ABO Retina and Vitreous 2 — Questions and Answers
Question 1: A 10-year-old boy has bilateral spoke-wheel foveal schisis and an electronegative ERG. Which gene is most likely mutated?
- RPGR
- RS1 (Correct answer)
- ABCA4
- BEST1
Correct answer: RS1
X-linked juvenile retinoschisis is caused by RS1 mutations and classically shows foveal schisis with a reduced b-wave (negative ERG).
Question 2: Which electrophysiologic finding is most characteristic of Best vitelliform macular dystrophy?
- Extinguished rod ERG
- Arden ratio below 1.5 on EOG with a normal full-field ERG (Correct answer)
- Delayed implicit time of 30 Hz flicker only
- Electronegative full-field ERG
Correct answer: Arden ratio below 1.5 on EOG with a normal full-field ERG
Best disease shows a markedly abnormal EOG (light-peak/dark-trough ratio usually below 1.5) with a normal full-field ERG.
Question 3: A patient on hydroxychloroquine for 6 years has parafoveal ellipsoid zone loss on OCT. Per AAO guidance, what is the recommended maximum daily dose to minimize toxicity risk?
- 5.0 mg/kg real body weight (Correct answer)
- 6.5 mg/kg ideal body weight
- 400 mg regardless of weight
- 3.0 mg/kg real body weight
Correct answer: 5.0 mg/kg real body weight
The 2016 AAO recommendation is 5.0 mg/kg real body weight per day or less for hydroxychloroquine.
Question 4: In Asian patients with hydroxychloroquine toxicity, where is retinal damage most often first detected?
- Far peripheral retina anterior to the equator
- Optic disc margin
- Parafoveal ring at 2-6 degrees
- Pericentral region beyond the arcades (Correct answer)
Correct answer: Pericentral region beyond the arcades
Asian patients frequently show a pericentral pattern of toxicity, so screening should include wider fields such as 24-2 or 30-2.
Question 5: Which ERG pattern is classic for melanoma-associated retinopathy (MAR)?
- Supernormal rod response
- Reduced a-wave with normal b-wave
- Electronegative ERG resembling complete CSNB (Correct answer)
- Isolated delayed cone implicit times with normal amplitudes
Correct answer: Electronegative ERG resembling complete CSNB
MAR antibodies target ON-bipolar cells, producing a negative ERG similar to complete congenital stationary night blindness.
Question 6: Elevated plasma ornithine with scalloped chorioretinal atrophy beginning in the midperiphery suggests which condition, and what deficient enzyme?
- Bietti crystalline dystrophy; CYP4V2
- Refsum disease; phytanoyl-CoA hydroxylase
- Choroideremia; REP-1
- Gyrate atrophy; ornithine aminotransferase (Correct answer)
Correct answer: Gyrate atrophy; ornithine aminotransferase
Gyrate atrophy results from OAT deficiency and is treated in part with an arginine-restricted diet and pyridoxine in responders.
Question 7: A fundus showing numerous small white dots throughout the midperiphery sparing the macula, with delayed rod recovery that normalizes after prolonged dark adaptation, is most consistent with:
- Fundus albipunctatus (Correct answer)
- Kandori flecked retina
- Familial drusen
- Retinitis punctata albescens
Correct answer: Fundus albipunctatus
Fundus albipunctatus (often RDH5) is a stationary night blindness with markedly delayed rod recovery that improves after extended dark adaptation.
ABO Retina and Vitreous 2
A 10-year-old boy has bilateral spoke-wheel foveal schisis and an electronegative ERG.
Which gene is most likely mutated?