10. Dati BIOMETRICI
Haigis Hoffer Q SRK/2 SRK/T HOLLADAY 1 HOLLADAY 2 Olsen
Axial Length YES YES YES YES YES YES YES
ACD YES NO NO NO NO YES* YES
Keratometry YES YES YES YES YES YES YES
Lens Thickness NO NO NO NO NO YES YES
Corneal Thickness NO NO NO NO NO NO NO
White to White NO NO NO NO NO YES YES
Pupil Size NO NO NO NO NO NO NO
Visual Axis NO NO NO NO NO NO NO
11. Biometry
Axial length distribution (n=15123) of cataract patients
biometry data from high precision immersion ultrasound (GBS)
AL [mm]
363432302826242220181614
frequency
6000
5000
4000
3000
2000
1000
0
0.3
95.6
4.1
0
20
40
60
80
100
AL<=20 20<AL<27 AL>=27
[%]
11.1
78.1
10.8
0
20
40
60
80
100
AL<=22 22<AL<25 AL>=25
[%]
12.
13. Final draft for European standard prEn ISO 11979-2, August 1999: Ophthalmic implants
– intraocular lenses. Part 2: Optical properties and testing procedures ISO/FDIS 11979-
2-1999:
Nominal dioptric power [D] *) Max. deviation allowed [D]
0 bis 15 0.3
> 15 bis 25 0.4
> 25 bis 30 0.5
> 30 1.0
*) : positive as well as negative dioptric power
15. 15
• forniscono valori diottrici maggiori per
l’emmetropia in occhi lunghi e calcoli inferiori per
occhi corti rispetto alle formule teoriche di base
Un gruppo successivo di formule nate dall’esigenza di
correggere i limiti di calcolo già evidenti in occhi lunghi o corti e
solo parzialmente migliorati con formule di regressione.
Hoffer
Shammas
• SRK II
• Binkhorst
16. 16
Formule di REGRESSIONE
• Derivate empiricamente dall’analisi
retrospettiva dei risultati refrattivi di
un ampio numero pazienti operati
• Equazione P= a –bL –cK
• Formula SRK (Sanders Retzlaff Kraff)
• Formula regressione più conosciuta
P = A – 2.5 L – 0.9 K
17. 17
Analisi seriate ampie
hanno evidenziato:
•Tutte le formule moderne si dimostrano superiori alle precedenti
•Non c’è differenza clinica tra Hollady SRK/T ed HofferQ nell’occhio
standard
•La Holladay 2 è più accurata della Holladay nell’occhio corto
18. 18
• Le formule moderne si collocano nell’intervallo di precisione tra le
originali formule teoriche
• Le formule moderne forniscono grossomodo gli stessi valori per
occhi medi (23.5mm 43.5D) e per occhi lunghi con cornea piatta (AL
26 K 41 D)
• Differenze tra le varie formule moderne esistono ancora, specie per
occhi lunghi e corti.
• La variazione si accentua in particolare al variare della curvatura
corneale
21. Ophthalmic Surgery 12 (4): 269-272, 1981
HOFFER KJ: Intraocular lens calculation:
the problem of the short eye. Ophthalmic
Surgery 12 (4): 269-272, 1981
AL=19 mm
22. Results of axial length measurements:
acoustical : AL = 26.66
mm
optical : AL = 28.25
mm
Haigis, 2005
23. PCI and US biometry in staphylomatous eyes
Pat.: E.T. *25.01.41: US B-scans
OS OD
nose
temporal temporal
Haigis, 2005
26. Pat. Heidi Puchert, 26.10.44, hhcleff.xls
Corneal power
Influence of a (hard) CL on radii and refractive power of cornea
OD R1 [mm] R2 [mm] axis [°] R [mm] K [D]
after CL-
removal
7.20 6.96 124 7.08 46.82
after 3 hrs. 7.12 7.28 157 7.20 46.04
Difference - 0.08 + 0.32 + 33 + 0.12 - 0.78
OS R1 [mm] R2 [mm] axis [°] R [mm] K [D]
after CL-
removal
7.32 6.89 63 7.11 46.66
after 3 hrs. 7.34 7.09 61 7.22 45.95
Difference +0.02 + 0.20 - 2 + 0.11 - 0.71
27. Eyes with high myopia
• Accurate axial measurement is critical for IOL power calculation
• Paraxial measurement in ultrasonic measurement due to posterior staphyloma
is likely to give a refractive surprise
• It is overcome by optical biometer using a fixation target
• Most of it is taken care in IOL master 700 by directly visualising fovea on the
OCT image during measurement
• IOL formula needs to be chosen accordingly
• Minus IOL powers have to be chosen carefully by reducing amount of minus
power
• The surgeon should aim for a -0.50 D to -1.00 D postoperative refraction as
most elderly will prefer being near-sighted
28. • As cornea with keratoconus is steep, using K reading of such eyes will yield an
overestimated reading due to ELP calculation error.
• Formulas which consider only axial length and not Keratometry to calculate
ELP gives better prediction of true IOL power.
• K reading has less of this effect in the
• Also, overestimation is not a factor with the Haigis formula as it does not use
the K reading in estimating the lens power.
29.
30. 30
Il principio di misurazione è una tecnica
interferenziometrica a doppia fascio di luce
infrarossa (λ 780nm) parzialmente coerente
lungo l’asse ottico quando il paziente guarda
la mira di fissazione.
Due fasci coerenti Lm e Lf vengono generati
Nell’interferometro di Michelson da un
laser a diodo(LD). I fasci vengono riflessi
dalle varie interfaccie oculari, specie cornea
C e retina R e catturati dopo deflessione
(Bs2) su un detector(PD). Il detector
percepisce l’interferenza delle onde riflesse
se la distanza variabile d è equivalente alla
OPD. I picchi di maggiore intensità verranno
generati dalla superficie anteriore corneale
e dall’epitelio pigmentato retinico.
31. Anterior segment
• tear film problems
• keratopathies
• central corneal scars
• mature cataract, PCO
• nystagmus
• dislocation of pupillary plane
by dermatocholasis
• lid abnormalities, ptosis
General
• bad general condition
• tremor
• respiratory problems
• insufficient compliance
Posterior segment
• vitreous hemorrhage
• membrane formation
• maculopathy
• retinal detachment
Haigis, 2005
34. 34
Riproducibilità
• Riproducibilità: deviazione standard media di cinque
serie consecutive di pazienti
• AL: 23µm ±15 IOLMaster 22±24 GBS imm
Le misurazioni ottenute con IOL Master
sono indipendenti dall’operatore
42. Eyes with silicone filled vitreous/
vitrectomized eyes
• The refractive index of the oil is much less than that of the
vitreous.
• Usage of a standard sound velocity can give an error of upto 8
mm.
• Difficulty of measuring the AL can be overcome by increasing
the ‘system gain’.
43. Eyes with silicone filled vitreous/
vitrectomized eyes
• Error in AL measurement occurs as ultrasound travels slower in silicon oil
compared to vitreous and thus taking a longer time to reach the probe
which is interpretated as longer wavelength.
• Usually a factor of (0.72) gives a rough estimate of the power.
• TAL = 1133/1550 × AAL.
• As silicone oil alters the optics of the eye due to its refractive index,
further adjustments in IOL power are required. However it is less affected
in optical biometer
• Usually, IOL required is 2 – 3 D stronger than indicated by standard power
calculation.