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Ординатура / Офтальмология / Учебные материалы / Vitreoretinal Surgery Second Edition Springer.pdf
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Useful Formulae and Rules

417

 

 

Visual Acuity

LogMar = log10 (denominator VA/numerator VA) Conversion chart for Snellen to Logmar. Holladay JT

(1997) Proper method for calculating average visual acuity. J Refract Surg 13:388Ð391

Schulze-Bonsel K, Feltgen N, Burau H, Hansen L, Bach M (2006) Visual acuities Òhand motionÓ and Òcounting ÞngersÓ can be quantiÞed with the Freiburg visual acuity test. Invest Ophthalmol Vis Sci 47:1236Ð1240

Snellen in feet

LogMar

Snellen in meters

20

10

−0.30103

6

3

20

20

0

6

6

20

30

0.176091

6

9

20

40

0.30103

6

12

20

50

0.39794

6

15

20

60

0.477121

6

18

20

70

0.544068

6

21

20

80

0.60206

6

24

20

90

0.653213

6

27

20

100

0.69897

6

30

20

110

0.740363

6

33

20

120

0.778151

6

36

20

130

0.812913

6

39

20

140

0.845098

6

42

20

150

0.875061

6

45

20

160

0.90309

6

48

20

170

0.929419

6

51

20

180

0.954243

6

54

20

190

0.977724

6

57

20

200

1

6

60

20

210

1.021189

6

63

20

220

1.041393

6

66

20

230

1.060698

6

69

20

240

1.079181

6

72

20

250

1.09691

6

75

20

260

1.113943

6

78

20

270

1.130334

6

81

20

280

1.146128

6

84

20

290

1.161368

6

87

20

300

1.176091

6

90

20

400

1.30103

6

120

20

500

1.39794

6

150

20

600

1.477121

6

180

20

700

1.544068

6

210

20

800

1.60206

6

240

20

900

1.653213

6

270

Counting Þngers

1.85

 

 

Hand movements

2.3

 

 

Perception of light

2.6

 

 

No perception of light

2.9

 

 

Diffusion

Fick’s Law

Diffusion Flux(J ) = D

c1 c2

Stokes-Einstein

Diffusion Coefficient(D) =

RT

 

6πμ rN

c = concentration

R = molar gas constant T = temperature

m = viscosity

r = radius of the molecule N = AvogadroÕs number

Stef‡nsson E (2009) Graefes Archives.

Barton KA (2007) Acta Ophthal Scand.

Convection and Permeability

Darcy’s Law

 

 

K

 

VFluid

= −

 

P

 

 

 

μFluid

vFluid = velocity of the ßuid K = hydraulic conductivity

mFluid = viscosity of the ßuid P = gradient of pressure

Starling’s Law

Hydrostatic and osmotic gradients in balance:

P Q = O

Drop in interstitial pressure may contribute to CMO.

418

Appendices

 

 

A rough guide to referral patterns: assume a routine referral of about one month, assume primary repair has been performed in trauma.

Condition

Characteristics

Referral

Why

RRD with PVD

Macula on

Immediate

Prevent macula detaching

 

Macula off less than 1 week

1Ð3 days

Macula should recover fully

 

Macula off 1Ð2 weeks

1 week

Macular should recover well

 

Macula off 2Ð6 weeks

1Ð2 weeks

Macula will show moderate recovery

 

Macula off >6 weeks

2Ð3 weeks

Macula unlikely to recover well

RRD without PVD

 

1Ð2 weeks

Slow progression

Macula hole

Duration <12 months

Refer routinely

Good surgical results

 

Duration >12 months

Discuss poor prognosis and refer if requested

Poor surgical results

Macular pucker

Duration <24 months

Refer routinely

Good surgical results

 

Duration >24 months

Discuss poor prognosis and refer if

Poor surgical results

 

 

requested

 

Trauma

Rupture

1Ð2 weeks

 

 

Penetrating

1Ð2 weeks

 

 

Penetrating with IOFB

Immediate

For antibiotics then IOFB removal

 

Contusion

1Ð2 weeks

 

Dropped nucleus

All

1 week

 

Complicated Cataract

 

Routine referral for assessment

Risk of RRD

Operation

 

 

 

Diabetic

Vitreous hemorrhage with PRP

Routine referral

 

 

Tractional RD with PRP

Routine referral

 

 

Vitreous hemorrhage without PRP

2Ð3 weeks

 

 

Tractional RD without PRP

2Ð3 weeks

 

 

Combined RRD/TRD

1 week

 

Non diabetic vitreous

PVD

1 week

 

hemorrhage

No PVD

2Ð3 weeks

 

 

Subretinal blood

2Ð3 weeks

 

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