gap (G) and the space (S) between the ferrite rings are considered. The new double ferrite structure not only corrects the eddy current, but also increases the sensitivity of the deflection without decreasing the performance.

APPLICATION OF INTEGRAL EQUATION METHOD TO METAL-PLATE LENS STRUCTURES

The present paper concerns the design, numerical analysis, and measurement for simple metal-plate lens structures. The power of electromagnetic waves can be concentrated by arranging flat strips parallel to one another and adjusting the transverse and longitudinal length of the waveguide regions. The simple designing procedures are described for the lenses with plane, concave, and convex profiles. These steps are practically applied to construct the lenses for the X band. In order to discuss the dependence of focusing properties on the lens and source types, we numerically analyze the scattering problems using the integral equations combined with the moment method. The lenses are made up by aluminum plates, and the field amplitude in the transmission region is measured. We confirm the formation of the focus near the design point.

On gravity currents propagating at the base of a stratified ambient: effects of geometrical constraints and rotation

The behaviour of an inviscid gravity current released from a lock and propagating over a horizontal boundary at the base of a stratified ambient fluid is considered in the framework of a one-layer shallow-water formulation. Solutions for two-dimensional rectangular and axisymmetric geometries, with emphasis on the rotation of the latter, were obtained by a Lax–Wendroff scheme. Box-model approximations are also discussed. The axisymmetric and rotating case admits steady-state lens structures, for which approximate and numerical solutions are presented. In general, the stratification reduces the velocity of propagation and enhances the Coriolis effects in a rotating system (in particular, the maximal radius of propagation decreases). Comparisons of the shallow-water results with Navier–Stokes simulations and laboratory experiments indicate good agreement, at least for the initial period of propagation. The major deficiency of this shallow-water model is the lack of incorporation of internal waves. In particular, if the propagation is at subcritical speed, the applicability of the model is restricted to the time prior to the first effective interaction between the head of the gravity current and the lowest-order internal wave; an estimate of this position is presented.

Dynamic aspects of accommodation: age and presbyopia

There has been no comprehensive study involving each of the primary dynamic components of accommodation in the same cohort as related to age and presbyopic onset; furthermore, the current findings are equivocal. Dynamic monocular components of accommodation (latency, time constant, peak velocity/amplitude relationship, and microfluctuations) were assessed objectively using an infrared optometer within the linear region of accommodation in 30 visually-normal human subjects aged 21–50 years. The time constant and the peak velocity/amplitude relationship did not change with age. However, latency progressively increased, and microfluctuation amplitude and frequency progressively decreased, with increasing age. The invariance in time constant suggests that the gross biomechanical aspects of the lens and related structures in the remaining linear region are relatively unaffected by age. In contrast, the decrease in microfluctuation activity with age suggests more subtle alterations in the biomechanical aspects of the lens to these very small perturbations, such as a response amplitude non-linearity. With respect to neurologic control, the progressive latency increase suggests a processing delay of the blur input, and this is consistent with age-related changes in reaction time measures. The lack of any age-related changes in the peak velocity/amplitude relationship implies normalcy of central and peripheral neuromotor control, as well as grossly normal first-order lens biomechanics, in this linear response region. The results are consistent with the Hess–Gullstrand theory of presbyopia.

Wave-front analysis: are we missing something?

W AVE-FRONT ANALYSIS OF ABERRATIONS HAS captured the attention and imagination of scientists and surgeons interested in refractive surgery. This exciting technology offers methodology to objectively measure lowand high-order aberrations within the optical system from the tear film to the surface of the retina. A number of different instruments based on Hartman-Shack aberrometry, ray tracing, and other methodologies are now commercially available. Linkage of the analyses obtained from these systems to excimer laser custom corneal ablation in laser in situ keratomileusis (LASIK), laser subepithelial keratomileusis (LASEK), and photorefractive keratectomy (PRK) has been the inspiration for efforts to optimize visual performance or even produce “super vision.” This new technology has already contributed to our understanding of issues such as decreased quality of vision after refractive surgery and the importance of higher order aberrations in vision quality.1–3 There are, however, already signs that this technology, although certainly useful, will have limitations. For example, it is now clear that the measured aberrations are dependent on pupil size, accommodative state, and changes that occur in the lens and other structures with age.1–3 These findings raise issues about long-term stability of the correction and which measurement parameters should be used to direct surgery in a particular patient. Physicians who have begun using the data provided by aberrometers in clinical practice have also observed notso-subtle observations about the clinical utility of the information for something as precise as laser vision correction. One obvious example is the correlation between refractions provided by aberrometers and manifest refractions with subjective refinement. There are significant differences between these measured parameters in many eyes studied. In some cases, the differences are notable. For example, in the wavefront analysis in Figure 1 analyzed over a 4-mm pupil, 1.86 diopters of astigmatism were detected, while the patient would only accept 1.25 diopters during manifest refraction refined with a .25 Jackson cross cylinder. The wavefront-derived refraction provided astigmatism powers of 1.77, 1.86, and 1.87 diopters with analyses at 3-, 4-, and 5-mm pupil sizes, respectively, in this eye. Such differences pose interesting dilemmas for treatment. Should treatments be applied based on the wavefront data alone or wave-front data adjusted according to the manifest refraction with subjective refinement? These differences have been ascribed to imperfections in the relatively new instrumentation, differences in pupil dilation during aberrometry and refraction, errors in registration, poor pupil centration, measurement noise, and other technical factors. However, there is likely another more fundamental factor that also contributes to the discrepancy. Simply put, most aberrometers and ray tracers provide no information about what happens to visual input during central nervous system processing from the retina to the visual cortex, but manifest refractions with subjective refinement do. The information provided by the manifest refraction is limited to lower order aberrations, but correction of lower order aberrations is an important determinant of visual quality after refractive surgery. Actually, clinicians have had some indications of the limitations of objective optical measurements for centuries. From time to time, every clinician examines a patient in whom objective refraction with a retinoscope reveals high astigmatism that the patient will not accept during subjective refinement with a Jackson Cross cylinder. Clinicians also deal with issues related to plasticity in central processing in patients who have adverse reactions to new prescriptions for glasses. Many of these patients adapt to the prescription change over time. However, some patients never seem to adjust to even minor changes. Ophthalmologists have learned to compromise and decrease changes to parameters such as level of astigmatism or astigmatism axis to smooth the patient adjustment. Hubel and Wiesel received the Nobel Prize in 1981 for their pioneering work on the architecture, function, development, and plasticity of the visual cortex.4 Their studies, and subsequent work by these and other authors, have shown that development of the visual pathways of the central nervous system is modulated by visual input Accepted for publication Feb 19, 2003. InternetAdvance publication at ajo.com June 13, 2003. From the Department of Ophthalmology, University of Washington, Seattle, WA. Inquiries to Steven E. Wilson, MD, Department of Ophthalmology, University of Washington, Box 356485, Seatlle, WA 98195.

Multiport-illumination-system-assisted phacoemulsification in eyes with dense vitreous hemorrhage during combined cataract and vitreous surgery

We describe the use of a multiport illumination system to enhance the red reflex during combined phacoemulsification and pars plana vitrectomy in 10 patients with cataract and vitreous hemorrhage. This method improves illumination and visualization of the lens structures and the instruments, which may reduce the risk of complication. To our knowledge, this approach has not been reported.

Diamond planar refractive lenses for third- and fourth-generation X-ray sources.

The fabrication and testing of planar refractive hard X-ray lenses made from bulk CVD diamond substrates is reported. The lens structures were generated by electron-beam lithography and transferred by reactive-ion etching into the diamond. Various lens designs were fabricated and tested at 12.4 and 17.5 keV photon energy. Efficiencies of up to 71% and gains of up to 26 were achieved. A line focus of 3.2 micro m (FWHM) was measured. These lenses should be able to withstand the extreme flux densities expected at the planned fourth-generation X-ray sources.

Surgical management of anterior chamber epithelial cysts

PurposeTo review management strategies for treatment of anterior chamber epithelial cysts. DesignRetrospective review of consecutive interventional case series. MethodsCharts of patients treated for epithelial ingrowth over a 10-year period by a single surgeon were reviewed. Cases of anterior chamber epithelial cysts were identified and recorded, including details of ocular history, preoperative and postoperative acuity, intraocular pressure (IOP), and ocular examination, type of surgical intervention, and details of further procedures performed. ResultsSeven eyes with epithelial cysts were identified. Patient age ranged from 1.5 to 53 years at presentation. Four patients were children. In four eyes, cysts were secondary to trauma, one case was presumably congenital, one case developed after corneal perforation in an eye with Terrien’s marginal degeneration, and one case developed after penetrating keratoplasty (PK). Three eyes were treated with vitrectomy, en bloc resection of the cyst and associated tissue, fluid–air exchange and cryotherapy. The last four eyes were treated with a new conservative strategy of cyst aspiration (three cases) or local excision (one keratin “pearl” cyst), and endolaser photocoagulation of the collapsed cyst wall/base. All epithelial tissue was successfully eradicated by clinical criteria; one case required repeat excision (follow-up, 9 to 78 months, mean 45). Two eyes required later surgery for elevated IOP, two for cataract extraction and one for repeat PK. Final visual acuity ranged from 20/20 to hand motions, depending on associated ocular damage. Best-corrected visual results were obtained in the more conservatively managed eyes. ConclusionsAnterior chamber epithelial cysts can be managed conservatively in selected cases with good results. This strategy may be particularly useful in children’s eyes, where preservation of the lens, iris, and other structures may facilitate amblyopia management.

Resolution limit of probe-forming systems with magnetic quadrupole lens triplets and quadruplets

Over the past decade, in MeV ion beam microanalysis efforts to achieve a spatial resolution better than 0.1 μm with a beam current of ∼100 pA have been connected with microprobes of new generation where the probe is formed by means of separated magnetic quadrupole lens structures [1]. However, as was pointed out in [2], no dramatic improvements in spatial resolution have been produced so far. For better understanding of the situation the authors carried out theoretical studies of multiparameter sets of probe-forming systems based on separated triplets and quadruplets of magnetic quadrupole lenses. Comparisons were made between the highest current values attained at different systems for a given beam spot size. The maximum parasitic sextupole and octupole field components were found whose contributions to spot broadening are tolerable. It is shown that the use of modern electrostatic accelerators [3] and precision magnetic quadrupole lenses [4,5] makes it possible to eliminate the effect of chromatic aberrations and second- and third-order parasitic aberrations resulting from distortions of the quadrupole lens symmetry. Therefore probe-forming systems with triplets and quadruplets of magnetic quadrupole lenses have a lower theoretical spatial resolution limit which is restricted mainly by intrinsic spherical third-order aberrations in state-of-the-art microprobes.

Biotin decreases retinal apoptosis and induces eye malformations in the early chick embryo

Proliferation, cell death and differentiation occur simultaneously in developing retina and are precisely orchestrated. We have studied the effects of biotin (vitamin H) on early retinal development. In vivo administration of biotin to early embryonic chick eyes at moderately elevated levels induced malformations, affecting retina and lens structures. The effects were strictly age dependent and were only found in embryos treated between Hamburger and Hamilton stage 14-17. Biocytin, a biotin analogue, mimicked biotin effects, while avidin could block the effects. At the cellular level, biotin did not affect proliferation but reduced apoptosis. These results suggest that an adequate content of biotin and a precise regulation of retinal cell death are required for the correct morphogenesis of the eye.

Submillimeter focusing of the University of Hong Kong positron beam

The slow positron beam facility Hong Kong submillimeter electron annihilator (HOSEA) at the University of Hong Kong has now been in operation for 6 years with a beam diameter of ∼6 mm and intensity ∼10 4e + s −1. It is now planned to improve the facility by narrowing the beam diameter to less than 1 mm, while increasing the intensity to ∼5×10 5e + s −1. The motivation behind the submillimeter beam is to make it a more effective tool in the study of MOS and MS systems that are hard to fabricate in larger than millimeter dimensions. In particular the development of positron deep level transient (thermal) spectroscopy (PDLTS) could also benefit from a beam of submillimeter dimensions. While consisting of a hybrid electric/magnetic lens structure close to the moderator to produce low canonical momentum phase space, the guidance to the target is purely magnetic. The beam structure is however unusual, consisting as it does of a recurrent re-focusing of the first primary positron focus produced by the hybrid focusing lens close to the moderator. The simulation program, SIMION, is employed to simulate the trajectories of positrons through possible hybrid lens structures and optimize the working parameters of the facility. The simulations show that an outstanding focusing diameter and a repetitive focusing can be obtained all the way to the target above beam energies of 1 keV.

Arrested differentiation and epithelial cell degeneration in zebrafish lens mutants.

In a chemical mutagenesis screen, we identified two zebrafish mutants that possessed small pupils. Genetic complementation revealed these two lines are due to mutations in different genes. The phenotypes of the two mutants were characterized using histologic, immunohistochemical, and tissue transplantation techniques. The arrested lens (arl) mutant exhibits a small eye and pupil phenotype at 48 hr postfertilization (hpf) and lacks any histologically identifiable lens structures by 5 days postfertilization (dpf). In contrast, the disrupted lens (dsl) mutants are phenotypically normal until 5 dpf, and then undergo lens disorganization and cell degeneration that is apparent by 7 dpf. Histology reveals the arl mutant terminates lens cell differentiation by 48 hpf, whereas the dsl lens exhibits a defective lens epithelial cell population at 5 dpf. Lens transplantation experiments demonstrate both mutations are autonomous to the lens tissue. Immunohistochemistry reveals the retinal cells may suffer subtle effects, possibly due to the lens abnormalities.

These Stars Have Eyes

The ability to detect and react to light can be critically important for an animal’s self preservation, and many varieties of eyes have been developed in the animal kingdom. Recently, a team of researchers from Bell Laboratories, Lucent Technologies, the Weizmann Institute, and the Natural History Museum of Los Angeles have found evidence for a novel photoreceptor system in some species of brittle stars. 1 1. J. Aizenberg, A. Tkachenko, S. Weiner, L. Addadi, G. Hendler, Nature 412, 819 (2001) https://doi.org/10.1038/35090573. Spiny brittle stars (top figure) are a class of echinoderms, relatives of starfish and sea urchins. With their wiggly arms, brittle stars are capable of very fast motion. These marine invertebrates lack anything immediately recognizable as eyes, yet some species, such as Ophiocoma wendtii, show a remarkable light sensitivity: As shown in the top figure, they change color from day (upper) to night (lower), and they can detect and dart into shadows or crevices when predators approach.This photosensitivity has been attributed to diffuse dermal receptors. Now, Joanna Aizenberg (Bell Labs) and colleagues have found that the skeletal elements (middle figure) that protect the upper (dorsal) part of the brittle star arms may form what’s essentially an extended compound eye in the light-sensitive species. As in all echinoderms, each of these skeletal elements is composed entirely of single-crystal calcite (calcium carbonate). Whereas the dorsal arm plates of light-insensitive brittle stars have an irregular porous structure, those of O. wendtii and other light-sensitive species have on their outer surface a regular array of nearly uniform nodules 20–50 µm in diameter (bottom figure).These protuberances have many properties of an engineered microlens array. Calcite is birefringent, but in these structures the optical axis is normal to the plates and parallel to the lens axis; this optimal orientation prevents the formation of double images. In addition, the researchers found that each protuberance has a nearly ideal double-lens shape that closely resembles the shapes proposed in the 17th century by Descartes and Huygens to minimize spherical aberrations. Such shapes maximize a lens’s light-gathering ability and sensitivity. The only other known calcitic lens structures like this in the animal kingdom are from the extinct trilobites, which thrived about 200–550 million years ago. 2 2. E. N. K. Clarkson, R. Levi-Setti, Nature 254, 663 (1975) https://doi.org/10.1038/254663a0. Aizenberg and company studied the optical properties of the microlens arrays from O. wendtii using photolithography. Similar to someone moving a magnifying glass up and down until focused sunlight ignites a piece of paper, the researchers exposed photoresist at various distances below the lens layer. From the sizes of the exposed spots in the resist, the researchers not only confirmed the focusing ability of the calcitic structures but also determined the focal length and the spot size in the focal plane. The possible role of these microlenses in the brittle star’s photoresponse system is supported by the presence of bundles of nerve fibers located just beneath the lens layer at the calculated focal points of the lenses. The sizes of the bundles also agree well with the experimentally determined focus spot size (about 3 µm). Furthermore, the color change in O. wendtii is due to mobile pigment-containing cells that act somewhat as irises, regulating the amount of light that reaches the lenses. Such a response explains why O. wendtii is sensitive to lower levels of illumination at night than it is during the day. Some questions remain, though, such as whether it is the nerve bundles themselves or associated tissue that is photoreceptive, and how the brittle star’s nervous system processes the signals received from the microlenses. With their regularity and precise curved shape and orientation, the brittle star microlens arrays should inspire new ideas of what may be possible in the emerging field of biomimetics, or “biologically inspired materials synthesis.”G. HENDLERPPT|High resolutionJ. AIZENBERGPPT|High resolutionJ. AIZENBERGPPT|High resolutionREFERENCESSection:ChooseTop of pageREFERENCES <<1. J. Aizenberg, A. Tkachenko, S. Weiner, L. Addadi, G. Hendler, Nature 412, 819 (2001) https://doi.org/10.1038/35090573. Google ScholarCrossref, CAS2. E. N. K. Clarkson, R. Levi-Setti, Nature 254, 663 (1975) https://doi.org/10.1038/254663a0. Google ScholarCrossref, CAS© 2001 American Institute of Physics.

Pax6 activity in the lens primordium is required for lens formation and for correct placement of a single retina in the eye

The Pax6 transcription factor plays a key role in ocular development of vertebrates and invertebrates. Homozygosity of the Pax6 null mutation in human and mice results in arrest of optic vesicle development and failure to initiate lens formation. This phenotype obscures the understanding of autonomous function of Pax6 in these tissue components and during later developmental stages. We employed the Cre/loxP approach to inactivate Pax6 specifically in the eye surface ectoderm concomitantly with lens induction. Although lens induction occurred in the mutant, as indicated by Sox2 up-regulation in the surface ectoderm, further development of the lens was arrested. Hence, Pax6 activity was found to be essential in the specified ectoderm for lens placode formation. Furthermore, this mutant model allowed us for the first time to address in vivo the development of a completely normal retina in the absence of early lens structures. Remarkably, several independent, fully differentiated neuroretinas developed in a single optic vesicle in the absence of a lens, demonstrating that the developing lens is not necessary to instruct the differentiation of the neuroretina but is, rather, required for the correct placement of a single retina in the eye.