1. The approximate volume of the orbit is: A. 60 mL B. 10 mL D. 45 mL

1. The approximate volume of the orbit is: A. 60 mL B. 10 mL D. 45 mL C. 30 mL 2. The best treatment for amblyopia is: A. Orthoptic exercises B. Occlusion D. Best treated after age 10 years C. Surgery 3. Embryologically lens originates from: A. Endoderm B. Mesoderm C. Neuroectoderm D. Surface ectoderm 4. Temporal crescent around disc is typically seen in: A. Astigmatism B. Hypermetropia C. Myopia D. None of the above 5. Colour vision is the function of: A. Rods C. Retinal pigment epithelial cells B. Cones D. None of the above 6. Difference in refractive status of two eyes is called: A. Anisoconia B. Anisometropia C. Anisocoria D. Anhydrosis

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Here are the answers to all 6 ophthalmology MCQs, with textbook-backed explanations:

1. Approximate volume of the orbit

Answer: C. 30 mL

The average volume of the adult orbit is 30 mL. This is confirmed in Scott-Brown's Otorhinolaryngology Head & Neck Surgery: "The average volume in the adult Caucasian orbit is 30 ml."

2. Best treatment for amblyopia

Answer: B. Occlusion

Occlusion (patching) of the normal/better eye to force use of the amblyopic eye is the most effective treatment for amblyopia. From Kanski's Clinical Ophthalmology (10th ed.): "Occlusion of the normal eye, to encourage use of the amblyopic eye, is the most effective treatment."

Amblyopia must be treated before age 7-8 years (the sensitive period for visual development) - waiting until after age 10 is incorrect as the treatment becomes far less effective.
Orthoptic exercises and surgery do not treat amblyopia directly.
Atropine penalization is an alternative to patching, but occlusion remains the gold standard.

3. Embryological origin of the lens

Answer: D. Surface ectoderm

The lens originates from surface ectoderm. The optic vesicle (neuroectoderm) induces the overlying surface ectoderm to thicken into the lens placode, which then invaginates to form the lens vesicle. From The Developing Human (Moore): "During development of the eye, the optic vesicle induces the development of the lens from the surface ectoderm."

4. Temporal crescent around the disc is typically seen in:

Answer: C. Myopia

A temporal (myopic) crescent is a classic finding in myopia, particularly high myopia. It appears as a crescent-shaped area of exposed white sclera or visible choroidal vessels on the temporal side of the optic disc, due to tilting of the disc and posterior stretching of the sclera. From Wills Eye Manual: "Myopic crescent - a crescent-shaped area of white sclera or choroidal vessels adjacent to the disc" seen in high myopia.

5. Colour vision is the function of:

Answer: B. Cones

Cones are responsible for colour (photopic) vision. The three types of cones (S, M, L - short, medium, long wavelength) contain different photopigments that allow discrimination of colour. Rods only detect light intensity (scotopic/dim-light vision) and cannot distinguish colour.

6. Difference in refractive status of two eyes is called:

Answer: B. Anisometropia

Anisometropia = difference in refractive error between the two eyes (e.g., one eye is -2.00D and the other is -5.00D). From Wills Eye Manual: "Anisometropia: a large difference in refractive error between the two eyes."
Aniseikonia (not "anisoconia") = difference in image size perceived by each eye
Anisocoria = difference in pupil size between the two eyes
Anhydrosis = absence of sweating (unrelated to ophthalmology)

Quick Summary Table:

#	Question	Answer
1	Volume of orbit	C. 30 mL
2	Best treatment for amblyopia	B. Occlusion
3	Lens embryological origin	D. Surface ectoderm
4	Temporal crescent around disc	C. Myopia
5	Colour vision function	B. Cones
6	Difference in refractive status	B. Anisometropia

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