OPHTHALMIC MATERIALS

Size: px

Start display at page:

Download "OPHTHALMIC MATERIALS"

Andrea Matthews
5 years ago
Views:

Matriculation Number: DEPARTMENT OF VISION SCIENCES SESSION: 2005/2006 DIET: 1ST OPHTHALMIC MATERIALS VISP209 LEVEL 2 MODULE LEADER: DR G WALSH B.Sc.

1 Matriculation Number: DEPARTMENT OF VISION SCIENCES SESSION: 2005/2006 DIET: 1ST OPHTHALMIC MATERIALS VISP209 LEVEL 2 MODULE LEADER: DR G WALSH B.Sc./B.Sc. (HONS) OPTOMETRY JANUARY 2006 DURATION: 2HOURS Formula Sheet (attached) SECTION A IS COMPULSORY (and worth 70 marks) Section A is to be answered on this question paper SECTION B ANSWER ONE QUESTION ONLY (worth 30 marks) Use a Separate Answer Book for Section B MATERIALS TO BE SUPPLIED/ALLOWED: Question Paper (Supplied) } Lined Examination Script (Supplied) } Calculator (Allowed) } Calculators which retain programming when switched off may NOT be used. All calcualtors must be switched off at start of examination THIS QUESTION PAPER MUST BE SECURED TO YOUR ANSWER BOOKLET AND HANDED IN AT THE END OF THE EXAMINATION Page 1 of 12

2 SECTION A Answer ALL questions Indicate the correct answer by scoring out the letter adjacent to it. There is only 1 correct answer 1. Which of the following is CORRECT if a prescription of DS at a back vertex distance of 11mm is dispensed such that its BVD is 14mm (to the nearest 0.12D) a) Its power must be increased to D. b) Its power must be increased to D. c) Its power must be decreased to D. d) Its power must be decreased to D. 2. A home-made Risley prism is being used to record a patient s vertical heterophoria. It is made from a two prisms. If the prism bases are set to 20 & 160, what is the vertical prismatic effect to the nearest 0.1? a) 10.4 base down. b) 6.8 base up. c) 18.8 base up. d) 7.3 base up. 3. Which of the following is CORRECT to the nearest 0.12D: a) A single surface of radius 2.0cm and refractive index 1.8 has a power in air of 0.40D. b) A single surface of radius of 22.0m and refractive index 1.71 has a power of 3.25D in air. c) A single surface of radius 175.0mm and refractive index 1.67 has a power of 3.82D in air. d) A single surface of refractive index of 1.8 and radius of curvature 3.0m has a power 2.67D in air. 4. Which of the following is CORRECT: a) The transposed form of / x 70 is / x 160. b) The transposed form of 7.25 / x / 2 is 1.25 / x 87 1 / 2. c) The transposed form of / x 42 1 / 2 is / x / 2. d) The transposed form of / x 57 1 / 2 is / x / 2. Page 2 of 12

3 5. Which of the following is CORRECT for a thin lens: a) The prescription / x 175 can be made up in the form: x 155 / x b) The lens / x 180 can be made up in the form x 90 / x 90 c) The lens / x 160 can be made up in the form x 70 / x d) The lens / x 65 can be made up in the form x 155 / x A lens measure is calibrated for crown glass and reads +0.25DS on the front surface and 11.00DS on the back of a lens. It reads on a flat glass plate. The focimeter reads 13.25DS with the lens and has no zero error. What is the refractive index of the lens? a) b) c) d) For a thick prism base up in air, n=1.7, apical angle 10 and light incident normally on its front surface, by how much is the light deviated? a) 17.2 upwards. b) 7.2 upwards. c) 17.2 downwards. d) 7.2 downwards. 8. For a patient wearing an addition of in a 45mm round segment bifocal, how far do objects at a distance of 2m jump as the line of sight crosses the segment edge. a) 4.5cm. b) 9cm. c) 90cm. d) 45cm. Page 3 of 12

4 9. Which of the following is identical to 10 base 30 RE (to the nearest 0.1 ). a) 8.7 base up and 5 base out. b) 8.7 base in and 5 base up. c) 8.7 base down and 5 base in. d) 8.7 base out and 5 base up. 10. Which of the following is the CORRECT prismatic effect for a point 10mm DIRECTLY below optical centre of a R lens / x 30 (to the nearest 0.1 ). a) 2.00 base down. b) 3.00 base up. c) 3.00 base down. d) 4.00 base up. 11. Which of the following materials would you expect to have the GREATEST amout of chromatic aberration for an Rx of if the lenses are centred identically in an identical frame. a) Anti-reflection coated glass, index 1.6 b) Photochromic plastic, index 1.6 c) Photochromic glass, index d) Anti-reflection coated plastic, index A lens measure is calibrated for crown glass and reads -0.75DS on the front surface and on the back of a lens of refractive index It reads on a flat glass plate. What are the radii of curvature of the lens? a) Front 4.67m, back 0.55m. b) Front infinite, back 55mm. c) Front 467mm, back 55mm. d) Front 1.13m, back 0.133m. 13. Which of the following is the prismatic effect at a point 20mm below and 10 mm in from the optical centre of a L lens of power +4.00DS (to the nearest 0.1 ). a) 8 base up and 4 base out. b) 8 base down and 4 base out. c) 8 base down and 4 base in. d) 8 base up and 4 base in. Page 4 of 12

5 14. Which of the following is INCORRECT: a) Surfaced, fused bifocal CR39 lenses are often anti-reflection coated after surfacing. b) Surfaced, solid bifocal glass lenses are often anti-reflection coated after surfacing. c) Surfaced, single vision CR39 lenses are often treated to increase ultraviolet absorption after surfacing. d) Surfaced, varifocal CR39 lenses are often anti-reflection coated after surfacing. 15. Which of the following is CORRECT: a) According to current British and European standards, the lower powered area around the edge of a lenticular lens is called the carrier. b) Blended bifocals have a larger good near optical zone that nonblended of the same nominal segment diameter. c) An aspheric varifocal suface has a better optical performance than a non aspheric one d) High plus aspheric lenticular lenses are optically superior to nonaspheric ones. 16. Which of the following is INCORRECT: a) Anti-reflection coatings are applied to glass lenses in a vacuum chamber. b) Some hard coatings are applied to CR39 lenses in a vacuum chamber. c) Some tints are applied to Polycarbonate lenses in a vacuum chamber d) Some glass lenses are hard coated in a vacuum chamber. 17. Which of the following aberrations does not affect the sharpness of the image produced by a lens. a) Spherical aberration. b) Coma. c) Distortion. d) Oblique astigmatism. 18. Which does the figure represent before any cutting to shape has occurred: a) A 38mm optic, solid lenticular CR39 uncut. b) A 22mm round segment solid CR39 bifocal uncut. c) A 36mm optic, fused lenticular CR39 uncut. d) A 24mm round segment solid CR39 bifocal uncut. Page 5 of 12

6 19. Relating to a D735 fused trifocal lens, which of the following is CORRECT a) The 7 refers to the refractive index of the near portion, n=1.7. b) The 7 refers to the distance of the segment top from the geometrical centre of the segment. c) The 7 refers to the distance of the segment top from the dividing line between near and intermediate portions of the lens. d) The 28 refers to the length of the top edge of the D shape. 20. Which of the following lens types would benefit most from the use of an anti-reflection coating if the distance correction is -5.00? a) CR 39 varifocal. b) Crown glass solid bifocal. c) 1.9 index glass single vision. d) 1.74 index plastics varifocal. 21. Which of the following is INCORRECT? a) The horizontal box eye size of a frame is usually greater than the vertical box eye size. b) The length to bend of a frame is normally greater than its horizontal box eye size. c) The distance between lenses of a frame is usually greater than its bridge width. d) The angle of side of a frame is usually less than the downward angle of drop. 22. A patient asks for a bifocal lens to be replicated. It is an unattractive greenyellow colour and has a paler segment shaped as illustrated. You tap the lens with a key and it is clearly glass. a) A photochromic d-segment bifocal. b) A photochromic c-segment bifocal. c) A vacuum tinted d-segment bifocal. d) A vacuum tinted c-segment bifocal. Page 6 of 12

7 23. Which of the following relative prismatic effects CAN NOT be obtained on a pair of solid bifocal lenses? a) 2 base down at near using different round seg sizes on a pair of lenses +2.00DS add +2.25DS R & L. b) 2 base up at near using different round seg sizes on a pair of lenses +2.00DS add +2.25DS R & L. c) 4 base down at near using different round seg sizes on a pair of lenses +2.00DS add +2.25DS R & L. d) 4 base up at near using different round seg sizes on a pair of lenses +2.00DS add +3.50DS R & L. 24. Which of the following aberrations is of least significance in a spectacle lens? a) Spherical aberration. b) Distortion. c) Oblique astigmatism. d) Transverse chromatic aberration. 25. Which of the following is a CORRECT definition according to current British Standards where applicable? a) A varifocal lens can also be called a multifocal lens. b) A bifocal lens has two or more areas of distinct focal power. c) An atoric lens has one or more atoral surfaces. d) A best form lens is the form which is cosmetically best. 26. Which of the following lens forms has the lowest amount of oblique astigmatism AND would be both sensible and cosmetically acceptable for a distance prescription of 5.00DS. a) Ostwalt. b) Brewster. c) Wollaston. d) Petzval. Page 7 of 12

8 27. A hypermetropic patient is seeking a new pair of lenses to replace damaged ones in his present frame. There is no change in prescription. The edge thickness of his present spectacles is 1.5mm and the maximum thickness of the lens is 6.5mm. The maximum distance from the centration point of the lens to its edge is 26mm. The refractive index is 1.5. Which of the following centre thickness predictions is closest to CORRECT if the minimum edge thickness and base curve of the lenses remain unchanged. a) If the frame is reglazed with material of refractive index 1.67, the maximum edge thickness will be approximately 5.23mm. b) If the frame is reglazed with material of refractive index 1.56, the maximum edge thickness will be approximately 6.38mm. c) If the frame is reglazed with material of refractive index 1.80, the maximum edge thickness will be approximately 8.0mm. d) If the frame is reglazed with a material of refractive index 1.71, the maximum edge thickness will be approximately 4.85mm. 28. A myopic patient is seeking a new pair of spectacles. There is no change in prescription (-8.00DS R&L). The centre thickness of his present spectacles is 1.5mm and the maximum edge thickness of the lens is 6mm. The new maximum distance from the centration point of the lens to its edge is 22mm, and the previous one was 28mm but your supplier can now only supply a minimum substance of 2mm. Which of the following edge thickness predictions is CORRECT if the refractive index and base curve of the lenses remain unchanged (to the nearest 0.1mm). a) 5.6mm. b) 5.2mm. c) 4.8mm. d) 4.4mm. 29. A myopic patient is seeking to replace the lenses in his present frame. His prescription has changed from -3.00DS to -6.00DS. The centre thickness of his present spectacles is 2.0mm and the maximum edge thickness is 3.9mm. Which of the following edge thickness predictions is CORRECT to the nearest 0.1mm if the centre thickness, refractive index and base curve of the lens remain unchanged. a) 5.8mm. b) 6.75mm. c) 7.8mm. d) 9.6mm. Page 8 of 12

9 30. Which of the following bifocals gives the greatest amount of jump at the top of the segment? a) Distance prescription -5.00, refractive index 1.5, add +2.25, D25. b) Distance prescription , refractive index 1.74, add +2.50, D45. c) Distance prescription -5.00, refractive index 1.5, add +1.75, round 38. d) Distance prescription -8.00, refractive index 1.8, add +2.00, round 22. Page 9 of 12

10 SECTION B Answer 1 Question from this Section Only Each Question is worth 30 marks 1. a) Calculate the prismatic effect at a point 17 mm down and 12 mm out from the optical centre of a right lens of power +5.00/-2.00x110. An exact solution is required. (5) b) Compare and contrast the properties of typical (approximately) 1.5 index plastics and glass lens materials. (4) c) Discuss the optical principles, role and benefits of vacuum-tinted spectacle lenses. What are the advantages of and potential problems with vacuum coatings. (6) d) Explain the terms nylon supra and Polymil. (2) e) A patient, prescription R&L -7.00DS is looking for a new pair of spectacles. Discuss the factors influencing the choice of frame, and the advantages and disadvantages of each type of lens that may be considered using only terms and diagrams that a patient of average intelligence is likely to understand. (10) f) Describe what is meant by a round segment, solid, 38 glass bifocal and how they are produced. (3) Page 10 of 12

11 2. a) A horizontally oval thin lens of power -4.00DS is to be made up on a 8.00DS base from plastic of refractive index 1.6. The minimum available thickness for the material is 2.0mm. The lens has a nasaltemporal width of 52 mm and the optical centre is to be on the horizontal centre line, 20 mm from the nasal edge of the lens. Calculate the nasal and temporal edge thicknesses of the lens. An exact solution is required. What is the thickness at the geometrical centre of the lens. (6) c) Discuss the optical principles, role and benefits of vacuum-tinted spectacle lenses. What are the advantages of and potential problems with vacuum coatings. (6) c) In ophthalmic lens design, explain what is meant by the term distortion. Discuss how its effects may be controlled in spectacle lens design and during spectacle dispensing? (5) d) Explain the meaning of the term best form in the contexts of spectacle lens design and production. (3) e) Explain the meaning of the term PAL and the advantages and disadvantages of these lenses to a newly presbyopic patient with whom you wish to discuss such lenses. Use only terms and diagrams that a patient of average intelligence is likely to understand. (10) END OF PAPER Page 11 of 12

12 Formula sheet, BSOO2 Ophthalmic materials (VISP209) It is assumed that all candidates will be sufficiently familiar with these formulae that neither the terms nor their units need defining v=fλ n sini = n sini 1 / l 1 / l = 1 / f L L = F F = (n n) / r θ = tan-1( /100) P=CF P v =C(F c cos 2 θ) n = 1 + (0.523 F f ) / F lm s = r ± (r 2 y 2 ) 1/2 sin2a = yf / [1000 (n 1)] s = y tana F e = F / (1 df ) L 1 = L 2 / (1 (t/n)l 2 ) F v = F 1 / (1-dF 1 ) +F 2 F v = F 2 / (1-dF 2 ) +F 1 F v = F 1 / [1-(t/nF 1 )] +F 2 s 1 / s 2 = y / y 2 s 1 / s 2 = F 1 / F 2 s 1 / s 2 = (n 2 1) / (n 1 1) approximately d = log 10 ( 100 / T% P=100 tan(d) D=(n-1)A ρ = [(n n) / (n = n)] 2 Page 12 of 12

PART 3: LENS FORM AND ANALYSIS PRACTICE TEST - KEY

PART 3: LENS FORM AND ANALYSIS PRACTICE TEST - KEY d 1. c 2. To determine the power of a thin lens in air, it is necessary to consider: a. front curve and index of refraction b. back curve and index of