Imbalance between intraocular pressure and cerebrospinal fluid pressure is important link to pathogenesis of glaucoma

J.Glaucoma News (Russia), 2015, 1, p. 101-103.

E.G. Gamm

Imbalance between intraocular pressure and cerebrospinal fluid pressure is important link to pathogenesis of glaucoma

Helmholtz Institute of Eye Diseases.

Moscow, Russia

K.I. Noishevsky [4] propounded the hypothesis about a role of imbalance between intraocular pressure (IOP) and cerebrospinal fluid pressure (CSF-P) in pathogenesis of glaucoma in 1908 and experimentally confirmed it in 1910. Since that time, the idea of ​​K.I. Noishevsky about the pathogenesis of glaucoma has not changed, however, this idea can be looked at more widely.

Keywords: glaucoma, pathogenesis, diagnosis, treatment

According to K.I. Noishevsky, the balance between IOP and CSF-P in glaucoma is violated due to the excess of IOP over CSF-P. Moreover, this occurs in all forms of glaucoma. Later it was proved [5,6,7,8] that the excess of IOP over CSF-P causes a backward deflection of the lamina cribrosa (a lattice membrane), and this leads to compression of the optic nerve fibers passing through the lamina cribrosa, their death and developing optic nerve atrophy. However, the balance between IOP and CSF-P can also be violated due to excess CSF-P over IOP (stagnant optic disc, hypotension eyes). In this case, the deflection of the lamina cribrosa going forward. This also causes a deformation of the membrane and destruction of optic nerve. That is, the direction of deflection of lamina cribrosa (backward or forward) is not significant in the mechanism of optic nerve damage. Examples of that are glaucoma and stagnant optic disc. In both cases the atrophy of the optic nerve occurs (with minor differences), although the direction of deflection of lamina cribrosa in these cases is opposite.

Both IOP and CSF-P may be normal, increased or decreased. Theoretically, the number of options of IOP to CSF-P ratio may by 10 [1]. For now, the existence of only four following forms does not require any proof: hypertensive glaucoma (increased IOP / normal CSF-P), normotensive glaucoma (normal IOP / decreased CSF-P), stagnant optic disc (normal IOP / increased CSF-P) and eye hypotension (decreased IOP / normal CSF-P). Whether the other forms of imbalance exist will be clear when the CSF-P investigation becomes a standard procedure. Instruments for non-invasive measurement of CSF-P already exist [3, 9], but they require extra refinement.

So the imbalance between IOP and CSF-P may be considered as a separate disease having several forms. Glaucoma in this disease has two forms: hypertensive and normotensive glaucoma (the term "hypertensive glaucoma" includes all forms of glaucoma with increased IOP). The name of the disease "the imbalance between IOP and CSF-P" is conditional. This disease is absent in today's International Classification of Diseases (ICD-10) although there is a serious reason to highlight the "imbalance between IOP and CSF-P" as a separate disease.

Diagnosis of "imbalance between IOP and CSF-P" must be based on the identification of imbalances while pathogenetic treatment should be based on elimination of the imbalance. The diagnosis of imbalance is obviously possible only at combined measurement of IOP and CSF-P. In the measurement of IOP and CSF-P the diagnosis of imbalance will specify form of the disease. For example, in the diagnosis of glaucoma the IOP and CSF-P measurement will not only detect glaucoma but also determine the hypertensive or normotensive form of glaucoma. In addition, the measurement of IOP and CSF-P gives opportunity to assess an imbalance degree. This information is important because the more imbalance between IOP and CSF-P the more severe disease will occur. In glaucoma the CSF-P is also necessary to know to determine a tolerant pressure [2]. The tolerant pressure in glaucoma is a safe level of IOP for an eye. The safe level of IOP takes place when there is a balance between IOP and CSF-P. In this case, a lattice membrane can return to its original position and the compression of the optic nerve fibers stops. It should be emphasized that the balance between IOP and CSF-P does not mean their equality. The IOP and CSF-P are different in normal conditions. So IOP (Po) normally ranges from 10 to 21 mm Hg but CSF-P from 5 to 15 mm Hg. However, they are overall figures; it is interesting to know the IOP to CSF-P ratio in normal and pathological conditions. And this data have yet to be investigated. For example, you need to find out what difference between IOP and CSF-P causes a risk of glaucoma. Of course, for the diagnosis of glaucoma other studies should be conducted (gonioscopy, tonography, perimetry, etc.). These auxiliary methods are needed for diagnosis clarification.

The more durable the lamina cribrosa, the more resistance to imbalance between IOP and CSF-P takes place and the less deflection of the membrane and less damage to the optic nerve occur. So-called "ophthalmohypertension" is, in fact, glaucoma for patients with durable lamina cribrosa. Consequently, for the prognosis of glaucoma it is important to have information about lamina cribrosa durability. There are various methods for determining the strength of the membrane, but, perhaps, the easiest method is ultrasonic echobiometry of eye. Increasing the size of the eye indicates the weakness of the sclera and, accordingly, the weakness of its most vulnerable area - lamina cribrosa. It should be emphasized that the weak lamina cribrosa is not the cause of glaucoma, but is a complicating factor for the disease. In order to glaucoma occurs imbalance must have place (increasing IOP or decreasing CSF-P). Usually, weak sclera happens in the axial myopia. However, it is known that myopia even higher degree only occasionally accompanied by glaucoma. So there is no correlation between glaucoma and myopia. But glaucoma accompanied by axial myopia makes the course of disease more complicated.

As mentioned above pathogenic treatment of imbalance between IOP and CSF-P including glaucoma should be based on removing the imbalance. Strictly speaking, ophthalmologists do conduct such treatment. Imbalance in hypertensive glaucoma is eliminated by reducing the IOP with conservative or surgical methods. In case of normotensive glaucoma, it is necessary to reduce the normal IOP. In normotensive glaucoma, increasing CSF-P to a normal level is more physiological, but ophthalmologists currently do not use such methods. Ideally, reduction of IOP in glaucoma should occur up to the level of tolerant pressure, i.e., the IOP is necessary to bring into equilibrium with the CSF-P. Without achieving a balance between IOP and CSF-P it is impossible to rely on the efficiency of the glaucoma treatment.

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