Human health and medicine

Retinoblast

Retinoblast: multipotent embryonic retinal progenitor cell of the optic cup that generates all retinal neurons and Müller glia; distinct from retinoblastoma, the Rb-gene childhood tumor.

Retinoblastoma is a childhood cancer of the retina, caused by RB1 tumor suppressor inactivation (Knudson two-hit hypothesis) or rarely MYCN amplification. Key sign is leukocoria; survival ranges from 99.5% in high-income to 57.3% in low-income countries.

Retinoid

Retinoids are vitamin A (retinol) derivatives, natural and synthetic, that signal through RAR and RXR nuclear receptors; used in acne, psoriasis, and leukemia, and teratogenic.

Retinol

Retinol (all-trans-retinol) is preformed vitamin A, found in liver, fish, eggs, and dairy; absorbed at 75–100%, RDA 700–900 mcg RAE, EFSA upper limit 3,000 μg RE/day for adults.

Retinopathy

Retinopathy is a general term for disease-related damage to the retina, the light-sensitive tissue at the back of the eye, most often from diabetes or high blood pressure.

Retinopathy of prematurity

Retinopathy of prematurity (ROP), formerly retrolental fibroplasia, is abnormal retinal blood vessel growth in babies born before 30 weeks or under about 3 pounds; staged 1 to 5, screened by dilated exam, treated with laser, anti-VEGF injections, or surgery.

Retinopexy

Retinopexy is a surgical procedure that seals a retinal tear by scarring it to the underlying tissue, using laser or freezing, to treat or prevent retinal detachment.

Oct 20, 2026

Retinoschisis

Retinoschisis: splitting of the neurosensory retina, either common acquired (senile, outer plexiform layer, ~7% over age 40) or X-linked juvenile (RS1 gene, males). Distinct from retinal detachment; OCT differentiates them.

Retinoscopes

Retinoscopes (skiascopy instruments): handheld streak or spot devices for objective refraction by observing the retinal light reflex; Copeland streak design (1927), FDA Class I code HKM, cycloplegic retinoscopy the pediatric refraction standard.

Retinoscopy

Retinoscopy, also known as skiascopy, is an objective refraction technique that measures refractive error and derives an eyeglass prescription by observing the retinal light reflex.

Retlirafusp alfa (SHR-1701)

Retlirafusp alfa (SHR-1701, 瑞拉芙普-α), Hengrui's bifunctional anti-PD-L1/TGF-βRII fusion protein, approved in China January 2026 with chemotherapy for first-line PD-L1-positive advanced gastric or gastroesophageal junction adenocarcinoma.

Oct 20, 2026

Retosiban

Retosiban (GSK221149A) is a non-peptide, orally bioavailable oxytocin receptor antagonist developed by GSK as a tocolytic for spontaneous preterm labor; Phase 3 ended with recruitment failure and the program was terminated.

Retreatment

Retreatment is the administration of a second course of care for an existing condition, either repeating the original agent or procedure or adding a different intervention.

Retrograde amnesia

Retrograde amnesia is loss of memories formed before the causative event, unlike anterograde amnesia. Key features: Ribot's law temporal gradient, medial temporal lobe damage, consolidation versus retrieval theories, and functional (dissociative) forms.

Retrograde ejaculation

Retrograde ejaculation (dry climax): semen travels backward into the bladder during orgasm because the bladder neck fails to close. Causes include diabetes, TURP, RPLND, and alpha-blockers; treated with pseudoephedrine, imipramine, or sperm retrieval from urine.

Retrograde intrarenal surgery

Retrograde intrarenal surgery (RIRS) is a minimally invasive urological procedure in which a flexible ureteroscope passed through the urethra and bladder reaches the kidney to treat stones with laser.

Oct 20, 2026

Retrograde Obturation

Retrograde obturation is the placement of a filling into a prepared cavity at a tooth's root end during apical surgery, sealing the canal system when root canal treatment has failed.

Retrograde perfusion

Retrograde perfusion is a cardiac surgery technique that delivers cardioplegia backward through the coronary sinus to arrest and protect the heart during valve and bypass operations.

Retrograde urethrogram

A retrograde urethrogram (RUG) is a fluoroscopic exam in which iodinated contrast is injected backward into the urethra, the gold standard for diagnosing and staging urethral strictures.

Retrolisthesis

Retrolisthesis: posterior slippage of a vertebra on the one below, opposite of anterolisthesis. Usually 2-3 mm, Grade I, common at L3/4, prevalence about 17%, often a compensatory sagittal-balance mechanism.

Retroperitoneal arteriovenous malformation

Retroperitoneal arteriovenous malformation (retroperitoneal AVM): a rare fast-flow vascular malformation with a dysplastic artery-vein nidus behind the abdominal cavity, causing heart failure, pulmonary hypertension, or bleeding; treated mainly by transcatheter embolization.

Retroperitoneal fibrosis

Retroperitoneal fibrosis (Ormond's disease) is a rare fibroinflammatory disorder in which fibrous tissue forms around the abdominal aorta and encases the ureters, causing obstructive uropathy; most cases are idiopathic, many linked to IgG4-related disease, and corticosteroids are first-line treatment.

Retroperitoneal lymph node dissection

Retroperitoneal lymph node dissection (RPLND) is a urologic operation that removes lymph nodes behind the abdominal organs around the aorta, used to stage and often cure testicular cancer.

Retroperitoneal space

Retroperitoneal space (retroperitoneum): abdominal space behind the parietal peritoneum, from diaphragm to pelvis, holding kidneys, aorta, IVC, pancreas, duodenum, and colon, divided into three fascial compartments and interfascial planes.

Retropharyngeal or parapharyngeal abscess

Retropharyngeal and parapharyngeal abscesses are deep neck space pus collections, usually from upper respiratory infection or foreign body trauma, causing odynophagia, neck pain, and fever; treated with antibiotics and drainage.

Retroverted uterus

Retroverted uterus (tilted or tipped uterus): a uterus tilted backward toward the sacrum instead of forward, a normal variant in roughly 16–25% of women, usually asymptomatic, occasionally linked to dyspareunia, prolapse, and rare pregnancy incarceration.

RETSEACSII trial

RETSEACSII (NCT05740059) is a completed single-center randomized trial at University Hospital, Montpellier, testing SvO2-adjusted restrictive red-cell transfusion (Hb <9 g/dL plus central SvO2 ≤65%) versus standard restrictive transfusion in 676 on-pump cardiac surgery patients.