On the nature and the role of the subsurface vesicles in the outer epithelial cells of the conjunctiva.

The layer of the tear film in contact with the conjunctiva is mucus. This mucus comes from two sources, the conjunctival goblet cells and the subsurface vesicles. These vesicles are found just below the surface of the conjunctival cells. They contain long chain mucus glycoprotein molecules that are joined to the vesicle membrane. The vesicles fuse with the surface membrane of the conjunctival cells and expose their mucus glycoprotein chains to the overlying mucus. Chemical and physical bonds between the two types of mucus help to bind the mucus layer to the conjunctiva. The vesicle membrane becomes incorporated in the cell membrane and supplies the membranes for the microvilli that cover the exposed surface.     

Normal variations of the position of the eye in the orbit

Photoradiographic measurements of projected corneal and nasion pituitary distances in Swedish adults and in white and black adults in the United States were transformed to true measurements. A new photographic method to compute nose-corneal distance was developed and compared to the photoradiographic and Hertel measurements. A new photographic method was developed to record interpupillary distance more accurately than earlier methods. A highly significant difference in eye position between white and black people was found. Variations in normal eye position in the same individual were studied in 39 subjects. Normal eye position was found to vary in an anterior-posterior direction, with an average variation of 1.5 to 2 mm (range, 0-3.7 mm). The interpupillary distance was found to be very stable. A difference of at least 2 mm, and perhaps 3 to 4 mm in exophthalmometric measurements is necessary to detect a pathological difference.     

Investigation of the temporal properties of the retina using the m-sequence

The mfERG provides a topographic map of function of the retina and has been used in numerous studies to identify macular, paramacular and peripheral retinal dysfunction. This study investigates the changes in response due to the presentation rate of the stimulus. Twenty subjects gave informed consent to take part in the study, which had local regional ethical committee approval. Only a single hexagon of 8° diameter was presented to reduce ambiguity when identifying the higher-order kernels (HOK). Six rates were tested using a 60-Hz CRT monitor by introducing blank (black ~0 cd/m2) filler frames (FF). The rates tested were 0FF; 1FF; 2FF; 4FF; 7FF; and 14FF. The first-order kernel had largest responses to the slower stimuli (4FF and above). HOK had largest amplitudes at faster rates with the second-order kernel peaking at 1FF. At rates with 4FF and slower, the higher-order kernels were indiscernible above the noise.     

Representation of the temporal raphe within the optic tract of the cat

The retinal topography of the cat's optic tract was determined by means of injections of the enzyme horseradish peroxidase (HRP) into the tract. This analysis was accomplished by the subtraction of all HRP injection sites not labeling a defined retinal area from those injection sites which resulted in ganglion cell labeling (Venn diagram analysis). Using this method, the following correspondences were demonstrated for the ipsilateral and contralateral projections: superior retina represented in medial optic tract; inferior retina in lateral tract; and area centralis in a dorsocentral location (which was part of a larger area representing the visual streak). The temporal raphe was represented in the ipsilateral tract as a band curving from the area centralis region toward the dorsomedial border of the tract. Contralateral fibers from a region superior to the optic disc were found to be displaced with respect to the general retinal representation in the optic tract and this appeared to be related to retinal development. The ratio of contralateral to ipsilateral fibers was determined and found to be nonuniform within the tract. Injection of HRP into the optic tract of the cat also allowed the axons from labeled retinal ganglion cells to be traced within the retina and optic disc. Axons from ganglion cells lying temporal to the raphe curve around the area centralis enter the optic disc on the lateral and inferior aspects. Ganglion cells lying nasal to the raphe send their axons more directly to enter the optic disc on its superior aspect. A schema is proposed whereby the retina is mapped onto the optic tract.     

Determination of the location of the fovea on the fundus

PURPOSE: To evaluate whether the distance between optic nerve head and fovea in healthy eyes determined by scanning laser ophthalmoscope may facilitate estimation of the location of the fovea relative to the optic disc in patients with macular disease. METHODS: The angular distance was measured, in horizontal and vertical directions, between the center of the optic nerve head and the fovea in 104 eyes of 104 healthy probands. For additional evaluation of intraindividual variation in 70 of these persons the contralateral eye was measured as well. RESULTS: The distance between the optic disc and the fovea differed vertically more than horizontally (-1.5 +/- 0.9 degrees [-3.65 to +0.65 degrees ] vs. 15.5 +/- 1.1 degrees [13.0-17.9 degrees ]). There was a mean angle between the fovea and the center of the optic disc versus the horizon of -5.6 +/- 3.3 degrees. The intraindividual difference between right and left eyes was markedly lower, with average angles being 0.2 +/- 1.3 degrees vertically and 0.0 +/- 1.1 degrees horizontally. CONCLUSIONS: The distance between the optic nerve head and the fovea does not allow for a meaningful determination of the location of the fovea in eyes in which morphologic changes have occurred. The angle of rotation of the fovea relatively to the center of the optic nerve head is relatively stable. Therefore, the size of a central scotoma can be determined by movement of the blind spot according to the change of the preferred retinal locus (PRL). In addition, the knowledge of the location of the fovea enables determination of the position in the contralateral eye of the same patient.     

Origin of the fast oscillation in the electroretinogram of the macaque

To investigate the origin of the fast oscillation, a phenomenon in the electroretinogram evoked with stimulus frequencies of about 8 mHz (a period time of about 2 min), we recorded responses from retina and pigment epithelium in the macaque. Micropipettes were placed in the subretinal space and in the vitreous close to the retina; the reference electrode was in the orbit behind the eye. Thus, simultaneous recordings were obtained of the trans-epithelial, the trans-retinal and the trans-tissue (vitreal) potential. At 10 mHz the trans-retinal and the trans-epithelial responses are of about equal magnitude but of opposite phase, resulting in a small and rather variable vitreal potential. The origin of the fast oscillation evoked with repetitive stimuli lies in subtle differences between retinal and pigment epithelial potentials, in which a pigment epithelial event plays an important role. For single stimuli lasting 60 s again the trans-epithelial and trans-retinal responses were of equal magnitude and opposite polarity. The epithelial responses were found to return more quickly towards the baseline than the retinal responses. In vitreal recordings this causes a trough between the c-wave and the light peak which is referred to as the "trough" fast oscillation. Most of the "trough" fast oscillation is caused by a pigment epithelial event. In view of the complexity of the fast oscillation evoked with repetitive stimuli it might be difficult to relate pathology to specific neuro-epithelial structures.     

On the relevance of the long-time follow-up of the cyclocryotherapy

In spite of the availability of cyclocryodestructive laser therapy there still appears to be an indication for cyclocryotherapy in different kinds of glaucoma. PURPOSE: Cyclocryotherapy very often appears to be the operation of choice in cases of progressive functional visual loss if a patient is not sufficiently helped with the maximum tolerated medical therapy. We investigated long-term IOP effects and possible complications in our group of patients undergoing cyclocryotherapy. PATIENTS: Cyclocryotherapy was performed on 109 eyes of 97 patients from 1988 to 1994. Cyclocryotherapy was performed as follows: 67 of 109 eyes were controlled for IOP for an average of 10 months (3-41 months). We applied cryotherapy six times 3-4 mm behind the limbus for an average duration of 50 to 60 s over half of the circumference. RESULTS: We achieved satisfactory IOP control (IOP K 22 mm Hg) in 40 eyes, however, with 30 additional operations. One eye developed phthisis bulbi, and 3 other eyes became blind because of complications in neovascular glaucomas. Neovascular glaucoma cases responded the least. CONCLUSIONS: Cyclocryotherapy produced a statistically significant IOP reduction in eyes with primary open-angle glaucoma or secondary glaucoma. Close long-term follow-up appears advisable in order to check the eyes for possible increase in IOP or complications of surgery.     

Rehabilitation of the hemianopsia patient from the viewpoint of the ergotherapist

Hemianopsia, above all if it is associated with other neuropsychological deficits (neglect, disturbances of spatial orientation) is very disturbing for the patient in daily life. The patient has difficulty dressing, exhibits poor spatial orientation, has difficulty construing spatial relations or reading. Ergotherapy tries to combat all these disorders. There are various methods of treatment at the ergotherapist's disposal: activities of everyday life, such as self-help and household training, functional games, craft skills and neurotraining, which aims in particular at improving intellectual function. In a well-protected environment the patient learns to judge his or her capabilities correctly once again and to make the best of his or her strength or weaknesses in daily life.     

Scintigraphy of the lacrimal ducts: the value of the lateral view in the postoperative period

Lacrimal scintillography, a simple, non traumatic, and physiological method, has been for a long time an useful exploration in the study of lacrimal excretory pathology. It allows an accurate diagnosis especially in the case of functional stenosis and, due to its ability to indicate the exact seat of obstruction, this technique is able to determine the surgical treatment required. This study underlines the contribution of lacrimal scintillography in the control of surgical anastomosis permeability, because of a modification in the initial technique: the use of scintillography in employing the lateral view rather than the front view, usually used, permits a better visualisation of the new surgically created excretory passage, particularly in the posterior area of nasal fossae.     

Numerical study of the influence of the shell structure of the crystalline lens on the refractive properties of the human eye

In this paper, the numerical model of the refractive properties of the human eye is given. A special account is given of the laminated structure of the crystalline lens. The crystalline lens is presented in the form of hundreds of shells with rotational symmetry, and with the refractive index constant within each shell. The shells have the form of two semi-ellipsoids joined along the equator. The refractive index increases from the cortical shell to the inner one, according to the exponential dependency. The cornea, approximated by two ellipsoidal surfaces, is added in front of the crystalline lens. A ray-tracing procedure is applied to study the refractive properties of such a system: refractive power, spherical aberration and energy distribution. The optical properties of the given model are analysed by changing some parameters such as refractive index profile and number of shells. Calculations show that the gradient of the refractive index inside the crystalline lens results in the generation of many focal planes in such an optical system.     

On the molecular biology of the vitreous in the aphakic eye

The vitreous of aphakic and phakic eyes was assayed for hyaluronic acid. Intracapsular cataract extraction was regularly followed by decreased hyaluronic acid concentration and studies on the distribution of hyaluronic acid within the vitreous cavity showed that removal of the lens facilitates diffusion of hyaluronic acid into the anterior chamber. Based on these studies certain postoperative features of the aphakic eye are discussed. The instability of the vitreous gel, as reflected by rupture of the anterior vitreous face and an increased incidence of vitreous detachment supports the hypothesis of hyaluronic acid as a stabilizer of the gel. The decreased adhesion of the neural retina in the aphakic eye might be caused by the loss of hyaluronic acid. Normally the high concentration of hyaluronic acid adjacent to the retina contributes to the resistance of bulk flow of fluid into the subretinal space making it possible for the active transport system of the pigment epithelium to maintain a pressure drop across the neural retina. It is anticipated that saccades create currents in the fluid vitreous close to the eye wall after vitreous detachment. Model experiments showed that these currents were greatly enhanced, when the concentration of hyaluronic acid was lowered.     

The choice of the radiation parameters in the laser reconstruction of the pupil

The phenomenon of a "local punch" of tissues in the zone of nano- or picosecond impulses of neodymium: YAG-laser radiation focusing allows to increase energy in the pulse by one order as compared with traditionally used energy. At this, in order to achieve the initial effect it becomes possible to reduce the number of shots by two orders and thus to increase the spot of radiation. The summary energy of action absorbed in the eye remains the same and that's why the number of complications doesn't increase. The widening of possibilities to choose a laser source for micro- and macroperforations allows, when prescribing the treatment, to more reliably consider clinical peculiarities in each concrete case.     

Chromatic properties of the retinal afferents in the thalamus and the tectum of the frog (Rana temporaria)

In order to clarify physiological mechanisms underlying colour-specific visually guided behaviour, we measured spectral sensitivities of On-fibres projecting to the thalamus and class 2 and 3 fibres passing to tectum opticum. In addition we recorded responses of these fibres to moving coloured papers with known spectral reflectancies. The latter method, here called paper colourimetry, allowed us to change the relative stimulations of the blue-, green- and red-sensitive photoreceptors in any direction desired. Under the photopic conditions used the tectal fibres were driven exclusively by red-sensitive receptors, while the thalamic fibres received strong On-inputs from both red- and blue-sensitive receptors. Due to a partly antagonistic interaction between these inputs the On-fibres acted in a dichromatic way, responding with specific extended low-frequency discharges to all relative increases in blue receptor stimulation, e.g. to a great reduction in red stimulation combined with unchanged blue stimulation. Thus they have functional characteristics which could serve a visual system showing colour constancy.     

The scope of the cataract problem in the Middle East and the Mediterranean

The region is characterized by diversity in cultural, political, economic and health conditions. Blindness in the region varies from 6.4% to 0.2% with cataract ranking highly as an underlying cause. There is a need to develop national policies to deliver affordable, technically suitable, and cost effective management plans to reduce cataract. Economic, demographic, health, and manpower statistics are essential information to be considered in formulating such policies.     

Theory of the T-incision of the cornea

T-incisions are used for surgical correction of moderate corneal astigmatism. No theoretical models to explain the curvature changes have yet been described in the literature. This paper describes a biomechanical model intended to facilitate understanding of the effect of corneal flattening. The incisions cause the stress inside the untouched layers of the cornea to increase. Subsequently the strain also increases and so the curvature radius of the meridian perpendicular to the incision also increases. The calculated changes in the refractive power of the cornea are in good agreement with clinical data. The influence of the depth of the incision is explained quantitatively. Secondary parameters, such as the length of the incision and the size of the optical zone, are discussed.     

微波对眼损害的调查和分析

本文报道了职业性微波引起的眼损害。对449名微波作业人员的眼损害作了调查分析,并把164名具有相似条件非微波接触者作为对照组加以比较。结果表明:接触组的视疲劳和微波白内障的发生率明显高于对照组(P<0.01),并显示微波白内障的发生与工龄、年龄有关系。同时探讨了微波白内障的发病机理。     

What the bird's brain tells the bird's eye: the function of descending input to the avian retina

As Cajal discovered in the late 19th century, the bird retina receives a substantial input from the brain. Approximately 10,000 fibers originating in a small midbrain nucleus, the isthmo-optic nucleus (ION), terminate in each retina. The input to the ION is chiefly from the optic tectum which, in the bird, is the primary recipient of retinal input. These neural elements constitute a closed loop, the centrifugal visual system (CVS), beginning and ending in the retina, that delivers positive feedback to active ganglion cells. Several features of the system are puzzling. All fibers from the ION terminate in the ventral retina and an unusual axon-bearing amacrine cell, the target cell, is the postsynaptic partner of these fibers. While the rest of the CVS is orderly and retinotopic, target cell axons project seemingly at random, mostly to distant parts of the retina. We review here the most significant features of the anatomy and physiology of the CVS with a view to understanding its function. We suggest that many of the facts about this system, including some that are otherwise difficult to explain, can be accommodated within the hypothesis that the images of shadows cast on the ground or on objects in the environment, initiate a rapid and parallel search of the sky for a possible aerial predator. If a predator is located, shadow and predator would be temporarily linked together and tracked by the CVS.     

原发性青光眼患者确诊途径调查

目的了解何种原因使得原发性青光眼患者到医院就诊,最终青光眼得以诊断。设计以医院为基础的问卷调查。研究对象 287例已确诊为原发性青光眼的连续患者。方法设计一组问题,对本组青光眼患者进行以医院为基础的问卷调查,问卷内容主要包括患者首次被诊断青光眼的医院;患者到眼科寻医的原因;患者求治的主要症状;以及其青光眼被诊断的主要依据。主要指标统计分析患者寻医的主要原因和症状,以及患者所了解的主要诊断依据。结果视力下降(87．7％),眼痛 (80．8％)和眼红是急性闭角型青光眼患者求医的原因。在慢性闭角型青光眼和开角型青光眼,分别有39．7％和46．2％的病例主诉有视力问题,部分患者主诉有眼部症状,但这些症状多与青光眼无关,约25％的患者没有任何症状。71％(205／287)的患者认为眼压升高对青光眼诊断最为关键。在慢性闭角型青光眼和开角型青光眼中,75％的病例在确诊时,至少有1眼已属于青光眼中晚期。结论急性闭角型青光眼因症状明显,常引导患者主动就诊。慢性闭角型青光眼和开角型青光眼早期多无症状,他们得以诊断的原因是因为其他非青光眼症状,或有青光眼家族史而到医院检查,或常规体检发现了青光眼。     

The oculomotor effects of the fractures of the floor of the orbit

PURPOSE: Fractures of the orbit floor have very disabling oculomotor after effects. The objective of this study was to report that close collaboration between the maxillo-facial specialist and ophthalmologist is necessary to avoid oculomotor after effects. METHODS AND PATIENTS: Our study included 10 cases of the fracture of the orbit floor. These cases were recorded between 1992 and 1996. RESULTS: This pathology affected young subjects aged between 20 and 40 years in 70 % of the cases. 80 % of the subjects were males. 90 % of the patients presented a vertical diplopia as a result of a transitory oculomotor deficit. 20 % of the subjects presented a permanent oculomotor deficit at the stage of after effects. All these deficits were of a mechanical origin and, contrary to other authors, we found no deficit with nervous sensory origin. CONCLUSION: Therapeutic success is based on early diagnosis and treatment that requires close collaboration between the maxillo-facial and ophthalmology teams.