Pterygium is an elevated, superficial, external ocular fibrovascular connective tissue overgrowth of bulbar conjunctiva mass and extends onto the corneal surface.  Pterygia can vary from a small atrophic quiescent lesion to a largely aggressive, rapidly growing fibrovascular lesion that can distort the corneal topography, and in advanced cases, they can obscure the optical center of the cornea. Pterygium is a very common degenerative condition seen in many countries. 
Pterygium causes visual problems due to induced corneal astigmatism or direct encroachment onto the visual axis.  The reasons for astigmatism are (a) the pooling of the tear film and (b) the mechanical traction exerted on the cornea and (c) the size of Pterygium, especially the double-headed Pterygium. This has been measured by keratometry, corneal topography, and refraction. Corneal astigmatism can be reduced by pterygium excision surgery, which involves the use of several techniques. 
Astigmatism is the unequal refraction of the same eye in two different meridians. Unlike the basic types of refraction- emmetropia, myopia and hyperopia- where all the light rays enter one focus (on the retina, behind it, or in front of it), in astigmatism, there is no a single focus.  In basic types of refraction, the cornea is spherical and it refracts equally in all the meridians. There are different surgical techniques for the correction of corneal astigmatisms such as bare sclera, conjunctival autograft, and amniotic membrane transplantation.  The present study was conducted to compare preoperative and postoperative changes in corneal astigmatism after pterygium excision by different techniques.
Subjects and Methods
The present study was conducted in the Department of Ophthalmology Mediciti institute of medical sciences from May 2018 to August 20018 on 69 patients of age range 20-55 years of primary Pterygium. Ethical approval was obtained from the institute prior to the study. All patients were informed regarding the study and written consent was obtained.
General information such as name, age etc. was recorded. Pterygium was graded depending on the extent of corneal involvement as follows:
Grade I: Just crossing the limbus,
Grade II: Midway between limbus and pupil,
Grade III: Reaching up to the papillary margin, and
Grade IV: Crossing the papillary margin.
Patients were divided into three groups of 23 each. Group I was treated with bare sclera (BS) technique, group II with conjunctival autograft (CAG) technique and group III with amniotic membrane graft (AMG) technique. All the patients were preoperatively assessed for visual acuity, anterior and posterior segments, autorefraction, and auto keratometry. After surgery, the patients were recalled on day 5, 1 month, and 3 months for the analysis. Results thus obtained were subjected to statistical analysis. A P-value of less than 0.05 was considered significant.
|Groups||Group I||Group II||Group III|
|Technique||Bare sclera||Conjunctival autograft||Amniotic membrane graft|
Table 1 shows the type of technique used and the number of patients in each group.
Table 2 shows that uncorrected visual acuity (UCVA) preoperatively was 0.57, on 5th day was 0.45, after 1 month was 0.34 and after 3 months was 0.35. The difference was significant (P< 0.05).
|Groups||Preop astigmatism||Postop astigmatism||P-value|
Table 3, Figure 1 shows that mean preoperative astigmatism value in group I was 3.45, in group II was 3.52 and in group III was 3.49. Postoperative astigmatism value in group I was 1.60, in group II was 0.92 and in group III was 0.81. The difference was significant (P< 0.05).
In astigmatism, variations in the curvature of the cornea or lens along different meridians prevent the light rays from focusing onto a single point. Corneal refraction depends on the corneal curvature. If the cornea is more curved, the power of refraction is higher and vice versa. Corneal and lenticular astigmatism can complement or cancel each other. Their summation represents the so-called “total astigmatism”.  Due to the lack of a single focus, an astigmatic eye is not able to see clearly without correction. Astigmatic patients complain of visual disturbances in both far (in myopia) and near vision (in hyperopia), which causes asthenopia problems (headache, dizziness, fatigue etc). Additionally, regular, symmetric objects might seem to them irregular, and /or elongated.  The present study was conducted to compare preoperative and postoperative changes in corneal astigmatism after pterygium excision by different techniques.
In the present study, we recruited 69 patients with astigmatism. Patients were divided into three groups of 23 each. Group I was treated with bare sclera (BS) technique, group II with conjunctival autograft (CAG) technique and group III with amniotic membrane graft (AMG) technique. Garg et al,  included 71 patients with primary Pterygium who underwent surgery. The reduction in the mean preoperative astigmatism of 3.47 ± 1.74 Diopters (D) to 1.10 ± 0.78 D 3 months after surgery was statistically significant. Bare sclera, conjunctival autograft, and amniotic membrane graft techniques exhibited changes in astigmatism amounting to 1.85 ± 0.88 D, 2.55 ± 1.26 D, and 2.67 ± 1.44 D, respectively. Pterygium excision surgeries using amniotic membrane graft and conjunctival autograft techniques were more effective than pterygium excision surgery using bare sclera technique in reducing astigmatism.
We found that uncorrected visual acuity (UCVA) preoperatively was 0.57, on 5th day was 0.45, after 1 month was 0.34 and after 3 months was 0.35. The mean preoperative astigmatism value in group I was 3.45, in group II was 3.52 and in group III was 3.49. Postoperative astigmatism value in group I was 1.60, in group II was 0.92 and in group III was 0.81.
Zaida et al,  conducted a study on 60 eyes of 60 patients. Ages were between 34 and 56 years, divided randomly into 3 groups; group A included 20 patients that were treated with pterygium excision with bare sclera technique plus MMC application for 3 minutes at site of excision. Group B: 20 patients that were treated with pterygium excision with conjunctival autograft. Group C: 20 patients that were treated with pterygium excision with limbal/conjunctival autograft. The postoperative assessment included refraction and pentacam on visits at 1, 3, and 6 months after surgery. In all groups, BCVA changes 6 months postoperatively were statistically significant, while Spherical and Cylindrical error changes were statistically insignificant. Average K and corneal thickness changes were statistically insignificant, while anterior corneal astigmatism changes were statistically insignificant in group A, and significant in groups B and C.
Pterygium grade also affects corneal astigmatism. Several studies conducted previously prove that the amount of induced corneal astigmatism increases with the increase in the size of Pterygium. Gumus et al,  found a significant correlation between the size of Pterygium and induced corneal astigmatism. Misra et al,  concluded that with the size of Pterygium extending from 2.5mm, preoperative astigmatism increases.
The authors found that amniotic membrane graft and a conjunctival autograft is better surgical techniques than bare sclera in reducing astigmatism.