Ординатура / Офтальмология / Английские материалы / LASIK and Beyond LASIK Wavefront Analysis and Customized Ablation_Boyd_2001
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Chapter 22
Figure 22-3: The day 1 postoperative topography of the left eye with very unusual appearance of steepening nasally and flattening temporally. This is due to a free cap created the day before with LASIK, having been placed incorrectley on the eye due to poor reference marks. The flap appeared hazy and the best corrected visual acuity (BCVA) was 6/7.5 with +3.00/-6.00 axis 160.
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Figure 22-4: 3 weeks later the flap was removed and rotated through 180 degrees. The corneal topography looks very similar to the previous one and the refraction is also very similar, namely +4.00 /-6.00 155. Best corrected vision now 6/12.
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FLAP COMPLICATIONS
Figure 22-5: 3 weeks later the flap was again completely removed and the corneal bed was debrided of any epithelium. The flap was replaced and repositioned again to give the most appropriate fit. This topography shows the day 1 appearance after this procedure. The unaided visual acuity was now 6/15and with a correction of +1.00/-1.25 axis 110 the visual acuity was 6/9+. One week later the refraction was +1.75/-1.25 axis 115 and the visual acuity 6/7.5+2. Four months later the refraction is +0.50/-0.75 axis 5 and the vision is 6/5. Unaided visual acuity is 6/9-. The refraction has remained stable at this level for the past 2 years. This case demonstrates the importance of aligning the flap correctly postoperatively and the importance of reference marks especially in the case of a free flap.
In almost all instances, the laser treatment can still be applied. The thin flap often results in sub-epithelial corneal scarring. If the flap is less than 100 microns thick, do not proceed. Replace the flap and wait for 6 to 12 weeks before recutting. If one was to proceed, you would notice severe sub-epithe- lial haze especially if the correction to be lasered is over 3 diopter spherical equivalent.
Perforated Flap
This rare complication arises when suction is inadequate and when the corneal curvature is very flat. A doughnut shaped flap is fashioned with the central area remaining uncut. Obviously it is impossible to laser in this situation and the flap must simply be replaced and there should be a waiting period of at least 3 months before this is attempted again. Scarring can occur along the margin of the perforation and this can be reduced with the use of cortisone drops.
(Note from Editor-in-Chief: The steroidal drops must be tapered approximately in a period of
3 to 4 months to reduce the amount of fibrous tissue observed in the borders of the perforated corneal flap.)
Incomplete Flaps
(Note from Editor-in-Chief: It is important to maintain the microkeratome path free of obstacles at the time of the keratectomy to avoid this type of complication. Sometimes this occurs from electrical failure, incorrect use of the automated microkeratome or gear obstruction by eyelids, lashes, speculum or drape.)
Half-Cut
The flap is replaced and allowed 3 months to heal at which time, the procedure is approached as any new procedure would be with new refraction, etc.
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Chapter 22
Cut
This flap can sometimes still facilitate treatment especially where a cylinder is involved. If the area to be treated can fit onto the exposed area, laser treatment can continue. If the area to be treated cannot fit onto the exposed area, the flap is replaced into position and a 3 months waiting period is entered into again before recutting the flap. Never try to enlarge the flap by manual dissection.
Dislocated or Moved Flap
This occurs approximately 0.5% of the times. More than 90% will displace or move within the first hour after surgery and for this reason, patients should be examined 1 hour postoperatively before being dismissed to ensure that the flap has not moved. The displacement is usually very minimal and the management required is to immediately return to the operating room, lift the flap, stretch it out, make sure that any epithelial tissue is removed from the corneal bed and then the flap is replaced and managed further in the usual way. 1 hour later the eye is reexamined to ensure that the flap is in position. Flaps can also move if the eye is rubbed or the patient blinks forcefully after the first hour. This has only happened twice in more than 4500 patients so it is a very rare finding. It is usually observed on the first postoperative day or earlier if the patient complains about any unusual or unexpected symptom afterwards and calls the office before the first day postoperative visit. The treatment is the same as with the earlier dislocation. It should just be noted that epithelial ingrowth or coverage of the exposed corneal bed can be substantial overnight and that the corneal bed and undersurface of the flap must be scrupulously cleaned from epithelial cells so as to minimize the chances of epithelial ingrowth occurring. A small PTK may be done over the area of ingrowth to destroy microscopic nests of epithelial cells.
flap. The majority of these are removed when the flap is being replaced after doing the laser treatment, but sometimes tiny particles might still remain. In clinics where there is a 1 hour postoperative examination, these particles are detected very early, and if it is deemed necessary due to the nature, size or position of the particle, they can be removed immediately by returning to the theatre, lifting the flap and rinsing away the particle. Where patients are seen the next day for the first time postoperatively, only more serious particles would justify going back to the theatre to remove them. Centrally located particles or any particles that might cause visual disturbances or increase the risk of infection, should be removed.
“Sands of the Sahara”
This term is used for a condition of sterile nonspecific interlamellar keratitis. It reflects a situation of considerable confusion as to the etiology. It is non-infectious as in no cases thus far has any culture been positive. There are many possible causes including toxic effects, side-effects of medications, sterile inflammations and more non-specific causes. It is our feeling that it occurs most likely due to the use of non-steroidal anti-inflammatory drops intra and postoperatively. We have had little experience of this condition, but since abandoning the use of NSAID’s, have not yet seen another case. The treatment is the early detection of the condition and the liberal use of topical steroids used hourly initially and tapered over the next 2 to 3 weeks. It seems appropriate to recommend that if you have not yet encountered this condition, don’t change anything in your intra and postoperative regimen. If you do encounter the phenomenon on a regular bases, change one variable at a time to try and establish the cause in your specific setting. This condition may have a variable number of criteria to meet before manifesting. The final outcome is usually good and very few cases proceed to corneal melt or loss of the flap.
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Foreign Bodies
Often foreign bodies like particles of eye make up, debris from linen sterile drapes, oil globules from the lid margin, etc. can land up beneath the corneal
Keratitis
Keratitis (non-infective) can occur as a result of reactions to the chemicals used to clean the equip-
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ment, the antiseptics used to clean the area around the eye as well as the eye and it may result from the use of eyedrops to which the patient is sensitive. It often blurs the vision and causes discomfort. Cylinders are also often induced by asymmetrical or paracentral areas of keratitis. The typical appearance is that of punctate superficial keratitis. It responds to topical lubrication with natural tears (preservativefree preferably) and low dosage cortisone preparations and may sometimes take 6 weeks or even longer to clear up. The condition usually clears up within 2 to 3 weeks however.
Microstriae
These are very fine vertical, horizontal or obliquely orientated folds or lines within the corneal cap. If they involve the central visual axis and are detracting from the visual acuity, it is advisable to lift the flap and reposition it again. The earlier the folds are detected, the greater the probability that they are resolved by lifting and repositioning the flap. If the folds are only detected during the later visits at the 3 month period, no visual benefit will be detected by lifting the cap and relifting it. It is also interesting to note that some fine microstriae present on day 1 have resolved by the 2nd week. It appears that microstriae are less of a problem with the downup keratomes (e.g. Hansatome, Chiron) that create a horizontal hinge than with the conventional microkeratomes that create a nasal vertical hinge.
Infection
Not much can be said about infection except that it would be a very unwanted complication. This is a problem that is extremely rare. The most likely place for the infection to manifest itself would be under the corneal cap. In the event that such an infection did occur, the most appropriate management would include the lifting of the corneal flap, the rinsing the washing away of the infected material (after taking a pus swab for culture) and then replacing the flap. Antibiotic drops would have been used from directly after the procedure anyhow, and these will simply continue and possibly other antibiotics added according to the culture and sensitivity profile of the
FLAP COMPLICATIONS
pus swab. Infection would rarely cause a serious loss of vision.
(Note from the Editor-in-Chief: On the area affected by the infection, either the stromal bed or the corneal flap, a corneal ulcer may develop with important limitations to the final visual acuity.)
Dry Eye Syndrome
The comforting and lubricating effect of tears on the eyes is well known. Tears are produced by the tear glands and are removed by evaporation with the remainder of tears being directed through the nasolacrimal duct to the nose. Contact lens wearers as well as people that wear glasses permanently have a much reduced evaporation rate of the tear film. Consequently, less tears are produced to maintain the appropriate wetting level of the eyes. Once the glasses or contact lenses are not being worn due to successful refractive surgery, the evaporation element of tear removal increases again. This results in a relative shortfall of tear production for a while until such a time that the production rate increases and the tear system is in equilibrium again. This usually takes about 6 months and can be lengthened by the use of certain medications e.g. hormones, antihypertensives, anti-cholesterol, anti-acne and others.
The second consideration is that the shape of the cornea changes after surgery with flattening of the central area being the most common change. This could result in poorer applanation between the lids and the cornea than previously. The result of this would be a cornea that is wet less satisfactorily. The use of natural tears for 3 to 6 months usually alleviates the symptoms.
Epithelial Ingrowth
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This complication occurs at different rates for different surgeons. Some might almost never encounter it while other surgeons see it a number of times per year. It tends to occur in situations where the flap might have been displaced on day 1 and was then repositioned. If the corneal bed was not cleaned up properly, some epithelial tissue might now find itself beneath the edge of the flap. These cells can continue to proliferate and grow in under the flap
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Chapter 22
and eventually involve central vision. Most often however, the cells will grow for a short while and then suddenly start regressing. It is thought that growth factors and stimulants for epithelial growth are not found under the flap and that growth eventually ceases. In cases where the ingrowth continues, it makes sense to surgically remove the epithelial ingrowth by lifting the flap and cleaning both the bed and the undersurface of the flap properly and removing all epithelial cells. This condition also occurs more readily in patients where it was noted intraoperatively that the epithelium has poor adherence to the corneal basement membrane. Ingrowth occurs more easily now as the affinity of the epithelium for the basement membrane is reduced for whatever reason, and the epithelial front of growing cells simply follows the path of least resistance. This phenomenon occurs less in those microkeratomes that have a high angle of attack such as the Hansatome (Chiron).
THE HANSATOME (“DOWN-UP”) MICROKERATOME
The Hansatome microkeratome came on to the refractive surgery market at a time when many surgeons worldwide had already operated a great number of LASIK’s using other microkeratomes and having had to go through the learning curve procedure. Obviously while learning a new technique, more complications are experienced as compared to an experienced surgeon doing the same procedure. The Hansatome has however taken a load off the shoulders of experienced surgeons and even more so, of surgeons learning to do LASIK.
Main Advantages
1. The primary advantage of this microkeratome is the fact that the hinge is now horizontal and situated beneath the upper eye lid. With each and every blink action of the lids, the flap is smoothed out into position in the direct postoperative period.
2.The quality of the flap created by the Hansatome is the best flap that either of us have seen. The flap is of uniform thickness with a very precise margin all the way round. The alignment of the flap postoperatively is also easier than most thanks to the quality of the flap and the tendency to want to “spring” back into position. Thus far using the Hansatome, we have had no thin flaps and no partially cut flaps.
3.The suction or vacuum generated by the vacuum unit is also superior to any other unit that we have used. The suction is so good that thin flaps have simply not occurred to date. Approximately 25% of patients to however have subconjunctival hemorrhages postoperatively due to the suction ring, but we feel that this is a small price to pay for the
superior flap that the microkeratome produces time
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The suction ring is elevated and surrounding |
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tissue (lids, conjunctiva, lashes, etc.) tend to post less |
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The Hansatome has another built in safety fea- |
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ing the suction ring to applanate poorly or even come |
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off the eye, the microkeratome stops its forward pro- |
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gression and in this way ensures that no free pieces |
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of flap can be created. |
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1. The suction ring is bigger than most others and sometimes poses a problem with getting it to fit into the interpalpebral fissure and to applanate well onto the eye. We normally use the nasal speculum made by Rumex (14-041) and when we experience difficulty with the applanation of the suction ring, try a different speculum. Different speculums give different amounts of exposure to the eye on a varying basis – one must try different ones until a suitable one, giving adequate exposure, is found. Cases do arise where no speculum can be found to give adequate exposure and in these cases one can simply go ahead without the use of a speculum. The vacuum on the Hansatome is so good that once it has been
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applied and the pressure risen to the desired amount, it is safe to go ahead and make the pass with the microkeratome in the absence of a speculum.
2. The Hansatome is relatively expensive but to date none of the disposable microkeratomes can give the quality of corneal flap on the consistent and predictable basis that the Hansatome does.
As with any piece of equipment, it is very important to know the equipment well and to check it before use. We recommend you test the Hansatome motor before connecting it to the microkeratome and ensure that the resistance (read out from the display on the unit console) is below 50mA. (Although mA is a unit of electrical current, it is indirectly reflecting the resistance that the motor is experiencing. The higher the resistance, the higher the current necessary to drive the motor and vice versa)). Once the head piece is fitted, test it again. Now the resistance should be lower than 100 mA. Also, test the microkeratome by making a run with it and checking the resistance once again on the console as well as listening to the sound it makes and observing the way it progresses. Having made these checks preoperatively and having found the machine to be in good working order, it is extremely unlikely that the microkeratome is going to malfunction on the eye.
Cleaning of the Instrument
During use, only sterile distilled water is used with the microkeratome. Only once the flap has been created and the microkeratome removed, do we start using BSS again. It is thought that the corrosive qualities of the salt in the BSS add to wear and tare of the microkeratome.
Following each patient, the microkeratome is cleaned with Palmolive concentrated liquid diluted with sterile water. Each part is gently cleaned using a soft toothbrush and is then placed in a dish of sterile water, where again all the parts are gently brushed to ensure that the liquid Palmolive is removed prior to sterilization.
At the end of each session, prior to storage, the distal 2 to 3 mm of the motor is dipped in 99% alcohol and is electrically driven forward and in re-
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verse for 15 seconds. The tip is then wiped with a Merocel spear sponge.
The motor is stored with the drive tip down. This prevents liquids from migrating down into the motor and gear box and will keep the motor clean and running smoothly.
If the motor becomes jammed, the distal 2 to 3 mm of the motor tip is soaked in 99% alcohol for up to one hour and is then cleaned as above.
The microkeratome is cleaned by soaking it in alcohol and by washing the gears with Palmolive soap. This keeps them well lubricated and prevents excessive wear and tare on the gears and motor.
Blades are supposed to be for single use only but are often used for 2 eyes of the same patient. Once a blade has been used, it may still be fit to make another safe cut. By inspecting it under the microscope and having considered it fit for further use, it can be sterilized again by soaking it for a minimum of 10 hours in Cidex long life solution. In poorer countries where new blades are at a premium, recleaned and re-sterilized blades can be used once more if they are found to still be in good condition following microscopic examination.
PEARLS TO ASSIST WITH THE MAKING OF A GOOD FLAP
First apply the suction ring to the eye and applanate it well before the suction is applied. It helps to stretch out the bulbar conjunctiva posteriorly as the suction ring is applied to ensure a good applanation and final suction. Check the intraocular pressure with the tonometer before proceeding and we always enquire about the vision at this stage. In most cases, it has already darkened in front of the eyes and even blacked out completely. This confirms that the suction ring is adequately applied and ready for the microkeratome pass.
Some surgeons reckon that it is better to have visual feedback on exactly what the microkeratome is doing and to look at the flap being created. Our feeling is that if your faith in the microkeratome is very good and that your complication record suggests that you are experienced with creating flaps,
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Chapter 22
that there is absolutely no advantage in being able to see the flap being fashioned. The possibility exists that the procedure can be unduly interrupted by a surgeon watching the flap being created and thinking that there is a problem, terminating the pass of the microkeratome. This could occur in spite of everything going ahead well.
Arthur Cummings, MB., ChB Mmed (Ophth)
FCS(SA) FRCS(Edin)
Wellington Ophthalmic Laser Clinic
2a Wellington Road, Ballsbridge
Dublin 4, Ireland
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FOLDS AND STRIAE OF THE DISC POST LASIK
Chapter 23
FOLDS AND STRIAE OF THE DISC POST LASIK
Canrobert Oliveira, M.D., Etelvino Coelho,M.D.
Because it is a very recent technique, some LASIK complications are still unsolved.
We have seen recently on the last meeting of the American Academy, many presentations about “ Sands of Sahara Syndrome” which the etiology still unknown, could not show us a definite treatment.
We have the same impressions about the folds and striae . The revision of the literature about the subject showed us how uniformed the authors are, relating to the definitions gave to the folds, striae and it’s respective treatments.
In this chapter, we propose, after the defini-
tion of each entity and indications for the specific
Figure 23-1: Folds
treatment and a logical name.
Definition
Folds are the thick waves of the disc, caused by accidental slipping of the disc over the stromal bed, generally traumatic. It is a emergency situation with tears and pain, associated to a low visual acuity, when affecting a optical zone. This frequently occurs during the first hours, although, it could result on late trauma (we have a case after six months of a surgery) (Figure 23-1).
Anatomically, the folds are constituted by the three layers which, compose the disc: the epithelium,
Bowman membrane and the stroma. It is caused by Figure 23-2: The three layers of the folds the adherence of the stromal side of the disc itself on
the waves (Figure 23-2).
That is why, it can not be dissolute with a simple massage with the finger or with a steel spatula. Striaes are microscopic wrinklings which affect just the Bowman membrane, secondary to the misalignment of the disc with the stromal bed
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Chapter 23
Figure 23-3: Striaes
(“the tent effect” secondary to the brake of the relationship between the content and the continent – the disc and the corneal stroma, after the stromal ablation by the excimer laser). We have noticed a pattern of striae similar to a broken glass (see figure 23-9) which does not keep any relation with the myopia grade and which appears immediately after a surgery, in which the cause is still obscure. The striae are not an emergency situation, and are always easy to identify in the immediate post op of Lasik. It never occurs later on. Although a decrease on the visual acuity is not so emphasized as in the folds, enabling the patients to read 20/25 or 20/30, the main complaint refers to a loss on the a vision quality (Figure 23-3).
Folds Treatment
The folds should be treated even if it is not affecting the central area of the cornea. The treatment is completely successful, because more than fixing the biomicroscopic esthetics on the slit lamp, it recovers the visual acuity.
Surgical technique: We look forward to identify on the slit lamp, the region in the which the border of the disc is far off the stromal bed border. This space has the aspect of a growing moon, that’s why we denominate it as “the sign of the growing moon ”. Depending on time of the accident occurred, the epitelization has already completely (Figure 23-4).
Figure 23-4: The sign of the growing moon
The first step to the surgery will be the remotion of the epithelium on the area of the “growing moon”, after a great irrigation, to avoid that the loosen epithelial cells remain in the surround surgical area of the stromal bed. The second step will be the detachment of the disc, through the introduction of a cannula over the epitelized disc, and after, with an BSS injection, we promote it’s hydrodissection. We prefer this method to the detachment with steel spatula, because it is less traumatic, though the corneal stroma is composed by 78% of water. During the third step, after reverting the disc, we rehydrate abundantly it’s stroma, till the edema of the lamellas promote a liberation of the stroma faces adhered. We know that the folds are undone when, we relocate the disc with a soft brush ( Martha Brush, for example), noticing the space in shape of a “growing moon” disappearing, signalizing that the board of the disc found the margin of the stromal bed (Figures 23-5, 23-6, 23-7).
If the folds are old, even though the border of the disc has found the margin stromal bed, we will still observe on the surgical microscope epithelial signs on the original place of the folds, which disappear in a few days.
Finally, we put a disposable contact lens and prescribe the habitual drops of the LASIK post op routine prescriptions. We have a successful case folds unmade, after six months of a LASIK surgery.
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278 SECTION IV
FOLDS AND STRIAE OF THE DISC POST LASIK
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Figures 23-5, 23-6 and 23-7: Rehidratation of the stromae
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