**5. Conclusion**

With much simplification, the eye can be described as having three power supplies and four excretory paths, controlled by two forced convection systems [10]. There are three sources of food: tear fluid (feeds the corneal epithelium and excretes through the nasal and mouth cavities as well as the digestive system), aqueous humor (feeds the lens and corneal stroma and excretes through the venous system), and through Bruch's membrane (the circulatory system feeds and excretes the retina). There are two systems of forced convection, the intrinsic muscles (the crystalline and Schlemm canal) and the extrinsic muscles (cornea, trabecular mesh, and retina), which drive mass transfer. The physical properties of a cleaning sponge can be used as a metaphor for four greatly simplified mass transfer models. The four adaptations are these: a cleaning sponge to represent bidirectional movements on its sides, for the feeding and excretion of the lens; a cleaning sponge with its closed sides, to represent the bidirectional movements on its two other sides for feeding and excretion of the retina (Bruch's membrane) [6]; a cleaning sponge with closed sides to represent the unidirectional passage on both sides for the passage of aqueous humor and metabolic residue (trabecular meshwork) [1, 11]; and finally, two cleaning sponges, juxtaposed to closed flat surfaces, to represent bidirectional movements on their free sides for feeding and excretion of the epithelium and corneal stroma (epithelium, Bowman's membrane, and stroma) [1, 6]. Intraocular metabolic residues are stored when mass transfer mechanisms are insufficient to maintain constant, concentration, and agitation of dissolved or suspended metabolic residue components in the moving mass. An insufficiency of these mechanisms causes the mobile mass to stagnate in both forced convection systems and to store the metabolic residue due to dehydration. Dehydrated residues are stored simultaneously in the cornea, trabecular mesh, Schlemm's canal, lens, and retina. Vicious and frequent habits can cause mobile mass stagnation.

Metabolic residue is released if there is a physical work of forced convection systems capable of excreting concentrated metabolic residue in solution or suspension in the mobile medium. The release of fixed metabolic residue depends on its rehydration to transform it into a solution or suspension. The cornea, trabecular mesh, lens, Schlemm's canal, and retina simultaneously excrete accumulated residues. Orthoptic exercises can stimulate the physical effort to excrete metabolic residue, as well as rehydrate the fixed residues; these, however, cause sleep. Cataract surgery stimulates the forced convection system because it unbalances the efforts of the extrinsic muscle due to increased light transmission and change in refractive power resulting from intraocular lens implantation. Therefore, postoperative symptoms caused by cataract surgery are similar to those caused by orthoptic exercises that excrete intraocular metabolic residue.

When stimulated, stored metabolic residues can be rehydrated and simultaneously expelled from all intraocular regions. The accumulated metabolic residues in the corneal epithelium can be expelled through the cavities, nasal and mouth, as well as through the digestive system. Through the nasal cavity, they can plug up the nostrils as well as become dehydrated and form a deposit in the nasal passages. Through the oral cavity, they can be expelled but, even without fever, can cause cough and inflammation of the throat and vocal cords, which makes swallowing difficult and often produces a hoarse or muffled voice. Through the digestive system there is nothing observed. Accumulated metabolic residue in the corneal, crystalline, and retinal stroma can be expelled through the venous system and cause slight body aches (feeling unwell, malaise) without fever. Corneal and crystalline residues cross the anterior chamber, trabecular meshwork, and Schlemm's canal before reaching the venous system. In addition to these symptoms, there may be the production of tears and headache. The production of tears is linked to cleansing and may be a photoneural perception of impeding light transmission across the anterior surface of the cornea. A headache may be linked to physical exertion between the Zinn ring and the eyeball because the most efficient treatment is the alignment of the eyes to a fixation point. This alignment can correct the diopter difference between the eyes and acts much faster than the use of analgesic; if delayed, its application impairs its efficiency. Patients after cataract surgery also eliminate intraocular metabolic residue, so they should have the same symptoms, depending on the eliminated mass. However, symptoms may appear only 2 months after surgery, because metabolic residues rehydration is a slow process. On the other hand, the slight body aches do not last more than a day, but throat inflammation can last up to 5 days. Under these circumstances and without fever, if the patient ever seeks medical attention, it is not likely to return to the ophthalmologist unless the patient receives guidance.

The stored intraocular residues simultaneously cause some physical and symptomatic pathologies. Among the major ocular pathologies are the increase in eye mass and volume, and, consequently, the eyeball changes the shape, inertia moment, position in the eye socket, refractive disposition and error in intraocular light transmission, dislocation of its mass center, saccadic movements, cyclotorsion, fixation instability, and increased intraocular pressure. Refractive disposition and error in intraocular light transmission are consequences of the formation of metabolic residue droplets. Error in intraocular light transmission causes error in image transmission. Error in image transmission is image refraction in different dimensions, intensity, and locations when there is slight variation in lens accommodation or visual axis angular displacement. This pathology was verified in Scheiner's experiments in 1619, *apud* [12]. In response, to maintain the fixation point on the fovea, the rectus muscles receive a compensatory movement impulse, in the opposite direction to the unwanted displacement of image projection on the retina, which results in saccadic movement. Importantly, the saccadic pathological movement occurs in conjunction with two other pathologies, cyclotorsion and fixation instability, which can aggravate the consequences. Then the initial thrust and final deceleration of saccadic movement occurs in a structurally unbalanced system, so it can produce physical effort between the attachment points of the eyeball. The eyeball has three fixation points on the superior orbital fissure (posterior orbit), the trochlea of superior oblique, and maxillary bone (origin of the inferior oblique muscle). Frequent acceleration and deceleration of saccadic movement can cause frequent and important impulsive physical efforts in the anteroposterior axis and in the opposite direction, causing frequent variations in intraocular pressure. Frequent impulsive physical efforts and variations in intraocular pressure can slowly damage the optic nerve. If this situation is combined with the patient's high intraocular

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**Figure 5.**

*Intraocular Forced Convection Mechanism Defect as Probable Cause of Normal-Tension…*

no public or private financial participation for publication in this work.

**A. Dynamic comparison of the state change agility between the activities of** 

**Figure 5** shows three graphs of Eq. (2), which is the analytical solution of state change in a first-order linear model. The graphs were obtained by replacing the time constant (τ) by the time constants (τC, τR, and τS) according to Eq. (3). The relation was defined from the numerical analysis compatibility, associated with the agility

Voluntary action, in order to observe an object of interest, requires the movement of the eyes toward it, under the rectus muscles control (τR). For this, it is necessary, in the first place, to focus on the object (τC) at the moment of its projection in the fovea. Therefore, focalization agility is then considered to be three times higher

*Muscle contraction percentage graph, Eq. (2), (C) Ciliary muscle contraction (time constant τC). (R) Rectus muscle contraction (time constant τR). (S) Superior oblique muscle contraction (time constant τS).* 

f(t) = 100 × (1 − e −t/<sup>τ</sup>

) (2)

3τ C = τ R = τ S/3 (3)

pressure, it would be very difficult to control the pressure alone by reducing the

The English text of this paper has been revised by Sidney Pratt, Canadian, MAT (The Johns Hopkins University), RSAdip-TESL (Cambridge University). There was

*DOI: http://dx.doi.org/10.5772/intechopen.89934*

**focusing, fixation, and images fusion**

**A.1 Analysis of the relationship τ<sup>C</sup> = τR/3**

production of aqueous humor.

**Acknowledgements**

for object visualization.

**Appendix**

*Intraocular Forced Convection Mechanism Defect as Probable Cause of Normal-Tension… DOI: http://dx.doi.org/10.5772/intechopen.89934*

pressure, it would be very difficult to control the pressure alone by reducing the production of aqueous humor.
