Mechanical behavior of the vitreous

A description of the experiments of the mechanical behavior of the vitreous body is presented. The experiments were performed with a photoelastic material surrounding both rabbit and human eyes. The results show that the vitreous body transmits forces isotropically as any newtonian fluid. Tests done on rabbits' eyes with a previous vitrectomy agree with the previous statements. Finally, a hypothesis of the effect of pressure on the posterior pole in myopia is given, stressing the changes clinically observed.

Drainage of microspheres and RBCs from the vitreous of aphakic and phakic eyes

The movements of plastic microspheres (7 to 10 mu in diameter) and autologous RBCs labeled with sodium chromate Cr 51 from the vitreous to the anterior chamber were studied in 24 rabbit eyes. Rabbits were made aphakic in one eye by intracapsular lens extraction of lensectomy via the pars plana, the fellow eyes serving as phakic controls. In phakic eyes the intravitreally injected microspheres and RBCs were retained inside the vitreous space, not gaining access to the anterior chamber. In aphakic eyes microspheres and RBCs moved to the anterior chamber and were usually seen on the corneal endothelium and in the chamber angle within two to ten days, although most particles remained in the vitreous for long periods of time. Removal of the lens thus improved forward drainage of particles from the vitreous space, but the structure of the vitreous seemed to preclude rapid clearance.

Intraocular lens weight and the vitreous

Intraocular lenses, or their components of various weights and designs, were placed on and within the viterous of fresh human autopsy eyes. All devices were supported on the surface of the intact viterous and within the formed vitreous. All sank promptly through the disorganized vitreous. Advice against anterior vitrectomies at the time of implant surgery is offered.

Vitreo-scleral fluid transfer in the rabbit

Experiments were carried out to see whether a radioactive tracer placed in the vitreous of a rabbit eye could be detected on the sclera. A solution of Xenon-133 dissolved in saline was injected into the vitreous of six rabbits and collecting tubes containing activated charcoal were placed on the sclera. The presence of Xenon in these tubes confirmed that vitreoscleral transfer had occurred. It was calculated that on average, 2% of the Xenon had appeared over the whole sclera. A mathematical analysis of the shape of the activity curve of the tracer on the sclera revealed that its appearance was probably due to diffusion across the outer layers of the eye.

A comparison of the proximal negative response and ganglion cell responses to sinusoidal flicker

In the mudpuppy retina, sinusoidal light stimulation of the proximal negative response (PNR) demonstrates two main components whose phases are essentially the same as those of the spike discharges of ON/OFF ganglion cells. Oscillations superimposed upon these components are synchronized with the spike discharges of ON/OFF cells, but not of ON or OFF cells. Intracellular recordings from ON/OFF ganglion cells reveal slow potentials with nearly identical waveforms and phases to those of the PNR. These results, together with previously published comparisons between the flesh-evoked PNR and amacrine cell responses, support the suggestion that the PNR arises from activity in the on/off system (amacrine and/or ganglion cells).

[Studies of the lymph drainage of the eye. 4. Drainage of lymphotropic radioactive tracers (99mTc-Microcolloid) after intravitreal injection (author's transl)]

In 7 rabbits the drainage of 99mTc-labelled Micro-colloid from the vitreous body of the eye was studied. In vivo measurements with an Anger-type camera were undertaken as well as in vitro measurements after dissection and excision of tissue-probes. From the data followed that indicator's elimination half-life from the vitreous body was on an average 7.8 hours. The drainage occurred partially along structures which are associated to the optic nerve. Furthermore drainage to the ipsilateral retrobulbar space and to the regional cervical lymph nodes, mainly to the bilateral deep cervical lymph nodes could be observed.

Vitreal syneresis in rhesus monkeys

The eyes of 15 rhesus monkeys were evaluated. Various degrees of vitreal syneresis were observed in 28 of the 30 eyes. The observed vitreal structures varied from fine strands randomly spaced throughout the vitreous to thick, intertwining, fibrous networks with some clumping of the collagenous condensate at the fiber junctions. Qualitatively, the degree of syneresis was slightly more extensive in the eight older mature males than in the seven younger animals. In all animals a clear view of the fundus could be obtained with the ophthalmoscope. The vitreous structures may be one cause of variability in ocular dose-response relationships for exposure to laser radiation. The effect on retinal exposure experiments of the finer vitreal structure is considered minimal.

[Study of zonular area (author's transl)]

The author presents a set of colored pictures which permits to delimitate 3 kinds of zonular fibers. 1. Short anterior fibers. 2. Short posterior or medial fibers, and 3. long posterior fibers. Describe also 3 irregular rings where the zonular fibers are firmly attached to the hyaloids and vitreous. 1. The Wieger's or Egger's ring. 2. The ciliary ring, and 3. the ora serrata ring. The first one attached to the posterior capsula, the second to the ciliary processes and ciliary body and the third to the peaks of the ora serrata. They are the 3 anterior support of the vitreous body. The 2nd is movile by the action of the circular ciliary muscle which acts like a diaphragm suspended from the flexible spur. When contracts relax the zonular fibers but pull the spur and trabeculum and would move the dense basal vitreous to the center pressing the fluid central vitreous.

A possible change of refractive index with age and its relevance to chromatic aberration

The Purkinje-Sanson images of the eyes were photographed in red and blue light in two groups of subjects, young (19-38 years) and old (52-63 years). Densitometric examination of the negatives showed a significant increase in the amount of red light and a significant decrease in the amount of blue light reflected from the anterior surface of the lens (third image) in the group of old subjects as compared to the group of young persons. There is also a significant decline in the blue light reflected from the posterior surface of the lens (fourth image) but no change in the red light in old versus young eyes. From these results it is suggested that the index of refraction of the lens increases for red (nC) and decreases for blue light (nF) in the aging eye and similarly the index of the vitreous varies differentially in blue and red light. These specific changes in the indices of the lens and vitreous are believed to account for the large decline of axial chromatic aberration of the aging eye. In addition, the examination of the first Purkinje-Sanson image tends to indicate that the index of refraction of the cornea does not vary with age.

[Transmission of the anterior chamber pressure to the center of the vitreous body and to the posterior pole of the eye of the miniature swine. Measurement of isovolumetric and direct pressure]

Experimental variations of the anterior chamber pressure (P.I.C.) are transmitted at about 300 ms to the middle of the vitreous. The response time to a sudden experimental increase in P.I.C. to the centre of the vitreous is variable and depends essentially on the control intra-ocular pressure: the more it is raised the shorter the response time. The pressure in the centre of the vitreous (P.I.V.) has a pulsatile character probably due to transmission of arterial pulsation. The higher the intra-ocular pressure the greater the amplitude of these pulsations. Recording of P.I.V. close to the surface of the retina show abrupt falls despite the fact that the P.I.C. and systemic arterial pressure remain stable. These results are discussed in relationship to autoregulation of the retinal circulation and the physiopathology of glaucoma.

Hydrodynamic events in the vitreous space accompanying eye movements. Significance for the pathogenesis of retinal detachment

The powers elicited in the vitreous body by eye movements have hardly been subjected to examinations, and the same goes for currents in the vitreous. Model experiments have demonstrated that intra-ocular currents are not elicited by translatory, but so much more by rotatory movements. Furthermore, it is demonstrated that a thin perforated membrane fitted on the inside of the wall of a glass cylinder filled with water, will detach, with rotatory movements. Even minimal rotational movements cause a flow through the hole. It is discussed whether these findings apply to the eye in vivo.