|Year : 1983 | Volume
| Issue : 7 | Page : 1031-1037
Krypton laser-clinical trial and preliminary observations
Kanti Mody, Asha Saxena
Jaslok Hospital and Research Centre, Mumbai, India
Jaslok Hospital and Research Centre, Mumbai-400 026
|How to cite this article:|
Mody K, Saxena A. Krypton laser-clinical trial and preliminary observations. Indian J Ophthalmol 1983;31:1031-7
Experimental, clinical and histological as well as electromicroscopic studies on the use of Krypton Laser (Red Light 647.3 nm) are reported by various international authorities.
A clinical study on use of Krypton Laseyin various fundus conditions at Jaslok Hospital and research Centre was conducted during the years 1981 and 1982. Preliminary clinical observations and the impression during this study are reported in this presentation.
| Materials and methods|| |
Followingg conditions were selected and included for the treatment in this study.
1. Dianetic Retinopathy
b) proliferative Diabetic retinopathy with High Risk Characteristics.
2. Idiopathic Central Serous Choroidopathy
3. Disciform Degeneration
Pre-Treatment evaluation and assessment
1. Complete history and Clinical Ophthalmic Examination of both eyes with fully dilated pupils. Direct and Indirect Ophthalmoscopy as well as 3-mirror Contest Lens Biomicroscopy Examination of the Fundus consisted of the essential parts of this examination.
2. Macular Function: Following examination was carried out to evaluate and assess the Macular Function.
-Central Visual Activity (near+distance)
-Visual fields (Central) -Photostress Test
-direct and indirect Ophthalmoscopy
-Goldmann Contact Lens and Hruby
Lens with Slit Lamp Biomicroscopy.
3. Colour Photographic documentation and Fundus Flourescein Angiography formed very important parts for the pre-treatment evaluation and assessment as well as for the post-treatment observations and follow-up study.
4. Krypton Laser 547.lnm (Red Light) was used for the treatment and Argon laser (514.5nm-Green Light) was used for comparative study.
1. Focal Maculopathy
Initial Vision varied from 6/9 to 6/24
Ophthalmoscopy: Microaneurysm, Haemorrhages as well as circinate or focal exudates and mild macular adema. Fundus Flouresce in Angiography showed adequate capillary perfusion with the areas of focal leakage.
Treatment: a) 100 to 200 microns size, moderate intensities with longer exposure time (0.2 or more)
b) Centres of Circinate Exudates and site of focal leakage were treated.
Results: Initial Vision was good
a) Vision : Improved 5 eyes
Stationary 3 eyes
Total No. of eye 8 No. of
b) Maculopathy Lesions showed regression.
2. Cystoid Maculopathy
-Initial Vision varied from 6/12 to 6/60 -Ophthalmoscopy revealed mic
roaneurysms, Haemorrhages and relatively few exudates. However marked macular edema with cystiod spaces (3 mirror Contact Lens Biomicroscopy) was observed.
Fundus Flourescein Angiography.: showed increased permeability of the vessels at the posterior pole with loculated leakages.
Treatment: Grid pattern (sparing the fovea) 100-200 microns, moderate intensities with longer exposure time (0.2 to 0.3 seconds).
Results: Initial Vision was either not good or bad
a) Vision : Improved 3 eyes
b) Stationary 3 eyes
c) Worse 2 eves
Total No. of eyes 8
No. of sessions 24 eyes
a) Maculopathy Lesions showed regression with either reduction or disappearance of macular edema.
3. IschemicMaculopath_v: Initial Vision varied from 6/12 part to 6/60.
Clinical Examination: Microaneurysms, few exudates, cystoid edema, grey pale are of the retina.
Fundus Flourescein Angiographv: showed Predominantly capillary non-perfusion in the macular and paramacular regions and leakage.
Treatment: Irregular Grid Pattern, 100-200 microns spotsize. Moderate intensity, 0.2 to 0.3 seconds, Exposure time, associated Panretinal Photocoagulation with about 400-600 burns were carried out. Results: Initial Vision was poor.
Vision : Improved 4 eyes
Stationary 5 eyes
Worse 3 eyes
Total No. of eyes 18
No. of sessions 24 eyes
Note: General deterioration of vision occured during the study. 2 eyes developed Disc Neovascularisation.
Maculopathy lesions: Did not show obvious evidence of regression, edema persisted to certain extent. No change was observed in the areas of non-perfusion. Leakage appeared to be less.
Additional Panretinal Photocoagulation seemed to prevent Disc Neovascularisation.
Focal Maculopathy -Results were encouraging
Cystoid Maculopathy-Definite conclusive evidence was not observed, thus requiring further study. Ischemic -Poor results; Disc
Maculopathy New vesseals should he treated.
Compared to the results with Argon Laser Photocoagulation. results with Krypton Laser were observed to he better, and more stable and more encouraging.
Initial Vision: Treatment should be started when vision deteriorates to 6/12. Results were poor where initial vision was 6/36 or worse (though in 2 eyes, the results were quite impressive).
Cystoid and Ischemic Maculopathies are prone to develop Epiretinal membrane formation, Macular Pucker, Traction and Hole Laser treatment is contraindicated in these situations.
B) Proliferative Diabetic Retinopathy with High Risk Characteristics
(Clinical Ophthalmic examination, Coloure Photographs and Fundus Flouresccin).
-sub 'Panretinel Photocoagulation" was carried out with a view to treating disc new vessels, New vessels elsewhere and the preventing severe visual loss.
Number of eyes treated: 20 eyes with Argon Laser and 20 eyes with Krypton Laser.
Treatment: 200-400 spot size.. Moderate intensity, 0.2-0.3 seconds exposure time, 1500 to 1800 burns.
Results: 1. Risk of severe visual loss was found to be less than one half that was found in centrol (untreated eyes) group.
2. Regression of Proliferative Diabetic Retinopathy, New Vessels and High Risk Characteristics, Regression: about 65-70%, Stationary: 15 to 20%, Worse: 10-15%
3. Treatment slowed down the progression of Proliferetive Diabetic Retinopathy.
In untreated eyes Proliferative Diabetic Retinopathy followed the natural history and the course leading to advanced Diabetic eye disease and severe visual loss.
Compared to the results ofArgon Laser, the results of Krypton Laser were favourable and probably superior.
| II. IDIOPATHIC CENTRAL SEROUS CHORODOPATHY|| |
Treatment Eligibility Criteria
1. Duration : About 3 months and longer
2. Recurrence : Several episodes with recovery of vision
3. Evidence of progressive deterioration of macular function.
4. Occupationl Requirement
5. Bilateral involvement.
6. Location in relation to the centre of fovea.
a) Within 100 microns-to wait for 4-6 months.
b) Between 100 microns and 400 micronsKrypton Laser (mild burn) c) More than 400 microns-Argon or Krypton (mild to moderate burn) A) Spontaneous Resolution 15 eyes
without Photocoagulation B) LASER photocoagulation
1) Argon 6 eyes
2) Krypton 6 eyes
Total No. of eyes 27
Technique: 1. When the lesion was within 250 to 400 microns from the centre of the fovea or Foveal Avascular Zone (FAZ), it was photocoagulated with Krypton Laser. In other cases Argon or Krypton was used.
2. Mild to moderate intensity burn, spot size 100 to 200 microns, Low power.
3. Longer Exposure for Krypton Laser (0.2 or more seconds) Shorter Exposure for Argon Laser.
4. Number of burns was determined by the size and location of the leak, but it was kept to as minimum as possible (more so when it was within 350 microns from the centre of the fovea).
Follow up: 1 week; 3 weeks; 6 weeks; 3 months, than every 4 to 6 months.
1. Krypton Laser was observed to be beneficial and safer for the leak located close to the Centre of Foveal Avascular Zone (FAZ).
2. Indications of Laser Photocoagulation 1) Duration : About 3 months and longer
2) Recurrence : Several episodes with recovery of vision
3) Evidence of progressive deterioration of macular function
4) Occupational Requirement
5) Bilateral involvement.
a) Even after Laser treatment risk of recurrence exists, though not at the same site. However, this was not observed during the follow-up until now in the present study.
b) Heavy Burns lead to the rupture of the Bruch's memberane with a risk of Choroidal Neovascular Membrane, Fortunately this complication was not observed during the follow-up period of 18 months.
| III. SENILE MACULAR DEGENERATION (DISCIFORM DEGENERATION)|| |
Eligibility Criteria for treatment
-V.A. (corrected) 6/24 part or better -Angiographic Evidence of Choroidal Neovascular Memberane at distanceof200 to 2500 microns from the centre of Foveal
Avascular Zone (FAZ) -Drusens
-Symptoms (Choroidal Neovascular Membrane), Low Visual Acuity, Amsler Grid
distortion, Matamorphosia etc.
-No Prior Photocoagulation
-No other ocular disease affecting the Visual Acuity
-Age 50 or older
Following were excluded.sub
-Fibrous Disciform Scars
-Choroidal Neovescular Membrane with
200 microns from the centre of Foveal
-Serous or Haemorrhagic Retinal Pigment Epithial Detachment.
-Geographic Retinal Pigment Atrophy -Drusen without Choroidal Neovascular Memberane (CNM)
a) For lesion beyond 350 microns from the Centre of Feveal Avascular Zone (FAZ). Argon Laser
Spotsize 200 microns, Exposure time 0.3 seconds and power stong enough to produce uniformaly white lesion (grade 3) treat the while lesion completely and extend Photocoagulation beyond Choroidal Neovascular Membrane by 100 to 125 microns alround.
b) For lesion 200 to 350 microns for centre of Foveal Avascular Zone (FAZ) : Krypton Laser
Spotsize 100 to 200 microns; Exposure time: 0.2 seconds and Power enough to produce uniformalywhite lesion (grade 3). Treat the whole lesion completely and extend it by 100 to 125 microns alround.
-Visual Acuity, Photographs, Fundus Flourescein Angiography Amsler grid etc.
-First follow-up 3 weeks, 6 weeks, 3 months and then every 6 months
-One eye was eligible for the study out of 18 eyes examined.
-10 eyes wer treated in 20 sessions
-10 eyes were considered as Control group.
a) Krypton Laser was quite effective and proved to be encouraging provided proper selections was made.
b) Twice as many treated Eyes maintained their initial Visual Acuity or showed improvement.
c) Three times as many untreated eyes lost vision from 4 to 6 lines
d) Laser treatment reduces the risk of Severe Visual Loss (SVL) for eyes with evidence of Senile Macular Deganeration and a symptomatic Choroidal Neovascular Membrane and least 200 microns away from the centre of Foveal Avascular Zons (FAZ).
e) The condition remains in treatable stage for a very short duration and should be treated urgently.
Caution to the patient who have lost central vision in one eye and other eye shows Drusen
i. To report immediately any distortion, blurred vision, scotoma etc.
ii. To observe daily at home with Amsler Grid and report any sudden change.
| SEROUS OR HAEMORRHAGE PIGMENT EPITHELIAL DETACHMENT WITH OR WITHOUT CHOROIDAL NEOVASCULAR MEMBRANE (CNM)|| |
Value of Laser Photocoagulationis doubtful. In fact recent study at Morfields Eye Hospital showed that the treatment is of no benefit and probably risky.
Pigment Epithetial Detachment in Younger age Group
This generally resolves spantenously not requiring laser.
| Transmission and absorption characterisitics|| |
Krypton Laser is transmitted almost fully through ocular media. As it is not absorbed by Xanthophylic Pigment. Krypton Laser passes through Lens Sclerosis having this pigment. Very little scatter occures by ocular media, thus requirement of total energy is less in case of Krypton laser.
Absorption: Krypton Laser is absorbed by Melanin Pigment found in the Pigment Epithelium and the Choroid. Its absorption by Haemoglobin is very little and it is not absorbed by Xanthophyllic Pigment in the macular area. Percentage figures of absorption of this laser by pigment epithelium and choroid show some variation or differences noted by various observers. According to Francis L'Esperance Pigment Epithelium absorbs 45% of Krypton (60% of Argon) and Choroid absorbs 55% (35% of Argon), Krypton damage is observed more in the outer layer of retina compared to Argon and it is claimed that nerve fibre layer damage is little. According Marshall and bird, 85% of the Krypton Energy incident on the pigment epithelium passes through to the choroid. It has been showed that 15% to 80% of the incident energy at the Argon wavelength is absorbed by the macular pigment but less than 1% is absorbed at the Krypton wavelength. Very little absorption of Krypton energy by haemoglobin makes it possible to treat the lesion e.g. Disciform Degeneration through retinal vessels without causing visible damage and to the lesion in presance of vitreous Haemorrhage, Absorption of Argon Laser by luteal pigment prevents irradiation of parafovealar, subretinal neovascular complexes. Absorption of Argon Laser by haemo globin in the retinal blood vessels may result in macular affection during the treatment of disciform lessions and the accidental coagulation of blood vessels may also occur during Pan Retinal Ablation for Diabetic Retinopathy.
Histopathological Observations: A ComparaLive histopathological study of Argon and Krypton Laser irradiation of the human retina at three locations i.e. fovea, macula and intraretinal vessels, by Marshall and Bird has demostrated the following. In the fovea Argon Laser irradiation resulted in damage to both the inner and outer retinal layers as a result of absorption within the pigment epithelium and mecular pigment. While Krypton exposures damage the outer retina and the choroid. In the macula, both systems resulted in damage to the outer retina and sufficient Krypton radiation passed through into the choroid to induce blood vessel occulusion, Haemorrhage and edema,. When intraretinal vessels were irradiated, only with the argon was sufficient energy absorbed within vessels to damage them and their surroundings in the inner retina. The implications of these observations are highly significant and instructive in relation to the therapeutic uses of Argon and Krypton Lasers. Clinical and Experimental studies, have domenstrated and established the significance, value and benefits or Krypton Laser in the Laser Photocoagulation of Macular diseases perticularly Disciform Degeneration and Diabetic Retinopathy as well as other Vascular Retinopathies.
Benefits of Krypton Lasar have been distinctly observed in the Laser Photocoagulation of macular diseases, subretinal neovascular complexes, Diabetic Retinopathy etc. It is possible to perform this treatment through Opaque media, e.g. sclerotic Lens (as Xanthophyllic Pigment of this lens does not absorbs Krypton) and Vitreous haemorrhage (as haemoglobin does not absorb Krypton). Dathage to inner retinal layers is minimum and nerve fibre bundle defects are highly unlikely to occur. Little absorption by Xanthophyllic Pigment of Macula allows closer treatment to the centre of Foveal Avascular Zone.
Possible Complication and Disadvantages Choroidal haemorrhage is known to occur with small spot size (less than 100 microns) and short exposure (i.e. less than 0.15 seconds). Once choroidal haemorrhage occurs, it is difficult to treat the same as it is not absorbed by Haemoglobin. More pain was experienced with Krypton Laser requiring Retrobulbar Anaesthesia. Peripheral Choroidal edema was more commonwith Krypton. It is likely that all these phenomena can be related to high transmission of energy to the choroid. During this study none of these problems was observed.
Parameters for Krypton Laser Photocoagulation In view of all the above mentioned observations, spot size of 100-200 microns and exposure duration of 0.2 to 0.4 seconds are recommended.
Conclusion Results of this study and studies by others have shown that Krypton Laser Photocoagulation for Macular diseases e.g. Disciform Degeneration, Idiopathic Central Serous Choroidopathy, Vascular retinopathies (e.g. Diabetic Retinopathy) is not only possible but it is better and more beneficial.
| References|| |
|1.||Bird A.C. & Grey R.H.B.. 1979, Brit. J. Ophthalmol. 63,669-673 |
|2.||Peyman G.A., 1981. Ophthalmic Surgery. Vol. 12. No. 7. |
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