12th Zoology

Cataract – Lens Replacement – Glaucoma – Nyctalopia

Cataract – Lens Replacement – Glaucoma – Nyctalopia


Cataract is the opacity in the lens of the eye. The normal lens allows
light to reach the retina when it becomes opaque and does not allow light to
reach the retina, the person is unable to see clearly. Cataract is due to
(coagulation) changes in the delicate protein fibres within the lens, cataract
never causes complete blindness but causes increased loss of transparency.
The clarity and the detail of the image is progressively lost. The front part of
the lens becomes densely opaque and whiteness is visible in the pupil.
The causes for cataract formation in the adult is related to aging, sun
light exposure, smoking, poor nutrition, eye trauma, systematic diseases like
diabetes mellitus, infection and injuries and certain medications such as
steroids. Sometimes German measles in pregnant mothers causes cataract in
the child.

To delay the onset of cataract one should have nourishing diet,
protect eye from excessive exposure to sun rays, X-rays, intense heat and
injuries. Diseases like diabetes and syphilis should be treated early and

Two types of cataracts are dense nuclear cataract (cataract in the
center of the lens) and Peripheral cataract (cataract in the periphery of the
lens). There is no medical treatment for cataract. The only treatment is
surgery. Once the cataract is removed, the eye is unable to focus, as there is
no lens. So one has to use an artificial lens. This can either be glasses,
contact lenses or insertion of introcular lenses.

Today modern medical advances have made cataract surgery very
successful. New surgical techniques and intracular lenses can restore
excellent vision (97%).

Lens Replacement

For individuals who are over 40 years of age, considering refractive
surgery to decrease dependence on glasses and contact lenses, Clear Lens
Replacement (CLR) is an exciting option. In essence, this procedure entails
removing the natural lens of the eye and replacing it with an intraocular lens
(IOL) implant.

CLR may be an excellent alternative to these procedures for people
already wearing bifocals since CLR requires removal of the natural lens of
the eye, the patient is subsequently unable to focus (accommodate) at near
by objects . This is why CLR is best suited for patients over 40 who are
already wearing bifocals. One potential solution to this problem of
accommodative loss is implantation of the multifocal IOL (Intra Occular Lens)
implant. This implant allows focusing at both near and far objects.


Glaucoma is a serious disorder of the eye and is a common cause of
blindness. Increased IOP (Increased Occular Pressure) compresses the
optic nerve at the optic disc with degeneration of optic nerve fibres and
cupping of the optic discs with progressive loss of visual acuity starting with
peripheral vision. The retinal artery which enters the eye ball at the optic disc is compressed causing retinal degeneration. In most cases the cause of
glaucoma is unknown but in some cases it may be due to infection or trauma
in the eye. When the IOP is very high (50-70 mm Hg) blindness occurs
within few days.


Vitamin A is necessary for resynthesis of visual purple. Nyctalopia
or night blindness is the first sign of vitamin A deficiency. Prolonged
deficiency of vitamin. A leads to degenerative changes in rods and cones and
nervous layers of the retina. Administration of vitamin A before degenerative
changes occur will restore retinal functions. Normal retinal function also
requires the presence of optimal amounts of other vitamins especially the B
complex just as other nerve tissues do.

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Human Physiology Introduction

  2. Nutrition

  3. Carbohydrates Poly hydroxyaldehydes (or) ketones

  4. Proteins (Polypeptides)

  5. Lipids

  6. Vitamins – Functions Of Vitamins

  7. Deficiency of Vitamin

  8. Minerals – Water – Role of water

  9. Balanced diet

  10. Obesity

  11. Digestive System

  12. Dental Caries (Tooth decay)

  13. Root Canal Treatment

  14. Peptic ulcer

  15. Hernia and Types

  16. Appendicitis (Appendix)

  17. Gall Stones

  18. Hepatitis

  19. Fractures – Types of fractures

  20. Mechanism of fracture

  21. Dislocation of joints

  22. Arthiritis

  23. Rickets and Osteomalacia – Orthopedics

  24. Muscles

  25. Mechanism of muscle contraction

  26. Types of muscle contraction

  27. Myasthenia Gravis

  28. Respiration – Process of pulmonary respiration

  29. Mechanism of Breathing

  30. Regulation of Respiration

  31. Pneumonia Tuberculosis Symptoms Treatment

  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes

  33. Circulatory System – Functioning of Human heart

  34. Cardiac Cycle

  35. Coronary blood vessel and its significance

  36. Myocardial infarction

  37. Angina pectoris

  38. Angiogram – Angioplasty

  39. Atherosclerosis

  40. Heart block Echo cardiography Heart Valves

  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)

  42. Blood Pressure

  43. Heart transplantation

  44. Pulse rate

  45. Cardio Pulmonary Resuscitation (CPR)

  46. Blood – Composition of plasma – Blood cells

  47. Clotting of Blood or Haemostasis

  48. Thrombosis

  49. Nervous system Co-ordination systems

  50. The Brain – Fore Brain, Midbrain, Hindbrain

  51. Memory

  52. Sleep – Types of sleep

  53. Stroke – Brain haemorrhage

  54. Alzheimer – Meningitis (Brain fever)

  55. Conditioned reflex

  56. Electroencephalography EEG

  57. Right and Left brain concept

  58. Spinal cord functioning

  59. Chemical co-ordination – Functions of Endocrine glands

  60. Hypothalamus

  61. Pituitary gland – hormone

  62. Hormones of Neurohypophysis – vasopressin

  63. Thyroid gland

  64. Parathyroid Gland

  65. Pancreas

  66. Adrenal gland

  67. Gonads

  68. Receptor Organs – Eye

  69. Photochemistry of Retinal visual Pigments

  70. Errors of refraction

  71. Optometry – Retinopathy

  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia

  73. Eye Infections and Eye Care

  74. Ear

  75. Mechanism of hearing

  76. Defects of the ear

  77. Hearing Aid – Noise pollution

  78. Skin and functions of skin

  79. Melanin functions

  80. Effects of solar radiation / UV radiation – Skin grafting

  81. Dermatitis

  82. Tongue – Mechanism of Stimulation

  83. Excretion Ureotelism Nephron

  84. Mechanism of urine formation

  85. Renal Failure, Dialysis, Kidney Machines

  86. Kidney stone – Kidney transplantation

  87. Diabetes mellitus

  88. Functioning of male reproductive system

  89. Functioning of female reproductive system

  90. Ovulation and fate of the ovum – Menstrual cycle

  91. Fertilization

  92. Birth control

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