An example of a what a patient sees when complaining of night vision symptoms
This picture shows how normal people see the same image. This is the target outcome for the treatment.
The problem for surgeons treating patients with night vision difficulties is how to evaluate the success of the treatment. Currently the subjective and contrast sensitivity change are proving to be the most useful clinical methods. We hope that objective measurements, especially the Wavefront, will provide a quantifiable understanding of the change in visual symptoms, however, interpreting the Zernike coefficients is now as straight forward as it seems The first problem is that most Zernike coefficients are vectors and so directly comparing the individual coefficients doesn’t tell you much about what you have achieved Spherical aberration (z4,0) appears to be at the root of night vision difficulties. This coefficient is symmetrical, so it can be compared. However, magnitude analysis confined to a particular pupil diameter might be misleading. The choice of analysis zone can change the aberrations dramatically as more spots are included for the Zernike fit. This is especially true for highly aberrated eyes.
This is a RAWS plot of the Z(4,0) coefficient sampled at 0.25-mm steps over the pupil diameter for pre & post CRS-Master Wavefront Guided repair In this example, looking at the change in spherical aberration in a 6-mm analysis zone indicates that the spherical aberration has been increased However, for a pupil size less than 5.5-mm there has been a reduction in spherical aberration. This demonstrates the misleading nature of looking at aberrations in a particular analysis zone
To quantify the improvement over the whole pupil, we calculated the area under the RAWS plot. In this example you can see that the spherical aberration area has been reduced after the repair treatment, whereas the analysis at a 6-mm zone had indicated that more spherical aberration had been induced.
The area under the RAWS plot could provide a single metric of success in changing the spherical aberration, and remove the uncertainty introduced by the arbitrary choice of analysis zone for magnitude analysis We set out to determine how useful this parameter is
The study that we performed was to look at the success in correcting night vision disturbances for repair eyes and then compare these results to a control group of routine LASIK patients. We know that LASIK and PRK induce large amounts of aberrations, especially with the older lasers, however, the percentage of patients complaining of severe night vision difficulties is low. With the latest technology, the percentage of patients complaining of even mild night vision difficulties is very low. This is due to aspheirc profiles reducing the induction of aberrations, however, there is still significant induction of aberrations. This tells us that the wavefront does not have to be “flattened”. The control group in this study is designed to provide a target amount of aberrations that needs to be achieved when treating the repair eyes.
The repair eye population only included eyes that were suffering from night vision problems where the reduction of spherical aberration was the primary goal.
This bar graph shows the average preoperative level of spherical aberrations for normal eyes before (blue) and after treatment (purple) and compares these to the average level that is seen in my practice amongst patients that present wishing to have their night vision improved. As would be expected, the repair eyes had significantly more spherical aberration than the post LASIK controls
After MEL80 CRS-Master Wavefront Guided retreatment, we found a statistically significant improvement in contrast sensitivity at all levels.
This chart shows the percentage of eyes that were within normal range before and after repair by wavefront guided treatment.
Subjectively, patients were highly satisfied with 76% of the eyes achieving at least an 8 out of 10 improvement and 88% achieving 6 out of 10 improvement.
Here is an example of one patient needing repair
This screen capture of the WASCA shows the pre operative wavefront with a large amount of induced spherical aberration – the z(4,0) coefficient
This screen capture of the WASCA shows the greatly reduced amount of spherical aberration 6 months after the wavefront correction The pre and post pictures are on a normalised scale so that you can see the overall improvement in flattening the wavefront
This is a RAWS plot for the same patient showing the improvement in spherical aberration of the whole pupil
Now look at the matched control for this example to evaluate the improvement with respect to normal patients Firstly, we see that spherical aberration is induced for the control group as expceted (light cf. dark blue lines) Secondly, we see that the repair eye has significantly more spherical aberration than the post LASIK control group, again as expected (dark blue cf. orange lines) Thirdly, we see an improvement in spherical aberration (orange cf. red lines) which turns out to be better even than the pre LASIK control group (red cf. light blue lines) This improvement is supported by an improvement in contrast and 8 out of 10 subjective improvement
Here is another example Again, we see that spherical aberration is induced for the control group as expceted (light cf. dark blue lines) In this example, we see that the repair eye actually has less spherical aberration than the post LASIK control group (dark blue cf. orange lines). This is an example of the range of tolerance to aberrations amongst patients. We see the improvement in spherical aberration (orange cf. red lines) This improvement is supported by an improvement in contrast and 6 out of 10 subjective improvement
This is the RAWS plot for the average spherical aberration for each group This shows the induction of spherical aberration for the control group It shows how much more spherical aberration was induced for the repair eye group And it shows the reduction in spherical aberration achieved
Looking at spherical aberration at a 6-mm zone we found significant differences between pre and post LASIK, post LASIK and repair cases, pre and post repair On average repair cases had 42% more than the post LASIK controls This was reduced to 17% after Wavefront Guided repair This agrees with the average improvement in contrast sensitivity and overall subjective improvement
Looking at the spherical aberration area, we found significant differences between pre and post LASIK, post LASIK and repair cases, pre and post repair On average repair cases had 104% more than the post LASIK controls (statistically significant) This was reduced to 49% after Wavefront Guided repair (statistically significant) The average after Wavefront Guided repair was not statistically significantly different to the average post-LASIK control group This agrees with the average improvement in contrast sensitivity and overall subjective improvement and suggests that the Wavefront repair treatments have reduced the higher order aberrations to a tolerable level
On average the spherical aberration had indeed been significantly reduced which supports the improvement in contrast sensitivity. However, there was no significant correlation between the change in contrast and change in spherical aberration for any frequency
Similarly, there was no correlation with subjective improvement
In conclusion, we are promising eagle vision but at the moment we are still little eagle chicks. Looking at the Z4,0 over the whole pupil is probably more useful than single diameter analysis. This could be easily provided by the Wavefront analyzer instruments. Current lasers still induce aberrations but the reports of night vision difficulties are rare. This provides a realistic goal for night vision repair and suggests that we don’t necessarily need to “flatten” the wavefront There are examples of patients complaining of NVDs with less spherical aberration than is normal for current lasers. This suggests that tolerance of aberrations varies from individual to individual. For this group of patients, NVDs remain a risk, so there is still work to be done in profile and laser design to reduce the induction of aberrations. This also poses the question of whether the susceptibility to NVDs can be evaluated.
Problem - evaluating success in repair eyes <ul><li>Clinical Methods </li></ul><ul><ul><li>Subjective reporting </li></ul></ul><ul><ul><li>Contrast sensitivity change </li></ul></ul><ul><li>Objective measures </li></ul><ul><ul><li>Topography </li></ul></ul><ul><ul><li>Wavefront - Zernike coefficients </li></ul></ul><ul><ul><ul><li>Most are vectors </li></ul></ul></ul><ul><ul><ul><li>Magnitude analysis confined to one pupil diameter </li></ul></ul></ul>20/20 20/20
Z4,0 Analysis confined to one diameter Plot of Average Z(4,0) Over Pupil Size
Z4,0 Analysis over the whole pupil Plot of example Z(4,0) Over Pupil Size
Aim <ul><li>To determine the value of analyzing the AREA under the RAWS plot as a single metric of success in night vision repair </li></ul>
Study Outline <ul><li>Perform NVD’s repair eye study </li></ul><ul><li>Match repair cases to post LASIK controls with no NVD’s </li></ul><ul><li>Determine differences in descriptive power between </li></ul><ul><ul><li>Single diameter Z4,0 change </li></ul></ul><ul><ul><li>Area under RAWS plot change </li></ul></ul><ul><li>Correlations with Contrast? </li></ul>
Repair Eye Population <ul><li>16 eyes from 9 patients </li></ul><ul><li>All complaining of night vision symptoms after routine LASIK (14 eyes) or PRK (2 eyes) </li></ul><ul><li>Diagnosis confirmed via Wavefront exams showing increased aberrations </li></ul><ul><li>Adequate residual stromal thickness confirmed by Artemis VHF Ultrasound </li></ul>
Matched Study <ul><li>How much positive spherical aberration can a patient tolerate without suffering from Night Vision Symptoms? </li></ul><ul><ul><li>This seems to vary from individual to individual! </li></ul></ul><ul><li>To develop a control group to the population of repair eyes, a matched set was found using the following criteria </li></ul><ul><ul><li>Four to one match: “happy” postop eyes for each repair eye </li></ul></ul><ul><ul><ul><li>Matched by pre-operative refraction </li></ul></ul></ul><ul><ul><ul><li>Treated using the Aberration Smart Ablation profile on the MEL80 CRS-Master </li></ul></ul></ul><ul><ul><ul><li>No night vision problems </li></ul></ul></ul>
Conclusions <ul><li>RAWS area is an interesting parameter, probably more useful than single diameter Z4,0 analysis </li></ul><ul><li>No correlation with CS changes </li></ul><ul><li>No correlation with subjective </li></ul><ul><li>Needs further thinking </li></ul>