International Journal of Virology Studies & Research

Efficacy of Photorefractive Keratectomy In Hyperopia Patients

The objective is to review the long-term efficacy, stability, and reliability of photorefractive keratectomy (PRK) treatment in hyperopia patients and to assess the complications that may arise during the follow-up period.

Döndü Melek Ulusoy, MD, Department of Ophthalmology done the review on 76 eyes of 42 patients who underwent PRK treatment for hyperopia. Patients were separated into two groups according to their spherical equivalent (SE) values.

Both groups were analyzed and compared in terms of postoperative refraction and vision acuity, post-operative complications, keratometry values, stabilization period and the results of interventions for treatment.

Hyperopia

Hyperopia is a common refractive error that is usually corrected with eyeglasses or contact lenses. Following the fast advancement in refractive surgery and technology, eyeglasses or contact lenses were no longer the single treatment option in refractive errors. Today, extraction of the transparent lens and intraocular lens implantation, phacic intraocular lens applications, and corneal surgeries are performed for correction and treatment of refractive errors.

Excimer Laser is the most widely used method in refractive surgery methods. In this method, the cornea is reshaped using 193 nm argon-flourine laser and cornea is corrected according to patient’s refractive error. Different techniques can be chosen for patients with differences in cornea structure, refraction errors and patient expectations. The most frequently used methods are PRK (Photorefractive keratectomy), LASIK (Laser in situ keratomileusis) and LASEK (Laser subepithelial keratomileusis).



Photorefractive Keratectomy

PRK is the first widely used excimer laser method. In this method, cornea epithelium is mechanically peeled and then an excimer laser is applied. PRK is used as a safe, efficient and predictable method in the correction of myopia and astigmatism as well as treatment of hyperopia. However, post-operative pain, corneal haze formation, high regression rate and late stabilization of visual acuity in patients with high-grade hyperopia (>+6.00) are the disadvantages of this method.

All patients were informed about the risks and present alternatives for the surgical procedure and a written consent was taken. Corneal haze evaluation was graded using the following objective criteria using the slit-lamp biomicroscopia:

Grade 0: Completely clear cornea
Grade 1: Traces of reticular subepithelial haze visible only with broad tangential illumination
Grade 2: Clearly visible reticular subepithelial haze diffusely distributed
Grade 3: Grade 2 haze with areas of confluence
Grade 4: Dence opacity completely obscuring details of intraocular structures.

Surgical Method

All patients were operated by the same surgeon (NC). First, after administering topical proparacaine 0.5%; (Alcaine, Alcon) and disinfection of the skin surface area around the eyes with povidone-iodine solution, area was draped and lid speculum was positioned. 8.0-9.00 corneal trephine was positioned over the cornea. The container was filled with 20% ethyl alcohol and kept for 20 seconds.

After that, the alcohol was absorbed using cellulose sponge and the cornea was washed with BSS. Epithelium was lifted and separated from incision edges using the crescent blade. After drying stroma, laser ablation was performed (SCHWIND ESIRIS excimer laser's ORK-CAM software [SCHWIND eye-tech-solutions, Kleinostheim, Germany]).

An antibiotic eye drop ofloxacin 0.3%; (Exocin, Allergan) was administered and a therapeutic contact lens was fitted. Topical antibiotic eye drops ofloxacin 0.3%; (Exocin, Allergan) qid and artificial tears hyaluronic acid 0.15%; (Eyestil, Teka) qid was used in post-operative period. Following the closure of corneal epithelium, the contact lens was removed and topical fluorometholone 0.1%; (Flarex, Alcon) qid was added to the treatment regime. The treatment period was completed to one month and patients were followed in an outpatient basis on the first week, first month, third month and sixth month of the operation and then in 6-month periods.

Statistical Analysis

SPSS for Windows Version 15.0 programme was used for statistical analysis. Numerical variables were summarized with average ± standard deviation, median, and minimum-maximum values; categorical variables were summarized with number and percentage. Continuous variables were compared with student's t-test and qualitative variables were compared with chi-square test between groups. The level of significance was set at 0.05 with 95% confidence interval.

Results

Twenty-eight (69.73%) male and 14 (30.26%) female patients were included in the study. Mean age of the patients was 33.97 ± 10.26 years (18-51) and mean patient follow-up period was 27.16 ± 8.43 (6-39) months.

Results of patients were assessed separately for each group.

Surgical treatment of hypermetropia tails away from treatment of myopia because of the fact that steepening cornea is more difficult than flattening cornea. Several methods such as hexagonal keratectomy, radial and diode thermokeratoplasty, contact and non-contact Ho: YAG, conductive keratoplasty, automatic lamellar keratoplasty, clear lens extraction, intrastromal corneal implants were tried in the treatment of hypermetropia.

But low predictability, refractive stability, and high complication rate were reported from these methods. A 193_nm excimer laser is used successfully in the treatment of myopia and astigmatism. This laser, generates a smooth ablation of peripheral corneal stroma, could be used in hypermetropia treatment with its promising results.

The efficacy and reliability of PRK therapy in hypermetropic patients up to +5.00 D were documented in several studies. It has been reported that in high hyperopia (˃5.00 D), PRK is a method that has less predictable results associated with higher regressions.

In our study, low and high-grade hyperopia patients that underwent PRK were analyzed and compared in terms of postoperative refraction and visual acuity, postoperative complications, keratometry values, stabilization period and the results of interventions for treatment. Our study also complements the literature by giving long-term results of high patient rates.

To sum up, PRK treatment is an efficient, reliable and predictable method even in the long term that can be used in the treatment of hyperopia patients. A study by O’Brart et al., conducted on 40 hyperopic eyes that underwent PRK treatment, divided the subjects into 4 groups according to their preoperative refractive errors (group 1:+1.50 D, group 2:+3.00 D, group 3:+4.50 D, group 4:+6.00 D).

Overcorrection was detected during the first month of the surgery. Emetropia was achieved between 3 to 6 months and refractive stability was reached at 12th month. Mean SE value at the 12th month was +0.55 D, which was measured as +0.83 D after 7.5 years of follow-up. Regression was not reported in any of the patients. El-Agha et al., did a study on 22 PRK received hyperopic eyes (≤+6.00 D) and found overcorrection at the first month and a fast refractive regression and myopic neutralization 6 months after surgery.

Refractive stability was achieved between 3 to 6 months. Similar results were also reported in Jackson et al’s study. Corones et al’s., the study performed on 38 eyes with SE values between +1.00 D and +8.00 D revealed that starting with overcorrection during post-operative period, mean SE value was found to be ± 0.20 D at the end of follow-up period. Refractive stability was achieved in a period longer than a year.

In our study, both groups were diagnosed with low myopic refractive values on the 1st month of the operation and values closer to emetropia were reached in the 3rd month. After 3rd month, a slight regression especially prominent in group 2 was seen. Refractive stability was achieved in 6.85 months in group 1 and in 4.67 months in group 2. These results are deemed to be more successful with lower regression rates and shorter stabilization periods found in the literature.

Conclusion

In the light of our findings, photorefractive keratectomy (PRK) was found to be a reliable, effective and predictable method for the correction of low and high-grade hyperopia.

Continue reading ... This research article published in IJOES Journal.




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