اولانريواجو ماثيو اوريوو

 

 

DEPARTMENT OF OPTOMETRY 

COLLEGE OF APPLIED MEDICAL SCIENCES

KING SAUD UNIVERSITY 

2007/08 (1428/1429) session  

Second Mid-term Exam

 

 

Course:                 OPTO 456 – Contact Lenses III

Course Director:   Dr. Ola M. Oriowo

  

Instructions: Answer all questions. Write your name and number on top of all pages. You can use the back pages for answer.

  

1. The following table below can be used a guide in general fitting approach for back surface toric lenses. Fill in the blank spaces (i.e. columns and rows).

4p

 

If	Corneal toricity less than 2.00D	Corneal toricity more than 2.00D
Refraction	Low residual astigmatism (<0.50)	Low to moderate refractive astigmatism
Use
Refraction	Moderate residual astigmatism (0.50 – 2.00D)	High refractive astigmatism (>2.00D)
Use

 

 

Answer: 1p for each correct column and row.

 

Fitting the back surface toric lens

 

If	Corneal toricity less than 2.00D	Corneal toricity more than 2.00D
Refraction	Low residual astigmatism (<0.50)	Low to moderate refractive astigmatism
Use	RGP spherical lens	RGP bitoric or soft lens toric
Refraction	Moderate residual astigmatism (0.50 – 2.00D)	High refractive astigmatism (>2.00D)
Use	Front toric RGP or soft lens toric (1.25 or 2.00D)	RGP bitoric or custom soft lens toric

 

 

2. Mention the 3 types of toroidal back optic and peripheral zone lenses available to the contact lens practitioners.

                                                                        3p

Ans:

1.      Toroidal back optic zone and peripheral zone

2.      Toroidal back optic zone and spherical peripheral zone

3.      Spherical  back optic zone and toroidal peripheral zone

 

3. Mention the 4 parameters that you need to verify in toric base contact lenses.

                                                                        4p

Ans:

 

1-      The optic zone radii of curvature

2-      The axis of the back surface cylinder

3-      The power of the lens in air (including cylinder axis), and

4-      The cylindrical power of the lens when in situ

4. When you order toric lenses, you consider the allowance for lens rotation as it is expected that the toric soft lens to be ordered will rotate when placed on the patient’s eye. Therefore an allowance must be made for this rotation, otherwise the cylinder axis of the lens when on the eye will not coincide with the required cylinder axis for the contact lens correction. Briefly describe the principle used for adding the allowance for rotation to the required cylinder axis when ordering toric contact lenses.

 

                                                                        2p

Ans: 0.5 for each correct description.

If left eye and nasal rotation – add

If left eye and temporal rotation – subtract

If right eye and nasal rotation – subtract

If right eye and temporal rotation – add

 

5. Suspicious signs in a keratoconus patient include history of multiple inadequate spectacle corrections of one or both eyes, which may include oblique astigmatism on refraction.

A)    True

B)    False.

                                                                        0.5p

Ans: True

 

6. In a keratoconus patient, all layers of the cornea are believed to be affected by the conical protrusion of the cornea, however there are certain most notable features. Briefly mention four of the most notable features of keratoconus.

                                                                        4p

Ans:

 

1. The thinning of the corneal stroma,
2. The ruptures in the Bowman layer, and
3. The deposition of iron in the basal epithelial cells, forming the Fleischer ring.
4. Breaks in and folds close to the Descemet membrane result in acute hydrops and striae, respectively.

 

7. Briefly describe two examples of clinical history of keratoconus.

                                                                        2p

Ans:

1. Patients often report decreasing vision (distortions, glare/flare, and monocular diplopia or ghost images) with multiple unsatisfactory attempts in obtaining optimum spectacle correction.
2. Soft contact lenses and spectacles may initially give satisfactory vision, but vision tends to decline over time and requires rigid gas permeable (RGP) contact lenses for correction.

8. Videokeratography commonly shows superior corneal steepening in keratoconus.

A)    True

B)    False.

                                                                        0.5p

Ans: False

9. Advanced keratoconus often results in keratometry values less than 52.00D.

 

A)    True

B)     False.

                                                                        0.5p

Ans: False

 

10. Select the best answer. In this type of Keratoconus, Vogt striae are seen in approximately 60% of eyes, and both Fleischer ring and/or scarring are seen in approximately 70% of eyes.

                                                                        0.5p

a. Moderate keratoconus

b. Mild keratoconus

c. A and B

d. None of the above

 

Ans:  d. None of the above

 

11. Pellucid marginal degeneration (PMD) is often considered a variant of keratoconus, in which corneal thinning occurs about 3 millimeter above the inferior limbus, resulting in advanced with-the-rule  corneal astigmatism that may be observed by keratometry or videokeratography.

                                                                        0.5p                                                                

A)    True

B)    False

 

Ans: False

                                                                       

12. Keratoglobus is an extremely rare corneal disease in which the only the central cornea (the entire cornea, from limbus to limbus) thins, sometimes to the point where spontaneous perforation becomes possible. KG probably is unrelated to KC.                                                                                            

A)  True

B)  False

0.5p

 Ans: False                                                                 

 

13. Briefly describe the images of keratometric mires in keratoconus.          1.5p

 

Ans: Images of the keratometry mires commonly will be steep, highly astigmatic, irregular, and often appear egg-shaped rather than circular or oval in keratoconus.

 

14. Terrien's marginal corneal degeneration is a type of corneal disease condition which is different from keratoconus. Briefly describe the Terrien's marginal corneal degeneration.                                                               2p

 

Ans: Terrien's marginal corneal degeneration is a mildly inflammatory disease, usually of the superior limbus, which also can induce irregular against-the-rule astigmatism and corneal thinning (often with vascularization and lipid deposits).

 

15. Briefly describe posterior keratoconus.

                                                                        1p

Ans: Posterior keratoconus is another extremely rare corneal disease in which the posterior corneal surface suffers a loss of substance. This condition is probably is probably unrelated to keratoconus (KC).

 

 

16. Laboratory workup may not be necessary to diagnose keratoconus. Name three clinical procedures that you can employ to diagnose keratoconus.

                                                                        1.5p

Ans: No laboratory workup is necessary. Careful refraction, keratometry, and slit lamp biomicroscopy allows the clinician to observe evidence of KC.

 

 

17. Contact lens fitting in the peadiatric population falls into three categories. Mention the largest group of the three categories.

                                                                        1p

 

18. Generally, aphakes make up the greatest number of patients in the largest group of the three categories in pediatric contact lens fitting. Briefly list at least 4 conditions of the largest group of the three categories as mentioned in question 17.

                                                                        2p

 

Answers for questions: 17 and 18.

Refractive

Cosmetic

Therapeutic

 

Refractive:

The largest group is the refractive group and of these the aphakes make up the greatest number. These are either congenital or traumatic, unilateral or bilateral.

 

Other refractive conditions include:

High myopia

Unilateral ametropia

High Hypermetropia

Strabismus with a high refractive error

Anisometropia

Corneal irregularity as a result of trauma (without aphakia).

 

19. Mention at least 4 common ocular conditions in pediatric patients that need cosmetic lenses.

                                                                        2p

Ans: Cosmetic:

The most common conditions which need cosmetic lenses are:

 

Aniridia (absence of iris)

Iris coloboma (absence of part of iris)

Albinism (light iris)

Cone dystrophy (rare)

Microphthalmos (small eye)

Unsighltly scars and opacities

 

20. Briefly discuss the disadvantages of monovision contact lens use for presbyopia.

                                                                        2p

Ans:

 

The following are limitations  of Monovision contact lens fitting

The downside of monovision is that each eye works more or less alone rather than "binocularly," meaning in concert with each other.  The result:

• Patient  may have to adjust his/her head position more often to see clearly.
• The patient  also may lose some depth perception.

21. Bifocal contact lenses are designed to give good vision to people who have a condition (called presbyopia) in which accommodative amplitude is insufficient.

A)  True

B)  False

0.5p

 Ans: True                  

22. Mention two factors that should be considered when choosing a bifocal contact lens for presbyopia prescription.                                                            2p

Ans: Pupil size and Patient’s ”Add”

Two factors that should be considered in choosing a bifocal contact lens are pupil size and patient's "add," or near prescription.

There are no hard and fast rules. But in general, low adds are better suited to an aspheric multifocal. Alternating vision, accomplished with a translating bifocal, is a better choice for high adds. Too large a pupil can be problematic for an aspheric multifocal lens.