Biometry and corneal disease

Dr Elsie Chan, FRANZCO

Royal Victorian Eye and Ear Hospital

Centre for Eye Research Australia, University of Melbourne

Doncaster Eye Centre, Melbourne Eye Specialists

June 2018 Conflicts of interest: nil

Benchmarks

Gale et al. Eye (Lond) 2009; 23: 149

Based on 3358 NHS cases, recommended:

85% within 1D

55% within 0.5D

Benchmarks

93% within 1.0D

72.7% within 0.5D

Recommend 90% within 1.0D

IOL formulae

Barrett

Vergence formula based on optics

Uses 5 variables

Incorporates posterior corneal astigmatism

Hill-RBF

Theoretical formula

Data driven (big data/ artificial intelligence)

12 419 eyes

https://rbfcalculator.com

Corneal factors that affect predictability

1. Ks

o Anterior curvature altered in corneal pathology

o Cannot predict posterior curvature based on anterior curvature (eg. post-LASIK, keratoconus)

2. Effective lens position

o May be less accurate as relies on anterior curvature

Ocular surface disordersdry eyes

EBMD

pterygia

Punctal plug

Gels

Cyclosporin 0.05%

Cyl = 2.2D

Case – Sjogren’s Syndrome

Lenstar:

Km 46.4, cyl 2.2

Sjogren’s Syndrome

Punctal plug

Gels

Cyclosporin 0.05%

Ointments

Autologous serum tears

Cyl = 0.8D

Case – Sjogren’s Syndrome

Lenstar:

Km 45.85, cyl 1.39

Before lubricants After lubricants

EBMD

• Affects acuity

• Affects biometry

• May need to treat pre-operatively

Pterygium

• Causes astigmatism

• Consider staged surgery

Post-op

Corneal scarring

Corneal scarring

Issues:

Regular or irregular astigmatism

Concurrent ocular surface disease

Need to optimise pre-op

Stable/ recurrent disease

RVEEH Medical Photography and Imaging Centre

IOLM

Km = 46.75

Cyl 6.95D at 147

+20.0

Corneal scarring - HSV

+17.0

Corneal scarring - HSV

IOL Master Ks

Monofocal

Aim -0.65

8 months post-op now

6/9 unaided

Astigmatism: Pre op

Refraction

1

Biometry

IOLM 700

6 spots at 1.5, 2.5, 3.5

IOLM 500 6 spots at 2.5mm

2

manual Ks

(3.2mm zone)

3

Pentacam Ks

(sim Ks 8mm; regular vs irregular)

4

Astigmatism: What if they don’t agree?

Repeat measurements if there is a big difference

Look for consistency between instruments

Use Pentacam to verify axis and regularity of astigmatism

Use manual Ks to verify power

If there is only small differences, an option is to use the Barrett toric calculator

Prior refractive surgery

Factors that affect predictability

• Cannot predict posterior curvature based on anterior curvature

• Effective lens position may be less accurate (relies on anterior curvature)

• Refractive laser (LASIK, PRK)

o Myopic 39-93% within 0.5D

o Hypermetropic 38-57% within 0.5D

• Radial keratotomies

o 27-58% within 0.5D

Prior refractive treatment

www.ascrs.org

Case 1 – previous RK

61F

Previous RK 1988

Right phaco 2010

6/12 with +2.25/+2.75x20 (SEQ +3.6)

Case 1 – previous RK

Right eye:

+24.0D IOL inserted

SRK formula 24.0D gives -1.3D

Using RK calculator

24.0 gives +3D (c/w post op SEQ +3.6)

28.0D gives emmetropia

Case 2 – previous RK

54yo M

RK 1981

Post-op approx. -2D

VAR s 6/120 (-5.0/-2.0x15 = 6/12)

NS3+

16 cut RK, with PAS

Central clear zone 2.7mm

Case 2 – previous RK

IOL calculation – ASCRS calculator

Aim -1.50D

Post-op (3 months)

UCVA 6/12

UCVA 6/9 = -1.50 / -0.75D

Summary

1. If there is astigmatism

Correct reversible cause

Multiple methods to verify power and axis• Manifest refraction

• Standard biometry

• Corneal topography/tomography

• Intraoperative aberrometer?

2. Manage expectations

Especially in post-refractive patients

3. Have a plan for post-operative refractive errorsSpectacles

CL

IOL exchange

Piggyback IOL

Refractive laser surgery