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(heim) An iron-containing nonprotein portion of the hemoglobin molecule wherein the iron is in the ferrous (Fe2+) state. Disorders of heme synthesis are known as the porphyrias. SEE: ferritin; hematin.

heme oxygenase

ABBR: HO. An enzyme that cleaves the ring structure of heme, releasing biliverdin, carbon monoxide, and iron. It is present in humans in two active forms: HO-1 and HO-2.


(hem″ĕ-ră-lō′pē-ă) [Gr. hēmera, day + Gr. alaos, blind + opia, eye] Diminished vision in bright light. In hemeralopia, vision is poor in sunlight and in good illumination; it is good at dusk, at twilight, and in poor illumination. This is noted in albinism, retinitis with central scotoma, toxic amblyopia, coloboma of the iris and choroid, opacity of the crystalline lens or cornea, and in conjunctivitis with photophobia.

 The term was formerly erroneously applied to nyctalopia (night blindness). SEE: nyctalopia. SYN: day blindness.

heme synthetase

The enzyme that catalyzes the chelation of iron (Fe++) to porphyrin, a crucial step in the synthesis of heme. SYN: ferrochelatase.


[Gr. hēmi-, half] Prefix meaning half.


SEE: -emia.


(hĕm″ē-ăn-ăl-jē′zē-ă) [″ + ″ + algos, pain] Lack of sensibility to pain (analgesia) on one side of the body.


(hĕm″ē-ăn-ĕs-thē′zē-ă) [″ + ″ + aisthesis, sensation] Anesthesia of half of the body.

hemianopia, hemianopsia

(hem″ē-ă-nōp′ei-ă, -nop′sē-ă) Blindness in one half of the visual field. SYN: half vision; hemiamaurosis; hemiamblyopia. hemianoptic (-ă-nop′tik), adj.

altitudinal h. Blindness in upper or lower half of the visual field of one or both eyes.

binasal h. Blindness in the nasal half of the visual field in each eye.

bitemporal h. Blindness in the temporal half of the visual field in each eye.

complete h. Blindness in half the visual field.

crossed h. Either bitemporal or binasal hemianopsia. SYN: heteronymous h.

heteronymous h. Crossed hemianopia.

homonymous h. Blindness of the nasal half of the visual field of one eye and of the temporal half of the other, or right-sided or left-sided hemianopsia of corresponding sides in both eyes.

incomplete h. Blindness in less than half of the visual field of each eye.

quadrant h. Blindness of a symmetrical quadrant of the field of vision in each eye.

unilateral h. Hemianopsia affecting only one eye.



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