Topographic anatomy and structures of the eyeball
The crystalline lens (lens) is located inside the eyeball (globe) and performs the crucial anatomical function of demarcating intraocular spaces. Together with the iris (iris), which, along with the ciliary body (ciliary body), forms the middle tunic of the eye, the lens divides the eyeball cavity into two main compartments:
- Anterior chamber: the space filled with aqueous humour (aqueous humour).
- Posterior chamber: according to the topographic division used in diagnostic radiology, this cavity is filled with the vitreous body (vitreous humour).
As a transparent part of the light-conducting structures, the lens ensures the unobstructed passage of light rays to the inner tunic of the eye — the retina (retina). Blood supply to the intraocular structures is provided by branches of the ophthalmic artery, while venous drainage is carried out via the superior and inferior ophthalmic veins.
The role of the lens in the optical system and refractogenesis
The lens is an integral element of the optical apparatus, whose refractive power changes dynamically during the body's growth.
- Primary refraction: Formed during the period of active development of the optical apparatus. In newborns, the refractive power is very high (on average 80 D), but due to the short anatomical axis, the main focus lies behind the eye. This causes physiological hyperopic refraction (about 4.0 D). By 3–5 years of age, the axis elongates, and the refractive power decreases to 60 D, shifting refraction toward emmetropia or mild myopia.
- Secondary (induced) refractogenesis: Acquired pathological changes in the refractive power of optical media (including the lens itself) lead to the formation of ametropias. Various lens pathologies, along with prematurity and elevated intraocular pressure, are frequent etiological causes of induced myopia.
Trauma and lens displacement (CT findings)
When performing computed tomography (CT) of the orbits in axial and coronal projections, various traumatic injuries affecting the lens and adjacent structures can be visualized.
- Anterior subluxation of the lens: This condition manifests clinically and radiologically as a change (decrease) in the depth of the anterior chamber of the eye. It is important to note that a similar symptom is also characteristic of lacerated corneal wounds.
- Posterior dislocation: Encountered in clinical practice significantly more often than anterior displacement.
- Bilateral dislocation or subluxation: An extremely rare phenomenon. When detected, it is necessary to rule out severe systemic connective tissue diseases in the patient, such as Marfan syndrome, Ehlers-Danlos syndrome, and homocystinuria.
- Differential diagnosis of trauma: On CT, lens displacements are differentiated from hyphema (increased X-ray density due to blood in the anterior chamber), globe rupture ("flat tire" sign due to hypotonia), and phthisis bulbi (phthisis bulbi — a shrunken, calcified globe following penetrating injuries).
Clinical evaluation and impact on visual acuity
Lens diseases are among the most frequent ophthalmological causes of reduced visual acuity (amblyopia) or complete blindness (amaurosis).
When taking a history and testing visual acuity (alternately in both eyes using special charts), it is important to distinguish pathologies of light-conducting structures from neurological deficits.
- If the visual reduction is caused exclusively by refractive errors, the use of correcting optical lenses (converging "+" or diverging "–", spherical or cylindrical) normalizes visual acuity. For example, converging lenses turn parallel rays into converging ones, correcting the focus.
- However, if optical lenses do not improve vision, and ophthalmoscopy reveals no changes in the refractive media (including the lens) and retina, this indicates a neurological cause. In such cases, the pathological process is usually localized in retrobulbar structures — the optic nerve (which is a brain fiber bundle myelinated by oligodendrocytes) or the optic chiasm.
To memorize the rare causes of bilateral lens dislocation, use the mnemonic MEG: Marfan syndrome, Ehlers-Danlos syndrome, Homocystinuria.
Class and exam questions
How does lens subluxation affect the anterior chamber of the eye?
Anterior subluxation of the lens leads to a clinically and radiologically visible decrease in the depth of the anterior chamber of the eye.
What does bilateral lens dislocation indicate?
This is a rare condition that requires the mandatory exclusion of systemic connective tissue diseases: Marfan syndrome, Ehlers-Danlos syndrome, or homocystinuria.
How to distinguish lens pathology from optic nerve lesions?
If visual reduction is not corrected by optical lenses, and during ophthalmoscopy the lens and other refractive media are unchanged, the pathological process is most likely localized in the optic nerve or chiasm.
What role does the lens play in the development of myopia?
Acquired lens pathologies can alter the refractive power of the eye's optical media, which is one of the causes of secondary (induced) myopia.
What else to study on this topic
- Primary and secondary refraction: age dynamics and pathogenesis
- CT signs of eyeball trauma: hyphema, rupture, and phthisis bulbi
- Anatomy of the retrobulbar visual pathway and chiasm
- Topical diagnosis of lesions of the optic tract and optic radiations
- Innervation of extraocular muscles by cranial nerves
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