**Core Concept**
The intact cornea provides a natural barrier against infections due to its avascular nature and the presence of the glycocalyx, a protective layer of mucopolysaccharides. Certain microorganisms are unable to invade this barrier, while others can penetrate and cause infection.

**Why the Correct Answer is Right**
Pseudomonas aeruginosa is a gram-negative bacillus that is commonly found in soil, water, and on the skin of humans. It is known to cause opportunistic infections, particularly in individuals with compromised corneal integrity or compromised immune systems. Pseudomonas is unable to invade an intact cornea due to its inability to adhere to the corneal surface and its inability to penetrate the glycocalyx. This makes pseudomonas less likely to cause infection in the absence of corneal trauma or pre-existing conditions.

**Why Each Wrong Option is Incorrect**
**Option A:** Gonococci (Neisseria gonorrhoeae) is a gram-negative diplococcus that can invade an intact cornea, particularly in neonates and adults with compromised immune systems. Gonococci can adhere to the corneal surface and penetrate the glycocalyx, leading to severe keratoconjunctivitis.

**Option B:** Corynebacterium diphtheriae is a gram-positive rod that can cause diphtheria, a disease characterized by the formation of a toxic membrane on the tonsils and pharynx. While it can infect the eye, it is typically associated with pre-existing conditions such as ulcers or trauma.

**Option C:** Meningococci (Neisseria meningitidis) is a gram-negative diplococcus that can cause meningitis and septicemia. While it can cause eye infections, it is less likely to invade an intact cornea compared to gonococci.

**Clinical Pearl / High-Yield Fact**
Pseudomonas aeruginosa is a common cause of corneal infections in contact lens wearers and individuals with compromised corneal integrity. It is essential to maintain good hygiene and proper lens care to prevent pseudomonas infections.

**Correct Answer:**
✓ Correct Answer: D. Pseudomonas