MRCS ophthalmology exams

Preparing for Part-2 MRCS Ophthalmology of Royal college of surgeons of Edinburgh requires lots of effort, patience and dedication.

It is a test of one's patience and perseverance which helps one carry through..

I will be posting few salient tips, questions which I made while preparing for the exams..

Here is the first set on retinoscopy and subjective refraction..

History
1. Age
2. Occupation
3. Special requirements- hobbies
4. History of eye disease- glaucoma
5. Previous spectacle/contact lens
6. Previous eye surgery/laser

Examination
1. Visual acuity- uniocularly
Distance/near/ unaided
2. Fog the fellow eye with a nystagmus with high plus lens
3. Poor VA check with ophthalmoscope (too much light- photostress induced reduction of VA)

Objective refraction

1. Cover/uncover test
2. Convergence
3. IPD measurement
4. Fit trial frame, taking care lens apertures centred on the pupil, with patient gazing ahead.
a. Level across face
b. Close to face as much lashes allow
c. High power trial lens in the back cell of trial frame

5. Retinoscopy in patient’s visual axis in order to measure true optical length of eye
Avoid blocking patient’s distant fixation –patient may accommodate if examiner comes in the way
6. Fog patient’s fellow eye rather than occlude
In presence of manifest squint dominant eye may have to be occluded to achieve steady fixation of non dominant eye
Young children with latent/ manifest squint- cycloplegic before retinoscopy
7. Dioptric value of working distance (+1.5D for 2/3 m)
8. High refractive error too dim and diffuse initial reflex- use+/- &D to bring reflex in view(alternatively use ophthalmoscope to view the fundus)
9. Remove the working distance lens after neutralization
10. Cylinder to be moved only by a small amount before rechecking the retinoscopy
11. Minus cylinders to be used during retinoscopy

The use of plus cylinders when refracting young hypermetropes may stimulate acomodation as eye is fogged in both meridians

Minus cylinders may overcorrect hypermetropia in elderly

Some may prefer plus cylinders with plus and minus with minus

Retinoscopy reflexes with opposite movement wise to use minus spheres and plus cylinders as it is easy to find the axis of astigmatism with plus cylinder using the with movement than against movement that goes with use of plus spheres and minus cylinders.

Power cross is drawn in orientation of principal meridians and angle of one meridian is marked

If result is transposed to a lens prescription (corrected for working distance) the axis of cylinder lies at 90* to the line of meridian


Scissor shadows- moving away and towards each other due to difference in refraction between zones of pupillary aperture
Seen in
· Different zones of dilated pupil
· Near end point (one area is myopic and other is hypermetropic)
· Apex of cone is darker than periphery (oil drop sign) in keratoconus

Subjective refraction

Occlude the fellow eye/ fog the fellow eye
Two methods to check sphere power at this stage
Duochrome (6/9 or more)
i. R>G an extra 0.5 makes green clear
ii. R=G young and hypermetropes
iii. Green clearest if accommodation needs to be stimulated
iv. If there is not 0.5D interval between R& G best to abandon duochrome
v. Less reliable in presence of accommodation (children), uncorrected astigmatism, large or small pupil, media opacities and colour vision anomalies
Use small plus or minus until no further improvement can be made (those with poor VA may be given +/- 0.5(start with additional plus otherwise patient may accommodate and confuse the result)
i. + little noticeable effect (if patient is already forced to accommodate)
+ blurred (if too much plus in place or sufficient plus)
ii. - little noticeable effect (if previous lens was corrector too much minus in place)
- clearer (if too much plus in place)
- smaller(forced to accommodate with new lens)

Verify axis of cylinder
Insert a -0.25/-0.50 to + accommodation
When accommodation is active it may be assumed that circle of least confusion will be focused on the retina
Look at a circular letter near their acuity limit
End point is when both positions are equally blurred
Verify power of cylinder
If cylinder power is changed by + 0.5D, change sphere power by - 0.25D in the opposite direction to keep patient’s accommodation stable, if power is altered recheck the axis
Large change is found in cylinder, it is wise to go back and check the sphere
Myopic patient- Duochrome test –monocular and binocular
Red letters clearly binocularly and ensure patient will be comfortable and not accommodating, when wearing spectacles
Prescription and acuity of each eye with binocular VA

Binocular tests

Record BVD if power of spherical lenses is>5D
Lens should be in back cell of trial frame
Ruler beside the arm of trial frame, while viewing patient from side.
Maddox rod for muscle balance for distance
Occlude each eye to ascertain if spot and light are visible
Uncover both eyes to see if able to perceive them simultaneously (uniocularly seen but binocularly absent- BSV absent or defective)

Presbyopic
Rule of thumb addition
Accommodation monocularly and binocularly(RAF rule) amplitudes should be equal in both eyes)
Addition = working distance (in dioptres)- 0.5 (amplitude)
Eg: WD= 33cm, amplitude is 4D, addition is
100/33= 3D; 3-0.5(4)= 3-2=1D
Near duochrome (if available)
Maddox wing near muscle balance
Convergence weakness by convergence excercises


Steps in cross-cylinder refraction

Adjust the sphere to give most plus/least minus that gives best VA
Use test figures ½ lines larger than patient’s best VA as cross cylinder causes blur
If no cylindrical correction look for astigmatism by testing with cross cylinder at 90*& 180* and subsequently 45* &135*
Refine axis first
Cross cylinder 45* from principal meridian
Plus cylinder to plus axis of the cross cylinder
Minus cylinder to minus axis

Refine cylinder power
Keep track of cylinder power added/subtracted
Compensate for change in position of circle of least confusion by adding half sphere in opposite direction
Eg: -0.5D cyl/+0.25D sph

After cross cylinder technique Sturms conoid is collapsed to a point on retina
Refine sphere again add + 0.25 till patient reports ê in vision.
If +0.25 not accepted then add –0.25 until maximum acuity-least minus
End point verified by duochrome test.

Binocular balancing
1. Fogging
2. Duochrome with fogging
3. Prism dissociation

Fogging
1. BCVA add + 2.0 both eyes, patient reports ¯ in vision (6/60-6/36) íHumphriss method (+0.75/+1.0) swap the other eye not possible if large squint.ý
a. Binocular addition once prescribed balance in place+0.25 in front of both eyes, ask if smallest letters are clear if prescription correct letters blur if not incorporate extra positive power and repeat tests)
2. Add –0.25 do alternate cover test and see which eye is clear
a. Eye is balanced eye with 0.25 clearer
b. Eye not balanced add/ subtract in 0.25 until clear

Duochrome with fogging
BCVA add +1.0 in one eye observe red green preference

Prism dissociation
1. BCVA add +1.0 both eyes, 4 D is placed in front of one eye
2. Project 6/12, patient able to see same line with both eyes simultaneously
3. Add +0.25 before one eye and then before another eye
4. Balanced- Eye with +0.25 blurred
5. Prism removed when balance is obtained and fog is reduced binocularly until maximum vision with highest plus/ least minus

Pinhole test
Any stage of refraction
+1D test
if VA is 6/6 +1DS should blur 6/12 to 6/18.

Books to read for the part-2

1. MCQ's and OSCE's in Optics and refraction by A Bhan

2. Success in part-2 MRCOphth by Chua CN

3. Clinical optics-Elkington

4. AAO- Clinical optics 2006-2007

5. The Opthalmology Examinations Review by Wong TY

6. Clinical orthoptics- Rowe F

Great website

www.mrcophth.com/

Yahoo groups

health.groups.yahoo.com/group/FRCOphth

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