eye-enigmas

eye-enigmas

The Theory of the Flow of Fluid within the Human Eye

Fluid Flow Patterns within the Human Eye

Aqueous humor, vitreous humor , Krukenberg's spindle, convection currents within the human eye, convection currents generally, fluid pathway, the 3 sisters, origins of the human eye, embryology of the eye, Boussinesq equation, keratoconus and convection currents, Diurnal variation in IOP, the new theory.

The theory behind the major flaws in MIGS, trabeculectomy, and deep sclerectomy, and the reasons why CyPass failed.

1. Introduction

Only, three things are known about the human eye with absolute certainty:

Firstly, one thing that is known about the human eye with absolute certainty is the fact that it is extremely difficult to get the human eye to reveal all of its secrets.

Secondly, another thing that is known about the human eye with absolute certainty is the fact that whoever designed the human eye knew exactly what they were doing.

Thirdly, another thing that is known about the human eye with absolute certainty is the fact that extremely complex physics, chemistry, and mathematics all occur within the human eye.

If you choose to read this article, then it can be guaranteed that you will be able to find out exactly what is going on within the human eye, even though you may know very little about complex physics, chemistry, or mathematics, because no complex mathematical formulae will be employed. Only clear logic and simple reasoning will be used.

2. Krukenberg`s spindle

I refer to the eye enigma known as "Krukenberg's spindle".

Friedrich Ernst Krukenberg (1 April 1871 - 20 February 1946) was a German physician who was a native of Halle an der Salle. He was a brother to orthopedic surgeon Herman Krukenberg (1863 - 1935) and Georg Heinrich Peter Krukenberg (1856 - 1899), who was ajust professor of gynecology at the University of Bonn. The ophthalmic term "Krukenberg's spindle " is named after him, which is a verticle, fusiform deposition of melanin pigmentation in the deep layers of the cornea.

Other descriptions of Krukenberg's spindle include :

Krukenberg's spindle, and contact lens induced edema. Bergenske PD Am J Optom Physiol Opt. 1980:

Krukenberg's spindle, a pigment deposit on the corneal endothelium, is frequently an inconsequential finding, although it can be associated with pigmentary glaucoma.

Unknown source Abstract :

Krukenberg, in 1899, was the first to report this unusual type of pigmentation of the cornea. He described the lesion as brown, spindle shaped and symmetrical and occupying the deepest layers of the cornea. The line of pigment ran in a verticle direction, and he referred to it as a bilateral, congenital, melanosis of the cornea. He described 3 cases, in all of which myopia was found, ranging from -1 to -9 D. The patients were all women over 45 years of age. Each had brown irides. Krukenberg expressed his belief that this condition occurred only in brown eyes. The size of the pigmented spindles varied from 4 ×3 mm to 3× 4.5 mm. No adhesions or precipitates were seen, and the pigmentation of the cornea and irides was of the same colour. 2 of his patients had floating, vitreous opacities and one had a bilateral, posterior staphyloma.

Another unknown source :

A congenital, verticle, spindle shaped, symmetrical deposition of brown pigment in the deep layers of the cornea, directed vertically. They occur most commonly in female myopic patients and male patients with megalocornea.

Another unknown source Abstract :

Despite the rarity of Krukenberg's spindle in ophthalmologic practice, it has been possible to accumulate a series of 202 cases for review in this study. 95 of these, not previously reported were collected through a questionnaire addressed to members of the American board of Ophthalmology in the United States and Canada, and a search of the literature has yielded 107 cases recorded in the 40 years since Krukenberg's original description in 1899.

How would one possibly be able to explain this most unusual phenomenon and rare eye enigma known as Krukenberg's spindle?

Some explanations have been provided so far:

3. Boussinesq Model of natural convection within the Human Eye

A Boussinesq model of natural convection in the human eye and the formation of Krukenberg's spindle

Jeffrey J. Heys, Victor H. Barocas 2002 Biomedical Engineering Society Abstract :

The cornea of the human eye is cooled by the surrounding air and by evaporation of the tear film. The temperature difference between the cornea and the iris causes circulation of the aqueous humor in the anterior chamber of the eye. Others have suggested that the circulation pattern governs the shape of Krukenberg's spindle, a distinctive verticle band of pigment on the posterior corneal surface in some pathologies. We modeled aqueous humor flow the human eye, treating the humor as a Boussinesq fluid and setting the corneal temperature based on infrared surface temperature measurements. The model predicts convection currents in the anterior chamber with velocities comparable to those resulting from forced flow through the gap between the iris and the lens. When paths of pigment particles are calculated based on the the predicted flow field, the particles circulate throughout the anterior chamber but tend to be near the verticle centerline. We conclude that the convective flow pattern of aqueous humor is consistent with a verticle pigment spindle.

The authors 2016, Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. Abstract :

In this research, a series of numerical simulations for evaluating the effects of saccadic eye movement on the aqueous humor flow field and movement of pigment particles in the anterior chamber was performed. ........ Langrangion particle trajectory analysis approach was used to find the trajectories of pigment particles in the eye. Particular attention was given to the relationship between the saccadic eye movement and potential formation of Krukenberg's spindle in the eye. The simulation results revealed that the natural convection flow was an effective mechanism for transferring pigment particles from the iris to near the cornea. In addition, the saccadic eye movement was the dominant mechanism for deposition of pigment particles on the cornea, which could lead to the formation of Krukenberg's spindle. The effect of amplitude of saccadic motion angle in addition to the orientation of the eye on the formation of Krukenberg's spindle was investigated.

Aqueous humor dynamics:

a review Manik Goel, et al. Bascom Palmer Eye Institute, University of Miami, Miami Florida USA, Abstract

Circulating aqueous humor flows around the lens and through the pupil into the anterior chamber. Within the anterior chamber, a temperature gradient creates a convective flow pattern, which is downward close to the cornea where the temperature is cooler, and upward near the lens where the temperature is warmer. The aqueous humor leaves the eye by passive flow via 2 pathways.

The convection flow of aqueous humor in the anterior chamber of the human eye, Abstract.

Ram Avtar and Swati Srivastava :

A simple mathematical model for the buoyancy driven flow of aqueous humor in the anterior chamber arising from the temperature difference between the anterior surface of the cornea and the iris is developed. The model is formulated using the lubrication theory limit of the Navier Stokes equations and classical Boussinesq model of the fluid density for thermal driven convention flow. The model takes into account the fact that the heat loss at the corneal surface takes place not only due to the convection but also due to the radiation and evaporation. The model also incorporates Beaver Joseph's slip flow condition at the porous corneal surface. The expressions for the temperature and velocity profiles are derived. The flow of a colourless fluid, aqueous humor in the anterior chamber of the human eye is essential for the maintenance of a positive intraocular pressure, to maintain the shape and stability of the visual system, for the nutrients transport, to nourish the avascular tissues, and for the removal of metabolic wastes .

Some very impressive examples of mathematical formulae were provided in this article.

What these authors are saying in effect is that within the eye we have a random flow of fluid in the form of a chaotic mixture of the aqueous humor which can be attributed to temperature differences that exist within the human eye. No one is arguing that the temperature differences in the human eye do not exist. They have been well documented.

For further details see:

Computational model for heat transfer in the human eye using the finite element method

Umit Cicekli

The question is whether or not they are responsible for contributing to fluid mixing within the human eye? Do convection currents really exist in the anterior chamber of the human eye and what evidence is there for their existence? The theory that I propose is somewhat different to their theory. One thing that can be known with certainty from all of this, is the fact that particles from the iris broke away from the iris and ended up on the underside of the cornea somewhere near the apex of the cornea. How they managed to get there is yet to be explained. Does this means of transport only occur in people with Krukenberg's spindle or does it occur in all eyes?

4. Convection currents within the human eye

I refer to the eye enigma known as the theory of convection currents within the human eye which is the currently accepted view of eye fluid movement within the human eye. Mention has been made of it previously, even if only briefly. According to this theory we find that within the anterior chamber of the human eye there are thermal convection currents which are responsible for moving aqueous humor from the region of the iris to somewhere near the cornea which is a somewhat cooler region than that found near the iris. We can even find complex mathematical formulae which tend to support this theory.

5. Convection currents generally

A temperature difference causes particles to move creating a current. In gases and liquids, a temperature difference leads to regions of high and low density where molecules move in to fill in areas of low pressure. In the end, hot fluids rise while cold fluids sink. Convection currents will continue until a uniform temperature is reached.

Convection is a heat transfer process. When currents are produced, material is moved from one location to another. So this is also a mass transfer process. Convection that occurs naturally is called natural convection or free convection.

Another way of looking at it is that convection currents form because a heated fluid expands and becomes less dense. The less dense fluid rises . As it rises it pulls cooler fluid in to replace it. This fluid is then heated and rises and pulls in more cool fluid and so the cycle repeats itself.

Natural convection will be more likely and more rapid with a greater difference in density between the 2 fluids. Natural convection will be less likely and less rapid with more rapid diffusion between the 2 fluids.

The onset of natural convection can be determined by the Rayleigh number (Ra).

Natural convection or free convection occurs due to temperature differences that affect the density and thus the relative buoyancy of the fluid. Heavier components will fall, while lighter components will rise, leading to bulk fluid movement. Therefore, natural convection can only occur in a gravitational field.

Convection currents may occur in fluids at all scales larger than a few atoms. Thus, there is nothing to preclude the formation of convection currents within the human eye. But do they really exist within the human eye? After all, the temperature difference between the cornea and the iris is only a matter of a few degrees and the difference in density between the 2 fluids is only slight?

How do astronauts manage to cope with this problem once they are suspended in outer space in zero gravity? Does all fluid movement within their eyes cease to exist once they leave the earth's gravity?

6. Fluid pathway within the Human Eye

Anyone reading this article right now is probably saying to themselves, who cares about what pathway eye fluid takes within the human eye? My eyes are perfectly fine and healthy right now, and anyway what use would such information be to me ? That may be the case right now, but that may not always be the case, and one day something will eventually go wrong with your eyes and that something may involve the pathway of fluid within your eyes. So that every man, woman, and child alive at the present time has a stake in ensuring that the information available about the human eye is the correct information.

You can even conduct your own little experiment on your own eyes by looking at them in the mirror and trying to spot fluid flow patterns within your own eyes. Apparently, they occur in the small , transparent, dome shaped object at the front of the eye called the cornea, which is the part in front of the iris. This is the only part of the eye that is visible to the average person. No matter how hard you try, you will never be able to spot the fluid flow patterns within the human eye. Everything looks as though it is perfectly still.

You may say that there are fluid flow patterns right in front of your nose, or in this case, in the very front of your eyes and you cannot even see them.

In fact, in 1900, every ophthalmologist in the world believed that the fluid within the human eye was stagnant. It was not until 1921, when a clever scientist by the name of Seidel published his work, that it was found that this theory was incorrect.

He infused indigo carmine from a reservoir through a cannula into the anterior chamber of a rabbit's eye. The reservoir was then lowered and it was found that aqueous humor entered the cannula and displaced the dye. The reservoir was then raised to increase the pressure to 15 mm Hg, and the dye went into the anterior chamber and appeared in the episcleral veins, thus proving that fluid is constantly moving into and out of the anterior chamber of the eye.

Since then, numerous experiments have been carried out by scientists confirming this theory.

For further details see:

Flow of aqueous humor in humans

by Richard F. Brubaker

What was not confirmed was the exact pathway of the fluid, the point at issue at the present time.

The mean rate of fluid flow was found to be 2.75 microlitres per minute.

7. The 3 sisters

The 3 sisters is a non ophthalmological term used to describe the ciliary body, the corneal endothelium, and the combination Schlemm's canal outlet and the uveoscleral outlet.

The ciliary body is a ring shaped thickening of tissue inside the eye that divides the posterior chamber from the vitreous body. It contains the ciliary muscle, vessels, and fibrous connective tissue. Folds on the inner ciliary epithelium are called ciliary processes, and these secrete aqueous humor into the posterior chamber. The aqueous humor then flows through the pupil into the anterior chamber. The ciliary body is attached to the lens by connective tissue called the zonular fibres, the fibres of Zinn. Relaxation of the ciliary muscle puts tension on these fibres and changes the shape of the lens in order to focus light on the retina. The ciliary body has 3 functions, accommodation, aqueous humor production, and resorption and maintenance of the lens zonules for the purpose of anchoring the lens in place. When the ciliary muscle contracts, the lens becomes more convex, generally improving the focus for closer objects. When it relaxes, it flattens the lens generally improving the focus for farther objects. The ciliary epithelium of the ciliary processes produces aqueous humor, which is responsible for providing oxygen, nutrients , and metabolic waste removal for the lens and the cornea, which do not have their own blood supply. 80% of aqueous humor production is carried out through an active secretion mechanism and 20% is produced through the ultrafiltration of plasma.

The corneal endothelium is an arrangement of flattened, mitochondria rich cells that line the posterior surface of the cornea and face the anterior chamber of the eye. The corneal endothelium controls fluid and solute transport across the posterior surface of the cornea and maintains the cornea in the slightly dehydrated state that is required for good transparency. How it manages to achieve this is a matter of great controversy and debate.

For more details see:

British Journal of Ophthalmology 1997 Mechanism of fluid transport across corneal endothelium and other epithelial layers: a possible explanation based on cyclic cell volume regulatory changes

by Jorge Fischbarg

Schlemm's canal is a circular lymphatic like vessel in the eye that collects aqueous humor from the anterior chamber and delivers it into the episcleral blood vessels via aqueous veins. It is named after Friedrich Schlemm ( 1795 - 1858). The canal is essentially an endothelium lined tube resembling that of a lymphatic vessel. On the inside of the canal, nearest to the aqueous humor , it is covered by the trabecular meshwork. This region makes the greatest contribution to outflow resistance of the aqueous humor. The canal has been considered a blood vessel, but studies published in 2014 showed that the molecular identity of Schlemm's canal is very similar to the one of lymphatic vasculature.

8. The origins of the human eye

The human eye is used for seeing. How it achieves this is by converting electromagnetic radiation into a nerve impulse. Light enters the human eye and emerges in the form of a nerve impulse. The front of the eye is devoted to forming a sharp image and the rest of the eye, the retina, is engaged in the task of converting that image into a nerve impulse which is sent off to the brain via the optic nerve, where the brain interprets the signal received. Unless a clear, sharp image is formed on the retina, then good vision can never be achieved.

The very first part of this whole long complicated process is the actual entry of light into the human eye. This is achieved by means of the cornea, a small, round, clear and transparent , dome shaped object at the very front of the eye. The cornea had to be of a round shape in order to focus the light properly, and it had to be clear and transparent, in order to allow the light to enter into the eye. The problem that immediately arose was the problem of what type of material could the cornea be made out of? The choices were very limited.

In the end collagen fibre was used. This material had the advantage that it was clear and transparent, and that it could be formed into a round shape, and above all it was an elastic material, which meant that it was capable of stretching, and it was capable of bouncing back to its original shape. Unfortunately, it had one distinct disadvantage. If left in contact with water, it had a tendency to absorb water and become cloudy. This was the beginning of the long , complicated, history of the human eye.

In order to solve this problem, a thin layer of cells called the endothelial layer was attached to the posterior side of the cornea. These were designed primarily to pump excess fluid from within the cornea back into the eye. Once this occurred, then another problem immediately arose. All living cells require oxygen and nutrients, and the disposal of waste products, a function usually carried out by the blood supply, in the case of humans.

How, was this to be achieved? Blood could not possibly be used inside the human eye because the red colouration would cloud the vision. So that in the end, aqueous humor, in effect a form of blood plasma, that is blood minus the red blood cells, produced by the ciliary body, was eventually used, which brings us back to the present problem.

What is the true pathway of the fluid within the human eye?

9. The case against convection currents

The case against convection currents within the human eye is the following:

Embryology of the eye

I refer to the article:

Embryology of the Eye

by Richard M. Hoar

Environmental Health Perspectives Vol. 44 , pp. 31- 34 , 1982

The aqueous chamber of the eye develops during the 7th week between the cornea and the iris, and between the iris and the lens, under the influence of the lens.

The ciliary bodies appear on the inner surface of the developing iris during the 9th week, and begin secreting aqueous humor.

The cornea is created from mesenchyme which invades between the developing lens and the surface ectoderm and is covered with a multilayered epithelium anteriorly and a single layered endothelium posteriorly. Under the influence of the lens, the cornea and the covering ectoderm become clear.

The eyelids appear during the 6th week as folds of ectodermal tissue with a mesenchymal core. They grow until they meet and fuse, during the 9th week, obliterating the palpebral opening, and they remain joined until about the 7th month.

Having considered the development of the eye during its major organogenises, between the 3rd and 9th week of gestation, one should remember that development of the eye continues into postnatal life.

Taking all of this information into account, we can safely conclude that by week 9, a fluid flow pattern has become fully established within the anterior chamber of the eye of the fetus.

The eyelids fuse during the 9th week and remain closed until about the 7th month. Thus the cornea would be maintained at the same temperature as the rest of the fetus, and no convection currents would be possible during this time period.

It is highly unlikely that the fluid flow pattern developed within the eye of the fetus , would change postnataly, and that the fluid flow pattern is not the same as the fluid flow pattern currently accepted by modern theorists, which is based on convection currents.

The Boussinesq equation

Joseph Valentin Boussinesq ( 13 March 1842 - 19 February 1929) was a French mathematician and physicist who made significant contributions to the theory of hydrodynamics, vibration, light, and heat. From 1872 to 1886, he was appointed professor at the Faculty of Sciences at Lille, lecturing in differential and integrel calculus. From 1896 until his retirement in 1918, he was professor of mechanics at the Faculty of Sciences in Paris.

John Scott Russell experimentally observed solitary waves in 1834.

Subsequently, this was developed into the modern day physics of solitons.

In 1871, Boussinesq published the first mathematical theory to support Russell's experimental observation.

In 1873, Boussinesq published his Boussinesq equation. This equation has the characteristics of being a 4th order nonlinear partial differential equation belonging to the family of KdV equations, and it defines the movement of long waves in shallow water, subject to gravity propagation in a bi directional way. The equation has a wide range of usage in areas of science such as physics, chemistry, biology, mechanics, in particular nonlinear wave phenomenon including ion sound in plasma, lattice waves.

The current theory of the flow of fluid within the human eye

The currently accepted theory of the flow of fluid within the human eye is based entirely on convection currents and the Boussinesq equation.

For those who are interested, diagrams are available on the world wide web, showing the flow of fluid within the human eye based on the current theory.

The eye fluid passes into the anterior chamber via the pupil, and it being warmer than the fluid in the anterior chamber, means that it will rise to the top of the anterior chamber flowing adjacent to the iris, assuming of course that the person is looking straight ahead, and is in a gravitational field.

Cooler fluid would then move in to take its place. Upon reaching the top of the anterior chamber, the eye fluid would then cascade down the cornea and would then form a circular convection current.

As the fluid cascades down the cornea, it would deliver O2, and other nutrients, and remove waste products. The current theory is based on sound scientific principles, and the well respected Boussinesq equation.

However, the Boussinesq equation was designed to be used for the movement of long waves in shallow water, subject to gravity propagation in a bi directional way, and was never designed to be used for convection currents within the human eye.

Besides, the human eye has a tendency to invent its own solutions to problems that appear to have no solutions.

In addition, the currently accepted theory of the flow of fluid within the human eye cannot really explain Krukenberg's spindle, and, unfortunately, it suffers from one major defect.

It cannot explain why people who suffer from keratoconus do not get corneal edema.

Keratoconus

Keratoconus is a rare eye condition in which the cornea assumes the shape of a distorted cone. If the currently accepted theory of the flow of fluid within the human eye is correct, then as the eye fluid flows down the cornea it would automatically miss the tip of the conical cornea, and all persons suffering from keratoconus should suffer from corneal edema at the apex of their corneas.

This does not happen, and persons suffering from keratoconus do not get corneal edema. Their corneas remain perfectly clear.

How would one go about explaining this most unusual phenomenon?

Diurnal variation in IOP

The current theory of the flow of fluid within the human eye cannot account for the diurnal variation in intraocular pressure.

I refer to the article:

A wireless pressure sensor for continuous monitoring of intraocular pressure in conscious animals

By Simon A. Bello and Christopher L. Passaglia Department of Ophthalmology, University of South Florida, Tampa, FL., Department of Electrical Engineering, University of South Florida, Tampa, FL., Department of Chemical & Biomedical Engineering, University of South Florida, Tampa, FL.

"Rat IOP was found to exhibit a diurnal rhythm, cycling between low daytime levels and high nighttime levels. A similar IOP rhythm has been observed in mice, rabbits, and humans, but not primates. The day night difference was 5 mm Hg in agreement with tonometry findings in rats. "

I refer to the article:

European Journal of Pharmaceutical and Medical Research

A Comparison of Diurnal Variation and Split Diurnal Variation in Intraocular Pressure: a Prospective Study

By Dr. Abha Shukla, et al.

"IOP varies spontaneously over time, and it is generally accepted that this spontaneous variation follows a conserved circadian pattern in both glaucomatous and non glaucomatous eyes. It has been hypothesized that each individual has a characteristic rhythm which is obstinately maintained. The existence of circadian control suggests that IOP rhythm could be constant and repeatable unless it is influenced by some external factors. "

According to my theory of the flow of fluid within the human eye, it is no longer a hypothesis that each individual has a characteristic rhythm which is obstinately maintained, but it is an established fact.

My theory of the flow of fluid within the human eye is based on the fact that there is a diurnal variation in intraocular pressure.

My theory of the flow of fluid within the human eye is entirely consistent with the diurnal variation in intraocular pressure in the human eye, and for that matter any other eye, and even predicts such a diurnal variation in intraocular pressure.

All humans, animals, and fish, including sharks have eyes that are subject to diurnal variation in intraocular pressure . Those that do not have a diurnal variation in intraocular pressure are destined for blindness.

Diurnal variation in intraocular pressure varies from person to person. For those who go to sleep at sunset and wake up at sunrise then their maximum eye pressure will be at sunrise. For those who suffer from insomnia, and go to bed at say, 6 a.m. and wake up at 3 p.m., then their maximum eye pressure will occur at 3 p.m.

Diurnal variation in intraocular pressure is not dependent on the rising and setting of the sun, but depends on when a person goes to sleep and wakes up.

The current theory of the flow of fluid within the human eye has a number of flaws, the latest being that it cannot explain the diurnal variation in intraocular pressure within the human eye.

Another flaw occurs when a person goes to sleep and closes their eyes. What happens to the convection currents that are supposedly present. Do they suddenly cease to exist, and does all fluid flow within the human eye cease. It should do so, because when a person closes their eyes their cornea will become at the same temperature as the rest of the eye, and no convection currents will be possible. As soon as a person wakes up in the morning, and opens his eyes, will the convection currents suddenly commence to operate again? One would hardly think so.

10. The proposed new theory of the flow of fluid within the human eye

The proposed new theory of the flow of fluid within the human eye is the following:

To be continued........................

Written by:

The Eye Enigma

This new theory, if it is correct, may have profound implications for trabeculectomy, deep sclerectomy, and even MIGS.

The new theory may even be able to offer a possible explanation as to why Cypass failed.

SOURCES:

I refer to the article:

Could Alcon`s Cypass Trouble be boon for Glaukos or bust for MIGS?

30 August 2018

by Tina Tan

"Endothelial cell loss could be a problem for all MIGS or even trabeculectomy or deep sclerectomy."

https://sites.google.com/view/haigis

https://sites.google.com/view/dryeye

https://sites.google.com/view/dryeye2

https://sites.google.com/view/dryeye3