Question

1) explain macular degeneration and its effects to your sight?

2) what role does Schemm's canal play in glaucoma and how is glaucoma treated.? can it lead to blindness if untreated? why?

3) explain cataract formation and what causes it.?

4) explain the following:

1) convergence

2) accomodation

3) refraction

Answer 1

1.Age-related macular degeneration (ARMD), also called senile macular degeneration, is a bilateral disease of persons over 50 years of age. It is a leading cause of blindness in developed countries, in population above the age of 65 years. It is of two types non-exudative and exudative.   
mild to moderate, gradual loss of vision. Patients may complain of distorted vision and difficulty in reading due to central shadowing.

2. The sclerosed endothelium lining of the canal of Schlemm.This leads to narrowing or collapse of canal of Schlemm. This causes glaucoma.   
The treatment options available at present are medicines, laser or surgery to lower the intraocular pressure.
1. Medical—It is always the treatment of choice in the early stages.   
• Latanoprost (0.005%) to be used HS,
• Travoprost (0.004%) to be used HS,
• Bimatoprost (0.03%, a prostamide) to be used HS,
and
  • Unoprostone (0.15%) to be used BID.
Topical beta-blockers
Adrenergic drugs.
2. Surgical—It is considered to be the last resort.
3. Argon or diode laser trabeculoplasty (ALT or DLT)—It is the most advanced technique.
4. Recent advanced procedures—These include laser filtration, seton valves, deep sclerotomy
and viscocanalostomy.
Yes if not treated patient becomes blind.

3. the term cataract refers to development of any opacity in the lens or its capsule. Cataract, thus may occur, either due to formation of opaque lens fibres (congenital and developmental cataracts) or due to degenerative process leading to opacification of the normally formed transparent lens fibres (acquired cataract).
Clinically, the term cataract refers to an opaci- fication of sufficient severity to impair the vision.   
I. Idiopathic
About 33% cases are sporadic and of unknown etiology.
II. Heredity
About one-third of all congenital cataracts are hereditary.
■ Inherited cases without systemic disorders. In these cases, the mode of inheritance is usually autosomal dominant.
■ Inherited cases with systemic disorders include:
• Chromosomal disorders (e.g. trisomy 21),
• Skeletal disorders (e.g. Stickler syndrome),
• Central nervous system disorders (e.g. cerebro-
oculo-facial syndrome),
• Renal system disorders (e.g. Lowe’s syndrome)
Common familial cataracts include:
• Cataracta pulverulenta,
• Zonular cataract (also occurs as nonfamilial),
• Coronary cataract and total soft cataract (may also
occur due to rubella).
III. Maternal factors
1. Malnutrition during pregnancy has been
associated with nonfamilial zonular cataract.
2. Infections. Maternal infections like rubella are associated with cataract in 50% of cases. Other maternal infections associated with congenital cataract include toxoplasmosis and cytomegalic
inclusion disease.
3. Drugs ingestion. Congenital cataracts have also
been reported in the children of mothers who have taken certain drugs during pregnancy (e.g., thalidomide, corticosteroids).
4. Radiation.Maternalexposuretoradiationduring pregnancy may cause congenital cataracts.
IV. Foetal or infantile factors
1. Deficient oxygenation (anoxia) owing to placental
haemorrhage.
2. Birth trauma, may cause cataract.
3. Metabolic disorders of the foetus or infant such
as galactosemia, galactokinase deficiency and
neonatal hypoglycemia.
4. Cataractsassociatedwithothercongenitalanoma-
lies e.g., as seen in Lowe’s syndrome, myotonia
dystrophica and congenital icthyosis.
5. Ocular diseases associated with developmental cataract include persistent hyperplastic primary vitreous (PHPV), aniridia anterior chamber cleavage syndrome retinopathy of prematurity,
lenticonus posterior and microopthalmos.
6. Malnutrition in early infancy may also cause
developmental cataract.

4. Refraction
Refraction of light is the phenomenon of change in the path of light, when it goes from one medium to another. The basic cause of refraction is change in the velocity of light in going from one medium to the other.

Accomadation.
As we know that in an emmetropic eye, parallel rays of light coming from infinity are brought to focus on the retina, with accommodation being at rest.However, our eyes have been provided with a unique mechanism by which we can even focus the diverging rays coming from a near object on the retina in a bid to see clearly. This mechanism is called accommodation.

Convergence.
It is simultaneous in ward movement of both eyes which results from contraction of the medial recti.