H
Haab’s pupillometer See pupillometer.
haemangioma, cavernous A benign orbital tumour in adults, mostly females. The tumour is composed of large blood-filled spaces possibly due to dilatation and thickening of the capillary loops. The most common site is the muscle cone behind the globe causing proptosis, hyperopia and choroidal folds. Visual acuity may be reduced. Treatment is surgical in most cases.
haemangioma, retinal A benign tumour affecting the retinal capillaries and sometimes the optic nerve. It is often associated with systemic lesions, such as von Hippel–Lindau disease. The retinal lesion grows from a small red nodule to a larger yellowish mass accompanied by dilatation and tortuosity of the supplying artery and draining vein, and perhaps hard exudates, macular oedema, epiretinal membrane and retinal detachment. Treatment includes laser photocoagulation, cryotherapy and radiotherapy.
haematoma A swelling containing blood. It may result from injury (e.g. black eye) or from some blood disease, such as leukaemia. Note: also spelt hematoma.
haematoma, ocular A swelling due to a large haemorrhage into the tissues of the eye.
haemophthalmia An effusion of blood into the eye.
haemorrhage The escape of blood from any part of the vascular system. Note: also spelt hemorrhage.
blot h. A form of intraretinal haemorrhage often noted in background (nonproliferative) diabetic retinopathy, branch retinal vein occlusion, carotid occlusive disease and child abuse. The haemorrhage is located within the inner retina and is limited by the orientation of the inner nuclear and plexiform layers. A small blot haemorrhage is often referred to as a ‘dot’ haemorrhage.
flame h. See haemorrhage, preretinal.
preretinal h. Haemorrhage occurring between the retina and the vitreous body. It is usually large and often shaped like a D with the straight edge at the top. Syn. subhyaloid haemorrhage. Others are flame shaped and occur at the level of the nerve fibre layer and tend to parallel the course of the nerve fibres (flame haemorrhage). Retinal haemorrhages are usually round and originate in the deep capillaries of the retina. Retinal and preretinal haemorrhages usually absorb after a period of time (except those that break into the vitreous), but subarachnoid haemorrhage (which is usually due to a rupture of an aneurysm in an artery of the circle of Willis) must be suspected as they often accompany it.
See retinopathy, proliferative.
subconjunctival h. A red patch of blood on the conjunctiva of the eye, due to the rupture of a small blood vessel beneath. The condition is nearly always unilateral and the haemorrhage absorbs spontaneously although it frequently alarms the subject. It may be associated with hypertension, especially in people over 50 years of age.
See disease, sickle-cell.
subarachnoid h.; subhyaloid h. See haemorrhage, preretinal.
Haidinger’s brushes An entoptic phenomenon observed when viewing a large diffusely illuminated blue field through a polarizer. It appears as a pair of yellow, brush-like shapes, which seem to radiate from the point of fixation. The brushes are believed to be due to double refraction by the radially oriented fibres of Henle around the fovea. This phenomenon is used in detecting and treating eccentric fixation.
Halberg clip See clip, Halberg.
half-eyes See spectacles, half-eye.
Haller’s layer See layer, Haller’s.
hallucinations, visual Visual perception not evoked by a light stimulus. They may be provoked by some pathological process anywhere along the visual pathway, or as a result of an organic brain disease.
See syndrome, Charles Bonnet.
halo A coloured ring of light seen around a light source as a result of aberrations, internal reflections, diffraction or scattering. It also appears when the eye is diseased and the cornea is oedematous, as in glaucoma.
haplopia Single normal vision, as distinguished from diplopia.
haploscope Instrument used mainly in the laboratory to study various aspects of binocular vision. It presents separate fields of view to the two eyes while allowing changes in convergence or accommodation of one or both eyes, as well as providing for controls of colour, intensity or size of target and field.
See amblyoscope, Worth; dichoptic; masking, dichoptic.
haptic 1. See scleral zone. 2. Pertaining to the sense of touch.
See lens, scleral contact.
Harada’s disease See disease, Harada’s.
hard resin See CR-39 material.
harmonious ARC See retinal correspondence, abnormal.
Hartman–Shack principle See aberration, wavefront.
Hasner’s valve See valve of Hasner.
Hassall–Henle bodies See cornea guttata.
head posture, abnormal A deviation in position of the head, aimed at mitigating the effects of diplopia. It may be due to a field restriction or shyness, but the most frequent reason is an incomitant strabismus. Patients usually adjust their heads to permit fusion. If the deviation is too large to achieve fusion, patients may adjust their heads so as to increase the separation between the diplopic images and thereby making the diplopia less troublesome. Examples: if the right medial rectus or the left lateral rectus is affected, the face may be turned to the left, and vice versa if the other horizontal muscles are affected; if the left superior oblique is affected, the face may be turned to the right, the chin may be depressed and the head may be tilted to the right. If the cause of abnormal head posture remains untreated it may produce torticollis.
See paralysis of the fourth nerve; paralysis of the sixth nerve; strabismus, paralytic.
head tilt test See test, Bielschowsky’s head tilt.
headache, ocular (HA) A headache believed to result from excessive use of the eyes, uncorrected refractive error, especially hyperopia and low grades of astigmatism, binocular vision anomaly or eye diseases. This headache typically occurs in the brow region but also in the occipital or neck regions.
See accommodative insufficiency; asthenopia.
headlamp 1. Lighting device fitted to a vehicle and used to provide illumination on the road. 2. A lamp strapped to the forehead of a surgeon or miner, enabling light to be directed where required leaving both hands free.
heliophobia Neurotic fear of exposure to sunlight.
Helmholtz’s law of magnification See law, Lagrange’s.
Helmholtz’s theory of accommodation See theory, Helmholtz’s of accommodation.
Helmholtz’s theory of colour vision See theory, Young–Helmholtz.
HEMA Transparent hydrophilic plastic used in the manufacture of soft contact lenses. It stands for 2-hydroxyethyl methacrylate.
See index of refraction; lens, contact.
hematoma See haematoma.
hemeralopia Term used to mean either night blindness in which there is a partial or total inability to see in the dark associated with a loss of rod function or vitamin A deficiency; or day blindness in which there is reduced vision in daylight while vision is normal in the dark. Syn. nyctalopia (this term is only synonymous with night blindness); night sight (this term is only synonymous with day blindness).
See atrophy, girate; blindness, congenital stationary night; choroideremia; disease, Oguchi’s; retinitis pigmentosa.
hemiachromatopsia Colour blindness in one half of the visual field of one or both eyes.
See achromatopsia.
hemianopia Loss of vision in one half of the visual field of one eye (unilateral hemianopia) or of both eyes (bilateral hemianopia) (Fig. H1). Syn. hemianopsia.
See quadrantanopia; reflex, hemianopic pupillary.
absolute h. Hemianopia in which the affected part of the retina is totally blind to light, form and colour.
altitudinal h. Hemianopia in either the upper or lower half of the visual field. A common cause is anterior ischaemic optic neuropathy.
binasal h. Hemianopia in the nasal halves of the visual fields of both eyes.
bitemporal h. Hemianopia in the temporal halves of the visual fields of both eyes.
congruous h. Hemianopia in which the defects in the two visual fields are identical. A common cause is a lesion in the posterior optic radiations.
heteronymous h. A loss of vision in either both nasal halves (binasal hemianopia) or both temporal halves of the visual field (bitemporal hemianopia). A common cause of the latter is a lesion in the optic chiasma.
homonymous h. A loss of vision in the nasal half of the visual field of one eye and the temporal half of the visual field of the other eye. Left homonymous hemianopia is a loss of vision in the temporal half of the visual field of the left eye and the nasal half of the visual field of the right eye. Right homonymous hemianopia is a loss of vision in the temporal half of the visual field of the right eye and the nasal half of the visual field of the left eye. Common causes are occlusion of the posterior cerebral artery (stroke), trauma and tumours.
See macular sparing.
incongruous h. Hemianopia in which the defects in the two affected visual fields differ in one or more ways. A common cause is a lesion of the optic tract.
quadrantic h. See quadrantanopia.
relative h. Hemianopia involving a loss of form and colour but not of light.
h. spectacles See spectacles, hemianopic.
hemianopsia See hemianopia.
hemidecussation The rearrangement of the fibres of the optic nerves occurring in the optic chiasma in which about half of them from each optic nerve pass on to the contralateral optic tract. Thus each optic tract contains one half of the fibres of the ipsilateral optic nerve (representing the ipsilateral half visual field) and one half from the contralateral optic nerve (representing the contralateral half visual field). Syn. semidecussation.
See decussation.
hemidesmosome See desmosome.
hemifield One half of the visual field, usually divided vertically through the fovea into the left or the right visual field. It occurs following transection of the optic chiasma. Hemifield neglect sometimes occurs following trauma to the posterior lobe of one hemisphere.
See visual neglect.
hemorrhage See haemorrhage.
Henle, crypts; glands of See glands of Henle.
Henle, fibre layer of See layer of Henle, fibre.
hepatolenticular degeneration See disease, Wilson’s.
Herbert’s pits See trachoma.
hereditary Pertains to a condition that is genetically transmitted from parent to offspring.
See acquired; congenital; familial; inheritance.
van Herick, Shaffer and Schwartz method See method, van Herick, Shaffer and Schwartz.
Hering’s after-image; after-image test See under the nouns.
Hering’s law See law of equal innervation, Hering’s.
Hering’s theory of colour vision; visual illusion See under the nouns.
Hering–Hermann grid A grid consisting of perpendicularly crossed white stripes on a black background. The observer sees a dark shadow at the intersections of the white stripes. This phenomenon is due to lateral inhibition and does not occur for the fixated point (Fig. H2). Syn. Hermann’s grid; Hermann’s visual illusion.
Hering–Hillebrand deviation See deviation, Hering–Hillebrand.
herpes simplex of the cornea See herpesvirus; keratitis, herpes simplex.
herpes zoster A viral infection of the posterior root ganglia of the spinal cord due to a reactivation of the varicella-zoster virus (also called chickenpox virus) which had remained latent. It is characterized by a circumscribed vesicular eruption of the skin and neuralgic pain in the areas supplied by the sensory nerves. This is due to the migration of the virus from the affected ganglia to the sensory nerves. Ocular manifestations include iritis, keratitis, scleritis, uveitis, and retinal necrosis. Syn. shingles.
herpes zoster ophthalmicus An inflammation of that portion of the gasserian ganglion receiving fibres from the ophthalmic division of the trigeminal nerve, due to an infection by a latent varicella-zoster virus identical to that causing chickenpox. The disease that occurs most commonly in people over 50 years of age begins with a severe, unilateral, disabling neuralgia in the region of distribution of the nerve. It is followed by a vesicular eruption of the epithelium of the forehead, the nose, eyelids and sometimes the cornea. The vesicles rupture leaving haemorrhagic areas that heal in several weeks. Pain usually disappears in about two weeks but in a few cases neuralgia persists for a long time. Ocular complications occur in approximately 50% of all cases of herpes zoster ophthalmicus. Corneal involvement appears as acute epithelial keratitis, which is characterized by small fine dendritic or stellate lesions in the peripheral cornea in association with a conjunctivitis. This keratitis usually resolves within a week. As the disease progresses it may give rise to mucous plaque keratitis, which occurs usually between the third and the sixth month after the onset of the rash. It is characterized by the plaque lines on the surface of the cornea, which can be easily lifted, and stromal haze. Iridocyclitis also accompanies this keratitis in approximately 50% of cases.
herpesvirus Any virus belonging to a group of DNA-containing viruses, which have similar structures but few other properties in common. They are: herpes simplex virus 1 (HSV-1) (human herpesvirus 1); herpes simplex virus 2 (HSV-2) (human herpesvirus 2); varicella-zoster virus (VZV) (human herpesvirus 3); Epstein–Barr virus (EBV) (human herpesvirus 4); cytomegalovirus (CMV) (human herpesvirus 5); human herpesvirus 6 (HHV-6); human herpesvirus 7 (HHV-7); and human herpesvirus 8 (HHV-8). Herpesviruses may cause infections including blepharoconjunctivitis, herpes zoster ophthalmicus, iridocyclitis, keratitis, uveitis, retinal necrosis, retinitis and cytomegalovirus retinitis.
See antiviral agents; virus.
herpetic keratitis See keratitis, herpetic.
Herschel prism See prism, rotary.
Hess after-image See after-image.
Hertel exophthalmometer See exophthalmometer.
hertz A unit of frequency equal to one cycle per second. Symbol: Hz.
Hess–Lancaster test See test, Hess–Lancaster.
heterochromatic iridocyclitis See iridocyclitis, Fuchs’ heterochromic.
heterochromatic stimuli Visual stimuli that give rise to different colour sensations.
heterochromia Difference in colour of the two irides or of different parts of the same iris. It is usually congenital but some cases are associated with some eye diseases such as cataract, corneal precipitates, glaucoma, iridocyclitis, iris melanoma or as a result of siderosis. Syn. anisochromia.
See syndrome, Fuchs’; syndrome, Horner’s; syndrome, Marfan’s.
heterodeviation A form of ocular alignment that differs from the normal orthophoria. These include the general groups of heterophoria
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