There is one correct answer for each question. The deadline for response is April 1

1 Which of the following statements is FALSE?
A A stable tear film is required for clear vision
B Wettability of contact lens materials has little influence on patient comfort
C A poorly wetting contact lens tends to be more prone to deposits
D A continuous pre- and post-lens tear film is required for biocompatibility

2 Surface tension can best be described as:
A The force of attraction between two molecules of the same substance
B The force of attraction between two molecules of different substances
C The force at a material surface resulting from uneven molecular interactions
D The adhesive force between a liquid and a solid

3 Which of the following does NOT enhance the wettability of a material?
A Lowering the surface tension of the test material
B Lowering the surface tension of the wetting liquid
C Lowering the interfacial tension between the liquid and the test material
D Increasing the surface hydrophilicity of the test material

4 Which of the following contact angles indicates the greatest in-vitro wettability?
A 45¡
B 30¡
C 5¡
D 70¡

5 Which one of the following statements is TRUE?
A The advancing contact angle measures the wettability of a previously dry surface
B The advancing contact angle measures the wettability of a previously wet surface
C The advancing contact angle is often smaller than the receding contact angle
D The advancing contact angle gives the most accurate measure of in-vivo wettability

6 Which one of the following can affect the accuracy of the captive bubble technique?
A The mobility of the polymer chains resulting in contact angle hysteresis
B Judgement of the point at which the bubble impinges on the material surface
C Bubble size and shape
D All of the above

7 Interfacial tension will be low if:
A There is greater interaction between the polar components of the liquid and the dispersive components of the solid across the solid/liquid interface
B There is greater interaction between the polar components of the liquid and the polar components of the solid across the solid/liquid interface
C There is greater interaction between the dispersive components of the liquid and the polar components of the solid across the solid/liquid interface
D None of the above

8 Which of the following factors influence in-vivo wettability?
A Lens material
B Patient tear characteristics
C Environmental conditions
D All of the above

9 Following a period of 12 hours' wear the contact angle of a rigid contact lens might be expected to be
A Higher than the initial contact angle of the unworn, untreated lens
B Equal to the initial contact angle of the unworn, untreated lens
C Lower than the initial contact angle of the unworn, untreated lens
D Equal to the contact angle of the unworn lens treated with wetting solution

10 Which of the following does NOT enhance the in-vivo wettability of a contact lens
A Treatment with a wetting solution
B Adherence of a multi-layer of tear lipid and mucin
C Increasing the surface tension of the lens material by plasma treatment
D Long-term protein deposition

11 Which of the following might be expected to have the highest in-vitro contact angle
A PMMA
B CAB
C Silicone rubber
D Fluorosilicone acrylate

12 Which of the following methods has NOT been used by manufacturers to enhance material wettability?
A Copolymerisation with hydrophobic monomers
B Gas plasma surface treatment
C Chemical surface treatment
D Grafting of a hydrophilic surface coatingModule C4836e To take part in this module online go to www.optometry online.net and click onto the education section. Follow the links for optician CET. Our CET is supported by Evolve. Online participation will allow participants to have an instant decision of success or the opportunity to repeat the exercise if unsuccessful. Alternatively, readers may still complete and submit the enclosed answer sheet as before should they not have internet access.