Pterygium excision can reduce higher-order aberrations
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Pterygium is a degenerative condition of the ocular surface. The growth is known to cause issues such as visual blur or recurrent inflammation. It can also induce astigmatism and corneal aberrations.
Pterygiums that are atrophic and thin are unlikely to cause complications. However, fleshy, thick pterygiums and those on or crossing the corneal limbus can cause significant corneal surface abnormalities. In this column, we describe a patient who had an improved higher-order aberrations profile after pterygium excision.
Source: Dhivya Ashok Kumar, MD, FRCS, FICO, FAICO, and Amar Agarwal, MS, FRCS, FRCOphth
Pterygium and corneal involvement
Pterygium is a triangular wing-shaped fibrovascular overgrowth of the subconjunctival tissue that encroaches on the cornea in the medial and lateral palpebral fissure, according to Sarkar and Tripathy. It has a cap, head and body, and it can present as progressive and atrophic. The progressive form of pterygium is thick, fleshy and vascular and encroaches toward the center of the cornea. It is an elastotic degeneration of the conjunctival stroma with fibroproliferative reaction. As the head encroaches on the cornea, Bowman’s layer is fragmented. Stocker’s line is seen in front of the head of the pterygium due to pigment deposition in the sub-epithelium. Deeper corneal involvement can cause scarring and rarely dellen formation. Visual disturbances occur in advanced pterygium involving the pupil region or induced astigmatism due to paracentral involvement. Pterygium is known to cause flattening of the horizontal axis.
Effect of pterygium excision on corneal topography
Fong and colleagues reported a mean magnitude of 0.99 D of preop astigmatism, with vector decomposition showing a flattening of the cornea in the horizontal meridian. They found a strong correlation between the horizontal extent of pterygium encroachment and astigmatic change after surgery. Kheirkhah and colleagues showed preoperative pterygium induced high astigmatism. Eyes with more advanced pterygium achieved higher surgically induced astigmatism postoperatively in their report. Surgery for pterygium was associated with significant changes in both front and back corneal surfaces. “Changes in corneal shape were mainly a decrease in midline corneal flattening,” Errais and colleagues reported.
Case report
A 53-year-old male patient presented to the outpatient department with blurring of vision for 6 months in his left eye. He was using glasses for reading, and there was no other systemic or ocular history. On examination, his visual acuity was 20/20 in the right eye and 20/200 in the left eye. On slit lamp examination, there was a thick, fleshy pink fibrovascular growth on the nasal conjunctiva encroaching the cornea, suggestive of progressive pterygium in the left eye. The pterygium involved the pupil axis also (Figure 1a). Corneal topography with aberrometry using Scheimpflug imaging was done. The preoperative astigmatism was 18.4 D. The preoperative corneal higher-order aberrations (HOA) root mean square (RMS) was 7.8 µm. The anterior segment and fundus examinations were normal in the left eye. His right eye was within normal limits.
The patient underwent surgical excision of pterygium with conjunctival autograft under local anesthesia (Figure 1b). Postoperatively, visual acuity improved to 20/20 at 1 month with good conjunctival wound healing. The postoperative HOA RMS reduced to 0.961 m (Figures 2a and 2b). Thus, there was significant reduction in corneal aberration. The astigmatism also reduced to 2.5 D postoperatively (Figures 3a and 3b). The patient was satisfied with reading glasses for near and was on lubricants for 1 month.
Pterygium excision and HOA changes
Pterygium can cause a significant increase in corneal and total higher-order aberrations, which can affect visual acuity. A study by Zare and colleagues reported that eyes with pterygium showed higher RMS of coma and trefoil as compared with normal fellow eyes. They also showed that with decreased uninvolved optical zone and increased size of the pterygium, RMS of all aberrations increased, with the differences statistically significant except for spherical aberration. There have been previous studies showing a reduction in HOAs after pterygium excision. Gumus and colleagues reported a decrease in RMS values of total aberrations and total HOAs at 3 months and 12 months after uneventful pterygium surgery. They noted coma and trefoil are the predominant significant HOAs to show a decrease in the early postoperative period. However, in a subsequent analysis at 1 year, all parameters except spherical aberration showed a significant reduction.
Conclusion
Pterygium and its size significantly affect high-order aberrations of the eye. Prompt surgical removal with good surface reconstruction with autograft or amniotic membrane graft will provide a good functional outcome. Avoiding allergens and continuous ultraviolet exposure can prevent further recurrences. Surgical excision of pterygium not only improves visual blur due to astigmatism, but it also improves the quality of vision by significantly changing the higher-order aberration profile. Hence, we prefer to recommend pterygium excision in eyes with a significant increase in higher-order aberrations. Preoperative and postoperative aberrometry should be mandatory for better analysis in such eyes for follow-up.
- References:
- Errais K, et al. Eur J Ophthalmol. 2008;doi:10.1177/112067210801800203.
- Fong KS, et al. CLAO J. 1998;24(2):115-117.
- Gumus K, et al. Cornea. 2012;doi:10.1097/ICO.0b013e3182431465.
- Kheirkhah A, et al. Can J Ophthalmol. 2012;doi:10.1016/j.jcjo.2012.07.002.
- Sarkar P, et al. Pterygium. In: StatPearls. StatPearls Publishing. Updated Aug. 25, 2023.
- Zare M, et al. Cornea. 2010;doi:10.1097/ICO.0b013e3181d3d689.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre, is the author of several books, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at aehl19c@gmail.com; website: www.dragarwal.com.
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