|Year : 2018 | Volume
| Issue : 4 | Page : 237-242
Evaluation of patients with keratoplasty in Tanta University Hospital using anterior segment optical coherence tomography
Zahraa M Elskhawy, Moataz M Sabry, Mohammed S Alshorbagy, Adel A Selima
Department of Ophthalmology, Faculty of Medicine, Tanta University, Tanta, Egypt
|Date of Submission||07-Feb-2018|
|Date of Acceptance||03-Jul-2018|
|Date of Web Publication||20-Dec-2018|
Zahraa M Elskhawy
9 Abd-Elhaleem Hafez Street, Tanta 31511
Source of Support: None, Conflict of Interest: None
Purpose This study aimed to evaluate patients with keratoplasty in Tanta University Hospital using anterior segment optical coherence tomography (AS-OCT).
Patients and methods This was a cross-sectional study that included 30 eyes of 22 patients who underwent keratoplasty in Tanta University Hospital from January 2016 till December 2016. The AS-OCT imaging using Topcon 3D optical coherence tomography; 3D OCT 2000(FA) was done. The preoperative pathology was corneal scarring in 16 (53.33%) eyes and advanced keratoconus in 14 (46.67%) eyes. Penetrating keratoplasty was done in 27 eyes, whereas deep anterior lamellar keratoplasty was performed in three eyes.
Results Comparing the base line characteristics between the keratoconus and the corneal scar groups, statistically significant differences were detected in age (P<0.001), best corrected visual acuity (decimal) (P=0.001), spherical equivalent in diopters (D) (P=0.018), and thickness disparity at the wound interface (μm) (P=0.026). The keratoconus group was younger and had better best corrected visual acuity than the corneal scar group. The total number of graft–host interface images from 30 eyes obtained by the AS-OCT was 120 cross sections. Of these, 22 (18.33%) cross sections had well-apposed junction and 98 cross sections had malapposed junction (81.67%). Protrusion (50 cross sections; 41.67%) was the most frequent misalignment type. When classifying the eyes according to the most frequent alignment pattern among the four cross sections, five eyes had well-apposed junction state (16.67%) (all were keratoconus cases) and 25 eyes had the malapposed junction state (83.33%) (corneal scar: 16 eyes, keratoconus: nine eyes). Among the 25 eyes with malapposed junction state, 12 eyes had protrusion, seven eyes had gap, and six eyes had step.
Conclusion The AS-OCT is a valuable tool for postoperative follow up of patients with keratoplasty. It helps in visualization of the internal surface of the graft–host interface. Thus, it can help in detecting the malapposition and so the cause of postoperative astigmatism can be recognized and can be managed early.
Keywords: anterior segment optical coherence tomography, corneal scar, deep anterior lamellar keratoplasty, keratoconus, keratoplasty, penetrating keratoplasty
|How to cite this article:|
Elskhawy ZM, Sabry MM, Alshorbagy MS, Selima AA. Evaluation of patients with keratoplasty in Tanta University Hospital using anterior segment optical coherence tomography. Delta J Ophthalmol 2018;19:237-42
|How to cite this URL:|
Elskhawy ZM, Sabry MM, Alshorbagy MS, Selima AA. Evaluation of patients with keratoplasty in Tanta University Hospital using anterior segment optical coherence tomography. Delta J Ophthalmol [serial online] 2018 [cited 2019 Mar 23];19:237-42. Available from: http://www.djo.eg.net/text.asp?2018/19/4/237/248091
| Introduction|| |
Optical coherence tomography (OCT) of the anterior segment has become a valuable tool for the cornea specialist as it provides digital images at high resolution without touching the cornea. In penetrating or lamellar keratoplasties, OCT can be used to assess the central corneal thickness (CCT) and for precise measurements of deep stromal opacities, thereby guiding the surgeon to choose the best method of treatment .
The OCT has also been used to evaluate the keratoplasty postoperatively, for early identification of possible postoperative complications, for example, The donor disc detachments in the endothelial keratoplasties. An OCT can also be used intraoperatively to assess the stromal bed regularity in anterior lamellar surgeries, especially for those techniques in which a bare Descemet’s membrane is the goal .
The precise apposition between the graft and the host is an important goal of penetrating keratoplasty (PKP) and is also The prognostic factor affecting the surgical outcome . A PKP has a success rate of 80% in those at low risk , but postoperative astigmatism still remains an important cause of low vision after PKP. Astigmatism after PKP can be caused by tension of uneven and relatively strong sutures, misalignment between the graft and the recipient, and delayed or irregular wound healing .
| Patients and methods|| |
This was a prospective cross-sectional study that included 30 eyes of 22 patients who underwent keratoplasty in Tanta University Hospital from January 2016 till December 2016.
Patients were excluded when it was difficult to acquire high-quality images because of poor co-operation.
Local Ethical Committee approval was obtained. All patients underwent full counseling and a written informed consent was signed by all participants.
All patients were subjected to thorough history taking including (age, sex, residence, occupation, history of ocular and systemic diseases, history of previous ophthalmological intervention, and family history of keratoconus), full ophthalmological examination including best corrected visual acuity (BCVA) using a decimal chart and slit lamp biomicroscopy, which included anterior segment examination and posterior segment examination with noncontact +78 diopters lens to detect any other eye disease. Intraocular pressure was measured using air puff tonometer, and anterior segment optical coherence tomography (AS-OCT) imaging was done by using Topcon 3D optical coherence tomography; 3D OCT 2000(FA) (Topcon Inc., Tokyo, Japan).
Anterior segment optical coherence tomography imaging
The evaluations were performed after all corneal sutures were removed. Each participant was positioned comfortably on the OCT headrest and requested to direct his/her gaze through the viewing path at the internal fixation point. Images were taken using the anterior segment option, set to provide a 3D scan. Corneal imaging was obtained by defocusing the lens and relaying the OCT beam to the cornea. During measurement, the patient was asked to fixate to the fixation beam and the probe beam was positioned to pass through the cornea bisecting the pupil horizontally. A 4-mm long scan was obtained from the central cornea overlying the entrance of the pupil. Computer software-controlled cursors were manually placed at the peak of the reflectivity spikes corresponding to the anterior corneal surface or the posterior corneal surface. Tissue thickness was calculated between peaks from the time-delay of the reflected light. All measurements were taken by a single examiner (A.N.). CCT, thickness disparity at the wound interface, the configuration of the graft–host interface and Descemet’s membrane attachment after deep anterior lamellar keratoplasty (DALK) were examined. Three consecutive measurements of CCT were taken by OCT and averaged. The examiner obtained four images of the graft–host interface.
For calculation of thickness disparity at the wound interface, an imaginary line was drawn perpendicular to the external and internal sides of the cornea, from the central point of the line where the donor and recipient met and the thickness disparity was calculated by measuring the thicknesses of the donor and recipient corneas, each at the point that was 1 mm away from the meeting point on the external side. The four calculated absolute values were averaged ([Figure 1]c). A single examiner (A.S.) interpreted the OCT images. Each graft–host interface was categorized according to alignment patterns of the corneal internal side as follows: well-apposed junction if the corneal internal side was aligned precisely without disconnection, gap if Descemet’s membrane and the inner stroma of the donor and recipient were not connected, but were aligned, step if the wound interface was similar to gap, but revealed thickness disparity between the graft and host and protrusion if Descemet’s membrane and stroma protruded toward the anterior chamber ([Figure 1]).
|Figure 1 Classification of wound profile using anterior segment optical coherence tomography (a) well-apposed junction, (b) step, (c) protrusion, and (d) gap.|
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According to the preoperative diagnosis, the patients were classified into keratoconus and corneal scar groups. The distribution of alignment patterns in each diagnosis group was evaluated. Visual acuity, intraocular pressure, spherical equivalent, keratometric astigmatism, CCT, and thickness disparity at the wound interface were compared between the alignment groups.
Statistical presentation and analysis of the current study were conducted, using the mean and SD by SPSS V.16 (SPSS Inc., South Wacker Drive, Chicago, Illinois, USA). Significance was considered when P value was less than 0.05. Insignificance was considered when P value was more than 0.05.
| Results|| |
Thirty eyes of 22 patients were included in this study. The age of the patients ranged from 19–65 years with a mean of 39.37±14.53 years. Twenty-seven eyes were PKP and three eyes were DALK. Sixteen (53.33%) eyes were operated due to corneal scar and 14 (46.67%) eyes were operated due to advanced keratoconus.
The mean follow-up period after keratoplasty was 14.30±2.14 months (range: 11–18 months). BCVA (decimal) ranged from 0.1 to 0.8 with a mean of 0.4±0.2. Spherical equivalent in diopters (D) ranged from −0.75 to −8.5 with a mean of −2.897±1.75. Keratometric astigmatism ranged from 0.25 to 8.15 D with a mean of 2.99±2.08 D. CCT (μm) ranged from 489 to 633 with a mean of 549.20±36.24. Thickness disparity at the wound interface (μm) ranged from 14 to 97 with a mean of 53.03±23.89. Graft oversize was either 0.25 or 0.5 mm. Size of trephination was 7.5 mm ([Table 1]).
Comparing the base line characteristics between the keratoconus and the corneal scar groups, statistically significant differences were found in age (P<0.001), BCVA (P=0.001), spherical equivalent (P=0.018), and thickness disparity at the wound interface (P=0.026). The keratoconus group was younger and had better BCVA than corneal scar group ([Table 2]).
|Table 2 Comparison of the baseline characteristics between keratoconus and corneal scar groups|
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The total number of graft–host interface images from the 30 eyes obtained by the AS-OCT was 120 cross sections. Of these, 22 (18.33%) cross sections had well-apposed junction and 98 (81.67%) cross sections had malapposed junction. Protrusion (50 cross sections, 41.67%) was the most frequent misalignment type.
When classifying the eyes according to the most frequent alignment pattern among the four cross sections, five eyes had well-apposed junction state (16.67%, all were keratoconus cases) and 25 eyes had the malapposed junction state (83.33%, corneal scar; 16 eyes and keratoconus; nine eyes). Among the 25 eyes with malapposed junction state, 12 eyes had protrusion, seven eyes had gap, and six eyes had step ([Figure 2] and [Figure 3]).
|Figure 2 Prevalence of various alignment patterns found in the internal graft–host junctions according to the most frequent alignment pattern among the four cross sections.|
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|Figure 3 Prevalence of various alignment patterns according to the preoperative diagnosis.|
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The distribution of alignment patterns was significantly different between the preoperative diagnosis groups (P=0.015). The most frequent type of alignment pattern in the corneal scar group was malapposed junction, whereas the keratoconus group showed a higher incidence of well-apposed junction ([Figure 3]).
Comparisons of various clinical parameters between the well-apposed junction and malapposed junction groups (combination of gap, step, and protrusion) showed that there were statistically significant differences regarding BCVA (P<0.001), spherical equivalent (P=0.011), and thickness disparity at the wound interface (P=0.001).
In the analysis of the factors related to the thickness disparity at the wound interface (μm), BCVA (P<0.001), spherical equivalent (P<0.001), and keratometric astigmatism (P<0.001) showed significant positive correlations.
Regarding the AS-OCT findings in cases of DALK, the Descemet’s membrane was totally attached in the three examined cases.
| Discussion|| |
In the current study, malapposed junction state was associated with higher degree of postoperative keratometric astigmatism than the well-apposed junction state. In addition, spherical equivalent was higher in the malapposed junction state than in the well-apposed junction state. BCVA was better and thickness disparity at the wound interface (μm) was lower in the well-apposed junction state.
On the basis that AS-OCT might provide additional information regarding graft–host relations, Nursal et al.  started using AS-OCT routinely in candidates for PKP, as well as in patients who had had this operation before this device was available for clinical use. In their study, they evaluated donor–host relationships and complications after PKP by AS-OCT. Ideal graft–host relations of the internal wound site were observed in more than 50% of the eyes. They have seen that graft–host junction variabilities mostly depended on the preoperative pathological characteristics of the host cornea and anterior chamber structures. For example, cases with thinner host cornea at the graft–host junction were all keratoconic eyes. Thicker host cornea, however, was almost always related to preoperative corneal pathologies, which had caused corneal thickening, such as pseudophakic bullous keratopathy.
Few reports investigated the alignment pattern of the graft–host interface after PKP using AS-OCT. Kaiserman et al.  reported that the degree of malapposition was associated with higher postoperative astigmatism. They handled eight images from one eye as eight different data sets in statistical analysis. However, since these eight data sets were obtained from one eye, it is inconclusive whether the statistical results are really significantly different.
Lang et al.  performed a histological analysis of postmortem corneas that underwent PKP and reported misalignment of Descemet’s membrane in 22 out of 30 eyes. In Nursal et al. (5) study, 60.5% of 392 graft–host junctions showed the malapposed state. Among the malapposed junctions, protrusion was the most common misalignment type. The result might be explained by the curling up of large donor on the wound interface. In addition, the tendency for stromal overgrowth induced by incomplete contact between the donor and recipient may affect the wound profile. When a tissue is injured and lost, migration and proliferation of connective tissue occur to fill in the defect as a normal wound-healing process.
In conclusion, the AS-OCT is a valuable tool for postoperative follow up of patients with keratoplasty. It helps in visualization of the internal surface of the graft–host interface. Thus, it can help us to detect the malapposition and so the cause of postoperative astigmatism could be recognized and can be managed early.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]