Effect of pterygiumseverity on visual acuity and contrast sensitivity

Vohra M.¹, Agarwal R.², Vohra J.³, Maggoo A.⁴, Rohatgi S.⁵

¹Dr. Malini Vohra, Assistant Professor, ²Dr. Ruchika Agarwal, Associate Professor; ³Dr. Jaya Vohra, Senior Resident, Government Medical College Ratlam, M P. ⁴Dr. Ashish Maggoo, Kanpur, U P, ⁵Dr. Sanjeev Rohatgi, Professor, ^1,2,5authors are affiliated with Rama Medical College and Research Centre, Mandhna, Kanpur, U.P. India.

Corresponding Author: Dr. Ruchika Agarwal, 7/57, Ratan Enclave, Tilak Nagar, Kanpur, Uttar Pradesh, India. E-mail:  ruchidrjain@yahoo.co.in

Abstract

Aim: To evaluate prospectively the effect of pterygium excision on visual acuity and contrast sensitivity before and after surgery. Material & method: A prospective observational study where in 63 eyes of 63 patients with primary pterygia were studied before and after surgery. Examination was done in which contrast sensitivity was measured with pellirobson chart pre-operatively and one month postoperatively following pterygium excision with Conjunctival Limbal Auto Graft. Result: As the grade of pterygium increases, decrement in contrast sensitivity occurs. The visual acuity significantly increased after the surgery. Mean contrast sensitivity following pterygium surgery improved from 1.49±0.21 to 1.70±0.20 (p value <0.001). Conclusion: Visual acuity and contrast sensitivity improved significantly following pterygium excision surgery.

Key words: pterygium, conjunctiva, fibrous connective

Manuscript received: 14th February 2019 Reviewed: 24th February 2019 

Author Corrected: 4th March 2019 Accepted for Publication: 7 th March 2019

Introduction

The pterygium is classically defined as a degenerative disease of the ocular surface with triangular fibrovascular tissue formation, which grows from the conjunctivatowards the surface of the cornea [1]. Although histopathogenesis has not been fully elucidated; it is verylikely that the pterygium represents a degenerativeresponse of the fibrous connective tissue to different stimuli. Among the risk factors, exposure to ultravioletradiation appears to play an important role in inducing damage to the limbal stem cells. As a result, there is a migration of the conjunctiva towards the cornea, chronic inflammation and fibrovascular tissue formation [2]. Other risk factors described related to the development of pterygium are the micro-traumas in the corneal limbus region and hereditary factors. The main risk factor is exposure to ultraviolet rays, and a possible explanation of this fact would be the location of pterygium, mainly in theinterpalpebral fissure, which is more exposed to sun raysand dust, leading to inflammation of the ocular surface.Recently, it was suggested that there is a mutation in thep53 gene on chromosome 17 as the cause of this disease,and changes in the expression of various growth factors,such as vascular endothelial growth factor A (VEGFA). Histologically, the pterygium is characterized by elastoticdegeneration of the conjunctival substantia propria, with eosinophilic and basophilic deposits and fibroblast proliferation [1]. Large pterygia occluding the visual axisdecrease visual acuity. However, even before entering theoptical zone, an advancing pterygium can cause visualimpairment by locally flattening the cornea and inducingwith-the-rule astigmatism and decreasing contrast sensitivity. Previous reports have demonstrated that the topographic changes in the cornea and visual impairment induced by pterygia can be reversed following removal [3]. Contrast sensitivity is reported to be involved in visual performance in daily life and in indoor activities such as face recognition[4,5].

The contrast sensitivity function has proved auseful tool for detecting visual disturbances when Snellen acuity failstoshow comparabledys function for in pterygia. Pterygium causes reduction in contrast sensitivity. Both spatial contrast sensitivity and glare dis­ability are worsened in patients with pterygia even when the Snellen visual acuity is minimally affected. The decline of contrastsensitivity in eyes with pterygium and relatively goodvision on Snellen's optotypes is the cause of somesubjective complaints of the patients and may be animportant factor in indication of pterygium surgery ofeyes with a relatively good visual acuity. We performedthis study in order to investigate the effect of pterygium surgery contrast sensitivity and visual acuity.

Materials and Methods

Type of study: Prospective interventional case study wasconducted.

Place of study: Cornea Clinic of Department of Ophthalmology, Rama Medical College and Research

Centre Mandhna, Kanpur. The study included 63 patientsattending the OPD and Cornea Clinic of the Departmentof Ophthalmology, Rama Medical College and Research Centre Mandhna, Kanpur.

Inclusion criteria: Patients with primary pterygium with ≥2D astigmatism were included in study.

Exclusion criteria: Pterygium with any anterior orposterior segment pathology was excluded from study.

Statistical method: re-operative and postoperative valueswere compared using paired t–test. Contrast sensitivity was compared against the grade of pterygium usingANOVA test.

Surgical Procedure: All surgeries were performed underperibulbaranesthesia.A small conjunctival incision was made medial to head of pterygium and sub conjunctival dissection carried out up to caruncle, superior and inferior fornix. The corneal epithelium 2 mm anterior of head was scrapped off with blade no. 11 Bard Parker blade and the pterygium head avulsed using a combination of blunt dissection and traction. The body of pterygium was then excised. Hemostasis was achieved by applying lightcautery to bleeders. After the pterygium mass was removed, a limbal-conjunctival auto graft was procured from the superior conjunctiva; the graft dissection was extended approximately 0.5mm into clear cornea to include the Vogt palisades and limbal stem cells. This graft was moved to cover the defective area and wassecured with 10-0 nylon sutures.The limbal end of the autograft was placed directly over the limbal area of thesurgical bed. The sutures were removed under the operating microscope after conjunctival epithelialization occurred.

Examination included: Snellen visual acuity, slit lamp examination, manual keratometry, contrast sensitivity

with pellirobson chart was done pre-operatively and one month post operatively. Nasal pterygium was graded

depending on the extent of corneal involvement.

Grade I – Pterygium crossing limbus < 2mm ontocornea.

Grade II – Pterygium crossing limbus onto ≥2 -4 mm ofcornea

Grade III – Pterygium crossing limbus onto > 4mm ofcornea and reaching up to pupillary margin

Grade IV- Pterygium crossing pupillary margin.

Contrast Sensitivity Examination: Contrast sensitivity was recorded using Pelli- Robson chart. Method of recording contrast sensitivity with Pelli- Robson chart: Subject was seated directly in front of Pelli-Robson chart at a distance of 1 meter with the best distance correction. Subject is asked to outline each letter on the chart. Test is concluded when the subject guesses two of the three letters of the triplet incorrectly. Subject’s sensitivity is indicated by the finest triplet for which two of the three letters are named correctly.

Table No.-1: Grade wise distribution of cases/eyes

Table 1 shows grade wise distribution of cases. In present study, 8 eyes had grade I pterygium, 27 eyes had grade II pterygium, 25 eyes had grade III pterygium and 3 eyes had grade IV.

Table No.-2: Comparison of grade wise pre-op and post op contrast sensitivity (CS)

The above table shows that pterygium excision surgery cause improvement in contrast sensitivity in all grades of pterygium. The improvement was significant in grade II,III,IV having p value (<0.001) and not significant in grade I p value (0.225).

Table No.-3: Comparison of pre-op and post op BCVA

The above table shows improvement of Bcva in all grades of pterygium following pterygium excision surgery. The improvement was significant in grade II,III,IV p value (<0.001) and not significant in grade I p value (0.184).

Discussion

A pterygium-induced refractive change often leads tovisual impairment. Pterygium leads to inflammation, foreign body sensation, tearing, dry and itchy eye. The indications for pterygium surgery are cosmetic disfigurement, visual impairment, recurrent inflammationand motility restriction. Surgical intervention resulted inan increase in the mean refractive power at one monthafter surgery, which indicates a steepening of flattened cornea. Pterygium induced astigmatism appears to be dueto alteration in tear film caused by lesion. As the head of pterygium approaches the apex of cornea, a tear meniscus develops between the corneal apex and the elevated pterygium, causing an apparent flattening of normal corneal curvature [6,7]. Previous studies have shown thatpterygium cause corneal distortion which induce a significant amount of astigmatism[8,9,10,11]. The exactmechanism of flattening in horizontal meridian due topterygium is not clear. It is thought to be caused by theformation of tear meniscus between the corneal apex [6,12]and the elevated pterygium, causing an apparentflattening of the normal corneal curvature[13]. As thisflattening is along the horizontal meridian, it usuallycauses with-the-rule corneal astigmatism. Pterygiumexcision induces a reversal of pterygium related corneal flattening[6,14]. Comparison of pre and post operative corneal topography also revealed significant changes in the majority of topographic parameters. Numerous studies have documented improvement in the corneal condition and topographic indices after pterygium excision [15,16,17]. Unlike Yasar et al[12] who considered no role for fibrovascular traction in pterygium induced corneal changes, Oldenburg et al[6] and Budak et al[18] hypothesized that flattening of the cornea and changes in the corneal topography may be produced by a pooling oftears at the apex of the pterygium or by its mechanical traction. These abnormalities and their effects on thecornea are mostly reversible by the surgery especially inthe cases of early intervention [17,15,24,21]. Previous studies have reported the association of pterygium and contrast sensitivity. Lin et al in 1989 showed that contrast sensitivity was lower at all spatial frequencies in thepatients with pterygium. Another study showed that contrast sensitivity at medium to-high spatial frequenciesof 6, 12, and 18cpd significantly improved after pterygium excision, while contrast sensitivity at low spatial frequencies of 1.5 and 3cpd did not change aftersurgery [20].

A Maliket al [21] found a significant negativecorrelation was seen between contrast sensitivity and thevertical, horizontal dimensions and the area of thepterygium. Maximum correlation was seen with thevertical dimension of pterygium, followed by area andthen horizontal width. In present study it was observedthat contrast sensitivity decreases with increase in gradeof pterygium. Contrast sensitivity reduced maximally ingrade IV and minimally in grade I. There was statistically significant correlation between grade of pterygium and, contrast sensitivity (p value<0.001). Our findings are inaccordance with the findings of another workers Lin et al in1989 [22]. Pterygium can cause an asymmetric distortion ofthe cornea, because the lesion typically extends radiallyfrom the corneal periphery. The disruption to the cornealsurface topography induces both coma and trefoil wave front errors (WFEs)[23,24]. There is commonly an increase incorneal and refractive astigmatism with pterygium as wellas an increase in Higher-order wave front error (HOWFE), with an effect proportional to the extent of thelesion [25,26]. Because the condition approaches lateral to thevisual axis, a change in Surface Asymmetry Index (SAI) is not usually a feature of the condition. Higher-orderwave front error is associated with correspondingreduction in visual acuity and contrast sensitivity [27].Studies indicate that contrast sensitivity testing may provide additional objective methods for documenting impaired vision in patients with pterygiumwhen Snellen visual acuity is minimally affected [28].Corneal astigmatism and contrast sensitivity values inpatients with pterygia are useful indicators for the needof pterygium surgery or as indicators of surgical success [29]. In the present study, 8 eyes had grade 1pterygium, 27eyes had grade 2 pterygium, 25 eyes hadgrade 3pterygium and 3 eyes had grade 4 pterygium. Ourfindings are in accordance with the findings of otherworkers[30].The preoperative mean astigmatism was3.29D±1.46. The astigmatism decreased significantly following pterygium excision. The mean preoperativerefractive cylinder decreased from 3.29D±1.46 D to1.49±0.82 D postoperatively (p<0.001). Pterygiuminduced impaired visual acuity may be caused by analteration in tear film or by mechanical effects of the lesion. Therefore, excision of the lesion may lead to reconstruction of the normal surface, and thus, improvement in the visual acuity [26]. Statistically improvement in BCVA in grade II, grade III and grade IVpterygium was due to reduction of astigmatism. Linet.al.in 1989 found that contrast sensitivity was lower atall spatial frequencies in the patients with pterygium.Another study observed that contrast sensitivity at mediumto-high spatial frequencies of 6,12, and 18cpdsignificantly improved after pterygium excision, whilecontrast sensitivity at low spatial frequencies of 1.5 and 3cpd did not change after surgery [30].In present study it wasobserved that contrast sensitivity decreases with increasein grade of pterygium. Contrast sensitivity reduced maximally in grade IV and minimally in grade I. There was statistically significant correlation between grade ofpterygium and contrast sensitivity. Our findings are in accordance with the findings of Lin et al in 1989. The contrast sensitivity improved significantly following pterygium excision. The mean preoperative contrasts ensitivity increased from 1.49±0.21 to 1.70±0.20 post operatively. Surgical removal of pterygium caused asignificant improvement in contrast sensitivity. The mean preoperative contrast sensitivity improved from1.69±0.20 to 1.83±0.20 post operatively (p=0.22) in grade Ipterygium, from1.51±0.13 to 1.74±0.14 was noticed in grade II. In grade III pterygium contrast sensitivityincreased and in grade IV contrast sensitivity increased from1.25±0.10 to1.45±0.10. The amount of contrast sensitivity increased significantly following pterygium excision ingrade II, grade III and grade IV but in grade I, the increase in the amount of contrast sensitivity after pterygium excision was not statistically significant (pvalue 0.22).

Conclusions

Surgical excision of pterygium improves contrastsensitivity, visual acuity and reduce astigmatism.Contrast sensitivity is reported to be involved in visual performance in daily life and in indoor activities such as face recognition. The contrast sensitivity function has provedauseful tool for detecting visual disturbances when Snellenacuity failstoshow comparabledys function for in pterygia. Contrast sensitivity testing may provide additional objective methods for documenting impaired vision in patients with pterygium when Snellen visual acuity is minimally affected. Corneal astigmatism and contrastsensitivity values in patients with pterygia are useful indicators for the need of pterygium surgery or as indicators of surgical success. The study demonstrates usefulness of visual acuity and contrast sensitivity tests and how they can be incorporated into the decision as to when to do pterygium excision surgery. The decline of contrast sensitivity in eyes with pterygium and relatively good vision on Snellen's optotypes is the cause of some subjective complaints of the patients and may be animportant factor in indication of pterygium surgery ofeyes with a relatively good visual acuity.

Current study Added to the existing Knowledge: Contrast sensitivity testing may provide additional objective methods for documenting impaired vision inpatients with pterygium when Snellen visual acuity is minimally affected. The study demonstrates usefulness of visual acuity and contrast sensitivity tests and how they can be incorporated into the decision as to when to do pterygium excision surgery.

Contribution from Various authors

·   Dr. MaliniVohra -Designing of study and manuscript preparation.

·   Dr. Ruchika Agarwal - Maintenance of data and follow up of patients

·   Dr. Jaya Vohra –Statistical analysis and collection of references

·   Dr Ashish Maggoo- Reference of patients.

·   Dr. Sanjeev Rohatgi- Critical analysis of the whole study

Conflicts of Interest: Nil

Funding: Nil

References

How to cite this article? 

Vohra M, Agarwal R, Vohra J, Maggoo A, Rohatgi S. Effect of pterygium severity on visual acuity and contrast sensitivity. Ophthal Rev: Tro J ophtha & Oto. 2019;4(1):42-47.doi:10.17511/jooo.2019.i1.09