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Axial Length

Axial Length

The mean axial length for the IOLMaster was 23.35 mm with a standard deviation (SD) of 0.90. The mean axial length with the LENSTAR was 23.06 mm, SD 1.36. There were 115 eyes that have measurements of the axial length on both the IOLMaster and the LENSTAR. The graph below shows the difference in axial length between the IOLMaster and the LENSTAR. As can be noted, the eyes where the LENSTAR measured the eyes longer than IOLMaster and are in the negative range, yet the eyes that were measured shorter by the LENSTAR and are in the positive range. There are 77/115 (67.0%) of the eye that fall within 0.1 mm, 2 out of 115 (1.7%) measure longer and 36 out of 115 (31.3%) that measure shorter.

Comparison of Axial Length by IOLMaster vs. LENSTAR

The following graph demonstrates the data acquisition through the time of the study. The large differences in measurement were concerning and therefore this chart helped us realize that large errors were not due to a learning curve in the use of the instruments.  The right and the left eye were marked separately on the graph for greater clarity.

Axial Length acquistion through time with LENSTAR

Axial length of each individual patient's two eyes was compared. With the IOLMaster there were 56 out of 62 (90.3%) patients that had a valid measurement of both eyes. When applying a threshold of 0.3mm, 50 out of 56 (89.3%) of the eyes were within 0.3mm in size.  When applying the 1.0 mm or more difference in axial length difference, there were 2 out of 56 (3.4%) patients, that met the criteria.

With the LENSTAR there were 56 out of 62 (90.3%) of patients that had a valid measurement of both eyes. When applying the same threshold of 0.3mm, 31 out of 56 (55.4%) of the eyes were within 0.3mm.  When applying the 1.0 mm or more difference in axial length difference, there were 12 out of 56 patients (21.4%), that met the criteria.

Comparison of the right eye vs. left eye by the two instruments, IOLMaster and the LENSTAR

Discussion of Axial Length Results:

The axial length is the most important measurement and the largest source of IOL calculation errors.  As a rule of thumb a 1 mm error in axial length leads to an approximately 3 diopter error in the spectacle correction post operatively.  When comparing the right and the left eye axial length with both instruments, it is very concerning that the LENSTAR has only 55.4% of the patient’s eyes measured within 0.3 mm of each other, yet with the IOLMaster, it is 89.3%. 

IOLMaster was used as the main source of calculation for all the patients in this study.  The results of all the patients were consistent with expectation.  When looking at the 12 out of 56 patients (21.4%) with 1 mm or more difference in axial length between the eyes as measured by LENSTAR, or the 2 out of 56 (3.4%) by the IOLMaster, it is clear that the measurement required greater evaluation for clinical consideration.

Neither the numbers nor the gates in the IOLMaster or the LENSTAR were manipulated for the purposes of this study.  What the instrument produced, was what is used to compare.  Most busy surgeons do not review every single measurement with scrutiny with software adjustment of gates, yet rely on the results from the instrument and the ancillary staff. 

In the age of refractive cataract surgery with the elevated patient expectations and demands for LASIK like delivery, the precision of the instruments is essential and the axial length is a major factor in such delivery.


With only 55.4% (vs.89.3%) of patients having an axial length measurement of their eyes within 0.3 mm and over 20% (21.3% vs. 3.4%) of patients having greater than 1.0 mm difference in axial length measurement between the right and the left eye with the LENSTAR (vs. IOLMaster), how confident can one be with the axial length measurements by LENSTAR?


 

To continue with the study pages:

Axial Length (Current Page)

Keratometry (Next Page)

Anterior Chamber Depth

Lens Thickness

White-To-White

Efficiency of the Instruments (and back to main page)

 

 


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