megalocornea

Megalocornea Description

Megalocornea is a rare nonprogressive corneal disorder characterized by an enlarged corneal diameter, typically exceeding 13 mm [1][2]. This condition is inherited and affects both eyes, with the cornea being larger than normal without any increase in intraocular pressure [3][4].

The ocular features of megalocornea include a deep anterior chamber and an enlarged corneal diameter at birth, ranging from 13.0 to 16.5 mm [5]. In some cases, male patients may develop early arcus, which is a condition characterized by the deposition of cholesterol crystals in the peripheral cornea [6].

Megalocornea is often associated with normal intraocular pressure and does not progress over time [1][2]. It is essential to note that megalocornea can be part of a syndrome, such as megalocornea-intellectual disability syndrome, which is characterized by intellectual disability, congenital hypotonia, and other systemic features [7].

In summary, megalocornea is a rare inherited condition affecting the cornea, characterized by an enlarged diameter without any increase in intraocular pressure.

References:

[1] Context 1: Oct 18, 2024 — The cornea is clear and of normal or slightly below normal thickness. Keratometry reveals normal to above normal steepness. [2] Context 5: Feb 17, 2020 — Megalocornea is a rare nonprogressive enlargement of the cornea to 13 mm or greater; in the setting of normal intraocular pressure. [3] Context 4: Megalocornea is an inherited eye disorder in which the corneal diameter is bilaterally enlarged (greater than 13 mm) without an increase in intraocular ... [4] Context 7: Megalocornea is an inherited eye disorder in which the corneal diameter is bilaterally enlarged (greater than 13 mm) without an increase in intraocular ... [5] Context 8: Ocular Features: The corneal diameter is enlarged at birth to between 13.0 and 16.5 mm and the anterior chamber is deep. [6] Context 8: Male patients may develop early arcus, which is a condition characterized by the deposition of cholesterol crystals in the peripheral cornea. [7] Context 6: Megalocornea-intellectual disability syndrome is a rare intellectual disability syndrome most commonly characterized by megalocornea, congenital hypotonia.

Megalocornea Signs and Symptoms

Megalocornea, a rare eye disease, presents with several distinct signs and symptoms. Here are the key features:

• Enlarged Cornea: The primary clinical feature of megalocornea is an enlarged corneal diameter, which can be noted at birth or later in life [3].
• Diminished Muscle Tone (Hypotonia): Most patients with megalocornea also experience diminished muscle tone, which can vary in severity [2].
• Visual Disturbances: In some cases, megalocornea can lead to visual disturbances associated with cataract, such as blurred vision and glare [5].
• Glaucoma: Patients may also be at risk for glaucoma, a condition that can cause damage to the optic nerve and lead to vision loss [5].
• Myopia: Megalocornea can manifest with mild to moderate myopia (nearsightedness) [6].
• Photophobia: Some patients experience photophobia, or sensitivity to light [6] and [7].
• Blepharospasm: Excessive tearing and blepharospasm (involuntary spasms of the eyelid muscles) are also common symptoms [7].
• Associated Complications: Megalocornea can be associated with other ocular disorders, such as cataract and ectopia lentis (dislocation of the lens), as well as systemic disorders like Marfan syndrome and Down syndrome [8].

These signs and symptoms can vary in severity and may not always be present. A diagnosis is typically made in the first year of life, depending on when treatment is sought.

References: [1] Not applicable [2] Context #2 [3] Context #3 [4] Context #4 [5] Context #5 [6] Context #6 [7] Context #7 [8] Context #8

Diagnostic Tests for Megalocornea

Megalocornea can be challenging to diagnose, but several tests and examinations can help confirm the condition. Here are some diagnostic tests used to evaluate megalocornea:

• Genetic testing: This is a crucial test to determine if megalocornea is associated with any underlying genetic conditions or syndromes.
• Corneal diameter measurement: A horizontal corneal diameter exceeding 13 mm typically indicates megalocornea.
• Intraocular pressure (IOP) testing: Measuring IOP is essential, as megalocornea can be associated with glaucoma.
• Optic disc cupping and corneal edema evaluation: These findings can differentiate congenital glaucoma from megalocornea [7].
• Electroretinogram (ERG): This test measures the retina's response to light, which can help diagnose megalocornea in some cases.
• Clinical examination: A thorough eye exam by an ophthalmologist is essential to rule out other conditions and guide treatment.

Additional Tests

Other tests may be used to evaluate associated conditions or syndromes, such as:

• DNA testing: To confirm the diagnosis of megalocornea and identify any underlying genetic conditions.
• Imaging studies: Such as ultrasound biometry, which can help distinguish megalocornea from buphthalmos [1].

References

[1] Ultrasound biometry may be useful in distinguishing megalocornea from buphthalmos; classically, the ratio of anterior chamber depth to axial length is relatively elevated in megalocornea compared with buphthalmos. [7] Findings that differentiate congenital glaucoma from megalocornea include elevated intraocular pressure, optic disc cupping, corneal edema, ... [10] Diagnosis is made through a clinical examination and confirmed by DNA testing.

Based on the available information, it appears that there is no specific drug treatment for megalocornea itself, as the condition is primarily anatomical and does not have a cure or treatment.

However, associated ocular conditions such as cataract, dryness due to exposure, and refractive errors can be treated with various medications. For example:

• Cataract can be treated surgically [1].
• Dryness due to exposure can be treated with artificial tears [6].
• Refractive errors can be corrected with glasses or contact lenses [4].

It's also worth noting that treatment of associated ocular or systemic issues are determined by a multidisciplinary team, which may involve medication as part of the overall management plan [6].

In terms of specific medications, there is no mention of any particular drug being used to treat megalocornea itself. However, it's possible that medications may be used to manage associated conditions or complications.

References:

[1] Surgical Care. Surgical amelioration of glaucoma and cataract is performed when necessary. [4] Oct 18, 2024 — Management/Therapeutic Considerations. Symptomatic primary megalocornea typically requires the correction of refractive errors. [6] Dryness due to exposure can be treated with artificial tears. Treatment of associated ocular or systemic issues are determined by a multidisciplinary team.

Differential Diagnosis of Megalocornea

Megalocornea, a rare nonprogressive enlargement of the cornea to 13 mm or greater in the setting of normal intraocular pressure [3], has several differential diagnoses. These include:

• Simple megalocornea: A condition where the cornea is enlarged without any underlying cause [5].
• Megalophthalmos anterior: A rare congenital anomaly characterized by an enlarged cornea and iris [5].
• Congenital glaucoma: A condition that affects infants and young children, causing increased intraocular pressure and enlargement of the cornea [4, 10].
• Keratoglobus: A rare congenital disorder where the cornea is thin and globular in shape [5].
• High myopia: A condition where the eyeball is too long, leading to an elongated shape and potential complications [5].

Additionally, megalocornea can also be associated with other conditions such as:

• Neuhäuser syndrome (Megalocornea-mental retardation syndrome) [6]
• Frank-Ter Haar syndrome [1]
• Buphthalmos: A condition where the cornea is enlarged due to increased intraocular pressure, often associated with congenital glaucoma [8].
• Crouzon syndrome: A rare genetic disorder that affects the development of the face and skull, including the eyes [6].

It's essential to note that definitive diagnosis of megalocornea requires genetic testing of the complete coding region of the X chromosome [2].