Contact Lens I Question Paper
Contact Lens I
Course:Optometry And Vision Sciences
Institution: Masinde Muliro University Of Science And Technology question papers
Exam Year:2013/2014
Question 1
a) Determine the effective power to the plane of cornea of the below sphero-cylindrical spectacle prescription: -5.50/+2.50×180; if the vertex distance is 12mm.
b) A diagnostic contact lens of known Base Curve of 42.50 DK and power of -2.50D was used to perform over-refraction. If the results of the over-refraction is -1.50D Sphere; determine:
I) The power of the contact lens of 42.50 DK Base curve required to correct the patient''s refractive error.
ii) The new power of contact lens required to correct the refractive error if:
a) Contact lens of 43.50 DK Base Curve was actually prescribed instead.
b)Contact lens of 42.00DK Base Curve was prescribed.
c) Determine the Calculated Residual Astigmatism (CRA) of a patient''s subjective refraction of -1.00/-1.50 × 90; if the corneal K-reading are 42.50 × 90 and 44.50 × 180
d) If a patient''s objective spectacle refraction is -10.00/-2.50 × 180 with a Vertex Distance of 13mm; Corneal K-reading 43.50×180 and 42.00×90 ; Contact Lens Base Curve of 42.50 DK;
Determine using long method of calculating Spherical contact lens prescription, the following;
I. Calculated Contact Lens prescription (RCL)
ii. Spherical equivalent of the spherical contact lens prescription to be ordered.
iii. Calculated Residual Refractive Error (CRE)
iv. Calculated Residual Astgmatism (CRA)
Question 2
a) Discuss the regional layouts and compositions of the various types of conjunctiva.
b) Briefly discus the anatomical features of the six accessory lacrimal glands.
c) Write short notes on the composition and functions of any TWO layers of the tears.
(20marks)
Question 3
a) Discuss in details the following principles of Keratometry.
-Instrumentation
- Optical
- Doubling
b) Discuss the features and properties of an ideal contact lens material.
(15marks)
Question 4
a) Discuss the advantages and disadvantages of the two methods of fabrication of Rigid Gas Permeable (RGP) contact lens.
b) Highlight the physical and chemical properties of Soft Contact Lenses (SCLs)
c) Discuss the factors that influence the high oxygen permeability of Soft Contact Lenses (SCLs)
(15marks)
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