Corneal diameter is increased in:
**Core Concept**
The corneal diameter is an essential parameter in ophthalmology, and its measurement can be affected by various conditions. The normal corneal diameter ranges from 11 to 12 millimeters in adults. An increase in corneal diameter can be associated with certain systemic and ocular conditions.
**Why the Correct Answer is Right**
The correct answer is associated with Marfan syndrome, a genetic disorder that affects the body's connective tissue. The condition is characterized by an abnormality in the fibrillin-1 gene, which leads to the production of defective fibrillin protein. This defective protein disrupts the normal structure and function of connective tissue, including the cornea. The increased corneal diameter in Marfan syndrome is due to the stretching of the corneal tissue, which is a result of the systemic connective tissue disorder.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because keratoconus is a condition characterized by a thinning and conical protrusion of the cornea, which can lead to a decrease in corneal diameter rather than an increase.
* **Option B:** This option is incorrect because ectasia of the cornea, often associated with keratoconus, can also lead to a decrease in corneal diameter.
* **Option C:** This option is incorrect because myopia, or nearsightedness, can be associated with a normal or even decreased corneal diameter.
**Clinical Pearl / High-Yield Fact**
Remember that Marfan syndrome is a systemic disorder that affects multiple organ systems, including the eyes, heart, and skeleton. The increased corneal diameter in Marfan syndrome is a subtle but important sign that can help clinicians diagnose this condition.
**Correct Answer: D. Marfan syndrome**