Are you looking for the causes of loss of vision? Then surely you are in the right place.
Unfortunately, medical science is not as simple as it seems, behind each abnormality there may be many causes which are cross linked & you have to rule out the right cause & same is the case with vision loss.
To make it simpler, we have tried to break down the most common causes of vision loss in such a way that it should be understandable for medical students as well as laymen. Before starting in depth, let’s start with the definition of vision loss/visual impairment because many people confuse visual impairment with blindness.
Define Vision Loss/Visual Impairment
Vision loss is a state of impairment of vision of the eye which can be complete or partial, permanent or temporary, unilateral or bilateral.
In case of partial impairment of part of the eye, the eye is able to see but not as efficiently as compared to the normal eye, whereas in complete visual loss, the eye is incapable to see objects at all.
In comparison, blindness is the complete absence of vision at the time of birth.
Cause of Vision Loss
We have classified vision loss into Sudden, Gradual, Painful & painless, loss respectively.
Sudden Painful Loss of Vision
Sudden painful loss of vision can be due to the following causes.
It is defined as inflammation of the cornea. Keratitis is either due to infective causes or due to non-infective causes.
● Bacterial > Gram +ve and gram – organism
● Viruses > Herpes simplex and herpes zoster virus
● Protozoa > Acanthamoeba species
● Fungi > Candida albican and Aspergillus fumigatus
Non infective causes
● Allergic reaction
● Autoimmune disease
● Chemical burns
● Nutritional deficiency
It is defined as inflammation of conjunctiva. Conjunctiva is thin translucent mucous membrane and covers the under surface of eyelids. On the basis of etiology can be classified as following.
● Bacterial conjunctivitis
● Viral conjunctivitis
● Fungal conjunctivitis
● Chlamydial conjunctivitis
Non infective conjunctivitis
● Allergic conjunctivitis
● Autoimmune conjunctivitis
● Chemical conjunctivitis
● Toxic conjunctivitis
Following features are considered for the diagnosis of conjunctivitis.
● Type of discharge (Exudate)
● Type of conjunctival response
● Subconjunctival hemorrhage
● Membrane formation
● Lymphadenopathy > enlargement of pre auricle nodes
● Corneal involvement > punctate keratitis
● Systemic symptom > Fever, malaise, upper respiratory tract infections etc.
It is defined as inflammation of the sclera. About 50% of cases present with associated systemic immunological diseases. To prevent long term complications it is necessary to treat the underlying causes. Anatomically it is classified in to 2 types.
Anterior scleritis (98%)
Necrotizing with or without inflammation
Nonnecrotizing diffuse or nodular
Posterior scleritis (2%)
It is defined as inflammation of the uveal tract. The uveal coat, a vascular layer of the eyeball is divided into 3 parts i.e. choroid, ciliary body, and iris. Anatomically it is divided into the following types
● Anterior uveitis. Iritis and iridocyclitis
● Intermediate uveitis. Cyclitis
● Posterior uveitis. Choroiditis
● Pan Uveitis. Inflammation of all parts of the uveal tract
(5) Angle closure Glaucoma
Glaucoma is defined as progressive optic neuropathy with visual defect and raised intraocular pressure, is one of major risk factor. Angle closure glaucoma is one which is bilateral and due to closure of angle there is rise in pressure. Women are affected more than men. Incidence is 1:1000 individual over 40 year of age.
Sudden Painless Loss of Vision
Sudden painless loss of vision can be due to the following causes.
(1) Retinal Vascular Occlusion
Any obstruction complete or partial, permanent or temporary, may affect the artery and vein of the retina. Artery and vein share the common sheath at two places. First when the artery and vein crossing over and second within optic nerve at lamina crib Rosa. These are of different types.
● Central retina vein & artery occlusion
● Branch retinal vein & artery occlusion
(2) Retinal Detachment
It is the separation of sensory retina from the retinal pigment epithelium by subretinal fluid. It is of two types.
● Rhegmatogenous. Also called primary retinal detachment, which occurs due to hole or lesion formation in the layer of the retina.
● Non rhegmatogenous. Also called secondary retinal detachment. It is further divided into 2 types
Tractional RD This is occurring due to pulling on the sensory retina by contracting vitro retinal membrane.
Exudative RD This is occurring due to damage in the retinal pigment epithelium which allows fluid from choriocapillaris to enter the subretinal space.
(3) Optic Neuritis
It is inflammation of the optic nerve which is occurring anywhere in the course of the optic nerve, from the optic disc to optic chiasmi. Demyelination is one of the causes of optic neuritis. It is of 3 types.
Papillitis Inflammation of optic nerve head characterize by hyperemia and edema of optic disc. Most common in children.
Retrobulbar Neuritis This is the inflammation of the orbital part of the optic nerve and the optic disc appears normal. Most common in adults.
Neuroretinitis This is papillitis which is associated with inflammation of retinal nerve fiber.
It is a congenital malignant tumor of primitive retinal cells of the sensory retina. It is present within 3 years of life and very rare after 3 years. The predisposing gene is 13q14 chromosome. It is of either heritable or non-heritable.
● Heritable Retinoblastoma. Result due to germ mutation.85% is bilateral.
● Nonheritable. Result due to somatic mutation. It is mostly 85% unilateral
Gradual Painful Vision Loss
Gradual painful loss of vision can be due to the following causes.
● Chronic iridocyclitis
These conditions are already explained above in the article.
Gradual Painless Loss of Vision
Gradual painless loss of vision can be due to the following causes.
A cataract is defined as the opacification of the crystalline lens of the eye. Cataract has been defined as following On the basis of the age of the patient.
● Congenital cataract
● Infantile cataract
● Juvenile cataract
● Adult cataract
● Senile cataract
Whereas another classification is On the basis of the location of opacity in the lens.
● Capsular cataract
● Subcapsular cataract
● Cortical cataract
● Supra nuclear cataract
● On the basis of the degree of opacity.
● Incipient cataract
● Immature cataract
● Intumescent cataract
● Mature cataract
● Hyper mature cataract
Cataract can also be classified as.
(2) Refractive Error
Normally rays of light focused on the fovea centralis when the refractive power of optical media i.e. cornea and lens correlate with the axial length of an eyeball. When any of these two factors do not correlate with each other, the ray entering the eye will not focused on the fovea centralis of the retina. This condition is called a refractive error. Refractive errors are of different types.
Hypermaetropia Form of refractive error in which rays are focused behind the retina with accommodation is at rest.
Myopia Form of refractive error in which parallel rays of light entering the eye are focused in front of the retina with accommodation is at rest.
Astigmatism Form of refractive error in which parallel rays of light entering the eye cannot form a point focus on the retina.
(3) Diabetic Retinopathy
Defined as a non-inflammatory disease of the retina which occurs in diabetes mellitus. It is the most important ocular manifestation of diabetes mellitus. It frequently caused blindness in patient aged of 20-60 years age.
(4) Age Related Macular Dystrophy
It is a degenerative disease of the macula causing an irreversible loss of vision. It is most often occurs after 50 years of age. And the most common cause of irreversible vision loss in developed countries.
(5) Retinitis Pigmentosa
It is the group of hereditary disease which is characterized by slowly progressive pigmentary retinal dystrophy predominantly affecting rods more than cones.