CHANGES IN VISUAL ACUITY AND CORNEAL TOPOGRAPHY FOLLOWING INTRASTROMAL CORNEAL SEGMENT IMPLANTATION Текст научной статьи по специальности «Клиническая медицина»

Купле Варвара

магистр оптометрии, Глазной центр доктора Соломатина, Латвия, г. Рига kuple.varvara@gmail. com

Петухов Даниил Валерьевич

к.э.н., доц., доцент отделения национальной экономики экономического факультета РАНХиГС при Президенте Российской Федерации, Россия, г. Москва [email protected]

Изменение остроты зрения и топографии роговицы у пациентов с кератоконусом после имплантации интрастромальных роговичных сегментов

Аннотация

Цель статьи - исследовать изменение остроты зрения и роговичной топографии у пациентов с кератоконусом после имплантации интрастромальных роговичных сегментов. Автор проводила исследование на базе Центра доктора И. Соломатина по глазной реабилитации и коррекции зрения, анализируя результаты операций по картам пациентов. Всего проанализировано послеоперационных данных по 30 глазам. Результаты: У всех субъектов исследования наблюдалось улучшение остроты зрения и параметров, характерных для кератоконуса. Выводы: Имплантация интрастромальных роговичных сегментов является эффективной операцией. Результаты операции не зависят от местоположения верхушки максимальной эктазии кератоконуса.

Ключевые слова:

кератоконус, интрастромальные роговичные сегменты, острота зрения, оптическая сила роговицы

Kuple V.

Master of Optometry, Dr. Solomatin's Eye Rehabilitation and Vision Correction Centre, Riga, Latvia

kuple.varvara@gmail. com

Petukhov D.V.

PhD (Economics), Associate Professor, Russian Presidential Academy of National Economy and Public Administration, Moscow, Russia [email protected]

Changes in visual acuity and corneal topography following intrastromal corneal segment implantation

Abstract

The aim of the Paper was to study the changes in vision acuity and corneal topography in patients with keratoconus following implantation of intrastromal corneal ring segments (ICRS). The author performed the study on the base of Dr. Solomatin's Eye Rehabilitation and Vision Correction Centre by analysing the results of operations as recorded in the patient cards. In total, the postoperative data of 30 eyes have been reviewed.

Results: All the study subjects showed improvement in vision acuity and in keratoconus-specific parameters.

Conclusions: Implantation of ICRS is an effective procedure. The operation results are not dependent on the location of keratoconus maximal ectasia apex.

Keywords

keratoconus, intrastromal corneal ring segments (ICRS), vision acuity, optical power of the cornea

Carrying out vision examinations on a day-to-day basis at my workplace, more and more often I come across patients whose visual acuity has reduced due to keratoconus. At the initial, or subclinical, stage, keratoconus is not easily identifiable and most often such patients only start seeking help when their visual acuity is already very low. Most of them are economically active young people who are not willing to put up with poor vision given the fact that some jobs have special vision requirements. It is difficult for patients with such a condition to correct their vision adequately with glasses or contact

© В.Купле, Д.В. Петухов, 2017

lenses that would fully satisfy the patient's wishes and provide good visual acuity and comfort when using optical correction.

Implantation of intrastromal corneal segments (ICRS) is an option for patients with keratoconus not only to formally improve corneal sphericity and reduce the optical strength of the maximum conus apex curvature but also to improve visual acuity and make it easier for them to get the necessary optical correction.

Of all the three Baltic states, implantation of intrastromal corneal segments is only available in Latvia. The very first surgery was conducted five years ago but until now the results have not been reviewed.

Initially, ICRS were initially designed to correct moderate and high degree myopia whereas the US Food and Drugs Administration only approved the use of ICRS for the treatment of low degree myopia up to -3.0D (dioptres). Then they started implanting ICRS in keratoconus patients to correct keratoconus-related refraction errors and delay or prevent the need for corneal transplantation. In June 2004, the US Food and Drugs Administration approved the use of intrastromal corneal ring segments for vision correction in people with keratoconus (Parker et al, 2015).

ICRS are implantable ring segments designed for improvement of corneal surface curvature, reduction of refraction errors, improvement of noncorrected and uncorrected visual acuity, and cases of corneal ectasia induced by keratoconus or by any other reason. According to Pietrini (2009), the main indications for such a surgery are:

• Keratoconus patients with reduced corrected visual acuity and contact lens intolerance;

• Progressive keratoconus;

• Pellucid marginal degeneration;

• Post-LASIK corneal ectasia;

• Regular or irregular high degree astigmatisms following corneal transplantation.

Pietrini (2009) also mentions the following contraindications:

• Keratometry greater than 60.00D;

• Express central corneal opacities;

• Severe atopic diseases;

Unreal patient's expectations of surgery results.

The ICRS system is quite universal -it allows for up to 40 various combinations of ring segment thicknesses, arc lengths and optic zone variations. The system avails of segment thicknesses of 150 to 300 microns at a pitch of 50 microns, arc lengths of 90° to 210° at a pitch of 30°, and optical zones of 5 mm, 5.5 mm and 6 mm. Depending on each specific case of keratoconus, one or two ring

segments with equal or various parameters may be implanted. The required segment number and parameters are determined by a computerized estimate on the basis of the corneal topography data (Pietrini, 2009).

Each corneal segment parameter is responsible for a concrete segment function. By increasing the thickness, we increase the segment effect. The arc length variation changes the impact on spherical and cylindric correction. By changing the optic zone value, we overcome the intricacies related to the corneal thickness or the pupil size when choosing the segment. By variating all those values and selecting the optimum ring segment parameters, one can significantly improve the patient's uncorrected and corrected visual acuity. It is one of the most important advantages of this method since any kind of refractive surgery is contraindicated in keratoconus patients, and optical correction is often hardly tolerable by them and does not produce the desired result (Pietrini, 2009, Parker et al, 2015).

Corneal segments are made of polymethylmethacrylate and are inserted into the corneal stroma through a specially created tunnel or 'pocket' in the stromal tissue. Such a tunnel may be created manually using a special manual spiral-shaped cutting edge or femtosecond laser dividing the stromal tissue by laser energy and forming a 'pocket' without mechanical cutting. No significant differences between the use of a manual mechanical cutting edge and femtosecond laser have been observed. The procedure is easily tolerated by the patient, and primary rehabilitation usually takes 5-7 days, when the patient has to use eyedrops to exclude the risk of inflammation. The procedure is fully responsible and the segment may be extracted if necessary. Complications are very rare and usually related to the choice of a wrong size ring segment or insertion depth. Segment expulsion is an extremely rare complication, which is most often caused by a too shallow placement of the segment. The best results

can be achieved by combined surgery, i.e. segment implantation plus corneal collagen crosslinking (Parker et al, 2015).

Patient Selection Criteria

A patient is enrolled in the study if

he/she:

• has undergone a ICRS implantation procedure;

• has visited an ophthalmologist both pre-operatively and 3-6 months after the procedure;

• has got all the necessary topography investigation data;

• has got data of corrected and uncorrected maximal visual acuity pre- and post-operatively.

In total, data on 30 operated eyes were obtained for the study - 5 eyes in female subjects and 25 eyes in males. Of those, 6 patients had both eyes operated, and 18 - one eye. The average age of the patients was 28 years, the eldest was 45 years old at the time of the surgery, and the youngest - 15 y. o.

Average indicators and average eye parameter improvements were calculated for the whole group of patients for the following items:

• corneal curvature (K1 and K2 dioptres) in the visual axis centre (changes in astigmatism);

• optical strength of the cornea (dioptres) at the point of maximum curvature;

• TKM index;

• uncorrected and best corrected visual acuity;

• spherical equivalent (SE).

To find out whether the parameter improvements are dependent on the location point of the maximum curvature apex of the keratoconus, with respect to the visual axis centre, the patients were grouped as follows:

• Group C - the apex location is up to 3 mm from the visual axis centre;

• Group P - the apex location is up to 3 mm to 6 mm from the visual axis centre;

To determine whether the parameter improvements are dependent on the patients'

preoperative uncorrected and best corrected visual acuity (decimal units), the following three groups were formed with 10 operated eyes in each group:

• Group 1 - the uncorrected visual acuity was 0.03 to 0.1 (the mean: 0.1), the best corrected visual acuity was 0.4 to 0.6 (the mean: 0.5) in the decimal system;

• Group 2 - the uncorrected visual acuity was 0.1 to 0.3 (the mean: 0.2), the best corrected visual acuity was 0.6 to 0.8 (the mean: 0.6) in the decimal system;

• Group 3 - the uncorrected visual acuity was 0.4 to 0.8 (the mean: 0.5), the best corrected visual acuity was 0.5 to 0.8 (the mean: 0.7) in the decimal system.

Preoperatively, the mean uncorrected visual acuity of the 30 eyes selected for the study was 0.3 in the decimal system. Patients with such a diagnosis had a strong need for high-degree cylindrical correction, which is hardly tolerable and does not provide the maximum possible visual acuity. The patients' mean corrected preoperative visual acuity was 0.6 in the decimal system. The patients' mean spherical equivalent was -2.8D preoperatively; the majority of the patients (80%) had first- and second-degree myopia with astigmatism.

Postoperatively, the mean uncorrected visual acuity has improved 1.7 times or by 2 rows in the decimal system and reached 0.5 in the decimal system. The difference is significant as shown by a statistical analysis by Wilcoxon test, i.e. the p value is low (p=0.002) (See Table 1). Whereas, the mean corrected visual acuity improved 1.3 times or by 2 rows in the decimal system postoperatively, and amounted to 0.8, i.e. according to the performed Wilcoxon test, the difference is statistically significant, the p value is low (p=0.003). The mean spherical equivalent has reduced by 1.8D postoperatively, although the difference is statistically insignificant and, according to the performed Wilcoxon test, the p value is high (p=0.37). The mean subjectively corrected

cylinder difference, which is significant for the patients, has reduced by a mean of 2.0D. It can be concluded that the reduction of the spherical equivalent was, mostly, at the expense of the astigmatism reduction.

Table 1 - The patients' pre- and postoperative mean uncorrected visual acuity, best corrected visual acuity and spherical equivalent, the changes and the p values

Preoperatively Postoperatively Improvement P value

UCVA 0.3 decimal units 0.5 decimal units 1.7x 0.002

BCVA 0.6 decimal units 0.8 decimal units 1.3x 0.003

SE -2.8D -1.0D 1.8D 0.37

According to the performed assessment of the maximum uncorrected visual acuity difference, 44% of the patients showed an improvement of 1-2 rows in the decimal system, in 23% of the patients the improvement was 3-4 rows in the decimal system, and in 23% patients the improvement was more than 4 rows in the decimal system. Uncorrected visual acuity has not changed post-operatively in 7% of the patients and has reduced by one row in 3% of the patients or in one operated eye (See Fig. 1).

Figure 1 - Maximum uncorrected visual acuity difference expressed in percentage points.

Whereas, when reviewing the maximum best corrected visual acuity

difference, 43% of the patients showed improvement of 1-2 rows in the decimal system, in 23% of the patients the improvement was 3-4 rows in the decimal system, in 7% of the patients - more than 4 rows in the decimal system. The postoperative best corrected visual acuity remained unchanged in 10% patients and reduced in 17% patients by one or more rows in the decimal system (See Fig. 2).

Figure 2 - Maximum best corrected visual acuity difference expressed in percentage points.

The main characteristics of keratoconus are corneal surface curvature in the main meridians (K1 and K2), and the difference between them, i.e. a cylinder (Cyl). A review of the said values using the Wilcoxon test showed statistically significant changes in the K2 values (p=0.044) and cylinder reduction (p=0.003). When compared with a subjectively determined cylinder size, the reduction in the corneal surface irregularities in the formed cylinder was smaller, it has reduced by 0.71D on the average, but, as mentioned above, the differences are statistically significant (See Fig.2.2). The preoperative optical strength of the mean maximal curvature apex (Kmax) was 58.48D, which has changed postoperatively by almost four dioptres on the average (See Fig. 2.2). Preoperatively, the mean TKM index was 51.62D, while postoperatively it reduced by 3.6D, on the average, amounting to 48.06D, which is close

to the limit of normal as per the TKM index distribution (See Table 2).

Table 2 - Keratometry, cylinder, conus maximum curvature apex (Kmax) and TKM index value pre- and postoperatively, and changes thereof.

I analysed how the patients' preoperative maximum uncorrected visual acuity (in decimal units) affected the uncorrected visual acuity difference value. The resultant image as given below shows that the patients with lower preoperative uncorrected visual acuity will have a bigger improvement in best corrected visual acuity postoperatively, in decimal units. The correlation between the values is weak (See Fig. 3), R=0.15, although there is a noticeable trend towards significance.

—ft9_l— 0,8 ♦

. , R* = 0,15

—e— ♦ * ♦ ♦

■2 0 2 4 6 8 10

Figure 3 - Preoperative maximum uncorrected visual acuity (UCVA) in relation to the maximum uncorrected visual acuity difference (d UCVA).

On the contrary, when reviewing the correlation between the uncorrected visual acuity difference and the best corrected visual acuity difference, a close correlation of R2=0.31 (Fig. 4) can be observed.

difference (d UCVA) in relation to the maximum best corrected visual acuity difference (d BCVA).

The postoperative uncorrected visual acuity (UCVA) differences in Groups C and P are practically the same: in Group C - 1.96 times or by 2.7 rows in the decimal system, and in Group P - 2.2 times or by 3 rows (See Fig.2.3). Also the maximum best corrected visual acuity (BCVA) in both groups has changed in a very similar way, namely, 1.3 times or by 1.5 rows in the decimal system in Group C and 1.2 times or by 0.8 rows in Group P (See Table3).

Table 3 - The mean values of visual acuity and spherical equivalent and the difference in Groups C and P_

Pre-operatively Postoperatively Difference

Group C UCVA 0.3 0.6 3x

BCVA 0.6 0.7 1.2x

SE -2.96 -1.04 1.91D

Pre-operatively Postoperatively Difference

Group P UCVA 0.3 0.6 3x

BCVA 0.7 0.8 1.1x

SE -2.22 -0.88 1.35D

The graphical depiction of how many times the uncorrected and best corrected visual acuity has improved in the patients of Groups C (C g.) and P (P g.) shows clearly that there is no difference between the patients of these groups. The patients of both groups show a slightly bigger difference in

Preoperative^ Postoperatively Difference P value

K1 49.67D 46.98D 2.69D 0.054

K2 46.09D 44.11D 1.98D 0.044

Cyl 3.58D 2.87D 0.71D 0.003

K Max 58.48D 54.53D 3.95D 0.07

TKM 51.62D 48.06D 3.56D 0.31

uncorrected visual acuity (UCVA) (See Fig. 5).

UCVA C g. BCVA C g.

UCVA P g. BCVA P g.

Figure 5 - Uncorrected and best corrected visual acuity improvement, by how many times it has improved as compared with the preoperative visual acuity, in patients of Groups C and P

When assessing the spherical equivalent reduction following an ICRS implantation surgery in correlation with the location of the maximal curvature apex of keratoconus, no statistically significant difference was found between the Groups. In Group C, the spherical equivalent reduced by 1.9±0.6D and in Group P - by 1.4±0.5D.

The keratometries K1 and K2 and the related postoperative reduction in astigmatism value is bigger in the patients of Group P - by 1.6D, whereas, in Group C the reduction amounts to 1.0D, but there is no statistically significant difference between these two Groups (p=0.14 by the Mann-Whitney test) and the error limiting values overlapped.

As regards the mean keratoconus maximum curvature apex (Kmax) difference in relation to the location of the keratoconus maximal curvature apex, the mean reduction of Kmax in Group C was 3.8±0.7D, but in Group P, Kmax reduced by 5.5±0.9D. It can be concluded that the biggest reduction in Kmax was in the patients of Group P, in which the conus maximal curvature apex is located more to the peripheral side of the cornea, 3-6 mm from the visual acuity centre.

However, when the Mann-Whitney test was used in the analysis of the two studied Groups, no statistically significant difference was found, and the p value was high (p=0,45).

The patients of Group 1 show the biggest improvements in the uncorrected and corrected visual acuity - the uncorrected visual acuity has improved, on the average, by 4 rows, and the best corrected visual acuity has improved by 2 rows on the average. The spherical equivalent difference in the Patients of Group 1, which showed the lowest visual acuity preoperatively, is also the biggest and amounts to 4.5D±1.1D (See Table 4).

Table 4 - The mean uncorrected (UCVA) and best corrected (BCVA) visual acuity, the differences thereof, and the differences of spherical equivalent by the groups

When comparing the way, in which the keratoconus patients' parameters are changing following an ICRS implantation surgery in relation to the preoperative uncorrected and best corrected visual acuity, it can be observed that the reduction in the maximum corneal curvature apex strength and the TKM index is very similar in all the Groups. Whereas the biggest cylinder reduction is in the patients of Group 3 and amounts to 1,2±0,5D, while the cylinder value in Group 1 has only reduced by 0.05±1.4D on the average (See Table 5).

When assessing the differences between the groups, one can see that the lower is the preoperative visual acuity, say, in Group 1, the bigger is the improvement in visual acuity. The aforesaid is more applicable to the uncorrected visual acuity (d UCVA) (See Fig. 6).

Table 5 - The mean conus maximal curvature (Kmax), TKM index, corneal anterior surface

curvature (K1 and K2) and cylinder differences by the groups

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d UCVA d BCVA

Figure 6 - Group-specific difference between the uncorrected (UCVA) and best corrected (BCVA) visual acuity

Patients with lower preoperative visual acuity will have a bigger improvement in visual acuity postoperatively, approx. 3.6±2SD visual acuity rows in the decimal system.

Following an ICRS implantation, one can expect reduction of corneal astigmatism (0.7D±3.0SD), reduction in the optical strength of the maximum curvature apex of the cornea (4.3D±2.8SD) and reduction in the TKM index (3.7D±1.8SD).

Irrespective of the location of the maximum curvature apex of keratoconus, the postoperative visual acuity and corneal parameter changes are similar in all cases.

An intrastromal corneal ring segment (ICRS) implantation surgery is an effective keratoconus treatment method, which in most cases provides improvement in visual acuity and favourable changes in corneal topography parameters.

List of References

1. Boxer Wachler, B.S. (2008). Modern Management of keratoconus. Jaupee Brothers Medical.

2. Coimbra, C. C., Gomes, M. T., Campos, M., Soter de Figueiroa, E., Barbosa, E. P. & Serapiai dos Santos, M. (2012). Femtosecond assisted intrastromal corneal ring (ISCR) implantation for the treatment of corneal ectasia. Arquivos Brasileiros De Oftalmol, 75-(2), 126130.

3. Coskunseven, E., Kymionis, G.D., Tsiklis, N.S., Atun, S., Arslan, E., Jankov, M.R. & Pallikaris, A.G. (2008). One-year results of intrastromal corneal ring segment implantation (KeraRing) using femtosecond laser in patients with keratoconus. American Journal of Ophthalmology, 45(5), 775-779.

4. El-Raggal, T.M. (2010). Sequential versus concurrent KeraRings insertion and corneal collagen cross-linking for keratoconus. British Journal of Ophthalmology, 95(1), 37-41.

5. Gharaibeh, A.M., Muhsen, S.M., AbuKhader, I.B., Ababneh, O.H., Abu-Ameerh, M.A. & Albdour, M.D. (2011). KeraRing intrastromal corneal ring segments for correction of keratoconus. The Journal of Cornea and External Disease, 31(2), 115-120.

6. Gomes, A. P, Tan, D., Rapuano, C. J., Belin, M.W., Ambrosio, R. Jr., Guell, J. L., Malecaze, F., Nishida, K., Sangwan, V. S. & group of Panelists of the Global Delphi Panel of Keratoconus and Ectatic Diseases (2015). Global consensus on keratoconus and ectatic diseases. The Journal of Cornea and External Disease, 34(4), 359-369.

7. Gordon-Shaag, A., Millodot, M. & Shneor. E. (2012). The epidemiology and etiology of keratoconus. International Journal of Keratoconus and Ectatic Corneal Diseases. 1(1) 715.

8. Mazotta,C., Traversi,C., Baiocchi,C., Caprossi,S., Sparano,O., Balestrazzi,M, C., Caprossi, A. & Corneal, A. (2008). Healing after riboflavin ultraviolet-A collagen cross-linking determined by confocal laser scanning microscopy in

vivo: early and late modifications. American Journal of Ophthalmology, 146(4), 527-530.

9. McKay, T. (1998). A Clinical Guise to the Humphrey Corneal Topography System. Humphrey Systems.

10. Parker, J.S., Korine van Dijk, & Melles, G.J. (2015) Treatment options for advanced keratoconus: A review. Survey of Ophthalmology, 60(5), 459480.

11. Pietrini, D. & Guedj, T. (2009). Corneal remodelling using the keraring. Cataract & Refractive Surgery Today Europe, 10, 16-22.

12. Rabinowitz, Y.S. (1998). Keratoconus. Survey Ophthalmology, 42(4), 297319.

13. Rabinowitz, Y.S. (2007). Diagnosing keratoconus and patients at risk. Cataract & Refractive Surgery Today, 5, 85-87.

14. Romero-Jimeneza, M., Santodomingo-Rubidob, J., & Wolffsohnc, J.S. (2010). Keratoconus: A review. Contact Lens and Anterior Eye, 33(4), 156-166.

15. Shabayek, M.H., & Alio, J.L. (2007). Intrastromal corneal ring segment implantation by femtosecond laser for keratoconus correction. Ophthalmology, 114(9), 1643-1652.

16. Sinjab, M. M. (2012). Classifications and Patterns of Keratoconus and Keratectasia. In: Quick Guide to the Management of Keratoconus. Springer Verlag Berlin Heidelberg. 13-57.

17. Stein,R., & Stein, R. (2011). Corneal collagen crosslinking: a major breakthrough in the management of keratoconus, pellucid marginal degeneration, and ectasia after LASIK. Ophthalmology Rounds, 9(1).

18. Tan, D.T.H., John Dart, J.K.G., Holland, J.E., & Kinoshita, S. (2012) Corneal transplantation. The Lancet. 379(9827), 1749-1759

19. Torquetti, L., Barbel, R. F. & Ferrara, P. (2009). Long-term follow-up of intrastromal corneal ring segments in keratoconus. Jurnal of Cataract & Refractive Surgery, 35(10), 1769-1773.

20. Torquetti, L., Ferrara, G., & Ferrara, P. (2012) Predictors of clinical outcomes after intrastromal corneal ring

segments implantation. International Journal of Keratoconus and Ectatic Corneal Diseases, 1(1), 26-30.

21. Zhou, A. J., Kitamura, K, & Weissman, B.A. (2003). Contact lens care in keratoconus. Contact Lens & Anterior Eye, 26(4), 171-174.