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   Table of Contents      
ORIGINAL ARTICLE
Year : 2001  |  Volume : 49  |  Issue : 4  |  Page : 235-40

Frequency doubled Nd :YAG (532 nm) laser photocoagulation in corneal vascularisation : efficacy and time sequenced changes.


Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Correspondence Address:
A Sharma
Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh
India
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Source of Support: None, Conflict of Interest: None


PMID: 12930115

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  Abstract 

PURPOSE: To evaluate the efficacy of frequency-doubled Nd:YAG (532 nm) laser treatment in quiescent corneal vascularisation, and to record the sequential changes in lasered vessels and complications in eyes with one and two quadrant vascularisation. METHODS: Thirty eyes (30 patients)--15 eyes (15 patients) with one-quadrant and 15 eyes (15 patients) with two-quadrant corneal vascularisation were treated. Frequency-doubled Nd:YAG laser (532 nm) was used at laser setting of 120-480 mw power, 50-150 mm spot size and 0.05 sec pulse duration. The area of corneal vascularisation, status of treated corneal vessels, area of corneal opacity and visual acuity were recorded before treatment, at one week after treatment and thereafter at monthly intervals up to three months. RESULTS: The mean area of corneal vascularisation decreased from 20.09% to 8.31% of the total corneal area in group I (p<0.01) and from 44.34% to 20.67% of the total corneal area in group II (p<0.01) at 3 months' follow-up. The mean reduction in the area of corneal vascularisation was 58.64% in group I and 53.38% in group II (p>0.05). Of 148 corneal vessels treated, 60 (44.6%) were totally occluded, 44 (30%) partially occluded, 37 (28%) recanalized and there was one shunt vessel at one week following laser treatment. At three months' follow-up, 80 (54.15%) vessels were totally occluded, 14 (9%) partially occluded, 52 (35.14%) recanalised and two shunt vessels appeared. Thus, at three months' follow-up, the number of totally occluded vessels increased and partially occluded vessels decreased. Superficial corneal haemorrhage was observed in 4 (14%) patients. CONCLUSION: Frequency-doubled Nd:YAG (532 nm) laser photocoagulation appears a safe and effective means of reducing the area of corneal vascularisation in quiescent eyes with vascularised corneal opacities.

Keywords: Adult, Cataract, complications, Corneal Neovascularization, complications, pathology, physiopathology, surgery, Female, Humans, Laser Coagulation, adverse effects,


How to cite this article:
Sharma A, Samal A, Narang S, Gutpa A, Ram J, Gupta A. Frequency doubled Nd :YAG (532 nm) laser photocoagulation in corneal vascularisation : efficacy and time sequenced changes. Indian J Ophthalmol 2001;49:235

How to cite this URL:
Sharma A, Samal A, Narang S, Gutpa A, Ram J, Gupta A. Frequency doubled Nd :YAG (532 nm) laser photocoagulation in corneal vascularisation : efficacy and time sequenced changes. Indian J Ophthalmol [serial online] 2001 [cited 2019 Dec 7];49:235. Available from: http://www.ijo.in/text.asp?2001/49/4/235/14695

Corneal diseases constitute a major cause of visual impairment and blindness in developing countries.[1] Vascularised corneal scars are a major indication for penetrating keratoplasty in India.[2] Patients with corneal opacities and vascularisation have a high risk of allograft rejection and subsequent graft failure.[3] Most authors consider two or more quadrants of corneal vascularisation a high risk factor. [4,5] The degree of vascularisation has been correlated with increased risk and shorter time interval between penetrating keratoplasty and onset of allograft rejection. A decrease in corneal vascularisation before penetrating keratoplasty may reduce the risk of rejection. [6,7]

Various treatment modalities to reduce stromal vascularisation have been described.[8-10] Corticosteroid and non-steroidal anti-inflammatory drugs reportedly have limited success in stable corneal vascularisation.[8-10] Rapamycin has been evaluated to treat corneal vascularisation and prolong allograft survival.[11] Favourable results have been reported in experimentally induced [12,13] and human corneal neovascularisation [14,15] following corneal laser photocoagulation using yellow dye laser (577 nm), argon laser (514 nm) and frequency doubled Nd;YAG (532 nm) laser. While the efficacy of frequency doubled Nd:YAG (532 nm) laser in experimental corneal vascularisation has been evaluated,[12] its use in human corneal vascularisation and the sequential changes in laser-treated vessels have not. In this prospective study, we report the results of corneal laser photocoagulation using frequency-doubled Nd:YAG (532 nm) laser and the sequential changes in lasered vessels.


  Materials and Methods Top


Thirty patients with vascularised corneal opacities in quiescent eyes were prospectively evaluated in the cornea service of the Postgraduate Institute of Medical Education and Research, Chandigarh. Informed consent was obtained from all the patients enrolled in the study. The study was cleared by the Institute Research Review Committee. The essential inclusion criteria were: 18 years of age or more with superficial and deep corneal vascularisation up to two quadrants and involvement of 50% or more of total corneal area with healed corneal disease. Patients with an active corneal stromal infiltrate, a corneal epithelial defect, adherent leucoma, uveitis, raised intraocular pressure (IOP) and/or dry eyes were excluded from the study.

Each patient underwent a detailed ophthalmic examination including recording of the best corrected visual acuity, IOP, extent of corneal opacity and vascularisation. Corneal vascularisation and opacity was measured using retroillumination on Haag Streit Slitlamp (X16 magnification). The extent of corneal vascularisation was mapped on colour coded grid diagrams (1 mm2 on grid representing 0.2 mm x 0.2 mm of cornea). Anterior segment photographs were also used to document the area of corneal vascularisation and opacity by the grid method.[15] The patients were divided into 2 groups of 15 patients (15 eyes) each. Patients with corneal vascularisation equivalent to one quadrant (up to 25% of total corneal area) formed group I and patients with corneal vascularisation equivalent to two quadrants (25% to 50% of total corneal area) constituted group II.

Laser photocoagulation was done using frequency-doubled Nd: YAG (532 nm) laser and Abraham contact lens. On slitlamp biomicroscopy, under high magnification (x 16) using retroillumination, the direction of blood flow in the corneal vessels was noted to identify afferent and efferent vessels. The afferent vessels were treated first and efferent vessels later. Laser parameters used were 120-480 mw of power, 50-150 mm spot size and 0.05 second pulse duration. Laser parameters were set after subjective verification of the diameter and position of corneal vessels. The ocular surface was anaesthetised using topical 4% xylocaine hydrochloride. Methylcellulose eye drop was used as coupling agent between the eye and the Abraham contact lens. The lens was placed on the corneal surface. The slitlamp beam and the red light spot were focused on the vessel to be lasered. The slitlamp beam was focused at 30°-45° oblique illumination and X16 magnification. The laser was applied on a segment of the corneal vessel. The cessation of blood flow [Figure:1a] or the appearance of "box-cars" within the lasered vessel [Figure:1b] was taken as the end point. The patients were prescribed topical betamethasone (0.1%) twice daily for one week following laser treatment.

The patients were followed up at one week, one month, two months and three months after the last laser treatment. The effect on laser-treated vessels was recorded as complete occlusion, partial occlusion, recanalisation and appearance of shunt vessels on slitlamp biomicroscopy (X16 magnification). Complete occlusion referred to complete cessation of blood flow distal to laser treated vessel or discontinuity of vessel wall at the point of laser treatment. Partial occlusion referred to the narrowing of the vessel distal to point of laser treatment or partial continuity of distal end with proximal end of treated vessel. Shunt vessel referred to the appearance of new vessels connecting the proximal end of the occluded vessel to its distal end. The observations were documented and statistically analysed using the paired 't' test.


  Results Top


There were 18 (60%) males and 12 females; their ages ranged from 29 to 54 years. Seventeen of 30 patients had been treated for infective keratitis in our cornea service, 11 patients for herpes simplex keratitis, 5 for bacterial keratitis and one for fungal keratitis. The remaining 13 patients had been treated by the referring physician for presumed infective keratitis. There were no corneal epithelial defects, infiltrates, oedema, or signs of intraocular inflammation in the eyes studied. All the eyes were quiescent at the time of laser treatment of corneal vessels.


  Area of corneal vascularisation Top


The mean area of corneal vascularisation in group I patients before laser treatment was 20.9% of the total corneal area; this decreased to 8.43% of the total corneal area one week after laser treatment (p<0.01). Subsequently, it was 8.20%, 8.52%, and 8.31% at one month, two months and at three months follow-up respectively (p<0.01) [Figure - 2]. The mean area of corneal vascularisation in group II patients before laser treatment was 44.34% of the total corneal area; this decreased to 25.4% of the total corneal area at one week after laser treatment (P < 0.01). The mean area of corneal vascularisation subsequently was 23.56%, 21.25%, and 20.67% at one month, two months and three months follow-up respectively (p<0.01) [Figure - 2].

Corneal vascularisation before laser treatment in a group II patient and disappearance of corneal vascularisation in the same patient following laser treatment at 3 months' follow-up. A clear corneal graft in the same patient 2 years (June 1999) after laser treatment and penetrating keratoplasty. The patient had undergone penetrating keratoplasty in January 1997 and had no episode of graft rejection till recent follow up (September 2001). The corneal graft was clear and the best corrected visual acuity was 6/9. Four patients underwent penetrating keratoplasty following laser treatment for corneal vascularisation. Two of them achieved a visual acuity of 6/18, another 6/12, and the fourth, 6/9.


  Area of corneal opacity Top


In group 1 the mean area of corneal opacity decreased from 31.17% to 30.6% at one week follow up. The area of corneal opacity further decreased to 27.66% at one month, 27.13% at 2 months, and 25.64% at 3 months. The reduction at 3 months' follow-up was statistically significant (p<0.01). In group II the mean area of corneal opacity decreased from 29.21% to 28.17% at one week follow-up. It further decreased to 27.25% at one month, 26.9% at 2 months and 25.97% at 3 months. The reduction at 3 months' follow-up was statistically significant (p<0.01). Two patients in group I and one patient in group II had associated lipid keratopathy. All the three eyes showed a decrease in the area and density of lipid keratopathy after laser treatment.


  Sequential changes in corneal vessels[TAG:2]

In all, 148 (group I,51; group II, 97) corneal vessels were treated; 66 (44.6%) vessels were completely occluded, 44 (30%) partially occluded, 37 (25%) recanalised and one shunt vessel appeared by the end of one week. At the end of 3 months, 80 (54.15%) vessels were totally occluded, 14 (9%) partially occluded, and 52 (35.14%) vessels recanalized. Two shunt vessels had appeared. During follow-up, the number of completely occluded and recanalized vessels increased and the number of partially occluded vessels decreased. Complete occlusion of the vessel following laser treatment and recanalisation of the treated vessel in the same eye.

[TAG:2]Visual acuity
 Top


Pre-laser visual acuity in group 1 patients ranged from hand-movements close to face to 6/18. At 3 months' follow up visual acuity improved in two patients. One improved from 6/60 to 6/36 and the other 6/18 to 6/9. In 13 patients there was no change in the best corrected visual acuity. Pre-laser visual acuity in patients of group II ranged from hand movements close to face to 6/36. At 3 months' follow-up none of the patients showed change in visual acuity.


  Complications Top


Superficial corneal haemorrhage occurred following laser therapy in two (13%) cases each in group 1 and in group II. Superficial corneal haemorrhage resolved within one week in all these patients without any treatment. There was no recurrence of herpes simplex keratitis; similarly corneal thinning, descmetocoele or corneal perforation following laser therapy did not occur in any of these patients.


  Discussion Top


Laser treatment of corneal vascularisation in the experimental models and clinical studies have shown encouraging results.[12-18] The efficacy of argon blue-green (488 nm),[19] argon green (514 nm) [20,21] and yellow dye (577 nm) laser, [12,14] and Q-switched Nd:YAG laser [22,23] in reducing corneal vascularisation has already been reported. This study now demonstrates that frequency-doubled Nd: YAG (532 nm) laser effectively reduces the area of corneal vascularisation by 58.64% and 53.38% in group I and group II respectively. In the study by Baer and Foster[14] the mean reduction in area of corneal vascularisation was 41% following yellow dye laser treatment at 9.3 months' follow up. The results of our study with frequency-doubled Nd: YAG (532 nm) are similar.

In the present study, we also evaluated the sequential changes in corneal blood vessels following laser treatment. During follow-up we found that the number of totally occluded corneal vessels increased while those partially occluded closed completely. In addition, the percentage of recanalised vessels increased from 25% at one week to 35% at 3 months. Recanalisation of vessels can occur if the effect of the laser is low and if the vessels are relatively deeper. As recanalization may occur in nearly 50% of the treated eyes, the procedure is still not considered the standard intervention in patients needing penetrating keratoplasty. Some of the partially occluded vessels, however, get totally occluded over a period of time due to thrombus formation in the lumen of vessels. [12,13] The pattern of sequential changes in the laser-treated vessels was similar in the two groups. Similar documentation of sequential changes in corneal vessels is not available in the literature for immediate comparison with our observations.

In the present study, the area of corneal opacity reduced from 31.18% to 25.64% in group I and from 29.21% to 25.97% in group II following laser treatment at 3 months' follow-up. Two patients in group I and one patient in group II had a decrease in the density of lipid exudation and in the area of opacity. Several authors have reported significant decrease in the extent and density of lipid keratopathy following argon laser therapy. [15,23] Baer and Foster[14] (577 nm laser) reported a mean reduction in the area of corneal opacity by 7% at 9.3 months' follow-up. In our study the reduction of area of corneal opacity was 5.54% in group I and 3.24% in group II.

Yellow dye (577 nm) laser has higher absorption by oxyhaemoglobin and reduced haemoglobin compound to argon laser. It requires half the exposure time, 15% to 20% less power for occlusion of corneal vessels and produces similar photocoagulation effect as argon laser.[24] Frequency-doubled Nd:YAG (532-nm) laser has been considered as effective as yellow dye (577 nm) laser and 15% more than argon (488 nm) laser. It has higher absorption by oxyhaemoglobin, reduced haemoglobin, pigments and 95% transmittance though ocular media.[25] Previous histopathological studies have demonstrated that vaso-occlusive effects of argon green (514 nm) and frequency-doubled Nd:YAG (532 nm) lasers are comparable.[26]

There are few reports of improvement of visual acuity following laser treatment of corneal vascularisation. It was 22% of cases in a one-year follow-up study by Marsh.[27] Baer and Foster[16] reported that using yellow dye (577 nm) laser, visual acuity of five (17.5) patients improved by 0.7 Snellen lines in 9.3 months' follow up. Two (7%) of our patients had improvement in visual acuity at 3 months' follow up. Visual acuity improvement coincided with the resolution of lipid keratopathy, and a subsequent decrease in the density of the opacity. Other studies have also demonstrated that the procedure is most effective in eyes with lipid keratopathy. [15, 20, 23]

The complications of laser therapy of vascularised corneal lipid keratopathy include bleeding into lipid keratopathy, corneal thinning, iris atrophy, crystalline deposits on iris and peaking of pupil following corneal laser therapy. [20, 27, 28] We observed superficial corneal haemorrhage in two (13%) patients each in group I and group II. Corneal haemorrhage resolved within one week in all four patients without any additional treatment.

Eyes with previous episodes of herpes simplex keratitis (HSK) are at an increased risk of recurrence of HSK following treatment with argon laser and hence need close follow-up. None of the patients in our study had a recurrence of HSK following laser treatment. Laser treatment for corneal vascularisation is not indicated in presence of active or recurrent inflammation. No other complications such as corneal thinning, descemetocele, corneal perforation and iris atrophy were observed following laser therapy in any of our patients. In a recent study, fine needle diathermy has been reported as a useful and inexpensive adjunct treatment for established corneal vessels.[29] However, intrastromal bleeding and crystalline deposits are not uncommon and the procedure may have to be repeated.[29]

Our study demonstrates that corneal laser photocoagulation using frequency-doubled Nd: YAG (532 nm) laser is a safe and effective method of decreasing the area of corneal vascularisation in quiescent eyes with vascularised corneal opacities. We recommend corneal laser photocoagulation (532 nm) for corneal vascularisation for lipid keratoplasty and prior to penetrating keratoplasty in high-risk patients. The procedure decreases the area of vascularisation, area of corneal opacity, and improves vision in a significant number of patients with lipid keratopathy. In our experience of a limited number of patients undergoing transplants following laser photocoagulation for corneal vascularisation, the procedure significantly improves the graft survival. Prospective studies comparing results of frequency-doubled Nd: YAG (532 nm) with argon green (514 nm) and yellow dye (577 nm) laser may demonstrate any differences in their efficacy in reducing corneal vascularisation.

 
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    Figures

  [Figure - 1], [Figure - 2], [Figure - 3]


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