1 Which of the following is not a requirement of an ideal RGP lens? (A) Adequate oxygen transmissibility; (B) Easy to manufacture; (C) Disposability; (D) No effect on corneal profile. The correct answer is C. On the contrary, a distinct advantage of an RGP lens is its durability. 2 What RGP Dk (in Fatt units) might be described as 'super'? (A) Over 150; (B) 100 to 150; (C) 60 to 100; (D) 30 to 60. The correct answer is B. The term super Dk describes values from 100 to 150. Anything above this may be described as hyper-Dk. 3By how much does the surface effect reduce the measured Dk value? (A) No effect; (B) 3 per cent; (C) 45 per cent; (D) 55 per cent. The correct answer is C. The surface effect is due to an intermediate water layer used in measurement, giving a Dk only 55 per cent of the measured value (a reduction of 45 per cent). 4 Which of the following has the highest wetting angle as measured by the captive bubble technique? (A) PMMA; (B) Boston XO; (C) Paragon HDS 100; (D) Fluoroperm 151. The correct answer is A. With a wetting angle of 60 degrees, PMMA has the greatest wettability. 5 Which of the following materials has the lowest specific gravity? (A) Optimum Classic; (B) Optimum Comfort (C) Optimum Extra; (D) Optimum Extreme. The correct answer is D. With a specific gravity of 1.155, Optimum Extreme has the lowest value. 6 Why was fluorine introduced into silicone acrylate materials? (A) To increase oxygen permeability; (B) To reduce lipid deposition; (C) To decrease protein deposition; (D) To reduce specific gravity. The correct answer is C. Once it was realised that the benefits of high oxygen transmission were being counteracted by the increased build up of surface protein, fluorine was incorporated to offer higher oxygen performance with a reduction in protein deposition. 7 What does the term 'annealing' refer to? (A) The heating of the material to 145 degrees for a short period followed by a slow return to room temperature; (B) The extrusion of molten material from a mould; (C) The changing of surface characteristics by coating; (D) Cutting from a button on a lathe. The correct answer is A. The annealing process involves heating the material to about 145 degrees for a short period then allowing it to slowly return to room temperature. 8 What is a recommended minimum edge thickness? (A) 0.12mm; (B) 1.2mm; (C) 0.03mm; (D) There is no minimum value. The correct answer is A. The thickness will depend upon the back vertex power but it should be a minimum of 0.12mm as any thinner may cause discomfort and prove fragile, particularly with positive lenses. 9 What is the typical eccentricity of aspheric RGP lenses? (A) 0.12; (B) 0.84; (C) 0.75 to 0.84; (D) 0.40 to 0.50. The correct answer is D. Aspheric lenses are typically made with an eccentricity of 0.40 to 0.50. 10 Which of the following is a pseudo-aspheric design lens? (A) Quasar (No 7); (B) Maxim Ultra (B&L); (C) Aquila (Ciba Vision); (D) Menicon EX. The correct answer is B: The Maxim Ultra (Bausch & Lomb) is an example of a pseudo-aspheric lens design. 11 Which of the following is a mainly spherical design with an aspheric periphery? (A) Quasar (No 7); (B) Maxim Ultra (B&L); (C) Aquila (Ciba Vision); (D) Menicon EX. The correct answer is D. The Menicon EX (and the Super EX) are mainly spherical with an aspheric periphery. 12 In the term Paflufocon B III 3, what does the B represent? (A) The stem; (B) Surface modification code; (C) Series suffix, indicating the second formulation of the polymer; (D) Dk range. The correct answer is C. The B represents the USAN series suffix, indicating the second formulation of the polymer.
