Refractive Surgery and Contact Lenses (LASIK, SMILE, PRK, Keratoconus Management) MCQs

Ophthalmology · 42 free questions with answers & explanations.

1. In small incision lenticule extraction (SMILE), the optical correction is achieved by:
2. Corneal collagen cross-linking (CXL) with riboflavin and UVA light is the treatment of choice for progressive keratoconus. The primary mechanism by which CXL halts progression is:
3. A patient with keratoconus has apical scarring reducing BCVA to 6/60 with spectacles but achieves 6/9 with a rigid gas-permeable (RGP) contact lens. The MOST appropriate definitive surgical management for this patient is:
4. The 'Munson's sign' in keratoconus refers to:
5. A 27-year-old with myopia of -6.0D, corneal thickness 510 µm, and normal topography is being evaluated for refractive surgery. The minimum acceptable residual stromal bed thickness after LASIK to reduce the risk of post-LASIK ectasia is:
6. SMILE (small incision lenticule extraction) differs from LASIK primarily in that:
7. A 24-year-old is diagnosed with forme fruste keratoconus (abnormal topography, Kmax 46.5D, no clinical signs). He desires refractive correction. The most appropriate management to both correct refraction and halt progression is:
8. A patient fitted with a silicone hydrogel extended-wear contact lens develops a peripheral corneal infiltrate with overlying epithelial defect, mild anterior chamber reaction, and no frank hypopyon. The most likely diagnosis and recommended first-line treatment are:
9. SMILE (Small Incision Lenticule Extraction) differs from LASIK in which of the following key aspects?
10. A 28-year-old patient presents for refractive surgery evaluation. Placido-based topography shows inferior steepening with an asymmetric bowtie pattern, I-S (inferior-superior) value of 1.6 D, and the Belin-Ambrosio Enhanced Ectasia Display (BAD-D) score is 2.1. Pachymetry shows central corneal thickness of 520 microns. The most appropriate management is:
11. Orthokeratology contact lenses achieve their refractive correction through which mechanism?
12. The Munnerlyn formula used in excimer laser refractive surgery calculates ablation depth as: Depth = (Optical zone diameter)² × Refractive correction / 3. For a myopic correction of -6D with a 6 mm optical zone, the approximate stromal ablation depth would be:
13. A 26-year-old wants LASIK. Corneal topography shows inferior steepening, an I–S (inferior–superior) asymmetry index of 1.8 D on Placido disc, and Scheimpflug imaging reveals posterior elevation of +18 µm above best-fit sphere at the thinnest point. The MOST appropriate management is:
14. In SMILE (small-incision lenticule extraction) surgery, the femtosecond laser creates two curved cuts within the corneal stroma to isolate a refractive lenticule. The main theoretical advantage of SMILE over LASIK regarding corneal biomechanics is:
15. Corneal collagen cross-linking (CXL) with riboflavin and UV-A light is primarily used for which purpose in keratoconus management?
16. A rigid gas-permeable (RGP) contact lens fitted for keratoconus provides better vision than spectacles primarily because:
17. The Munnerlyn formula relates the intended refractive correction (D) and the optical zone diameter to the depth of the ablation. If the optical zone is kept constant, doubling the attempted correction (e.g., from -3D to -6D) will approximately change the central ablation depth by a factor of:
18. SMILE (Small Incision Lenticule Extraction) differs from LASIK in which FUNDAMENTAL structural aspect?
19. Corneal collagen crosslinking (CXL) with riboflavin and UV-A light halts keratoconus progression primarily through which mechanism?
20. A patient wearing soft hydrophilic contact lenses develops a painful red eye with a ring infiltrate at the peripheral cornea, minimal epithelial defect, and sterile culture. The MOST likely diagnosis is:
21. SMILE (Small Incision Lenticule Extraction) differs from LASIK in that SMILE:
22. Corneal collagen cross-linking (CXL) with riboflavin and UV-A light in keratoconus acts by:
23. The minimum recommended residual stromal bed (RSB) thickness after LASIK to avoid post-LASIK ectasia is:
24. Rigid gas-permeable (RGP) contact lenses are preferred over soft lenses in keratoconus primarily because:
25. In SMILE (Small Incision Lenticule Extraction), a femtosecond laser creates intrastromal lenticules. Compared to LASIK, which biomechanical advantage does SMILE offer?
26. A 28-year-old nurse is found to have forme fruste keratoconus — asymmetric topography with subtle inferior steepening, normal pachymetry (540 μm), and best-corrected VA of 6/6. She requests LASIK. What is the most appropriate counselling?
27. Post-LASIK ectasia is detected 2 years after surgery in a 31-year-old. Pentacam shows progressive anterior elevation and thinning. Which treatment has the strongest evidence for halting ectasia progression?
28. A patient needs IOL power calculation for cataract surgery but has a history of prior myopic LASIK. Which formula/method best accounts for the altered anterior corneal curvature and provides the most accurate power?
29. A -6.0 D myope is found to have a minimum corneal thickness of 485 μm on Pentacam. LASIK is planned with a residual stromal bed of at least 250 μm. Using the Munnerlyn approximation (ablation depth ≈ D × S² / 3, where S = optical zone diameter in mm), the MAXIMUM safe optical zone diameter for this patient is approximately:
30. Corneal collagen cross-linking (CXL) for keratoconus uses riboflavin (vitamin B2) with ultraviolet-A light. The mechanism by which it halts keratoconus progression is:
31. A contact lens wearer presents with a painful red eye and a corneal infiltrate with a hypopyon. Confocal microscopy shows highly reflective double-walled cysts. The MOST likely pathogen is:
32. A hypermetropic patient wears a +4.0 D spectacle lens at a vertex distance of 12 mm. If a contact lens is fitted on the eye (vertex distance = 0), the required contact lens power is:
33. A 28-year-old patient wants LASIK surgery. Corneal topography shows inferior steepening with an asymmetric bowtie pattern and posterior elevation of +18 μm above the best-fit sphere. The correct clinical interpretation and management decision is:
34. SMILE (Small Incision Lenticule Extraction) differs from LASIK in which fundamental way?
35. Corneal collagen crosslinking (CXL) for keratoconus works through which primary mechanism?
36. Rigid gas-permeable (RGP) contact lenses are superior to soft contact lenses for correcting irregular astigmatism in keratoconus because:
37. A 28-year-old software engineer with −5.5 D myopia and −0.75 D astigmatism is being evaluated for LASIK. Corneal topography shows a mild inferior steepening and the thinnest point is 498 μm. The Ectasia Risk Score (ERS) is elevated. What is the MOST appropriate recommendation?
38. SMILE (Small Incision Lenticule Extraction) differs from LASIK in that it:
39. A 32-year-old with Amsler grid distortion, progressive myopia (spectacle power changed by −2 D over 3 years), and corneal topography showing inferior steepening with I-S asymmetry >1.4 D is diagnosed with keratoconus stage II (Amsler-Krumeich). He is contact lens intolerant. The MOST appropriate management to halt progression AND improve visual acuity is:
40. A patient who wore extended-wear soft contact lenses (EW-SCL) for 6 days continuously develops acute red eye, severe pain, and a white corneal stromal infiltrate with an epithelial defect. Confocal microscopy of the cornea shows highly reflective round cysts 15–30 μm in diameter with a double-walled appearance. The causative organism is MOST likely:
41. A 28-year-old with -6.00 D myopia, 530 µm central corneal thickness, and regular topography wishes to undergo refractive surgery. Corneal topography shows a normal Amsler-Krumeich pattern. The minimum residual stromal bed thickness after LASIK to avoid iatrogenic ectasia is:
42. A 22-year-old contact lens wearer is diagnosed with keratoconus based on inferior corneal steepening of 51 D, I-S value > 1.5 D, and a skewed radial axis on Placido disk topography. Simulated keratometry (SimK) is 50 D / 47 D. The progression is confirmed over 6 months. Spectacle-corrected visual acuity is 6/18. The most appropriate next step is: