Evaluation of Post-Trabeculectomy
Visual Function Using Orbscan
Kozue Kasai MD1
Tadashi Nakano MD1
Hideki Matsuda MD1
Masayuki Tatemichi MD2
1
Takahiko Noro MD1
Yoshinori Itou MD1
Hiroshi Tsuneoka MD1
The Jikei University School of Medicine
Department of Ophthalmology
2 Showa University
Purpose
1. To evaluate changes in corneal topographic
characteristics of patients
after trabeculectomy (LEC).
2. To study the relationship of central corneal
thickness using Orbscan.
Methods and Patients
Post-trabeculectomy group with OAG
24 eyes
Control group
16 eyes
(nonoperated eyes of post-LEC patients or volunteer eyes)
TOTAL
40 eyes
(24 patients were examined with Orbscan at our glaucoma outpatient clinic)
Methods
Post-LEC group
20 patients
24 eyes
Control group
13 patients
16 eyes
58.8±15.2
67.3±5.6
0.580
Sex (man / woman)
11 / 9
8/5
0.508
Visual acuity (log)
0.60±0.58
1.00±0.17
0.001
Spherical equivalent [D]*
-3.72±3.45
-1.14±3.50
0.001
Corneal astigmatism [D]*
-1.59±0.96
-0.80±0.50
0.004
Tonometry [mmHg]
11.4±4.72
16.3±5.64
0.009
Corneal thickness [m]
556±38.6
558±43.7
0.978
Postoperative period [months]
48.1±51.3
Age (years)
* NIDEK ARK-700A
p value**
** Mann-Whitney U-test
ORBSCAN ver 3.0
Evaluation items
Using an illuminated ring pattern and a beam of light,
Orbscan shows surface power and the front and back shapes.
Not effected by eye dryness. Time: less than 2 seconds
Using two groups
(3-mm and 5-mm
zone irregularity [ZI])
Irregularity =
√
(Standard deviation of Mean power*)2 +
(Standard deviation of astigmatic power**)2
* Mean power: The average of the maximum and the minimum of the cornea refractivity in the arbitrary measurement point
** astigmatic power: The difference of the maximum and the minimum of the cornea refractivity in the arbitrary measurement point
Methods
1. Zone Irregularity
3-mm ZI
5-mm ZI
Central corneal Irregularity
miosis (daytime condition)
Corneal irregularity of paracentral quadrants
mydriasis (night condition)
2. Corneal thickness
Corneal thickness was measured by
Orbscan slit scan pachymetry.
A representation of the central corneal thickness.
(within a 3-mm circle from the center)
5-3-mm ZI
Difference between
5-mm ZI and 3-mm ZI (5-3-mm ZI)
as an index of the peripheral area
Results 1
Irregularity
7
Irregularity vs treatment
*
6
5
*
*
4
3
2
1
0
Post-LEC Control Post-LEC Control Post-LEC Control
3-mm Zone
5-mm Zone
5‐3-mm Zone
* P < 0.5 ** P < 0.01 *** P < 0.001
Mann-Whitney U-test
Irregularity was greater in the Post-LEC group than
in the control group in all zones.
Results 2
Irregularity
12
**
Irregularity vs Corneal thickness
**
10
*
8
6
4
2
0
<540 m ≧540 m
<540 m ≧540 m
<540 m ≧540 m
3-mm Zone
5-mm Zone
5‐3-mm Zone
* P < 0.5 ** P < 0.01 *** P < 0.001
Mann-Whitney U-test
Irregularity was greater with corneal thickness < 540m than
with corneal thickness ≧540 m in the zones.
Report of Evaluation of Post-trabeculectomy
1. Video-keratoscopy
After LEC, the peripheral parts of the cornea near the scleral flap area become steep.
After LEC, visual acuity decreased with topographic changes near the scleral flap.
2. TMS-1 TMS-2 Video-keratoscopy
After LEC, there are no changes in SRI or SAI as indexes of astigmatic irregularity.
3. TMS-1
After LEC, The steep area around the cornea does not influence the corneal center.
4. OPD-scan
After LEC, surgically induced astigmatism and higher-order aberrations increase
significantly. Contrast sensitivity is decreased.
Back Ground
1. The importance of quality of vision (QOV) is widely recognized.
2. Towards the Standaridization of QOV (Quality of vision),the list of clinical useful
parameters need to be evaluated.
3. Corneal astigmatism is a factor in QOV. It can’t be predicted before surgery.
4. The irregularity astigmatism is important, but postoperative QOV deteriorates
because of the regular astigmatism.
Conclusion 1
1. Irregularity was significantly greater in the post-LEC group.
ZI may serve as a new index of postoperative quality of vision.
2. Irregularity was significantly greater when corneal thickness
was less than 540m.
Central cornea thickness may be a useful predictor of surgically
induced astigmatism.
Conclusion 2
1. Orbscan is an effective method for evaluating
visual function after trabeculectomy.
2. The results of this study suggest that corneal
thickness may have a significant effect on changes
in corneal shape after glaucoma surgery.
References
1. Rosen WJ, Mannis MJ, Brandt JD : The effect of trabeculectomy on corneal topography.
Ophthalmic Surg. 1992 Jun;23(6):395-8.
2. Claridge KG, Galbraith JK, Karmel V, Bates AK : The effect of trabeculectomy on refraction, keratometry
and corneal topography. Eye. 1995;9 ( Pt 3):292-8.
3. Vernon SA, Zambarakji HJ, Potgieter F, Evans J, Chell PB : Topographic and keratometric astigmatism up to
1 year following small flap trabeculectomy (microtrabeculectomy). Br J Ophthalmol. 1999 Jul;83(7):779-82.
4. Cunliffe IA, Dapling RB, West J, Longstaff S: A prospective study examining the changes in factors that
affect visual acuity following trabeculectomy. Eye. 1992;6 ( Pt 6):618-22.
5. Maeno A, Hayashi K, Oshika T et al : Fourier analysis of corneal astigmatism after trabectomy.
Rinsho Ganka (Jpn J Clin Ophthalmol) 54(4): 587-590. 2000
6. Toyokawa N, Miyata M, Kimura H et al : The effect of glaucoma surgery on postoperative visual function.
Rinsho Ganka (Jpn J Clin Ophthalmol) 62(4): 461-465. 2008
7. Jordan JF, Joergens S, Dinslage S, Dietlein TS, Krieglstein GK : Central and paracentral corneal pachymetry
in patients with normal tension glaucoma and ocular hypertension.
Graefes Arch Clin Exp Ophthalmol. 2006 Feb;244(2):177-82. Epub 2005 Aug 2.
8. Radford SW, Lim R, Salmon JF : Comparison of Orbscan and ultrasound pachymetry in the measurement
of central corneal thickness. Eye. 2004 Apr;18(4):434-6.

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