Prospective Corneal Topographic Analysis in Surgery for Postkeratoplasty Astigmatism George T. Frangieh, MD; Sergio Kwitko, MD; Peter J. McDonnell, MD \s=b\
Computer-assisted
photokeratos-
used to evaluate the topographic characteristics of corneas preoperatively and postoperatively in seven patients who underwent surgery for correction of postkeratoplasty astigmatism. The steep hemimeridians were typically separated by an angle other than 180\s=deg\ (mean, 162.5\s=deg\)and the flat hemimeridians were often not orthogonal to the steep hemimeridians. Asymmetry of power (1.5 or more diopters) between these two major hemimeridians was also observed in three patients. Relaxing incisions were placed in the two steep hemimeridians and compression sutures were placed in the flat hemimeridians. The mean percent of reduction of astigmatism (vector\x=req-\ corrected) was 81.1%. The amount of keratometric astigmatism, and the degree of asymmetry of the hemimeridians were not correlated with the percent of reduction of astigmatism after placement of the relaxing and compression sutures.
copy
was
Computer-assisted topographic analysis may prove useful in planning transverse keratotomies centered on the steep hemimeridians and in placement of compression sutures in flat hemimeridians.
(Aren Ophthalmol. 1991;109:506-510)
espite the high likelihood of obtain¬ ing clear corneal grafts and im¬ proved techniques to reduce postoper¬ ative astigmatism, corneal toricity and irregular astigmatism after pénétrât-
ing keratoplasty remain major limita¬ tions of postoperative visual outcome in these patients. The incidence of high astigmatism (>5 diopters [D]) follow¬ ing keratoplasty varies between 10%1,2 and 27%,s and is higher following pene¬ trating keratoplasty for keratoconus.3 Preexisting corneal thinning and vascularization, and especially preexisting astigmatism such as accompanies kera¬ toconus, have been associated with
a
high frequency of astigmatism follow¬ ing penetrating keratoplasty.3 Asym¬
metric suture tension with the Flieringa ring, the type of trephine, the configuration and centration of corneal trephine opening, the alignment of do¬ nor to recipient bed, graft-vs-host dis¬ parity, and the tension, length, depth, and configuration of corneal sutures have also been implicated as causative factors.1'41 Despite the advent of auto¬ mated trephines and new suturing
techniques, astigmatism following pen¬ etrating keratoplasty is still common. Attempts to correct postkera¬ toplasty astigmatism with surgery planned according to keratometry readings might not succeed, in part, because the keratometer gives little insight into the complex and irregular corneal topography that results from penetrating keratoplasty. New meth¬ ods for evaluating corneal curvature have improved our understanding of corneal topography, especially that of very irregular corneas such as in kera¬ or after refractive surgery and after penetrating keratoplasty.'1* In this prospective study, we describe the correction of astigmatism
toconus
Accepted for publication November 21, 1990. From the Doheny Eye Institute and the Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles. Reprint requests to Doheny Eye Institute, 1355 San Pablo St, Los Angeles, CA 90033 (Dr McDonnell).
following penetrating keratoplasty with relaxing incisions and compres¬ sion sutures using computer-assisted
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corneal topography
surgical procedure.
analysis to plan the
PATIENTS AND METHODS A prospective study of surgery for post¬ keratoplasty astigmatism based on corneal topographic analysis was conducted on sev¬ en eyes of seven consecutive patients at the Cornea Service of The Doheny Eye Insti¬ tute, Los Angeles, Calif. To be enrolled in the study, patients were required to have a centered graft, stable postkeratoplasty astigmatism of at least 8 D measured by the keratometer, and a minimum elapsed time of 3 months following removal of all corneal sutures. The mean postoperative follow-up period after the astigmatic procedure was 15.6 months (range, 9 to 19 months). The patients included six men and one woman, ranging in age from 19 to 76 years (mean age, 49.1 years). All patients were contact
lens intolerant. Best corrected Snellen visu¬ al acuity, cycloplegic manifest refraction, keratometry (Bausch & Lomb keratometer, Rochester, NY), and computer-assisted topographic corneal analysis using the Cor¬ neal Modeling System (CMS; Computed Anatomy Ine, New York, NY") were ob¬ tained before and after surgery for each eye. For the CMS measurements, the patients were instructed to fixate on the central fixation light; a total of three videokeratographs were taken for each eye by the same experienced examiner at the time of each visit. These examinations were repeated until three ring image photographs had been captured that were free of dry spots, had minimal shadow from the lashes, and appeared to be precisely focused. The three images were then digitized by the computer and the process observed by the examiner. Of the three images, the highest-quality photograph with minimal shadows from the lashes and without apparent errors when the rings were digitized was then selected for analysis. Two color-coded scales were used to display the topographic information:
Table
1.—Preoperative Data Contact Lens Tolerance
Between Steep Hemimeridians
Power Difference Between Steep Hemimeridians, D
Intolerant
160°
0.6
Intolerant
165°
9.0
Intolerant Intolerant
175°
1.5
150°
0.7
Angle Patient No./
Sex/Age,
y
Visual
Refraction, D Not available
2/M/42 3/M/38
Acuity
Keratometry, D
20/200
38.00/56.00 X 15° 43.00/51.25 X180°
8.25
20/100
41.00/52.00X130°
11.00
20/200
44.00/53.50X50° 41.50/50.00X90°
-12.75 +6.00 X180°
-4,00 +10.00 X130°
4/M/19
Not available
5/F/55 6/M/76
+ 12.00 +14.00 X94°
7/M/64
+6.50 +10.50 X165°
-8.00 +8.00 X90°
Keratometric Cylinder, D
20/100 20/30
40.62/53.00 X84°
12.38
42.75/51.37X160°
8.62
Table
Intolerant 0.4
2.—Postoperative Data Angle
Visual Acuity With Patient No.
Refraction,
D
0.00 +2.00 X95°
With
Spec- Contact
facies
Lenses
Keratometry,
D
46.50/48.50X100° 49.00/49.25X100° 45.25/48.75 X35°
20/30
Kera-
Keratometric
tometric, Cylinder,
Cylinder Reduction,
D
D
2.00
16.00
% Reduction of
Between
Post¬
Steep
operative Period,
Hemi¬ Optic Astigmatism meridians Correction 175° 89 Spectacles
8.00
20/30
+ 2.25+0.75X176°
20/50
-9.50 +6.00 X90°
20/100
20/40
42.50/48.50X100° 45.37/48.50 X68°
2.63
9.70
79
Spectacles
20/30
20/30
44.50/48.50X180°
4.00
4.62
53
Contact lens
20/30
7.50
129
47.50/48.25 X175°
-6.50 +4.25 X48° -3.25 +3.75 X5°
3.50
110°
the absolute scale, ranging from 9.0 to 101.5 D, with 1.5-D increments between 35.5 and 50.5 D; and the normalized scale, distribut¬ ing the range in anterior corneal curvatures among 11 colors (steepest area, red; flattest area, purple), with a constant increment between colors as determined by dividing the range of curvatures for that cornea by 11. Using the interactive cursor, the central and peripheral corneal curvatures were evaluated. The angle between the steep hemimeridians was measured by delineat¬ ing the borders of both steep hemimeridians and measuring the vector line between these borders, using the normalized scale on the color-coded topographic map. The asymmetry between power of both steep hemimeridians was evaluated by comparing the corneal curvature of each steep hemimeridian measured at 1.5 mm from the corneal apex on the vector line described above. The absolute-scale color-coded video keratograph was used intraoperatively in plan¬ ning incision location and extent. Based on the individual variation in preoperative cor¬ neal irregularity and asymmetry, we per¬ formed transverse keratotomies and placed compression sutures centered on the steep and flat meridians, respectively. The inci¬ sions were therefore typically not located exactly 180° apart, and were often unequal in length; similarly, the compression su¬ tures were not exactly orthogonal to the relaxing incisions. All surgeries were performed under ster¬ ile conditions using topical anesthesia. Af¬ ter application of topical anesthesia, pa¬ tients were asked to fixate on a pinpoint
145°
fiber-optic light source within the operatingmicroscope that was coaxial with the sur¬ geon's view. Preoperatively, the location of limbal landmark such as a limbal vessel noted. Intraoperatively, the Méndez marker was oriented with the aid of the limbal landmark, and used to guide incision and suture placement in accordance with the computer-assisted keratographs that were taken to the operating room. To mini¬ mize the intraoperative variables, all trans¬ verse keratotomies were performed with a single diamond blade (model RK-5000 dia¬ mond micrometer knife, I-Tech Industries, Addison, 111) at a uniform depth of 0.5 mm (blade extension verified intraoperatively with a coin guage (model RK-350, I-Tech Industries); incisions were located 1 mm inside the graft-host interface and varied in length between 2 and 4 mm, based on the maximum arc length between the red bor¬ ders of the steep hemimeridians. For each clock hour of the steep hemimeridians, as indicated by the angular separation of the two margins of the steepest (red) zone at a distance of 1.5 mm from the center of the a
was
computer-assisted videokeratographs, a relaxing incision was made on the corresponding region of the cornea. A total of six compression sutures, 11-0 mersilene, were placed at the graft-host interface 2-rara
(three in each side) in the flat meridians, 1 mm apart; these were tightened until the end result of reversal of astigmatism in their direction was achieved, as determined
by intraoperative keratoscopy using the Placido intraoperative disk (Hi-Line Medi¬
cal, El Toro, Calif). The amount of keratoscopic cylinder reversal varied from 50% to 100% of the
140° 125°
preoperative keratometric cyl-
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19
Contact lens Contact lens
-12.00+0.25X95° -4.50 +3.00 X50°
20/30
mo
Spectacles
10
Contact lens
20
inder. Gaping of the relaxing incision wounds was achieved in all cases, as deter¬ mined by visual inspection at the end of each procedure. Following completion of the operation, the incisions were irrigated with balanced salt solution and the eyes were patched following instillation of a cycloplegic and an antibiotic drop. When postoperative keratometric astig¬ matism was higher than 3.00 D, sutures were removed on the basis of computerassisted keratographs, beginning no sooner than 6 weeks after surgery, and completed within 12 weeks after surgery. Correlations were made between the per¬ cent of reduction of astigmatism and preop¬ erative variables such as amount of kerato¬ metric astigmatism, asymmetry of power, and axis between the two steep hemimeri¬ dians.
RESULTS
Preoperative and postoperative data presented in Tables 1 and 2, re¬ spectively. None of the patients had an obvious wound abnormality (eg, wound uplift or faulty trephination) to account for the high degree of postker¬ atoplasty astigmatism. Five of the seven patients had im¬ proved postoperative best corrected are
acuity of one line or more with spectacles. Two patients maintained their preoperative visual acuity with spectacles but became contact lens tol¬ erant. All patients were contact lens visual
intolerant before surgery; after sur¬ gery, three patients were content to
Fig 1. —Patient 4. Computer-assisted videokeratograph of patient with 10 D of refractive cylinder and 11 D of keratometric astigmatism (left) demonstrates asymmetry of power of 9.0 D and an angle of 165° between the two steep hemimeridians (red). Relaxing incisions of 3.5 and 1.5 mm in length were made, centered on the 3:00 and 8:45 clock positions, respectively; two sets of three 11 -0 mersilene sutures were placed, centered on the 7:45 and 11:00 clock positions (center). Keratometric astigmatism decreased from 9.50 to 0.75 D; postoperative computer-assisted keratograph reveals decreased corneal cylinder (right).
Fig 2. —Patient 3. Computer-assisted videokeratograph showing postoperative symmetric astigmatism in power and axis (left). Symmetric relaxing incisions 2.5 mm in length were made between the 9:30 and 11:30 and the 3:30 to 5:30 clock positions.Three orthogonal compression sutures were placed in each of the flat hemimeridians between the 1:30 and 2:30, and between the 7:00 and 8:00 clock hours, respectively. After surgery (right), corneal topography showed less toricity; keratometric astigmatism decreased from 11.00 to 3.50 D.
Fig 3. —Patient 5. Preoperative (left) and postoperative (right) computer-assisted videokeratograph. Asymmetry of power of 1.5 D and an angle of 175° between the two steep hemimeridians (red) is present before surgery. Relaxing incisions 2.5 and 1.5 mm in length were made between the 5:30 and 8:00 and between the 11:30 and 12:30 clock positions, respectively. Three compression sutures were placed in each of the flat hemimeridians between the 8:30 and 10:00 and between the 2:30 and 4:30 clock hours. Keratometric astigmatism decreased from 8.50 to 2.50 D.
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Table 3.—Previous Studies of Relaxing Incisions for Astigmatism Following Penetrating No. of
Source, y Troutman and Swinger,2 1980 Krachmer and Fenzl,20 1980 Sugar and Kirk," 1983 Mandel et al,'6 1987 McCartney et al," 1987 Limberg et al,16 1989
Cases
21 10
Cohen et al," 1989 Maguire and Bourne,19 1989 Present
* AK indicates arcuate keratotomy within the and CMS, Corneal Modeling System.
continue with four patients
spectacle were
The
mean
Reduction,
AK
Keratometer
4.25
Keratometer
7.50
AK and CS RI and CS CS AK
or
RI
Keratometer
67.0
Intraoperative keratoscope Intraoperative keratoscope Photokeratoscope Photokeratoscope
68.0
7.95
48.0
5.10
CMS
81.1
D
Postoperative Period,
correction and
9-12
37.7
preoperative keratometric
12.3 D. After surgery, the mean keratometric cylinder was 2.7 D, with a mean (±SE) decrease in keratometric cylinder of 8.2 ±1.7 D. The mean percent reduction of kerato¬ metric astigmatism was 81.1% (range, 29% to 129%). Suture removal, per¬ formed between 6 and 12 weeks after surgery, included removal of all six sutures in two eyes, two sutures in one eye, one suture in one eye, and no sutures in the remaining three eyes. re¬
vealed asymmetry of both power and angle of separation between the two major hemimeridians. The preoper¬ ative angle between the steep hemi¬ meridians ranged between 145° and 175°, with a mean of 160°. The preoper¬ ative asymmetry of power between the two steep hemimeridians was less than 1.0 D in four patients, between 1.5 and 2.0 D in two patients, and 9.0 D in one
patient. Figures 1 and 2 are examples of asymmetric postkeratoplasty astigma¬ tism that was treated with asymmetric relaxing incisions and compression su¬ percentage reduction of
keratometric astigmatism in these two cases was 92% and 29%, respectively, on the last postoperative follow-up vis¬ it. Although there was only a 29% reduction of astigmatism in the latter case, this patient was successfully fit¬ ted with a contact lens after surgery. Figure 3 exemplifies a symmetric postkeratoplasty astigmatism, in which orthogonal relaxing incisions were made 90° away from the compres¬ sion sutures. Eighteen months after surgery, and 15 months after removal of all sutures, the corneal (keratome¬ tric) astigmatism was reduced from 11.0 to 3.5 D, with a shift in axis of about 90°, indicating overcorrection.
The preoperative amount of kerato¬ metric astigmatism, and degree of asymmetry of power and axis between hemimeridians were not correlated with the percent of reduction of astig¬ matism after relaxing incisions and
compression sutures.
COMMENT
Transverse
keratotomies
in
the
graft bed,2 intraincisional relaxing in¬ cisions,9 graded relaxing incisions,1" trapezoidal relaxing keratotomy," ar¬ cuate relaxing incisions/ wedge re¬ sections,12 combined arcuate and semi-radial incisions,13 circumferential relaxing incisions,14 and compression sutures10 have all been used to cor¬ rect postkeratoplasty astigmatism, but poor predictability is a major limitation
procedures. The limited surgical success in correcting postker¬ atoplasty astigmatism (Table 3) might be, at least in part, a result of false preoperative assumptions, lack of un¬ derstanding of intraoperative vari¬ ables, and arbitrary postoperative of all of these
management.
Relaxing incisions alone, in or out of keratoplasty wound,2,9 compression sutures alone,lj and a combination of
the
these two methods14,1"17 have been tried
to correct postkeratoplasty astigma¬ tism. In most of these previous stud¬ ies, the steep corneal meridians were determined preoperatively by the ker¬ atometer, an instrument that mea¬ sures only the central 3.0 mm of corne¬ al curvature, and assumes the corneal
surface topography to approximate that of a spherocylindrical lens. The steep meridian is assumed to be com¬ posed of two hemimeridians radially symmetric about the corneal apex, separated by 180° from each other and by 90° from the flat meridians. Keratometry readings of the irregular post¬
keratoplasty cornea may provide lim¬ insight into the complex topo¬ graphic features, and surgery based on ited
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mo
8.2 NA 6-9
NA 8.20
keratoplasty wound; CS, compression sutures; RI, relaxing incisions central to the keratoplasty wound; NA,
was
tures. The
Astigmatism
8.40
contact lens tol¬
Computer-assisted keratographs
of
Keratometer
erant.
cylinder
Planned
Keratoplasty*
Keratometric Cylinder
AK
RI and CS
study
Surgery Using
Surgical Technique
% Reduction
not
available;
keratometry might therefore have lim¬ ited
success.
Computer-assisted video keratography may be more helpful than kera¬ tometry in planning astigmatic proce¬ dures after penetrating keratoplasty." Prospective analysis of photokeratoscopy for arcuate keratotomy to correct astigmatism following penetrating ker¬ atoplasty has shown a good correlation between change in ring ovality and keratometric astigmatism change."
The CMS allows even more detailed assessment of the corneal surface, both quantitatively and qualitatively, span¬ ning almost the entire corneal sur¬ face,6·' and has been shown to be as accurate and reproducible as the Bausch & Lomb keratometer when measuring calibrated steel balls" and reproducible to within ±0.25 D for 83% of measurements in normal eyes.1" It is possible that an experienced ob¬ server may be able to appreciate some of the topographic complexities of postkeratoplasty corneas by visual inspection alone, but Maguire and Bourne19 stated in a retrospective se¬ ries that "visual inspection of the kera¬ toscope photographs did not allow the complexity of the surface optics to be understood in sufficient detail to allow the surgeon to make a reasonable deci¬ sion on incision location." We used the CMS to assess the preoperative corneal topography of seven consecutive contact lens-intoler¬ ant patients with high degree of post¬
keratoplasty astigmatism (>5 D). Using the computer-assisted videokeratographs, we were able to mea¬ sure most of the graft curvature from the apex to the graft-host junction. With the keratographs, analysis of re¬ gional corneal surface power helped us design what we thought might be more accurate surgical plans. Asymmetry of power between the two steep meridi¬ ans was seen in three cases; also, the
steep meridians
were
separated by
an
at least 10° less than 180° in five seven cases, and the flat meridi¬ ans were orthogonal to the steep me¬ ridians in only one of seven cases. Maguire and Bourne19 also found asym¬ metry of power of the two steep hemi¬ meridians in six patients with postker¬
angle
of the
and an angle asymmetry between the major hemi¬ meridians in two of the six patients, although they did not vary surgery on the basis of these findings. With the patient fixing on the positioning light of the CMS, photokeratoscope, or ker¬
atoplasty astigmatism,
atometer, the center of the graft may not coincide with the center of the
keratograph or keratoscope photo¬ graph; the clock-hour positions on the keratographs will not necessarily, therefore, correspond to the clockhour positions on the graft, introduc¬ ing a potential error for the placement of incisions and sutures. We attempted to minimize this error by having pa¬ tients fixate on a coaxial fiber-optic fixation target within the operating microscope during the surgery, so that the reference for the clock hours would be similar. Regardless of the pathogenesis, for greater central flattening, deeper, more central, and longer keratotomies are thought to increase the surgical effect. ™ In this study, the length of the transverse keratotomies varied from 2 to 4 mm, depending on the arc length of the steep hemimeridian, keeping the depth of the cut constant at 500 µ , and the location of the cut constant at 1 mm central to the graft-host inter-
face. The variable width of steepening of the two hemimeridians, as deter¬ mined by the CMS, may be a partial determinant of the outcome of astig¬ matic surgery. A very large study randomizing patients to classic sym¬ metrical surgery vs asymmetrical sur¬ gery based on specific preoperative topographic features would be re¬ quired to prove the value of this
approach.
We believe that
intraoperative as¬ astigmatism, by means of either a keratoscope or a keratometer, is important to monitor the reversal of preoperative astigma¬ tism, as emphasized in previous stud¬ ies.21015"17,2""22 In addition, it is our im¬ pression that the use of a mersilene suture is advantageous over nylon su¬ sessment of corneal
ture, because the former is less biode¬
to a more stable corneal curvature. Even with mersi¬ lene, however, we tended to have undercorrections in our series, with only one eye being overcorrected. That inci¬ sions alone, after removal of compres¬ sion sutures, can occasionally result in shifts in keratometric cylinder of 10 D or more attests to the apparent vari¬ ability in wound healing and, perhaps, to the stress to which the cornea is subjected at the site of the incisions. Our prospective study suggests that computer-assisted video keratographic analysis of postkeratoplasty astigma¬ tism prior to relaxing incisions and
gradable,2" leading
compression sutures may prove helpful planning more accurate surgery. We
in
were
able to reduce the
postkerato-
plasty astigmatism by 81.1%, a result that compares favorably with those of previously published series using re¬ laxing incisions (Table 3), except for the results reported by Troutman and Swinger.2 They reported a 75% reduc¬ tion of astigmatism in four patients using relaxing incisions based on pre¬ operative and intraoperative keratometry; however, their sample size was small and the follow-up period after the astigmatic procedure was only 4 months. In our small study, we were
unable to find any correlation between the amount of asymmetry of astigma¬ tism and response to surgery. Despite achieving a high percentage of astig¬ matic correction (81.1%), we could not prove the value of computer-assisted video keratography in planning sur¬ gery for postkeratoplasty astigmatism. To have an 80% likelihood of detecting a statistically significant (P
Computer-assisted
photokeratos-
used to evaluate the topographic characteristics of corneas preoperatively and postoperatively in seven patients who underwent surgery for correction of postkeratoplasty astigmatism. The steep hemimeridians were typically separated by an angle other than 180\s=deg\ (mean, 162.5\s=deg\)and the flat hemimeridians were often not orthogonal to the steep hemimeridians. Asymmetry of power (1.5 or more diopters) between these two major hemimeridians was also observed in three patients. Relaxing incisions were placed in the two steep hemimeridians and compression sutures were placed in the flat hemimeridians. The mean percent of reduction of astigmatism (vector\x=req-\ corrected) was 81.1%. The amount of keratometric astigmatism, and the degree of asymmetry of the hemimeridians were not correlated with the percent of reduction of astigmatism after placement of the relaxing and compression sutures.
copy
was
Computer-assisted topographic analysis may prove useful in planning transverse keratotomies centered on the steep hemimeridians and in placement of compression sutures in flat hemimeridians.
(Aren Ophthalmol. 1991;109:506-510)
espite the high likelihood of obtain¬ ing clear corneal grafts and im¬ proved techniques to reduce postoper¬ ative astigmatism, corneal toricity and irregular astigmatism after pénétrât-
ing keratoplasty remain major limita¬ tions of postoperative visual outcome in these patients. The incidence of high astigmatism (>5 diopters [D]) follow¬ ing keratoplasty varies between 10%1,2 and 27%,s and is higher following pene¬ trating keratoplasty for keratoconus.3 Preexisting corneal thinning and vascularization, and especially preexisting astigmatism such as accompanies kera¬ toconus, have been associated with
a
high frequency of astigmatism follow¬ ing penetrating keratoplasty.3 Asym¬
metric suture tension with the Flieringa ring, the type of trephine, the configuration and centration of corneal trephine opening, the alignment of do¬ nor to recipient bed, graft-vs-host dis¬ parity, and the tension, length, depth, and configuration of corneal sutures have also been implicated as causative factors.1'41 Despite the advent of auto¬ mated trephines and new suturing
techniques, astigmatism following pen¬ etrating keratoplasty is still common. Attempts to correct postkera¬ toplasty astigmatism with surgery planned according to keratometry readings might not succeed, in part, because the keratometer gives little insight into the complex and irregular corneal topography that results from penetrating keratoplasty. New meth¬ ods for evaluating corneal curvature have improved our understanding of corneal topography, especially that of very irregular corneas such as in kera¬ or after refractive surgery and after penetrating keratoplasty.'1* In this prospective study, we describe the correction of astigmatism
toconus
Accepted for publication November 21, 1990. From the Doheny Eye Institute and the Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles. Reprint requests to Doheny Eye Institute, 1355 San Pablo St, Los Angeles, CA 90033 (Dr McDonnell).
following penetrating keratoplasty with relaxing incisions and compres¬ sion sutures using computer-assisted
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 08/20/2016
corneal topography
surgical procedure.
analysis to plan the
PATIENTS AND METHODS A prospective study of surgery for post¬ keratoplasty astigmatism based on corneal topographic analysis was conducted on sev¬ en eyes of seven consecutive patients at the Cornea Service of The Doheny Eye Insti¬ tute, Los Angeles, Calif. To be enrolled in the study, patients were required to have a centered graft, stable postkeratoplasty astigmatism of at least 8 D measured by the keratometer, and a minimum elapsed time of 3 months following removal of all corneal sutures. The mean postoperative follow-up period after the astigmatic procedure was 15.6 months (range, 9 to 19 months). The patients included six men and one woman, ranging in age from 19 to 76 years (mean age, 49.1 years). All patients were contact
lens intolerant. Best corrected Snellen visu¬ al acuity, cycloplegic manifest refraction, keratometry (Bausch & Lomb keratometer, Rochester, NY), and computer-assisted topographic corneal analysis using the Cor¬ neal Modeling System (CMS; Computed Anatomy Ine, New York, NY") were ob¬ tained before and after surgery for each eye. For the CMS measurements, the patients were instructed to fixate on the central fixation light; a total of three videokeratographs were taken for each eye by the same experienced examiner at the time of each visit. These examinations were repeated until three ring image photographs had been captured that were free of dry spots, had minimal shadow from the lashes, and appeared to be precisely focused. The three images were then digitized by the computer and the process observed by the examiner. Of the three images, the highest-quality photograph with minimal shadows from the lashes and without apparent errors when the rings were digitized was then selected for analysis. Two color-coded scales were used to display the topographic information:
Table
1.—Preoperative Data Contact Lens Tolerance
Between Steep Hemimeridians
Power Difference Between Steep Hemimeridians, D
Intolerant
160°
0.6
Intolerant
165°
9.0
Intolerant Intolerant
175°
1.5
150°
0.7
Angle Patient No./
Sex/Age,
y
Visual
Refraction, D Not available
2/M/42 3/M/38
Acuity
Keratometry, D
20/200
38.00/56.00 X 15° 43.00/51.25 X180°
8.25
20/100
41.00/52.00X130°
11.00
20/200
44.00/53.50X50° 41.50/50.00X90°
-12.75 +6.00 X180°
-4,00 +10.00 X130°
4/M/19
Not available
5/F/55 6/M/76
+ 12.00 +14.00 X94°
7/M/64
+6.50 +10.50 X165°
-8.00 +8.00 X90°
Keratometric Cylinder, D
20/100 20/30
40.62/53.00 X84°
12.38
42.75/51.37X160°
8.62
Table
Intolerant 0.4
2.—Postoperative Data Angle
Visual Acuity With Patient No.
Refraction,
D
0.00 +2.00 X95°
With
Spec- Contact
facies
Lenses
Keratometry,
D
46.50/48.50X100° 49.00/49.25X100° 45.25/48.75 X35°
20/30
Kera-
Keratometric
tometric, Cylinder,
Cylinder Reduction,
D
D
2.00
16.00
% Reduction of
Between
Post¬
Steep
operative Period,
Hemi¬ Optic Astigmatism meridians Correction 175° 89 Spectacles
8.00
20/30
+ 2.25+0.75X176°
20/50
-9.50 +6.00 X90°
20/100
20/40
42.50/48.50X100° 45.37/48.50 X68°
2.63
9.70
79
Spectacles
20/30
20/30
44.50/48.50X180°
4.00
4.62
53
Contact lens
20/30
7.50
129
47.50/48.25 X175°
-6.50 +4.25 X48° -3.25 +3.75 X5°
3.50
110°
the absolute scale, ranging from 9.0 to 101.5 D, with 1.5-D increments between 35.5 and 50.5 D; and the normalized scale, distribut¬ ing the range in anterior corneal curvatures among 11 colors (steepest area, red; flattest area, purple), with a constant increment between colors as determined by dividing the range of curvatures for that cornea by 11. Using the interactive cursor, the central and peripheral corneal curvatures were evaluated. The angle between the steep hemimeridians was measured by delineat¬ ing the borders of both steep hemimeridians and measuring the vector line between these borders, using the normalized scale on the color-coded topographic map. The asymmetry between power of both steep hemimeridians was evaluated by comparing the corneal curvature of each steep hemimeridian measured at 1.5 mm from the corneal apex on the vector line described above. The absolute-scale color-coded video keratograph was used intraoperatively in plan¬ ning incision location and extent. Based on the individual variation in preoperative cor¬ neal irregularity and asymmetry, we per¬ formed transverse keratotomies and placed compression sutures centered on the steep and flat meridians, respectively. The inci¬ sions were therefore typically not located exactly 180° apart, and were often unequal in length; similarly, the compression su¬ tures were not exactly orthogonal to the relaxing incisions. All surgeries were performed under ster¬ ile conditions using topical anesthesia. Af¬ ter application of topical anesthesia, pa¬ tients were asked to fixate on a pinpoint
145°
fiber-optic light source within the operatingmicroscope that was coaxial with the sur¬ geon's view. Preoperatively, the location of limbal landmark such as a limbal vessel noted. Intraoperatively, the Méndez marker was oriented with the aid of the limbal landmark, and used to guide incision and suture placement in accordance with the computer-assisted keratographs that were taken to the operating room. To mini¬ mize the intraoperative variables, all trans¬ verse keratotomies were performed with a single diamond blade (model RK-5000 dia¬ mond micrometer knife, I-Tech Industries, Addison, 111) at a uniform depth of 0.5 mm (blade extension verified intraoperatively with a coin guage (model RK-350, I-Tech Industries); incisions were located 1 mm inside the graft-host interface and varied in length between 2 and 4 mm, based on the maximum arc length between the red bor¬ ders of the steep hemimeridians. For each clock hour of the steep hemimeridians, as indicated by the angular separation of the two margins of the steepest (red) zone at a distance of 1.5 mm from the center of the a
was
computer-assisted videokeratographs, a relaxing incision was made on the corresponding region of the cornea. A total of six compression sutures, 11-0 mersilene, were placed at the graft-host interface 2-rara
(three in each side) in the flat meridians, 1 mm apart; these were tightened until the end result of reversal of astigmatism in their direction was achieved, as determined
by intraoperative keratoscopy using the Placido intraoperative disk (Hi-Line Medi¬
cal, El Toro, Calif). The amount of keratoscopic cylinder reversal varied from 50% to 100% of the
140° 125°
preoperative keratometric cyl-
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19
Contact lens Contact lens
-12.00+0.25X95° -4.50 +3.00 X50°
20/30
mo
Spectacles
10
Contact lens
20
inder. Gaping of the relaxing incision wounds was achieved in all cases, as deter¬ mined by visual inspection at the end of each procedure. Following completion of the operation, the incisions were irrigated with balanced salt solution and the eyes were patched following instillation of a cycloplegic and an antibiotic drop. When postoperative keratometric astig¬ matism was higher than 3.00 D, sutures were removed on the basis of computerassisted keratographs, beginning no sooner than 6 weeks after surgery, and completed within 12 weeks after surgery. Correlations were made between the per¬ cent of reduction of astigmatism and preop¬ erative variables such as amount of kerato¬ metric astigmatism, asymmetry of power, and axis between the two steep hemimeri¬ dians.
RESULTS
Preoperative and postoperative data presented in Tables 1 and 2, re¬ spectively. None of the patients had an obvious wound abnormality (eg, wound uplift or faulty trephination) to account for the high degree of postker¬ atoplasty astigmatism. Five of the seven patients had im¬ proved postoperative best corrected are
acuity of one line or more with spectacles. Two patients maintained their preoperative visual acuity with spectacles but became contact lens tol¬ erant. All patients were contact lens visual
intolerant before surgery; after sur¬ gery, three patients were content to
Fig 1. —Patient 4. Computer-assisted videokeratograph of patient with 10 D of refractive cylinder and 11 D of keratometric astigmatism (left) demonstrates asymmetry of power of 9.0 D and an angle of 165° between the two steep hemimeridians (red). Relaxing incisions of 3.5 and 1.5 mm in length were made, centered on the 3:00 and 8:45 clock positions, respectively; two sets of three 11 -0 mersilene sutures were placed, centered on the 7:45 and 11:00 clock positions (center). Keratometric astigmatism decreased from 9.50 to 0.75 D; postoperative computer-assisted keratograph reveals decreased corneal cylinder (right).
Fig 2. —Patient 3. Computer-assisted videokeratograph showing postoperative symmetric astigmatism in power and axis (left). Symmetric relaxing incisions 2.5 mm in length were made between the 9:30 and 11:30 and the 3:30 to 5:30 clock positions.Three orthogonal compression sutures were placed in each of the flat hemimeridians between the 1:30 and 2:30, and between the 7:00 and 8:00 clock hours, respectively. After surgery (right), corneal topography showed less toricity; keratometric astigmatism decreased from 11.00 to 3.50 D.
Fig 3. —Patient 5. Preoperative (left) and postoperative (right) computer-assisted videokeratograph. Asymmetry of power of 1.5 D and an angle of 175° between the two steep hemimeridians (red) is present before surgery. Relaxing incisions 2.5 and 1.5 mm in length were made between the 5:30 and 8:00 and between the 11:30 and 12:30 clock positions, respectively. Three compression sutures were placed in each of the flat hemimeridians between the 8:30 and 10:00 and between the 2:30 and 4:30 clock hours. Keratometric astigmatism decreased from 8.50 to 2.50 D.
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Table 3.—Previous Studies of Relaxing Incisions for Astigmatism Following Penetrating No. of
Source, y Troutman and Swinger,2 1980 Krachmer and Fenzl,20 1980 Sugar and Kirk," 1983 Mandel et al,'6 1987 McCartney et al," 1987 Limberg et al,16 1989
Cases
21 10
Cohen et al," 1989 Maguire and Bourne,19 1989 Present
* AK indicates arcuate keratotomy within the and CMS, Corneal Modeling System.
continue with four patients
spectacle were
The
mean
Reduction,
AK
Keratometer
4.25
Keratometer
7.50
AK and CS RI and CS CS AK
or
RI
Keratometer
67.0
Intraoperative keratoscope Intraoperative keratoscope Photokeratoscope Photokeratoscope
68.0
7.95
48.0
5.10
CMS
81.1
D
Postoperative Period,
correction and
9-12
37.7
preoperative keratometric
12.3 D. After surgery, the mean keratometric cylinder was 2.7 D, with a mean (±SE) decrease in keratometric cylinder of 8.2 ±1.7 D. The mean percent reduction of kerato¬ metric astigmatism was 81.1% (range, 29% to 129%). Suture removal, per¬ formed between 6 and 12 weeks after surgery, included removal of all six sutures in two eyes, two sutures in one eye, one suture in one eye, and no sutures in the remaining three eyes. re¬
vealed asymmetry of both power and angle of separation between the two major hemimeridians. The preoper¬ ative angle between the steep hemi¬ meridians ranged between 145° and 175°, with a mean of 160°. The preoper¬ ative asymmetry of power between the two steep hemimeridians was less than 1.0 D in four patients, between 1.5 and 2.0 D in two patients, and 9.0 D in one
patient. Figures 1 and 2 are examples of asymmetric postkeratoplasty astigma¬ tism that was treated with asymmetric relaxing incisions and compression su¬ percentage reduction of
keratometric astigmatism in these two cases was 92% and 29%, respectively, on the last postoperative follow-up vis¬ it. Although there was only a 29% reduction of astigmatism in the latter case, this patient was successfully fit¬ ted with a contact lens after surgery. Figure 3 exemplifies a symmetric postkeratoplasty astigmatism, in which orthogonal relaxing incisions were made 90° away from the compres¬ sion sutures. Eighteen months after surgery, and 15 months after removal of all sutures, the corneal (keratome¬ tric) astigmatism was reduced from 11.0 to 3.5 D, with a shift in axis of about 90°, indicating overcorrection.
The preoperative amount of kerato¬ metric astigmatism, and degree of asymmetry of power and axis between hemimeridians were not correlated with the percent of reduction of astig¬ matism after relaxing incisions and
compression sutures.
COMMENT
Transverse
keratotomies
in
the
graft bed,2 intraincisional relaxing in¬ cisions,9 graded relaxing incisions,1" trapezoidal relaxing keratotomy," ar¬ cuate relaxing incisions/ wedge re¬ sections,12 combined arcuate and semi-radial incisions,13 circumferential relaxing incisions,14 and compression sutures10 have all been used to cor¬ rect postkeratoplasty astigmatism, but poor predictability is a major limitation
procedures. The limited surgical success in correcting postker¬ atoplasty astigmatism (Table 3) might be, at least in part, a result of false preoperative assumptions, lack of un¬ derstanding of intraoperative vari¬ ables, and arbitrary postoperative of all of these
management.
Relaxing incisions alone, in or out of keratoplasty wound,2,9 compression sutures alone,lj and a combination of
the
these two methods14,1"17 have been tried
to correct postkeratoplasty astigma¬ tism. In most of these previous stud¬ ies, the steep corneal meridians were determined preoperatively by the ker¬ atometer, an instrument that mea¬ sures only the central 3.0 mm of corne¬ al curvature, and assumes the corneal
surface topography to approximate that of a spherocylindrical lens. The steep meridian is assumed to be com¬ posed of two hemimeridians radially symmetric about the corneal apex, separated by 180° from each other and by 90° from the flat meridians. Keratometry readings of the irregular post¬
keratoplasty cornea may provide lim¬ insight into the complex topo¬ graphic features, and surgery based on ited
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mo
8.2 NA 6-9
NA 8.20
keratoplasty wound; CS, compression sutures; RI, relaxing incisions central to the keratoplasty wound; NA,
was
tures. The
Astigmatism
8.40
contact lens tol¬
Computer-assisted keratographs
of
Keratometer
erant.
cylinder
Planned
Keratoplasty*
Keratometric Cylinder
AK
RI and CS
study
Surgery Using
Surgical Technique
% Reduction
not
available;
keratometry might therefore have lim¬ ited
success.
Computer-assisted video keratography may be more helpful than kera¬ tometry in planning astigmatic proce¬ dures after penetrating keratoplasty." Prospective analysis of photokeratoscopy for arcuate keratotomy to correct astigmatism following penetrating ker¬ atoplasty has shown a good correlation between change in ring ovality and keratometric astigmatism change."
The CMS allows even more detailed assessment of the corneal surface, both quantitatively and qualitatively, span¬ ning almost the entire corneal sur¬ face,6·' and has been shown to be as accurate and reproducible as the Bausch & Lomb keratometer when measuring calibrated steel balls" and reproducible to within ±0.25 D for 83% of measurements in normal eyes.1" It is possible that an experienced ob¬ server may be able to appreciate some of the topographic complexities of postkeratoplasty corneas by visual inspection alone, but Maguire and Bourne19 stated in a retrospective se¬ ries that "visual inspection of the kera¬ toscope photographs did not allow the complexity of the surface optics to be understood in sufficient detail to allow the surgeon to make a reasonable deci¬ sion on incision location." We used the CMS to assess the preoperative corneal topography of seven consecutive contact lens-intoler¬ ant patients with high degree of post¬
keratoplasty astigmatism (>5 D). Using the computer-assisted videokeratographs, we were able to mea¬ sure most of the graft curvature from the apex to the graft-host junction. With the keratographs, analysis of re¬ gional corneal surface power helped us design what we thought might be more accurate surgical plans. Asymmetry of power between the two steep meridi¬ ans was seen in three cases; also, the
steep meridians
were
separated by
an
at least 10° less than 180° in five seven cases, and the flat meridi¬ ans were orthogonal to the steep me¬ ridians in only one of seven cases. Maguire and Bourne19 also found asym¬ metry of power of the two steep hemi¬ meridians in six patients with postker¬
angle
of the
and an angle asymmetry between the major hemi¬ meridians in two of the six patients, although they did not vary surgery on the basis of these findings. With the patient fixing on the positioning light of the CMS, photokeratoscope, or ker¬
atoplasty astigmatism,
atometer, the center of the graft may not coincide with the center of the
keratograph or keratoscope photo¬ graph; the clock-hour positions on the keratographs will not necessarily, therefore, correspond to the clockhour positions on the graft, introduc¬ ing a potential error for the placement of incisions and sutures. We attempted to minimize this error by having pa¬ tients fixate on a coaxial fiber-optic fixation target within the operating microscope during the surgery, so that the reference for the clock hours would be similar. Regardless of the pathogenesis, for greater central flattening, deeper, more central, and longer keratotomies are thought to increase the surgical effect. ™ In this study, the length of the transverse keratotomies varied from 2 to 4 mm, depending on the arc length of the steep hemimeridian, keeping the depth of the cut constant at 500 µ , and the location of the cut constant at 1 mm central to the graft-host inter-
face. The variable width of steepening of the two hemimeridians, as deter¬ mined by the CMS, may be a partial determinant of the outcome of astig¬ matic surgery. A very large study randomizing patients to classic sym¬ metrical surgery vs asymmetrical sur¬ gery based on specific preoperative topographic features would be re¬ quired to prove the value of this
approach.
We believe that
intraoperative as¬ astigmatism, by means of either a keratoscope or a keratometer, is important to monitor the reversal of preoperative astigma¬ tism, as emphasized in previous stud¬ ies.21015"17,2""22 In addition, it is our im¬ pression that the use of a mersilene suture is advantageous over nylon su¬ sessment of corneal
ture, because the former is less biode¬
to a more stable corneal curvature. Even with mersi¬ lene, however, we tended to have undercorrections in our series, with only one eye being overcorrected. That inci¬ sions alone, after removal of compres¬ sion sutures, can occasionally result in shifts in keratometric cylinder of 10 D or more attests to the apparent vari¬ ability in wound healing and, perhaps, to the stress to which the cornea is subjected at the site of the incisions. Our prospective study suggests that computer-assisted video keratographic analysis of postkeratoplasty astigma¬ tism prior to relaxing incisions and
gradable,2" leading
compression sutures may prove helpful planning more accurate surgery. We
in
were
able to reduce the
postkerato-
plasty astigmatism by 81.1%, a result that compares favorably with those of previously published series using re¬ laxing incisions (Table 3), except for the results reported by Troutman and Swinger.2 They reported a 75% reduc¬ tion of astigmatism in four patients using relaxing incisions based on pre¬ operative and intraoperative keratometry; however, their sample size was small and the follow-up period after the astigmatic procedure was only 4 months. In our small study, we were
unable to find any correlation between the amount of asymmetry of astigma¬ tism and response to surgery. Despite achieving a high percentage of astig¬ matic correction (81.1%), we could not prove the value of computer-assisted video keratography in planning sur¬ gery for postkeratoplasty astigmatism. To have an 80% likelihood of detecting a statistically significant (P
