Archive for September, 2009

Accommodation is a function of the eye which has long been overlooked in eye surgery because we just haven’t had the technology to do anything about it.  The term accommodation refers to the ability of the eye to change focus from things that are very far away (like when we are driving) to things that are very close up and small (like reading or threading a needle).  If you’ve used a camera before, you have probably been aware of hearing the auto focus feature or noticed the lens move as the camera adjusts to the distance of the main objects in your picture.  If it didn’t do so, the picture would appear blurred.  Your eye has the same auto focus feature which allows us to keep the main objects in sharp focus regardless of their distance.
However, as we age, the lens in our eye begins to harden and loses this auto focus capability.  Eventually, everybody begins to wear reading glasses or bifocals because of this aging effect called presbyopia.  Over the years, people have tried to figure out how to eliminate presbyopia surgically, but there is no perfect way to do so.  Only recently have new developments in intraocular implants given us the ability to truly mimic accommodation as it occurs in the youthful eye.  Most notably, the crystalens intraocular implant has been used very successfully in cataract surgery in elderly people.  This surgery using the crystalens not only improves the patient’s distance vision by removing the cloudy lens (cataract) but it also gives improved near/reading vision.  The crystalens is a premium lens implant that has the ability to move in a certain way after it is placed inside the eye which is similar to the auto focus of a camera.  With careful preoperative measurement, calculation, and planning, this surgery can improve distance vision while reducing the need for reading glasses or bifocals.
When we do Lasik surgery, however, we do not have the ability to implant a new lens inside of the eye.  Lasik surgery is done on the cornea which is the outer surface or clear dome shaped structure at the front of your eye.  In this case, your normal lens remains intact and if you have reached the age where your lens has stiffened, it will remain so.  I often have patients that want some flexibility in terms of still being able to read after Lasik surgery and we do what we can to maximize their reading without significantly compromising their Lasik outcome for distance vision.  Many surgeons do a “monovision” correction on their Lasik patients.  Monovision is the practice of leaving the non-dominant eye nearsighted while fully correcting the dominant eye for distance.  The concept goes as far back as the monocle, the one-eyed lenses seen worn in the 19th and early 20th century especially in Germany.
Often, in my opinion, surgeons will overdo the monovision effect and leave the patient too nearsighted.  Although, it gives very good reading vision, the large difference between the two eyes often creates problems with depth perception or dizziness.  Also the compromise in distance vision becomes very noticeable to the patient and the brain is not adequately able to fuse or coordinate the different images from the two eyes.
I have had a much higher degree of success using a mini-monovision technique where I leave only a small amount of residual nearsightedness in the non-dominant eye.  With this technique, I target good intermediate distance vision rather than close reading/threading-a-needle vision.  The residual correction is probably only -1/2 to -1 diopters at most for these patients.  This allows much better distance vision and good intermediate vision and some close reading ability.  In general, in the modern world, most of our close work is done at the computer distance.  Mini-monovision accomplishes this goal and reduces confusion between the two eyes or loss of depth perception.  Ultimately, my goal is to maximize the patients’ distance vision while giving them the ability to work on a computer, see their cell phone or watch, and read a menu.  More extensive small print reading like sitting down to read the newspaper or a novel would probably require reading glasses.  For most people, this set-up eliminates the use of glasses for 90+% of their day.
Surgical options for correction of accommodation have come a long way in recent times and continue to develop. If you have questions about accommodating intraocular lenses for cataract surgery, or about options when considering Lasik surgery, discuss them with your surgeon (not just a technician) prior to proceeding.