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It has been known for over a century that the basic organization of the retina is conserved across vertebrates. It has been equally clear that retinal cells can be classified into numerous types, but only recently have methods been devised to explore this diversity in unbiased, scalable, and comprehensive ways. Advances in high-throughput single-cell RNA-sequencing (scRNA-seq) have played a pivotal role in this effort. In this article, we outline the experimental and computational components of scRNA-seq and review studies that have used them to generate retinal atlases of cell types in several vertebrate species. These atlases have enabled studies of retinal development, responses of retinal cells to injury, expression patterns of genes implicated in retinal disease, and the evolution of cell types. Recently, the inquiry has expanded to include the entire eye and visual centers in the brain. These studies have enhanced our understanding of retinal function and dysfunction and provided tools and insights for exploring neural diversity throughout the brain. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Purpose: To study the practical use of the Rubric for Assessment of Eye Bank Professionals for Eye Retrieval (RAEPER) as a competency assessment tool by organizing a workshop in two eye banks – one in India and other in America. Methods: Two-day workshop was conducted in two eye banks – named Shroff's Charity Eye Hospital (SCEH) in India and Miracles in Sight (MIS) in America. Day 1 of workshop comprised of didactic lectures and discussions and day 2 was eye retrieval assessment done on human eyes in a wet lab setting. Assessment was done using RAEPER by two independent senior eye bank managers. Results: MIS had 27 participants, 15 males and 12 females (mean age: 38.8 years, range: 28-55) and SCEH had 11 participants, 10 males and 1 female (mean age: 48 years, range: 22–68). All participants were in house technicians, who had a minimal experience of at least 150 eye retrievals. At MIS, step 19 (crystalline lens check) got a score of 3 (Competent) 93.5% of the time. At SCEH, step 6 (conjunctival removal) and step 4 (Irrigation of cornea with sterile saline) were high scoring with 90.11% and 72.7% scoring 3, respectively. Conclusion: India's cornea blind population is expected to reach 10 million by 2020. Steps need to be taken to improve cornea retrieval rates in the country and make various eye banks self-sufficient. Incorporating such training modules not only improves the cornea utilization rates, but also helps standardize the entire eye banking process.

Three-dimensional magnetic resonance imaging (3D MRI) of the eye is a powerful tool to visualize the entire shape of the eye. Using 3D MRI, posterior staphylomas can be observed in its full extent and how the entire eye shape changes in parallel. It has also been shown that some specific eye shape is related to poor visual outcome.

This study compared the axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), mean anterior corneal radius of curvature (Rm), and postoperative refractive outcomes obtained from two different swept-source optical coherence biometers, the ARGOS (Movu, Aichi, Japan), which uses the segmental refractive index for each segment, and the IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany), which uses an equivalent refractive index for the entire eye. One hundred and six eyes of 106 patients with cataracts were included. The refractive outcomes using the Barrett Universal II, Haigis, Hoffer Q, and SRK/T formulas were evaluated. The mean AL, CCT, ACD, and Rm differed significantly (P 0.05). The accuracy of the intraocular lens power calculations was clinically acceptable with both biometers, although the ocular biometry using these two biometers exhibited certain differences.

Quality of vision has been emphasized in ophthalmologic clinical practice in recent years. The optical or visual performance of the human eye is not static and fluctuates over time. Considering the major origins of temporal fluctuations in optical or visual performance, quantitative assessment of the dynamic changes in the optical quality of the entire eye is important. This review provides an overview of the clinical application of the objective methods for assessing dynamic changes in optical quality, particularly those associated with accommodation, the precorneal tear film, the prelens tear film, and contact lens movement and fitting.

Purpose:To assess the correlation between the scleral shape and corneal astigmatism.Methods:Twenty-two participants (11 nonastigmatic and 11 astigmatic) aged from 19 to 36 years and with no previous ocular surgeries were included in this study. Three-dimensional (3D) corneoscleral maps from both eyes (44 eyes) were acquired using a corneoscleral topographer (Eye Surface Profiler). Each 3D map was split into 13 concentric annuli, each 0.5-mm wide, starting at 1.0-mm radius from the corneal apex to the scleral periphery at 7.5 mm from the apex. Each ring was fitted to a quadratic function of the radial distance to the apex, to calculate the elevation difference between the raw data and the fitting surface ring. For each ring, the resulting elevation difference between the original and fit data profile was fit to a sum of sine function. Decentration and astigmatic terms obtained from the sinusoidal fit were analyzed and compared between nonastigmatic and astigmatic groups.Results:In astigmatic eyes, corneal and scleral asymmetry are highly correlated, but both appear independent of each other in nonastigmatic eyes. No significant difference between astigmatic and nonastigmatic eyes was found for the decentration term [P > 0.05/N (Bonferroni)], whereas for the astigmatic component, the differences were statistically significant [P < 0.05/N (Bonferroni)].Conclusions:Corneal and scleral shapes are correlated in astigmatic eyes, which suggests that astigmatism is not restricted to the cornea but should rather be considered a property of the entire eye globe.

This article outlines a suite of techniques in light microscopy (LM) and electron microscopy (EM) which can be used to study the internal and external eye anatomy of insects. These include traditional histological techniques optimized for work on ant eyes and adapted to work in concert with other techniques such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM). These techniques, although vastly useful, can be difficult for the novice microscopist, so great emphasis has been placed in this article on troubleshooting and optimization for different specimens. We provide information on imaging techniques for the entire specimen (photo-microscopy and SEM) and discuss their advantages and disadvantages. We highlight the technique used in determining lens diameters for the entire eye and discuss new techniques for improvement. Lastly, we discuss techniques involved in preparing samples for LM and TEM, sectioning, staining, and imaging these samples. We discuss the hurdles that one might come across when preparing samples and how best to navigate around them.

PURPOSE To investigate how age and other factors affect astigmatism in Japanese adults over a period of 5 years. METHODS We included 512 Japanese participants who had undergone systemic and ophthalmological examinations both in 2005-2007 and in 2010-2012 in Funagata town, Yamagata, Japan. Astigmatism was evaluated using power vector analyses, where J0 represents the power of orthogonal astigmatism. Positive values of J0 indicate with-the-rule astigmatism, whereas negative values indicate against-the-rule (ATR). RESULTS In this cross-sectional investigation, J0 represented the power of orthogonal astigmatism, and multivariate regression revealed that both J0 and corneal J0 (cJ0) declined with increasing age (both P < 0.001). In a longitudinal investigation spanning 5 years, the mean amounts of change (Δ) in J0 and ΔcJ0 were -0.045 ± 0.308 and -0.072 ± 0.278, respectively. This confirmed an ATR shift with increasing age in most individuals. The age-divided distribution of the magnitude of differences indicated that older age was associated with a larger astigmatic change over a 5-year period in both the cornea and the entire eye. Using multivariate logistic regression, we observed that older age at baseline was a risk factor for low ΔJ0, indicating a large shift toward ATR astigmatism. CONCLUSIONS We confirmed that a refractive and keratometric shift toward ATR astigmatism occurs with aging. Older age at baseline was also associated with a larger magnitude of astigmatic changes over the subsequent 5 years.

Purpose The rate of conventional aqueous humor outflow is the highest nasally. We hypothesized that this is reflected in regionally different outflow structures and analyzed the entire limbus by high-resolution, full-thickness ribbon-scanning confocal microscopy (RSCM). Methods We perfused pig eyes by anterior chamber cannulation with eight lectin-fluorophore conjugates, followed by optical clearance with benzyl alcohol benzyl benzoate (BABB). RSCM and advanced analysis software (Imaris) were used to reconstruct a three-dimensional (3D), whole-specimen rendering of the perilimbal outflow structures. We performed morphometric analyses of the outflow tract from the level of the trabecular meshwork (TM) to the scleral vascular plexus (SVP). Results Except for pigmented structures, BABB cleared the entire eye. Rhodamine-conjugated Glycine max agglutinin (soybean [SBA]) labeled the outflow tract evenly and retained fluorescence for months. RSCM produced terabyte-sized files allowing for in silico dissection of outflow tract vessels at a high resolution and in 3D. Networks of interconnected lumens were traced from the TM to downstream drainage structures. The collector channel (CC) volumes were 10 times smaller than the receiving SVP vessels, the largest of which were in the inferior limbus. Proximal CC diameters were up to four times the size of distal diameters and more elliptical at their proximal ends. The largest CCs were found in the superonasal and inferonasal quadrants where the highest outflow occurs. Conclusion RSCM of cleared eyes enabled high-resolution, volumetric analysis of the outflow tract. The proximal structures had greater diameters nasally, whereas the SVP was larger in the inferior limbus.

The detection of early forms of keratoconus is still a challenge for clinicians. Beside clinical examination and diagnosis of keratoconus, a series of examination techniques has been established in clinical routine to assist in the diagnosis of early forms of keratoconus: corneal topography for measuring the geometry of the corneal front surface, tomography for measuring the geometry of structures of the anterior segment of the eye, aberrometers for evaluation of optical aberrations of the entire eye, and a system for investigation of the biomechanical properties of the cornea. These instruments provide software tools which are designed for diagnostic support in keratoconus. In this review article, we provide an overview over the spectrum of measurement systems currently on the market focussing on their performance for detecting (early forms of) keratoconus. In detail, we focus on dedicated keratoconus screening software modules of topography, tomography, aberrometry and biomechanics.

Evisceration is an ophthalmic surgery that removes the internal contents of the eye followed usually by placement of an orbital implant to replace the lost ocular volume. Unlike enucleation, which involves removal of the entire eye, evisceration potentially causes exposure of uveal antigens; therefore, historically there has been a concern about sympathetic ophthalmic (SO) associated with evisceration. However, critical review of the literature shows that SO occurs very rarely, if ever, as a consequence of evisceration. Its clinical applications overlap with those of enucleation in cases of penetrating ocular trauma and blind painful eyes, but it is absolutely contraindicated in the setting of suspected intraocular malignancy and may be preferred for treatment of end-stage endophthalmitis. From a technical standpoint, traditional evisceration has a limitation in the orbital implant size. Innovations with scleral modification have overcome this limitation, and accordingly, due to its simplicity, efficiency, and good cosmetic results, evisceration has once again been gaining popularity.

Background Normally, we see the street through our high-resolution, high colour-sensitive foveal vision and it is this that provides the definition of what we see – the contrasts between colours, the edges and surfaces we need to see to enjoy or avoid. This part of our vision is served by half the photoreceptors in the eye and these are concentrated in an area of less than 1% of the surface of the retina at the back of the eye. The other half are less colour sensitive, lower resolution, and are spread across the rest of the retina, generally becoming less densely located towards the outer edge. These receptors are, however, well-attuned to detect movement. This research project aim to explores the way in which our peripheral vision contributes to our perception of the street environment and it does provide information about the environment which can helps in our interpretation of the street environment. Methods We designed experiment to test what participant could see with their peripheral vision when their foveal vision is paying attention elsewhere. Firstly, we asked participants to participate in imaging and testing of their peripheral retina. We used a non-invasive imaging method called OPTOMAP, an ultrawide-field laser scanning ophthalmoscope to capture colour and autofluorescent images of the back of the entire eye. For functional testing we then asked our participants to participate in wide field automated perimetry measurement called MonCV1. Both of these equipment are CE marked and used routinely in clinical setting. Results This research suggest that peripheral vision need to be considered in designing a healthy streets because peripheral vision influence various transport planning policies such as designing active travel mode to promote healthy living by reducing carbon emission, and tackling the obesity in the city. Conclusions Peripheral vision does provide a perceptual background against which the more detailed imaging of the foveal vision is presented; b) there was a consistency in some of the participants interpretation of the images and this was corresponded to their description of comfort; c) there was a correlation between the colour and pattern of the image with participant comfort and d) there is a link between the past memory of individual participant with their sense of comfort and translating the images by the peripheral vision. This research project suggested that peripheral vision has a direct influence of our perception in the environment such as street.

Embryonic lethality in mice with targeted gene deletion is a major issue that can be circumvented by using Cre-loxP-based animal models. Various inducible Cre systems are available, e.g. such that are activated following tamoxifen treatment, and allow deletion of a specific target gene at any desired time point during the life span of the animal. In this study, we describe the efficiency of topical tamoxifen administration by eye drops using a Cre- reporter mouse strain (R26R). We report that tamoxifen-responsive CAGGCre-ER (TM) mice show a robust Cre- mediated recombination throughout the entire eye.

During our routine postmortem examination, we found a female infant with "True Cyclopia." The two entire eye balls had fused completely to form one midline organ. The infant was a female who weighed 2910 g. The gestation period was 35 weeks. Infant lived for a short period of less than 20 minutes. The birth was a product of a 4(th) pregnancy.

To assess the repeatability of axial biometry of the entire eye using ultra-long scan depth optical coherence tomography (OCT) and to investigate the agreement with IOLMaster measurements (Carl Zeiss Meditec).Prospective, observational case series.There were 37 adult subjects enrolled in group 1 and 12 adult subjects enrolled in group 2. Using ultra-long scan depth OCT, the left eyes of these groups were measured in 2 separate sessions. The images were processed by a manual method and custom-developed automatic software. A model eye was imaged for verification. The subjects in group 2 were imaged using ultra-long scan depth OCT and using the IOLMaster for axial length measurement comparison.All measured parameters of the model eye matched the geometric parameters. In group 1, there were no significant differences in all measured parameters using automatic and manual segmentation methods (P.05, paired t test). The percentage of coefficient of repeatability of segments ranged from 0.3% to 3.9%. The corresponding interclass correlation coefficients ranged from 0.946 to 0.999. The correlation between the results using automatic and manual segmentation methods appeared to be strong (R(2) = 0.999; P.05). In group 2, the axial length of the eye measured by the IOLMaster matched the results obtained by ultra-long scan depth OCT with the automatic method (R1(2) = 0.987; P.05) and the manual method (R2(2) = 0.988; P.05).Automatic axial biometry using ultra-long scan depth OCT successfully measured each segment of the entire eye with good repeatability. With further development of automatic segmentation, ultra-long scan depth OCT seems to be a promising tool in the axial biometry of the entire eye.

Ocular imaging plays a key role for the diagnosis of various ocular diseases. In this work, we have developed an ocular imaging system based on the photoacoustic tomography. This system has successfully imaged the entire eye of a mouse, from its iris to the retina region, and the imaging is label-free and non-invasively. The resolution of this system reaches several micron meters, allowing the study of microstructures in various ocular tissues. Our system has the potential to be a powerful non-invasive imaging method for the ophthalmology.

Postoperative inflammation is one of the oldest complications of cataract surgery. It was described by the Indian Susruta as early as 500 BC. Following the introduction of cataract extraction by Daviel in 1745, these operations attracted increasing interest. In 1786 de Wenzel distinguished two types of postoperative inflammation. In the dangerous type there was involvement of the entire eye and severe pain; in the benign type, which began in the first few postoperative days, the conjunctiva and lids were not involved, and even if hypopyon developed there was no severe pain. During the 19th century, the possible causes of the benign type of iritis were discussed, including infection, phacoanaphylaxis, trauma, toxicity of irrigation solutions etc. In the early days of implantation of intraocular lenses, from 1949 onward, postoperative inflammation was common. However, it was not until 1980 that the term "toxic lens syndrome" was introduced. The clinical descriptions do not differ much from other descriptions of benign iritis published during the last 200 years. Therefore, it does not seem that there is any great advantage to be gained by using this new term.

The relative contributions of optical aberrations of the cornea and the crystalline lens to the final image quality of the human eye were studied. The aberrations of the entire eye were obtained from pairs of double-pass retinal images, and the aberrations of the cornea were obtained from videokeratographic data. Third-order spherical aberration and coma were significantly larger for the cornea than for the complete eye, indicating a significant role of the lens in compensating for corneal aberrations. In a second experiment retinal images were recorded in an eye before and after we neutralized the aberrations of the cornea by having the subjects wear swimming goggles filled with saline water, providing a direct estimate of the optical performance of the crystalline lens.

Nidek's FinalFit/NAVEX is likely the most comprehensive customized ablation platform currently available. This software/laser platform offers a full range of customized ablation treatments from aspheric ablation, topography-based, and (entire eye) aberrometry-based custom ablation. With the plethora of options available, a surgeon can treat a full spectrum of cases, ranging from primary eyes to highly aberrated eyes and those requiring retreatments due to previous refractive surgery. As with any new indication or surgical technique, a learning curve is involved and one should proceed step-by-step and carefully monitor his/her initial results.

Immediate illumination after sensitizer administration is currently often applied in PDT-trials in ophthalmology. The extent of possible damage to healthy ocular tissue after i.v. administration of the photosensitizers bacteriochlorin a (BCA) or mesa (tetrahydroxyphenyl) chlorin (mTHPC) and subsequent illumination with light of the appropriate wavelength and dose was assessed in rabbit eyes. Both hydrophobic drugs were formulated in 30% polyethylene glycol, 20% ethanol and 50% water to obtain an iv injectable suspension. Rabbits destined for BCA-PDT received a single dose of 10 mg/kg.bw. Rabbits destined for mTHPC-PDT received a dose of 0.3 mg/kg.bw. BCA- treated animals were illuminated immediately and 1, 2 and three hours after administration of the dye with an experimental Philips laser diode (760 nm, c.w., 100 mW/cm2, 100 J). To illuminate the eyes of the mTHPC- treated animals a Krypton laser was used (648 nm, c.w., 100 mW/cm2, 20 J). Illumination of these animals was performed immediately, 24, 48 and 72 hours after administration of the dye. BCA or mTHPC without illumination or illumination without administration of a sensitizing dye did not affect normal ocular tissues as judged by histology. Illumination of the entire eye of BCA-treated animals, immediately after administration of the dye caused a lesion in the macula area with a diameter of 3 mm. At the lesion side the photoreceptors were destroyed, ganglion cells were swollen and the sclera was affected. No skin photosensitivity was observed at anytime. Skin photosensitivity was observed in animals treated with mTHPC. Illumination caused swollen eyelids in all animals except when performed immediately after dye administration.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Background: Although there are excellent techniques to photograph gross ocular pathology specimens, it is difficult to view or photograph the entire eye from a glass slide using equipment designed for photomicrography. This investigation was initiated to develop a technique to image the entire eye from a glass slide. Methods: The glass histopathologic slide, placed in a carrier intended for 35-mm film transparencies, is inserted into a 35-mm slide scanner. The glass slide is scanned, creating a digital color image which may be converted to black and white with enhancement of certain histologic features. One may use a digital film recorder to produce 35mm photographic transparencies or a dye sublimation printer to produce high-resolution color or black and white prints. Results: More than 400 ocular whole-mount preparations have been digitized in the authors' laboratory to generate illustrations suitable for publication or for analysis in morphologic research. Conclusion: Digital techniques provide easier control over density and contrast than conventional photographic methods. Digitized images are well-suited for morphologic analyses in research. These techniques allow one to publish black and white photographs for books or journals while retaining the original color image for potential CDROM editions.

This chapter discusses the tears and the lids. They serve the eye in many different but important ways. The tear layer serves several purposes. The most important function of the tear film is to form an almost perfectly smooth optical surface on the cornea. Its second purpose is to serve as a lubricant for the eye and lids as the latter move over the exposed surface of the eye. A third function is to provide bactericidal action as a protection of the sensitive corneal epithelium. The enzyme lysozyme in the tears can destroy bacteria that enter the tear film. The aqueous part of the tear film forms by far the largest part of the tear liquid. The tears can function properly only if the tear film covers the entire eye and is reestablished quickly and completely after a blink. The lids are a movable cover for the exposed portions of the eye. They protect the sensitive eye tissue. Any action that is interpreted as a possible danger to the eye elicits an immediate reflex blink reaction that closes the lids. The lids close the eye during sleep, thereby reducing the level of external stimuli reaching the nervous system. Although the need for an occasional blink is easy to explain in terms of tear renewal, it is much more difficult to explain the observed normal rate of involuntary periodic blinking.

Purpose: To compare and evaluate the total and internal aberrations measured by two aberrometers: the laser ray tracing aberrometer (iTrace, Tracey Technology) and the automatic retinoscope aberrometer (OPD Scan, Nidek). Methods: A total of 54 healthy eyes were enrolled in the study. Following pupil dilation, aberrations were measured with the iTrace and OPD Scan. We compared the aberrations obtained from measurements obtained at pupillary diameters of 4 mm and 6 mm with the OPD Scan and iTrace. Aberrations of internal optics and total aberrations were compared for the two aberrometers. For each aberrometer and each eye, the averaged Zernike data were used to calculate various root-mean-square (RMS) data. These parameters, together with the refractive parameters, were then analyzed and complimented by paired t-tests. Results: At a pupil diameter of 4 mm, the number of total aberrations in the entire eye showed significant differences for the mean values of spherical aberrations (Z4,0) obtained with the OPD Scan and iTrace aberrometers (p=0.001). Aberrations of the internal optics showed significant differences in the mean values of total RMS, coma (Z3,-1), and trefoil (Z3,3) between the iTrace and OPD Scan (p

The eye grows by the addition of new ommatidia rather than by an increase in size of existing ones. New ommatidia develop as a result of induction of epidermal cells by functional ommatidia. The eye has great regenerative ability, but following removal of the entire eye and the growth zone that surround it regeneration does not occur. Transplanted eye cells or epidermal cells from normal-eyed or from lavender-eyed mutants resulted in the development of normal eye pigmentation in a mutant that lacked any pigmentation in the eye. Only the eye to which the graft had been made developed pigments. The development of pigments was a result of tissue contact, not of a blood-borne factor. When epidermal tissues from the prothorax of normal-eyed roaches were placed above the developing eye of a mutant with no pigment in the eye they were eventually incorporated into the eye as it grew. When these cells became eye cells, normal eye pigments were synthesized. Growth of the eye is by a constant recruitment of epidermal cells that express their own genetic capability when they become eye cells.

Diabetes mellitus can lead to blindness through its effects on the retina and lens, yet diabetes is a systemic disease influencing the entire eye. The current interest in extended wear contact lenses emphasizes the need for the practitioners to have a thorough knowledge of the pathophysiology of the anterior eye and cornea of the diabetic. The current literature is reviewed, and its relevance to contact lens wear is discussed.

The applicability of the basic principles of the correlation model to the description of the activity of a movement detecting neuron in the third optic ganglion of the fly's visual system has been investigated. This wide field neuron is supposed to sum the outputs of a large number of correlators (i.e. multiplying units followed by time averagers) that are distributed over almost the entire eye. The model describes and predicts the experimental results in a satisfactory way if a uniformly distributed system or correlators is assumed. The sampling base of the correlators in this system equals the interommatidial angles deltaphi. The half width of the spatial sensitivity distribution of the visual inputs of the correlators, deltarho, is equal to the half width of the retinula cells of the 1--6 system.

From 1954 through 1971, 47 patients with malignant tumors of the nasal cavity and paranasal sinuses were treated with an entire eye included in the tumor dose volume. All patients were treated with megavoltage radiation and received approximately 6,000 rads in 30 fractions in six weeks. Two thirds of the patients treated by irradiation alone had no problems with vision or difficulties related to treatment of the eye. When 5-fluorouracil (5-FU) was used in conjunction with high-dose radiotherapy, loss of vision was much more frequent and all patients had either visual loss or major clinical difficulties.

THE AUTHORITATIVE description of the eye in porphyria1lays emphasis on the clinical features. Stokes2has described in some detail the clinical features of the conjunctiva, sclera, and cornea in a case of porphyria, and the histological features of a conjunctival biopsy. This appears to be the first histological description of an entire eye associated with a case of proven porphyria, as noted by N. Ashton and L. Zimmerman (written communications, Oct 21 and 23, 1969). Report of a Case A male Negro, aged 51 years, gave a history of gradual loss of vision in his left eye over a ten-year period. A similar deterioration of vision in the right eye began on Sept 9, 1969, one year prior to admission. No ocular pain was experienced, but bitemporal headaches were common and persistent. On inquiry, a history of recurrent blistering and superficial abrasions of hands was given

1) If an entire eye is removed from an embryo ofRana palustris, the tissues of the head are incapable of regenerating a new one. 2) There is no development of an eye if all of the eye-forming region of the fore-brain is destroyed before the medullary folds have closed. 3) Destroying any part of the fore-brain except the eye-forming region does not interfer with the normal development of the eye. 4) The eye-forming tissue of the fore-brain appears to have the power of self-differentiation as it will develop into a more or less normal optic cup when removed from its connection with the rest of the brain and without the presence of a lens. 5) Any ectoderm of the head appears to have the power to produce a lens provided it receives the proper stimulus. 6) Contact between the optic cup and the ectoderm is not necessarily the stimulus that leads to the development of a lens, as a lens can be formed from the ectoderm when the optic cup is some distance beneath the surface of the body. 7) A lens-like structure may be formed from the ectoderm when there is no optic cup on the same side of the head. The process appears to be a self - differentiation of lens-forming tissue of the ectoderm. 8) It seems probably that, under certain conditions, a lens can develop from the upper edge of the optic cup as is the case in the regeneration of the lens in the eye ofTriton.

Unplanned extracapsular cataract extractions resulting in retention of lenticular material present a formidable problem in postoperative management to the ophthalmic surgeon. The incidence of complications in such an eye is significantly greater than an eye from which this residual lens material has been removed. However, it is frequently impossible at the time of initial surgery to extract this residuum without endangering the entire eye. Rarely, this problem of retained lenticular material becomes apparent at the first or second postoperative dressing after an operation which was thought to be an uneventful intracapsular extraction. More commonly, the surgeon is faced with the task of removing loose cortical and capsular material after a traumatic cataract with simultaneous rupture of the capsule. The purpose of this report is to describe how enzymatic zonulysis may facilitate the more complete and safe removal of retained lens material. Since Barraquer's8initial report, many papers have appeared