ABO Study Guide 2026

Retinoblastoma is the most common primary intraocular malignancy in children, and its classic presenting sign is leukocoria, or a white pupillary reflex. This 'cat's eye reflex' occurs when light reflects off the tumor mass within the eye. Early detection is critical for successful treatment and preservation of vision and life.

Amblyopia, or 'lazy eye,' is reduced vision in an eye that did not develop normal sight during childhood. Strabismus, a misalignment of the eyes, is the most common cause because the brain suppresses the image from the misaligned eye to avoid double vision, leading to a lack of visual stimulation and development in that eye. Early detection and treatment are crucial for improving visual outcomes.

The power in the principal meridians of a spherocylindrical lens can be determined by analyzing the prescription. The sphere power (-2.00 D) is present in all meridians. The cylinder power (-1.00 D) is at its maximum at 90 degrees away from its axis. The axis is 180, so 90 degrees away is the 90-degree meridian. Therefore, the total power in the 90th meridian is the sum of the sphere and cylinder powers: -2.00 D + (-1.00 D) = -3.00 D.

The structures of the angle from posterior to anterior are: Ciliary body band, Scleral spur, Trabecular meshwork, and Schwalbe's line. Therefore, the ciliary body band is the most posterior structure.

Horner's syndrome is caused by a disruption of the oculosympathetic pathway. This results in the characteristic triad of ipsilateral ptosis (mild drooping of the upper eyelid due to paralysis of Müller's muscle), miosis (a constricted pupil due to unopposed action of the parasympathetic system), and anhidrosis (decreased sweating on the affected side of the face). [9, 10, 12]

Fluorescein angiography is a highly useful diagnostic tool for evaluating posterior uveitis. This test involves injecting a fluorescent dye into the bloodstream and taking rapid photographs of the retina. It helps visualize the retinal and choroidal vasculature, detect leakage from inflamed vessels, identify areas of ischemia, and assess macular edema, all of which are crucial for diagnosing and managing posterior segment inflammation.