Lens Flashcards
pg 179-186 (87 cards)
What is hypermetropia?
A condition where the eyeball is too short or the lens is not strong enough, causing difficulty in focusing on near objects
Also known as farsightedness
How can hypermetropia be corrected?
By placing a convex lens in front of the eye
This is typically done using eyeglasses
What happens to light rays in hypermetropia?
They fall behind the retina
This occurs because the lens cannot sufficiently bend the light rays
What is myopia?
A condition where the eyeball is too long or the lens is too strong, causing difficulty in focusing on distant objects
Also known as nearsightedness
How can myopia be corrected?
By placing a concave lens in front of the eye
This diverges the light rays
What happens to light rays in myopia?
They fall in front of the retina
This occurs because the image cannot be focused properly on the retina
What is presbyopia?
A condition caused by the loss of lens elasticity with age, leading to difficulty in focusing on near objects
It primarily affects older individuals
What corrective lenses are often used for presbyopia?
Bifocal glasses
The upper part is for distant vision, while the lower part is for near vision
What is the primary issue with the lens in presbyopia?
The lens cannot assume a spherical shape
This affects the ability to accommodate for near vision
In what condition is a person unable to focus on a near object?
Hypermetropia
This results in the need for accommodation to see distant objects clearly
In what condition is a person unable to see a distant object clearly?
Myopia
This occurs because the image is focused in front of the retina
What happens to the nucleus of the lens with increasing age?
It becomes sclerosed and yellowish
The increasing refractive index compensates for the flattening of the lens, but increased density reduces visual acuity.
What is a cataract?
A condition where the lens becomes opaque
Senile cataract is the most common form and must be distinguished from nuclear sclerosis.
What is the cause of senile cataract?
Not known
It is characterized by the accumulation of metabolic products and osmotic balance disturbance.
What are other forms of cataract besides senile cataract?
Congenital cataracts, cataracts associated with intraocular diseases, ocular trauma, and systemic diseases
Examples of systemic diseases include diabetes mellitus and scleroderma.
What is the most commonly performed type of cataract surgery?
Phacoemulsification
This procedure involves breaking up the dense nucleus of the lens using ultrasound.
Describe the phacoemulsification procedure.
The dense nucleus is emulsified and removed by vacuum
Various methods exist for breaking up the lens, including dividing it into pieces.
What is the ‘phaco chop’ technique?
A method that splits the lens along its fracture lines using pressure from a cleaving instrument
This technique can be applied from the front or back of the lens.
Why is knowledge of the lens capsule important in cataract surgery?
It helps in understanding its consistency, dimensions, and ability to stretch for intraocular lens insertion
The resilient nature allows for capsulorrhexis procedures.
What is capsulorrhexis?
The careful removal of a circular piece of the anterior wall of the lens capsule
If done without tearing, it can be safely dilated for lens insertion.
What happens to the lens capsule after the removal of lens substance in adults?
It collapses and its diameter increases to approximately 9.5 to 10.5 mm
After implantation, it assumes an oval shape.
What is the maximum equatorial diameter of the lens capsule after lens insertion?
12.0 mm
The introduction of a lens can stretch the equator from approximately 10.5 mm to 11.9 mm.
True or False: The equatorial diameter can exceed 12.0 mm if the capsule remains intact.
False
The intact capsule cannot stretch beyond this measurement.
What happens to lens fiber cells during development?
They lose their nuclei and cytoplasmic organelles become specialized for the production of lens proteins known as crystallins.
