a. Absolute hypermetropia = + 2.00D
(absolute hypermetropia is
defined as the least amount of plus lenses needed for clear vision
b. Manifest hypermetropia = + 4.00D
is defined as without cylcoplegia, the most plus correction that can be
tolerated without blurring of vision)
c. Facultative hypermetropia = + 2.00D
is defined as the difference between absolute and manifest hypermetropia
+ 4.00D - + 2.00D = + 2.00 D)
d. Latent hypermetropia = + 2.00 D
is defined as the difference between manifest hypermetropia and hypermetropia
measured with cycloplegia + 6.00D - + 4.00D
= + 2.00D)
a. You can make a Galilean telescope whereas your friend
can make an astronomical telescope.
(You use +2.00D as the objective lens and -8.00D
as the eyepiece lens. Your friend use +2.00D as the
objective lens and +5.00D as the eyepiece
b. Your telescope length is 37.5cm whereas your friend's telescope
(In Galilean telescope, the secondary focal point
of the plus lens ie. objective lens coincides with the primary
focal point of the minus lens ie. eyepiece
lens. Therefore 50cm - 12.5cm = 37.5cm.
In astronomical telescope, the secondary focal
point of the objective lens coincides with the primary focal
point of the eyepiece lens. Therefore 50cm
+ 20cm = 70cm.)
c. Your telescope will provide more magnification.
(The magnification of a telescope is calculated as the
power of the eyepiece divided by the power of the
Therefore your telescope magnification = 8 / 2 =
your friend's telescope
= 5 / 2 = 2.5X)
d. The image formed by Galilean telescope is erect whereas the image
formed by astronomical
telescope is inverted and real.
a. Hyperostosis of the left lateral portion of the sphenoid
with left proptosis.
b. Sphenoid wing meningioma.
Better bony definition than MRI especially in detecting orbital fractures
and bony metastasis
Detecting metallic foreign body within the orbit or globe (contraindicated
Shorter running time than MRI
Less expensive than MRI
a. Humphrey field analyser is a static automated perimetry.
( In this test, the patient maintains fixation on a central target
and the computer randomly presents a brief (about 0.2 seconds) and
non-moving ie. static light stimulus at different loci throughout the visual
field. The intensity of the light stimulus that the patient can see is
b. The total deviation measures the difference (in db) between the
patient's threshold values
and that of the age-corrected values.
c. The pattern deviation adjusts the total deviation for any shift
in the patient's overall
sensitivity. This allows localised area of field
loss to be clearly demonstrated.
( Many conditions other than glaucoma can cause poor vision
for eg. cataract or corneal oedema. Therefore, to find out how much of
a patientís relative insensitivity to light is due to glaucoma rather than
to something else, it is important to "subtract out" these other factors.
This can be done because these others conditions tend to produce a similar
pattern of diffuse visual field loss, while glaucoma tends to produce localized
areas of visual field loss.)
d. Superior arcuate scotoma.
(Visual field should not be interpreted without reference
to ocular examination. An arcuate scotoma
open angle glaucoma with inferior loss of arcuate nerve fibre layer
optic disc pit
inferior branch retinal vein occlusion
can occur in other conditions
other than open angle glaucoma as mentioned above)
a. + 4.00 / - 1.50 x 70 = + 3.50 / + 1.50 x 160 ; compound
b. + 1.25 / - 3.00 x 90 = - 1.75 / + 3.00 x 180 ; mixed astigmatism.
c. PL / + 1.50 x 45 = -1.50 / - 1.50 x 135 ; simple hypermetropia
d. - 2.00 / + 2.00 x 50 = PL / - 2.00 x 140 ; simple myopic astigmatism.
e. - 1.75 / - 2.00 x 135 = - 3.75 / + 2.00 x 45 ; compound myopic
Compound astigmatism occurs when the two principal meridians of an eye
are either both hypermetropic
ie. compound hypermetropic astigmatism or both myopic ie. compound
myopic astigmatism. Mixed
astigmatism occurs when one principal meridian is hypermetropic and
the other myopia. Simple astigmatism
occurs when one principal meridian of the eye is emmetropia and the
other myopia ie. simple myopic
astigmatism or hypermetropic ie. simple hypermetropic astigmatism.
a. OS and therefore left eye.
(OS = right eye)
b. A = anterior lens echo
B = posterior lens echo
C = retinal echo
c. Power of the intraocular lens needed for emmetropia
= 118 - 2.5 (22.3) - 0.9 (43)
The power needed would be 23.50D as the implant comes
in step of 0.5D
d. The resultant refraction would be hypermetropic if the axial length
a. Infinity to 3.3cm.
(The range of accommodation is the linear
distance between the far point and the near
point. In the absence of accommodation, the
boy is in focus at infinity. With maximal
accommodation, he is in focus at 1/30 = 0.033m
(To be in focus in infinity, the man needs
to use up +10.00D of his accommodation
amplitude. As a result, he has only 20 - 10
= 10 D for near vision. His near point is
1/10 = 0.10 m = 10 cm)
c. The near point is 5 cm and the range of accommodation is infinity
to 5 cm.
(With hypermetropic correction he does not need
to use up any of his accommodation
and can therefore use all the 20 D for near vision.
The near point is therefore
1/20 = 0.05m = 5cm. The range of accommodation is
therefore from infinity
to 5 cm)
a. The base curve is 8.6mm, the diameter of the lens is
13.5 mm and the power is +10.00D
(The first number denotes the base curve,
the second the diameter and the last the lens power.)
b. + 9.09D
(Using the formula for lens effectivity
the new lens power
= 10 / (1- (-0.01)10)
= 10 / 1.1
= 9.09D )
c. Problems of aphakic glasses include:
ring scotoma. When the patient looks laterally the object seems to disappear
occur due to the prismatic effect of the lenses. As a result, the
patient has problem
with peripheral vision
pincushion effect because the periphery of the image is more magnified
than the centre
altered depth perception
weight of the glasses