ABSTRACT
Aim: to compare the central corneal thickness measurements using ultrasonic pachymetry and the orbscanII in normal Egyptian subjects
Methods: 60 eyes of 30 normal subjects visiting the ophthalmology outpatient clinic at Benha-Faculty of Medicine were enrolled in this study. All were informed about the study and its aim and those willing to share were enrolled Every subject was examined by two examiners .The first examiner performed pachmetry using the orbscan II in the first room and kept the results away from the second examiner. The patient was then transferred to another room where he was examined by the second examiner who performed ultrasonic pachymetry using the Torney ultrasonic pachymetry. At the end of the study both data collected by both examiners was collected and statistically analyzed using the student t test
Results: the mean difference in central corneal thickness in normal individuals when measured by both methods was 1.22 micro m = 3.6 [SD] with P value of more than 0.05 [statistically insignificant] when the orbscan II was used utilizing the default linear correction factor LCF. But when the orbscan II was used without the default LCF, the mean difference in central corneal thickness was 42.0 micro m +/- 28.8 [SD] which was statistically significant [P > 0.0001]
Conclusion: the measurements of central corneal thickness using both the orbscan II and the ultrasonic pachymetry are more or less similar in normal subjects when using the default built in LCF in contrast to the preliminary reports that were released when comparing ultrasonic pachymetry to pachmetry using the orbscan I which did not utilize a linear correction factor in its software
ABSTRACT
Aim: to evaluate actual versus expected laser in situ keratomileusis [LASIK] flap thickness using the Moria M2,130 microkeratome head
Methods: 50 eyes of 25 patients scheduled for LASIK surgery for myopia where enrolled in this study. Patients were prepared for surgery. On the day of surgery they were admitted to the LASIK room where the lids were sterilized and draped. A suction lid speculum was applied to one eye after instilling one drop of Benox into the conjunctiva2 sac, the eye was then washed with balanced salt solution BSS and the suction of the lid speculum activated to assure there was no excess BSS in the conjunctival sac then a final preoperative ultrasonic central corneal pachymetry reading using the sterile probe of the Tomey AL-2000 pachymetry was recorded. The suction ring of the Moria 1112 microkeratome was centered on the cornea and immediately after the lasilc3[lap was fashioned and the suction ring removed the flap was elevated then an intra operative central stromal bed pachmetry reading was recorded using the sterile Tomey AL- 2000 pachymetry probe. The actual flap thickness was calculated by subtracting the intra operative central stromal thickness from the preoperative central corneal thickness
Results: the mean actual flap thickness created by the Moria M2 130 head microkeratome for the first cut was 153.8 +/- 17 [range 120 micro m- 188pm] and for the second cut 148.4 +/- 15.82 [range 118- 185]. The mean difference in flap thickness between the3rst and second cur was 4.4 micro m 1.7 m with the tendency of the second flap to be slightly - thinner than the first. This difference was found to be statistically insignificant [P>0.05, paired t test]. The mean difference between the actual and expected flap thickness was 9.9 micro m +/- 1.7 and this was found to be statistically significant [P >0.001]
Conclusion: the difference between the actual and expected flap thickness using the Moria M2 microkeratome was statistically significant and care should be taken when making assumptions about flap thickness based upon the manufacturers labeling to calculate the residual bed thickness, having in mind that the flap may be thinner in some cases and thicker in others. The latter must be thought of well to avoid violating the rule of leaving at least 250 micro m of stromal bed after laser ablation, which may lead to postoperative ectasia , keratoconus and even intraoperative stromal penetration. It is recommended to do an intraoperative pachymetry in all LASIK cases if possible