Individual and External Risk Factors of LASIK
It is important to consider external and individual risk factors before undergoing IntraLASIK, LASIK, Epi-LASIK, LASEK, PRK. External risk factors that can be minimized are, for instance, missing quality standards like  ISO 9001 in the ophthalmic clinic, technically obsolete laser systems and insufficient experience of the surgeon. More important, however, are individual risk factors.
LASIK Risk Score Predicts Postoperative Outcome
An easy model to predict postoperative outcome is the lasik risk score. It depends on the presence of individual variables of the patient that might increase risk of unsuccessful LASIK.
The score can vary from 1 to 14 with values between 1 and 4 considered low risk for complications, values between 5 and 9 moderate risk, and values above 10 high risk.
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Risk Factor
|
Measure
|
Score
|
|
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<3
|
1
|
|
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3 to 5
|
2
|
|
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>5
|
3
|
|
|
<3
|
2
|
|
|
>3
|
3
|
|
|
<1
|
0
|
|
|
1 to 2
|
1
|
|
|
>2
|
2
|
|
Age (y)
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<40
|
0
|
|
|
40 to 50
|
1
|
|
|
>50
|
2
|
|
Minimal preoperative K <43 D *
|
|
1
|
|
Enhancement
|
|
1
|
|
|
|
1
|
|
|
|
1
|
|
|
|
1
|
|
|
|
1
|
|
|
|
1
|
|
Total
|
|
?
|
|
*K = corneal curvature (K reading) in diopters
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|
|
 Source: Najjar DM. LASIK Risk Score: an easy method to predict postoperative outcome. J Refract Surg. 2005 Jul-Aug;21(4):399-400.
Individual Risk Factors of Halos, Loss of Contrast Sensitivity, Glare and Starbursts after LASIK
1. Flat Cornea
Since LASIK flattens the cornea one risk factor is this procedure in combination with mesopic and scotopic pupil sizes.
Source: Holladay JT, Dudeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography. J Cataract Refract Surg. 1999 May;25(5):663-9.
The study conducted by Hammond et al. Quality of vision and patient satisfaction after LASIK. Curr Opin Ophthalmol 15:328-332 states on page 329 that flat corneas present a risk for starburst:
"Lower preoperative minimum corneal curvature was associated with reduced postoperative satisfaction: each additional 1.00-D decrease in corneal curvature resulted in a 30% increased odds of a patient not recommending LASIK to a friend. Subjects who experienced starbursts had significantly flatter preoperative minimum corneal curvature values."
2. Pupil Size
The study by Schallhorn SC et al. Pupil Size and Quality of Vision after LASIK. Ophthalmology 2003;110:1606-1614 is often cited to support the thesis that the pupil size doesn’t present a risk factor for visual side effects:
"No relationship between pupils and symptoms was noted at 6 months after surgery in ether the ANOVA or regression analysis group."
However, there are some objections to this study for it includes only 100 patients – versus 795 patients in the study conducted by Pop M, Payette Y. Risk Factors for Night Vision Complaints after LASIK for Myopia. Opthalmolgy 2004;111:3-10. Also, Schallhorn et al don’t differentiate between patients with low / medium / high myopia. This is a methodical error. A patient with -4 dpt and 6 mm mesopic pupils will naturally have less visual side effects than a patient with -7 dpt and 6 mm mesopic pupils.
The study by Helgesen et al. Pupil size and night vision disturbances after LASIK for myopia. Acta Ophthalmol Scand 2004: 454-460 sees a clear correlation between pupil size and visual side effects:
"Large pupil size measured preoperatively is correlated with an increased frequency of subjectively experienced post-LASIK visual disturbances during scotopic conditions."
The above mentioned study conducted by Hammond comes to differentiated conclusions regarding the subject of pupil size and states the following on page 329:
"The role of pupil size on LASIK outcome and patient satisfaction remains controversial. Large pupils tend to increase the exposure of corneal aberrations, which can reduce visual acuity in untreated patients and LASIK patients."
The study by Lee et al. Quality of vision after laser in situ keratomileusis. Influence of dioptric correction and pupil size on visual function. J Cataract Refract Surg 2003; 29:769-777 concludes:
"Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity in post-LASIK patients with "uniform" topography who had scotopic pupils not larger than 7.0 mm."
This is a methodical error because especially patients with scotopic pupils >7 mm complain about visual disturbances under difficult light conditions.
3. Further Risk Factors
Pop M, Payette Y. Risk Factors for Night Vision Complaints after LASIK for Myopia. Opthalmolgy 2004;111:3-10
"Using 12-month postoperative data, age over 50, attempted spherical correction of >5 D, OZ of <6mm, and a postoperative spherical equivalent outside 0.5 D of emmetropia were the main factors that had statistically significant OR without stratification."
It can be concluded that individual risk factors need to be weighted. When they are added they make up the LASIK risk score which can predict the postoperative result.
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